Wednesday, June 30, 2010

Sensory Motor

A sensation is an awareness of external or internal changes whether we are aware of them or not.  General senses have receptors that are widely spread throughout the body and include the skin, various organs and joints.  Special senses are specialized receptors confined to structures in the head. 

Sensory Receptors:
Sensory receptors are going to be either complex or simple.  General sensory receptors are rather simple.  They have no structireal specializations in free nerve endingst that provide us with pain, tickle, itch, and temperature.  Our special sensory receptors are very complex structures and include vision, taste, hearing and smell. 

There are several types of receptors.  They include mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors and pain receptors (aka nociceptors).  Mechanoreceptors are for touch, pressure, hearing and equilibrium.  Thermoreceptors are for temperature.  Photoreceptors are for light intensity.  Chemoreceptors are for chemical changes.  Pain receptors are for physical or chemical changes to our tissues. 

The receptive field is the area of the body that when stimulated will cause a response from an afferent neuron.  Basically it is the area around a receptor.  There are different sizes of receptive fields. 

Adaptation is a change in sensitivity to long lasting stimuli or the ability to ignore unimportant stimuli.  A decreased response from receptors occurs from a particular stimulus.  The sensory impulses become less frequent and can even stop.  We have two types of adapting receptors.  They are either fast or slow.  The rapidly adapting receptors include smell, pressure and touch and are specialized for detecting pain.  Slowly adapting receptors are for pain, body position, and chemical composition of the blood.  Their nerve impulses continue as long as the stimulus persists. 

The rest of this entry is about general senses.  Specialized senses are special and have their own. 

Receptors for the general senses exist all over our bodies.  We have exteroceptive senses that are associated with the body surface for touch, pressure, temperature and pain.  We have visceroceptive senses that recognize changes in the viscera includeing blood pressure stretching blood vessels and ingesting a meal.  And lastly we have proprioceptive senses that are associated with changes in muscles and tendons.

Meissner corpuscles or corpuscles of touch are egg-shaped masses of dendrites enclosed by a capsule of connective tissue.  These are rapidly adapting receptors.  They are found in the dermal papillae of hairless skin (fingertips, hands, eyelids, tip of tounge, lips, nipples, clitoris and tip of penis).  They generate impulses mainly at the onset of a touch. 

Hair root plexuses are also rapidly adapting touch receptors.  They are found in our hairy skin.  Their free nerve ending wrap around the hair follicles and deduct movements on the skin that disturb the hair. 

Merkel discs are also called tactile discs or type I cutaneous mechanoreceptors.  These are slowly adapting touch receptors.  They are saucer-shaped flat free nerve endings. They are found in our fingertips, hands, lips and external genitalia.

Ruffini corpuscles are also called type II cutaneous mechanoreceptors.  They are elongated, encapsulated receptors that are located deep in the dermis and ligaments and tendons.  They are only found in the hands and soles.

Pacinian or lamellated corpuscles are large, oval structures that are composed of a multilayered connective tissue capsule that enclose a dendrite.  They are found in joints, tendons and muscles and in the periosteum., our mammary glands, external genitalia, pancreas and urinary bladder.

Somatic tactile sensations summary:
Touch is either crude or discriminate. Crude touch is the ability to perceive that something has touched the skin.  Discriminate touch provides our brains with location, size and texture of source.   Pressure is always sustained over a large area.  A vibration is a set of rapidly repetitive sensory signals. An itch is from a chemical stimulation of free nerve endings and a tickle is the stimulation of free nerve endings only by someone else.  Some types of somatic tactile sensations are more rapidly adapting than others. 

Thermoreceptors respond to changes in temperature.  They are located in our skin and our hypothalamus.  Our thermoreceptors are free nerve endings that are approximately 1 millimeter thick.  They are rapidly adapting receptors.  Our warm receptors are in the dermis and respond to temperatures at 25 degrees Celsius, but are unresponsive at temperatures greater than 45 degrees.  Cold receptors are in the stratum basale and are sensitive to temperatures between 10 and 20 degrees.  Pain receptors respond to the extremes. 

Pain nerve pathways also have two parts.  There are acute and chronic pain pathways.  Acute pain fibers are also known as A-delta fibers.  They are thin and myelinated and conduct rapid impulses.  They are associated with sharp pain and are very localized.  Chronic pain fibers are exactly the opposite.  They are C fibers, they are thin, but unmyelinated.  They conduct slow impulses over a large pain. 
Pain is regulated through the thalamus, which allows us to be aware of the pain.  It is then cent to the cerebral cortex which judges the intensity of the pain, locates the source and produces the emotional and motor responses necessary. Pain inhibiting substances include ekephalins, serotonin and endorphins.  Pain relief comes from multiple sites of analgesic actions.  Aspirin and ibuprofen block the formation of prostaglandins that stimulate nociceptors in the hypothalamus.  Novacain blocks the conduction of nerve impulses along pain fibers (aka no more sodium channels).  Morphine, as well and percocet and vicoden lessen the perception of pain in the brain. 

Proprioceptors send information to the spinal cord and centeral nervous system about body position and length and tention of muscles.  The main kinds of proprioreceptors are pacinian corpuscles (speed of joint movement), muscle spindles (are in the skeletal muscles) and golgi tendon organs (which are in tendons and protect from over stretching). 

Baroreceptors and viscreal function provide information on the pressure or volume of organs. 

Chemoreceptors are a major part of homeostasis. 

Somatic sensory pathways relay information from somatic receptors to the cerebral cortex.  A first order neuron conducts the impulse to the central nervous system. Then, the second order neurons conduct impulses from the brain or cord to the thalamus.  When the impulse crosses over to the other side of the body, this is called decussate.  The third order neurons conduct impilses from the thalamus to primary somatosensory cortex (aka the postcentral gyrus of the parietal lobe).  An axon collateral of the somatic sensory neurons simultaneously carry signals into the cerebellum and the reticular formation of the brain. 

Spinothalamic pathway of the central nervous system has both lateral and anterior tracts.   The lateral spinothalamic tract carries impulses for pain, cold and warmth.  The anterior spinothalamic tract carries ticke, itch, crude touch and pressure.  The first cell body is in the dorsal root ganglion.  The second cell body is in the cray matter of the cord and sends fibers to the other side of the cord and up through white matter to synapse with the thalamus.  The third order cell body is in the thalamus and projects to the cerebral cortex.

Motor information goes away from the brain in a similar pattern to somatic sensory pathways.  The upper motor neurons extend from the cerebral cortex to either the brain stem or the cord.  The neural circuits involving basal ganglia and cerebellum regulate the activity of upper motor neurons.  Lower motor neurons extend from the brain stem (via cranial nerves) and the spinal cord (via spinal nerves) to skeletal muscles.  If you have spastic paralysis, there is damage to the upper neurons.  If you have flaccid paralysis, you have damage to lower motor neurons. 

A direct pathway carries voluntary control to skeletal muscles.  It foes from the motor area of the cerebral cortex to the spinal cord and out to the muscles.  An indirect pathway carries involuntary control for subconscious movements.  They include synapses in basal ganglia, thalamus and reticular formation. 

The amount of the cortex devoted to a muscle is proportional to the number of motor units in that muscle.  Muscles that produce precise movements have gross motor units.  Muscles of the legs have few motor units.

The cerebral cortex initiates and controls precise movements.  Basal ganglia help establish muscle tone and integrates semi-voluntary movements. The cerebellum helps make movements smooth and maintains posture and balance.  Descussation occurs in the medulla oblongata such that one side of the brain controls the other side of the body. 

Integrative functions include sleep, wakefulness, memory and emotions.  The hypothalamus establishes a circadian rhythm.  A portion of the reticular formation increases activity of the cerebral cortex.  Many sensory stimuli can activate RAS - pain, movement, bright lights, and alarm clocks.  RAS consists of neurons whose axons projkect from the reticular formation through the thalamus to the cerebral cortex.  We have increased activity of the RAS which causes awakening from sleep. 

Learning is the ability to acquire new knowledge or skills.  Memory is the structural and functional changes that represent the experience in the brain.  Neurons make new proteins and sprout new dendrites to the new information.  Immediate memory lasts only for a few seconds. Short term memory lasts for hours related to electrical and chemical events.  Long term memory lasts for days to years and it is said to be related to anatomical and biochemical changes at synapses. 

The Autonomic Nervous System (mainly)

We have two main parts of our peripheral nervous system.  There is the somatic nervous system and the autonomic nervous system.  The autonomic nervous system is then broken down into two systems: the parasympathetic and the sympathetic systems.

Here is a quick overview of the autonomic and somatic...
The autonomic nervous system operates via reflex arcs (it's involuntary and unconscious).  The sensory input comes from the organs and the somatic nervous system.  Motor output is via both the parasympathetic and the sympathetic nervous systems.  It is regulated by the hypothalamus and brain stem.  The function is for involuntary control of vital organs.  These include viscera and cardiac/smooth muscles and glands. The autonomic nervous system regulates visceral activities by either increasing/decreasing (exciting/inhibiting) ongoing activities.
The somatic nervous system controls the skin, muscles and joints.  Sensations are consciously perceived.  There are special senses (taste, smell, hearing, equilibrium, and vision) and somatic senses (touch, temperature, pressure, pain from body).  The motor neurons innervate skeletal muscle to produce conscious, voluntary movements.  Motor neurons are always excitatory. 
A comparison:
The SNS is a single efferent.  The efferents release acetylcholine. 
The ANS has two efferents in a series - to and from the ganglion.  The first neuron cell body is in the Central nervous system (preganglionic body).  It is a mylinated axon that extends to the cell body of the second efferent.  Efferents release acetylcholine.  The first motor neuron may extend to the adrenal medullae instead of an autonomic ganglion.  The second neuron cell body is in the ganglion.  It is a nonmyelinated axon that extends to an effector.  The efferents here will release either acetylcholine or norepinepherine. 

Autonomic Divisions: most nerves are dually innervated as one division acts as the brake and the other is the gas
Sympathetic Division is our flight or fight response:
speeds up metabolism
speeds up heart rate
speeds up breathing
originates in the thoracic and lumbar segments.

Parasympathetic is our rest and digest response
slows down metabolism
slows down heart rate
slows down breathing
originates in the brain and sacral segments

The sympathetic division is called the thoracolumbar division.  The preganglionic cell bodies are in the lateral gray horns of the 12 thoracic and 2 lumbar segments.   Then, the preganglionic fibers leave the spinal nerves through white rami and enter paravertebral (autonomic) ganglia.  Paravertebral ganglia and fibers that connect them make up the sympathetic trunk.  Postganglionic fibers extend from ganglia to viscera.  The fibers pass through gray rami and return to a spinal nerve before proceeding to an effector.  The exception, as previously mentioned is to the adrenal medulla.  A single supathetic preganglion fibner has many axon collaterals and may sunapse with 20 or more postganglionic neurons.  The postganglionic axons typically terminate in several visceral effectors and therefore the effects of a sympathetic stimulation are more widespread than the effects of a parasympathetic stimulation.

The parasympathetic division is also known as the craniosacral division. The preganglionic cell bodies in the cranial nerves (only III, IV, IX, X) and lateral gray horns of the 2nd-4th sacral segments of the cord.  The presynaptic neuron usually only synapses with 4-5 postsynaptic neurons at the viscera.  The ganglia are terminal ganglia that lie very, very close to or actually within a visceral organ.  They have short postganglionic fibers that continue to their specific muscle or glands.

Cholinergic Neurons and Receptors
Cholinergic neurons release acetylcholine.  All of the preganglionic neurons release acetylcholine.  All parasympathetic postganglionic neurons release acetylcholine.  Sympathetic postganglionic neurons that innervate most sweat glands release acetylcholine. 
Cholinergic receptors are membrane proteins the postsynaptic cell's plasma membrane that binds to acetylcholine.  Nicotinin receptors are fast and are on the postganglionic neuron.  This causes excitation.  Muscarinic receptors are slow and can excite or inhibit depending on the cell that has the receptor. 

Adrenergic Neurons and Receptors
Adrenergic neurons release norepinepherine.  They include most sympathetic postganglionic neurons.  The adrenal medulla also releases epinephrine. The main types of adrenergic receptors are alpha (a1, in arteries and causes vasoconstriction) and beta (b1 in heart and b2 in lungs; causes bronchodilation and increased heart rate).  The effects triggered by adrenergic neurons are typically longer lasting than those triggered by cholinergic neurons. 

The sympathetic response is fight or flight.  This is also known as increased stress causes increased flight-or-fight response.  More ATP is produced, the pupils are dilated, the heart rate and blood pressures increase, airways dilate and constriction of blood vessels that supply the kidneys and the gastrointestinal tract.  There is an increase in supply of blood to skeletal muscles, cardiac muscle, liver and adipose tissue.  Glycogenolysis and lypolysis levels increase, causing a rise in blood glucose levels.  This is the shoot reflex, such as in orgasm. 

The parasympathetic response is our rest and digest response.  It is the point reflex - genital engorgement.  We conserve and restore body energy, increase our a digestive and urinary function and decrease body functions that support physical activity. 

To control our autonomic nervous system, we use the hypothalamus, medulla oblongata and the limbic system.  The hypothalamus is our autonomic tone.  It is a balance between the sympathetic and parasympathetic activity.  The hypothalamus controls visceral functions including body temperature, hunger, thirst, and water and electrolyte balance.  The medulla oblongata modulates the hypothalamus signals regarding cardiac, vasomotor and respiratory activities.  The limbic system and cerebral cortex send input to the cerebellum regarding emotional response. 

Monday, June 28, 2010

The brain and cranial nerves

Just as a recap, the nervous system is composed of two major parts: the central nervous system and the peripheral nervous system. The central nervous system is only composed of the brain and spinal cord, while the peripheral nervous system is made of all the nerves in the body.

While the brain is only about 2% of a person's body weight, it uses almost 20% of the body's glucose and oxygen.  Oxygen and glucose, remember, are major players in aerobic respiration to make ATP.  Blood flow increases to the parts of the brain which are most active.  This is the reason that we can look for problems within the brain on a cat scan.  If we are unable to get oxygen for four minutes, potentially lethal damage can start occurring. Without oxygen, lysosomes explode and release their low pH fluid, which destroys the brain.  The brain needs a constant flow of glucose because it doesn't store any.  The first signs of low blood sugar include dizziness and fainting.

Blood is brought to the brain by internal carotid arteries and basilar artery.  Blood is then drained into the dural sinuses and the jugular veins.  The dural sinuses sit beneath the skull and in between the dura mater layer of the meninges and looks kind of like a V.  There are several jugular veins that are located both on the posterior and anterior sides of the body.  The blood brain barrier prevents harmful substances and pathogens from passing into the brain.

There are three layers to the meninges of the brain.  They are the exact same as the spinal column.  From superficial to deep they are: dura mater, arachnoid and pia mater.  In the brain, the meninges help create the separations of the hemispheres and other differentiations in the brain. The Falx cerebri is a longitudinal fissure that separates the hemispheres of the cerebrum.  The falx cerebelli separates the two regions of the cerebellum.  The tentorium cerebelli separates the cerebellum from the cerebrum.   Meningitis (see I told you I'd talk about it again) is the inflammation of the pia mater, the arachnoid and the cerebral spinal fluid filled subarachnoid space.  Signs and symptoms include fever, chills, headaches, stiff neck, back, abdominal and extremity pains, nausea and vomiting.  These signs and symptoms are often pushed off as the flu until it is too late.  Bacterial meningitis may be caused by an infection  of the ear, upper respiratory tract, frontal sinus or carried through the blood from the lung.  These might include Pneumococcus or Menigococcus.  Viral meningitis is commonly caused my mumps, polio viruses, and occasionally from herpes simplex.

Brain bleeds are very dangerous because there isn't any room for extra fluid.  Brain bleeds increase intracranial pressure, compress and move the neurons and glia (which move them off tract from where they should be and messages don't get to where they are supposed to go).  If the bleeding occurs in the epidural space, it is an artery bleed and it occurs very rapidly.  If it is in the subdural space, the veins are bleeding and it slower.  Veinous bleeding can take days or even weeks to find.

Brain herniations occur when intracranial pressure pushes the brain out of position. These can include: a displacement of a cerebrum hemisphere under the faux cerebri to opposite side; downward displacement of the hemisphere, diencephalon and midbrain; temporal lob under dura can cause cerebral peduncle to be pinched; and brain tissue being compressed against the skull.

Cerebrospinal Fluid:
There are four deep ventricles that are fluid-filled spaces that form, contain and circulate cerebrospinal fluid.  The lateral ventricles are known as the first and second vents and look like ram horns.  The third ventricle is inferior and deep to the first and second vents.  The fourth ventricle runs with the brain stem. Cerebrospinal fluid is a clear liquid that contains glucose, proteins and ions.  CSF is used to circulate nutrients and waste products between brain and the blood stream.
CSF is formed in the choroid plexuses.  Choroid plexuses are capillaries covered by Ependymal cells (in ventricles).  Ependymal cells control substances that can enter the CSF from the brain.  The CSF is reabsorbed into blood through arachnoid villi in the dural sinuses.  IT then flows into jugular veins that drain out of the head.  We reabsorb CSF at the same rate we produce it: 20 ml/hour.
The CSF is formed in the choroid plexuses of each lateral ventricle.  From the lateral ventricles it flows into the third ventricle through interventricular foramina.  Then, the fluid moves  into the aqueduct of the midbrain which moves the CSF into the fourth ventricle.  The choroid process in the fourth ventricle adds more CSF.  CSF enters the subarachnoid space through three openings in the roof of the fourth ventricle.   Through those openings, the CSF circulates the central canal of the spinal cord and the subarachnoid space around the surface of the brain and spinal cord.

There are four major regions of the brain.  They are the cerebral hemisphere, diencephelon, cerebellum, and the brain stem.  Each of the four regions of the adult brain come from the development of the embryonic brain.  At three-four weeks, there are three primary vesicles.  There is the prosencephalon (the forebrain), the mesencephalon (the mid-brain), and the rhombencephalon.  These three regions change into five regions at the five-week stage. The wall of the three-four week embryo creates the following:  The prosencephalon splits into the telencephalon (cerebrum) and the diencephelon (the thalamus, hypothalamus and epithalamus).  The mesencephalon remain the midbrain.  The rhombencephalon splits into the metencephalon (which creates both the pons and the cerebellum) and the myelencephalon (medulla oblongata).  The cavities of the three-four week embryo creates the following:  The prosencephalon splits into the telencephalon which makes the lateral ventricles and the diencephelon which creates the third ventricle.  The mesencephalon makes the aqueduct of the midbrain.  The rhombencephalon splits into the metencephalon makes the upper part of the fourth ventricle and the myelencephalon makes the lower part of the fourth ventricle.

Just a few key words to remember:
Sulcus: a valley.  sulking-down in the dumps...
Gyrus: a bump.  Gyrus kinda sounds like joyous which is an up
Corpus callosum: the connection for communication between the left and right hemispheres of the cerebrum.

There are several functions of the cerebrum.  It interprets impulses, initiatives voluntary movement, stores memories, retrieves memories, reasons, and is the seat of intelligence and personality.
The cerebrum is made of the frontal lobe, parietal lobes, temporal lobes, occipital lobe and the insula.  A few landmarks include the Central Sulcus and the cerebri falx.  The gray matter of the cerebrum is approximately 2 millimeters thick.  Gray matter is also known as the cerebral cortex.  It is unmylinated axons, dendrites and cell bodies.  It covers the largerst portion of the brain. The cerebral cortex is the thin layer of gray matter that contains 75% of al neurons in the entire nervous system.  White matter is known as cerebral medulla.  It is deep to the cerebral cortex.  It includes the asociation fibers between gyri in the same hemisphere.  Commissoral fibers connect from one hemisphere to the other (they make up the corpus collosum).  Projection fibers form ascending and descending tracts.

There are two major areas that control speech in the brain.  The Broca area controls for the motor area and is in the frontal lobe.  The Wenike area is for speech interpretation and is located on the temporal lobe.  The are both only found on the left side of the brain.

The longitudinal fissure separates the brain into left and right hemispheres.  The left hemisphere is more for verbal, logical, analytical and rational functions; while the right side is more for nonverbal, intuitive and creative functions.  Males have more specialized hemispheres than females; males tend to use more side more than females.  Females have a larger corpus callosum.  If someone has a stroke on the left side, it is called aphasia and on the right side it is causes speech with no emotion or inflection.

The Limbic System consists of the frontal and temporal lobes, the hypothalamus, the thalamus,  the basal nuclei and other deep nuclei.  The functions of the limbic system include controlling emotions, producing feelings and interpreting sensory impulses. 

The Diencephelon consists of the thalamus (a relay station for the sensory information.  It is kind of like the post office of the brain); the hypothalamus (this part of the brain regulates basic functions: temperature, water, balance, metabolism, sex, appetite, emotions, pituitary gland and the autonomic nervous system); the epithalamus (which contains or is also called the pineal gland. this produces melatonin [the sleep horomone]); and the optic tracts, optic chiasm, infundibulum and the pituitary gland.  The diencephelon surrounds the third ventricle.  The superior portion is the thalamus, while the inferior part of walls and floor is the hypothalamus. 

The cerebellum integrates sensory input from the eyes, ears, joints and muscles about the present position of body parts.  The cerebellum helps us maintain balance and posture, have smoothly coordinated voluntary movements and learn new motor skills such as playing the piano or hitting a baseball. The cerebellum is posterior to the mid-brain, pons and medulla oblongata (aka the brain stem). 

The brain stem consists of the mid-brain, pons and medulla oblongata. 
The midbrain is the station for relaying messages and reflexes.  It contains the cerebral aqueduct between the third and fourth ventricles.  It also has the cerebral peduncles between the bundles of fibers between the cerebellum and cord.  The corpora quadrigemina has two parts: the superior colliculi which is involved in visual reflexes and the inferior colliculi which deals with auditory reflexes. 
The pons is a bridge of axons traveling between the cerebellum and the rest of the central nervous system. The pons helps regulate rate and depth for breathing. 
The medulla oblongata is a vital center for regulating heart beat, breathing and blood pressure.  It is a nonvital center for reflexes such as coughing, sneezing, swallowing and vomiting. 
The reticular formation is a network of nerve fibers scattered througout the brain stem into the diencephalon.  It is the center for reticular activating system.  The reticular formation connects centers of the hypothalamus, cerebellum and cerebrum.  The reticular formation filters incoming sensory information and arouses the cerebral cortex into state of wakefulness. 

Cranial Nerves:
There are twelve cranial nerves and they are labled C-I through C-XII.  The only two that we have to identify on a model are I and II, the olfactory and optic nerves.
Here is a brief list:
I: Olfactory: from olfactory receptors
II: Optic: from eyes of retina
III: Oculomotor: to eye muscles
IV: Trochlear: to eye muscles
V: Trigerminal: from mouth and to jaw muscles
VI: Abducens: to eye muscles
VII: Facial: from taste buds and to facial muscles and glands
VIII: Glossopharyngeal: from inner ear
IX: Accessory: from pharynx and to pharyngeal muscles
X: Vagus: to and from internal organs
XI: Hypoglossal: to and from back and neck muscles
XII: Vestibulocochlear: to tongue muscles

Now, we'll go into each of the nerves just a little bit deeper and in reverse :) When I refer to a mixed nerve, it means that it is both a motor nerve and a sensory nerve. 

 XII: Hypoglossal nerve
The hypoglossal nerve is 5 cranial nevers that arise from the medulla (8-12).  The hypoglossal nerve controls muscles of the tongue during speech and swallowing.  If your hypoglossal nerve is injured, your tongue will fall to the side with the injury when you protrude it.  The hypoglossal nerve is mixed; however it is primarily motor. 

XI: Spinal Accessory Nerve
There are two portions: cranial and spinal.  The cranial portion arises from the medulla and controls skeletal muscle of the through and soft palate.  The spinal portion arises from the cervical spinal cord and controls the sternocleidomastoid and the trapezius.  The spinal accessory nerve is mixed. 

X: Vagus Nerve
The vagus nerve receives sensations from the viscera.  It controls cardiac muscle as well as the smooth muscle of the viscera.  The vagus also controls secretion of digestive fluids.  The vagus nerve can slow down heart while resting by inhibition. 

IX: Glossopharyngeal Nerve
The glossopharyngeal nerve controls the sternocloidomastoid.  It lifts the throat during swallowing, secretions from the parotid gland, salivary gland, aids in somatic sensations and taste on posterior 1/3 of tongue.  It is a mixed nerve. 

VIII: Vestibulocochlear Nerve
The vestibulocohlear nerve has two branches: cochlear and vestibular.  The cochlear branch begins in the medulla receptors of the cochlea.  It aids in hearing and if it is damaged, deafness or tinnitus is produced.  The vestibular branch begins in the pons receptors in the vestibular apparatus. It aids in the sense of balance, vertigo and ataxia.  The glossopharyngeal nerve is mixed, but mainly sensory.  

VII: Facial Nerve
The facial nerve has a motor portion and a sensory portion.  The motor portion controls facial muscles, salivary, nasal, and oral mucous glands and tears.  The sensory portion of the facial nerves are the taste buds on the anterior 2/3's of the tongue.  The facial nerve is a mixed nerve. 

XI: Abducens Nerve
The abducens nerve controls the lateral rectus eye muscle.  The abducens nerve is a mixed nerve, but mainly motor. 

V: Trigeminal Nerve
The trigeminal nerve has a motor portion and a sensory portion.  The motor portion works on mastication. The sensory portion receives touch, pain and temperature of the fave.  The three branches are ophthalmic, maxillary and mandibular.  The trigeminal nerve is mixed. 

IV: Trochlear nerve
The trochlear nerve controls the superior oblique eye muscle.  The trochlear nerve is mixed, but mianly motor. 

III: The oculomotor nerve
The oculomotor nerve conttrols many muscles of the eye. These include the levator palpabrae, four of six extrinsic eye muscles (superior, inferior and medial recti and inferior oblique).  It is a motor nerve of the autonomic nervous system and works with two intrinsic eye muscles of the lens and pupil.  It is also the part that accomadates and constricts the pupil. 

II: The Optic Nerve
The optic nerve connects to the retina to supply vision.  It is strictly a sensory nerve. 

I: The Olfactory Nerve
The olfactory nerve extends from the olfactory mucosa of the nasal cavity to the olfactory bulb.  It aids in the sense of smell.  The olfactory nerve is strictly a sensory nerve. 

Thursday, June 24, 2010

Spinal Cord and Nerves

The spinal cord is pretty interesting.  It is a cord that extends from the base of the brair through the vertebral canal, that of course we know by now is formed by the vertebrae.  The functions of the spinal cord include reflexes, integration and being a highway for the traveling sensory (upward, afferent) and motor (downward, efferent) neurons. 
The spinal cord begins at the foramen magnum (the largest foramen in the skull) as a continuation of the medulla oblongata (the most inferior portion of the brain).  It is approximately 16-18 inches in length and terminates near the second lumbar vertebrae.  It contains two enlargements: the cervical and lumbar.  These are the origin points for nerves to the extremeties.  More specifically, the cervical enlargement is the origin of the spinal nerves to our arms while the lumbar enlargment is the origin of the spinal nerves to our legs.
The cuada equana or "horse's tail" are the dorsal and ventral roots of the lowest spinal nerves.
The conus medularis is the tappered end of the spinal cord near lumbar vertebrae 1 and 2.
The filum terminale is an extension of the pia mater. 

Protection of the spinal cord comes from the vertebrae, epidural space filled with fat, the dura mater, the arachnoid, and the pia mater.  The dura mater is literally translated to the stong mother.  It is a dense irregular connective tube and has a subdural space filled with interstitisal fluid.  The arachnoid portion of the protection is a spider web of collagen fibers that can take compression when doing any activity.  This portion has a subarachnoid space that is filled with cerebral spinal fluid.  The pia mater translates to delicate mother.  It is a thin layer that also covers the blood vessels.  The denticulate ligaments hold the pia mater in place.

Meningitis is the inflammation of the meninges.  To determine if someone has meningitis, a spinal tap (or lumbar puncture) is done to test the cerebral spinal fluid of the subarachnoid space.  More information to come on Meningitis in my next post...

There are three areas of both gray and white matter.  The Dorsal (posterior) Horn, the Ventral (anterior) Horn and the Lateral Horn (of the autonomic nervous system).

Here are some important parts of the spinal cord, but I can't remember what each of them do right now:
Lateral white column
lateral gray horn
anterior gray horn
gray commissure
anterior white commissure
anterior white column
anterior median fissure
posterior gray horn
posterior median sulcus
posterior white column
central canal
axon of interneuron
cell body of somatic motor neuron
axons of motor neurons
axon of sensory neuron
cell body of autonomic motor neuron
cell body of sensory neuron

The tracts of the cord are the highways we mentioned earlier.  Sensory tracts ascend and motor tracts descend.  The tracts are named by the position and direction of the signal.  An example from the lecure is the Anterior Spinothalamic Tract.  The impulses travel from the cord to the thalamus and it is found in the anterior portion of the cord.  The tracts that we need to know are corticospinal (controls voluntary movements), the reticulospinal and rubrosprinal (automatic movements for tone, posture and balance), the fasciculus gracilis and cuneatus (touch, pressure, propriception) and the spinothalamic (pain, warmth, and itching).  Some tracts cross over the spinal cord to the other side before it reaches the thalumus.

Lou Gehrig's Disease is also known as Amyotrophic lateral sclerosis (ALS).  It is the degeneration of motor neurons in the cord, brainstem and cortex by free radicals.

There are 31 pairs of spinal nerve.  One half of each pair goes to either the left side or right side of the body.  The pairs are named and numbered according to the region and level of the spinal cord from which they emerge.  There are 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and 1 pair of coccygeal nerves.  Roots are the two points of attachment from the spinal nerves to the spinal cord.   The roots are either called dorsal or ventral.  The easiest way to tell the two apart is by looking for the dorsal root ganglion. 

Like muscles, nerves have several connective tissue coverings.  The endonurium is the wrapping around each nerve fiber (aka axon).  The perineurium surrounds a group of nerve fibers forming a fascicle.  The epinurium covers the entire nerve and blends into the dura mater at intervertebral foramen. 

Spinal nervers branch into dorsal and ventral rami.  The dorsal rami only supply the skin and muscles of the back.  Ventral rami form plexus for the anterior trunk and limbs.  A nerve plexus is the joining of nevertal rami of spinal nerves to form nerve networks or plexuses.  They are found in the neck, arms, low back and sacral regions. There is not a plexus in the thoracic region. 
The cervical plexus are the ventral rami of spinal nerves C1-C5.  They supply part of the head, neck and shoulders.  The phrenic nerve (C3-C5) keeps the diaphragm alive.  Damage to the spinal cord above C3 causes respiratory arrest. 
The brachial plexuses are from C5-T1.  They lie deep with in the shoulders.  Musculocutaneous nerves supply the muscles of the anterior arms and skin of forearms.  The unlar and median nerves supply the muscles of forearms and hands; these nerves are on the medial side of the body.  The radial nerves supply the posterior muscles of arms and the skin of forearms and hands. Axillary nerves supply the muscles and skin of anterior, lateral and posterior arms. 
There are no plexuses in the thoracic region.
The lumbar plexus is the lumbar rami of L1-L4.  It supplies the abdominal wall, external genitals and the anterior/medial thigh.  If you injure your femoral nerve, you may lose the ability to extend your leg as well as sensation in your thigh.  If you obturator nerve is damaged, there may be paralysis of the adductors. 
Lumbrosacral plexuses extend from the lumbar region into the pelvic cavity.  Obturator nerves control motor impulses to adductors of thighs.  Femoral nerves control motor impulses to muscles of anterior thigh and sensory impulses from skin of thighs and legs.  Sciatic nerves control muscles and skin of thighs, legs and feet. 
The sacral plexus is the ventral rami L4-L5 and S1-S5.  It is anterior to the sacrum and supplies buttocks perineum and part of lower limbs.  A peroneal nerve injury causes foot drop or numbness.  A tibial nerve injury produces calcaneovalgus (the loss of function on anterior leg and dorsum of foot). 
The sciatic nerve branches include the common peroneal (or fibular) nerve and then tibial nerve behind the knee.  Sciatica pain extends from the buttocks down the leg to the foot. 

Dermatomes are the area of skin that sensory fibers of a spinal nerve innervate.  If there is a damaged region on a cord, the patterns of numbness can determine which dermatome it is.  Infusing local anesthetics or cutting roots has to be done over three adjacent spinal nerves, otherwise, some pain may still exist.  A spinal cord transection is an injury that severs the cord loss of sensation and motor control below the injury. 

Reflexes do not occur with cognitive thought.  A good reaction that can be tested is the Babinski Sign.  The Babinski sign is tested by running a dull object over the lateral edge of the foot.  The big toe will either flex or extend.  This test checks for descending motor system damage.  A positive sign is normal in infants, but indicates a problem in adults.  In adults, no Babinski sign... The toes should curl under. 

Tuesday, June 22, 2010

Nervous Tissue

The nervous systems works in conjunction with the integument system.  It helps the body keep controlled conditions within limits to maintain health and homeostasis.  The nervous system is responsible for all of our behaviors, memories and movements.  Neuroscience is the branch of medicine that deals with the normal functioning and disorders of the nervous system.
The nervous system has several functions.  The sensory function senses changes in internal and external environment through sensory receptors.  Sensory neurons, aka afferent neurons, serve this purpose.  Integrative function analyzes sensory information, stores some aspects and makes decisions regarding appropriate behaviors.  Association or inter-neurons serve this function.  The motor function responds to stimuli by actions.  Motor neurons or efferent neurons serve this function.  

Nerve tissue contains two types of cells: Neurons and Glial Cells.   The neurons are cells that transmit impulses.  Neurons are the functional unit of the nervous system. They produce action potential (which I'll describe better in a bit).  Action potential is the electrical excitability of a cell.  Neurons are made of the neuron, axons and dendrites.  Neurons have a single nucleus and organelles. dendrites bring information to the cell, while Axons send information away from the cell.  Glial cells support and nourish the neurons.  Within the nervous system, there are also blood vessels and connective tissues.
Neurons have the capacity to produce action potentials.  They are electrically excitable and then act upon that impulse.  Cell bodies have a single nucleus with a prominent nucleolus.  They also have nissl bodies that are chromatophillic substances.  There is an endoplasmic reticulum and lots of free ribosomes for protein synthesis.  There are more neurofilaments that give the cells shape and support, as well as microtubules that move material in the cell.
Dendrites conduct impulses to the cell body.  They are typically short and highly branched.  They have surfaces that are specialized for contact with other dendrites.  They also contain neurofibrils and Nissl bodies.
Axons move neurotransmitters which are made in the Golgi.  Fast axonal flow occurs in one direction and moves at 1-5mm per day.  Slow axonal flow moves organelles and materials along the surface of microtubles at 200-400mm per day.  Transports in both directions.

One way Neurons are classified by how many branches they have.  If they are multipolar, there are several dendrites and one axon and are the most common in the body.  Bipolar neurons have one main dendrite and one main axon.  They are found in the retina, inner ear and olfactory.  Unipolar neurons have only one process, an axon.
Another classification mechanism used to define neurons is their function. Sensory neurons (afferent neurons) transport sensory information from skin, muscles, joints, sense organs and viscera to the central nervous system.  Motor neurons (efferent) send motor nerve impulses to muscles and glands.  Interneurons (association) connect sensory neurons to motor neurons and are the most common in the body.

Neuroglial cells are more than 50% of the central nervous system and are 50 times more numerous.  They have many functions including holding the nervous tissue together, metabolizing glucose, producing myelin and phagocytosis.  They can divide.  If they divide too quickly, it can cause tumor formations. There are four types of neuroglial cells in the central nervous system:
astocytes: astrocytes are star-shaped cells.  They form a sheath by covering blood capillaries.  The control chemical movement around neurons.  They metabolize glucose and provide structural support.
oligodendrocytes: this is the most common type of glial cell.  each forms myelin around more than one axon in the central nervous system. They are analogous to Schwaan cells of the peripheral nervous system.  There is little regrowth of these cells after damage occurs.
Microglia and small cells found near blood vessels.  They have a phagocytic role and clear away dead cells.  They are derived from cells that also give rise to macrophages and monocytes.
Ependymal cells: form epithelial membrane lining cerebral cavities and central canal cord.  They produce cerebrospinal fluid along with capillaries in brain.

*the blood brain barrier prevents large molecules from passing through.  however, small molecules can.  But the problem is that it cannot distinguish between harmful and helpful chemicals. 
*gray and white matter. white matter is mylinated processes. gray matter is nerve cell bodies dendrites, axon terminals in bundles of unmyelinated axons and neuroflia.  IN the cord, gray matter is H-shaped inner core surrounded by white matter.  IN the brain, there is a thin outer shell of gray matter and in clusters called nuclei inside the central nervous system.  A nucleus is a mass of nerve cell bodies and dendrites inside the central nervous system.  A nucleus is a mass of nerve cell bodies and dendrites inside the central nervous system.

Neuroglia of the peripheral nervous system is completely surrounded by axons and cell bodies.  Schwann Cells encircle the peripheral nervous system and satellite cells are flat cells that surround cell bodies of neurons in the peripheral nervous system ganglia. 
Satellite cells are flat cells that surround the neuronal cell bodies in periheral ganglia.  They support the neurons in the PNS.
Each Schwaan cell encircles a PNS axon.  Each cell also produces part of the myelin sheath surround an axon in the PNS.  They help speed us neurtransmission.

Regeneration and repair:
Plasticity is maintained throughout life.  New dendrites sprout and new proteins are made.  There are also changes in the synaptic contacts with other neurons.  There is limited ability for repair.  The central nervous system cannot repair itself but the peripheral nervous system can repair some damaged dendrites or axons.  They can only be repaired if the neuron body remains intact, the Schaan cells remain active and form their tubes and scar tissue does not form too rapidly.  When an axon is damaged, there are changes called chromatolysin in the cell body.  24-48 hours after the injury, Nissl bodies break up into fine granular masses in the cell body.  This causes the swelling of cell bodies and peaks 10-20 days later.  By the 3rd-5th day, degeneration of the distal portion of axons and myelin sheath occurs.  Afterward, marcophages phagocytize the remains.  Retrograde degineration of the proximal portion of the fiber extends only to the first neurofibral stage.  Within several months, regeneration follows choratolysis.  The synthesis of RNA and protein accelerate, favoring the rebuilding of the axon, but it can take several months.  Neurolemma is on each side of the injury repairs the tube.  Nerve growth factors are released bu the glia and axonal buds grow down the tube to reconnect.
Neurogenesis is the formation of new neurons from the stem cells occurs in the hippocampus. This is a critical area for learning.  There is a lack of neurogenesis in other regions of the brain and spinal cord.  Factors that prevent neurgenesis in the central nervous system include inhibition by neuroglial cells creates and absence of growth stimulating factors, a lack of neurolemma and rapid formation of scar tissue by astrocytes.

An action potential is a nerve impulse that is an electrochemical change that travels along the length of a neuron fiber.  Transmission of signals between neurons is dependent on neurotransmitter molecules.
The resting potential (RMP) is when a cell has more positive ions on the outside than the inside.  There are more sodium molecules outside than inside and more potassium molecules inside than outside.  The axon is not conducting an impulse.  Resting membrane potential exists because of the concentration of ions that are different between the inside and outside of a cell.  The extracellular fluid is rich in sodium and chloride.  The intracellular fluid is full of potassium, organic phosphate (to change ADP to ATP) and amino acids.  Membrane permeability differs for sodium and potassium with a 50-100 times greater permeability for potassium.  There is an inward flow of sodium that cannot keep up with the outward flow of potassium.  A sodium/potassium pump removes sodium as fast as it leaks in.
The action potential is a rapid change in the membrane carried down the axon.  Sodium gates will open and let sodium into the cell creating a positive charge (depolarization). The cell says oh shit and opens potassium channels to give the cell a negative charge again (repolarization).  Depolarization and repolarization  occur like a wave going down an axon.  The sodium/potassium pump will then kick into gear and bring the levels back to normal.
If and when a neuron responds, it will respond completely.  A nerve impulse is conducted whenever a stimulus of threshold  intensity or above is applied to an axon.  The strength of the impulse will remain the same for the entire length of an axon. 
Local anesthetics are used to block pain and or other sensations.  They prevent the opening of sodium channels so nerve impulses cannot pass the obstructed region. 
An action potential spreads or propagates over the surface of an axon membrane.  As the sodium flows into the cell during depolarization, the voltage of neighboring areas is effected and their sodium channels also open.  This is called self-propagation.  The traveling action is called the nerve impulse. 
A synapse is the functional junction between neurons or between a neuron and an effector (which could be a muscle or a gland).  Depending on the neurotransmitter and the receptor, response by the post-synaptic neuron can be excitation or inhibition. Integration is the summing of the signals received by a postsynaptic neuron. 

Small molecule neurotransmitters include acetylcholine, amino acids, drugs such as marijuana, biogenic amines, neuropeptides and alcohol. Acetylcholine is released by many peripheral neurons and some central nervous system neurons.  They are excitatory on neuromuscular junctions.  They are inactivated by acetylcholinesterase.  Amino acids include glutamate which is release by nearly all excitatory neurons in the brain.  They are inactivated by glutamate specific transporters.  GABA is inhibitory neurotransmitter for 1/3 of all brain synapses.  (Valium is a GABA agonist-enhancing its inhibitory effect.) Biogenic amines are modified amino acids (from tyrosine).  Norephinephrine regulates mood, dreaming, and awakening from deep sleep.  Dopamine regulates skeletal muscle tone, the reward center in the brain and ecstasy.  Seretonin is similar to epinepherine and controls the mood, temperature regulation and induction of sleep.  These are removed from synapse and recycled or destroyed by enzymes.  Marijuana is a GABA antagonist and prevents the release of GABA.  GABA usually inhibits the second neuron from firing, but without it, the 2nd neuron fires like crazy.  It is also a dopamine reuptake inhibitor.  It allows dopamine to hang out in the cleft between neurons longer so it can bind to more receptors.  This stimulates the reward center and produces happy feelings and analgesia. 

Neuropeptides are synthesized by neurons in the brain or spinal cord.  THey are modulators of neurotransmitters. Enkephalins block pain.  Beta endorphins are a natural pain reliever. Substance P enables transmission to brain and cord.

Removal of neurotransmitters occurs through diffusion (down the concentration gradient), enzymatic degradation (acetylcholinesterase) and reuptake by neurotransmitters.  Both excitatory and inhibitory neurotransmitters are present in the central and peripheral nervous systems.  The same neurotransmitter might do the opposite effect in different locations.

Drugs that effect neurotransmitters:
synthesis drugs can stimulate or inhibit
releasae drugs can block or enhance
removal drugs can be stimulated or blocked
receptor site can be blocked or activated
agonist drugs enhance a transmitter's effects while antagonists prevent the neurotransmitter from working

Alcohol is a central nervous system depressant.  It inhibits NMDA.  It is an agonist for GABA, seretonin and dopanine and opiods.  Alcohol enters the first neuron and makes it release even more neurotransmitters.  All the GABA is dumped out and inhibits motor skills and makes you sleepy! It also dumps out more and more serotonin, which causes an increase in sexual desire, food cravings and aggression.  Dopamine is also released and tells us that alcohol is a good thing.  Endorphins are also released which prevent pain!

Sunday, June 20, 2010

Muscle System

Skeletal muscles are the muscles that relate to movement by exerting force on tendons.  This action pulls on bones or other structures.  Articulating bones typically do not move equally in response to contraction.  The origin is the point of attachment of tendon to the stationary bone.  The insertion is the point of attachment of the muscles other tendon to the bone that moves.  But, guess what, that's all you need to know about that.

Lever Systems and Leverage:
A lever is a rigid structure that moves around a fixed point, called the fulcrum.  Levers are acted on by two different forces: resistance (or load) and effort.  Resistance (or load) opposed movement.  For example, weight of muscle and bone.  The Effort causes movement.  It is the force due to muscle contraction. There are three types of levers that differ based on the location of the effort, load and fulcrum.
First class levers are not very common.  The fulcrum is between the effort and the load.  A none-body related example are scissors.  The best body example is the neck.  The effort comes from neck muscles, the fulcrum is the atlas/axis joint and the load is your face.  (at least that's the way the picture looks).
Second class levers are not very common either.  The load is between the fulcrum and the effort.  A none-body example is a wheel barrow.
Third class levers are the most common in our bodies.  The effort is between the fulcrum and the load.  A none body example would be tweezers.  A good example in our bodies are our elbows.  The load is our hand, the effort is our arm muscles and the fulcrum is our elbow.

Fascicle arrangements can be kinda interesting.  A contracting muscle shortens to approximately 70% of its original length.  All of the fibers within a fascicle are parallel to one another.  But, fascicles can form patterns with respect to their tendons.  Fascicles must compromise between power and range of motion.

Movement occurs in coordination within muscle groups.  The prime mover is the main mover of the bone.  The antagonist causes the opposite action of the prime mover.  Antagonists relax as as prime movers contract.  Synergists are muscles that stabilize nearby joints.  Grators stabilize the origin of the prime mover. 

Skeletal muscles can be named by several different factors. These include: direction of fiber, location, size, number of origins, shape, points of attachment, and action.

Now onto the muscles themselves and their actions!
I'm going to break them up by categories as to location of the body.

Muscles of Facial expressions:
Epicranious (frontalis and occipitalis): the frontalis raises the eyebrows. the occipitalis pulls the scalp posterior.
Orbiticularis oculi: various parts can be activated individually.  functions in blinking, closing, squinting and drawing the eyebrows inward. 
Orbiticularis oris: closes the mouth and protrudes the lips. 
Buccinator: draws back the corners of the mouth and compresses cheeks medially. 
Zygomaticus (major and minor): raises lateral corners of the mouth upward.
Platysma: depresses the mandible and pulls lower lip back.  

Extrinsic Eye Muscles:
4 rectus muscles: (these muscles make sense.  they are located where their names say they are and they pull the eye in that direction).
inferior: below the eye, pulls eye inferior and medial.
superior: above the eye.  pulls eye superior and medial
medial: medial to the eye and pulls it medially.
lateral: lateral to the eye and pulls it laterally.
2 oblique muscles: (these muscles are located oppositely where one would think they are.)
inferior: above the eye and pulls it superiorly and laterally.
superior: below the eye and pulls it anteriorly and laterally.
Levataor palpabrea: raises eye lids.

Muscles of Mastication:
Masseter: elevates the mandible
Temporalis: closes jaw. elevates and retracts mandible. 
Pterygoid (medial and lateral): move mandible.

Muscles that move the head and vertebral column:
Sternocleidomastoid: flexion. general resistance, rotation of head toward opposite shoulder.
Splenius Capitus: as a group, it extends or hyperextends the head or allows head to rotate
Semispinalis Capitis: acting together, extend head and vertebral column.  not together, rotation of head.
Errector Spinae: extend and bed vertebral column laterally. Fibers also extend head.

Muscles that move the pectoral girdle:
Trapezius: extends the head, moves the scapula used in shrugging.
Rhomboideus Major: pulls scapula medially.  stabilizes scapula.
Levator Scapulae: elevate and adducts scapula.
Seratus Anterior: moves scapula anteriorly. abduction/raising of arm
Pectoralis Minor: moves ribs or scapula depending on which is flexed.

Muscles that move the arm:
Pectoralis Major: prime mover of arm flexion.  adducts and medially rotates
Teres Major: extends, medially rotates and adducts humerus
Laissimus dorsi: prime move of arm extension.  adducts and medially rotates arm.
Supraspinatus: assists abduction of humerus.  stabilizes shoulder.
Deltoid: Acting as a whole prime mover of arm abduction.  can aid in flexion, extension and rotation.
Infraspinatus: lateral rotation of the humerus. also stabilizes the shoulder.

Muscles that move the forearm:
Biceps Bracii: flexion of elbow.  supination of forearm.
Brachialis: a major flexor of forearm
Brachioradialis: synergist in forearm flexion
Triceps Brachii: powerful forearm extensor.
Supinator: acts with biceps brachii to supinate forearm
Pronator Teres: acts synergistically with pronator quadratus to protnate arm.

Muscles that move the hand:
Flexor Carpi Radialis: powerful flexor of wrist abducts wrist
Flexor Carpi Unlaris: powerful flexor of wrist. adducts wrist
Flexor Digitorium (Superficialis and Profundus): flexes wrist and middle phalanges.
Extensor Digitorium: prime move of finger extension.  extends wrist. abducts fingers (in fan motion)

Muscles of the abdominal wall:
External oblique: flexes and rotates the vertebral column, increases abdomen pressure, aids back muscles
Internal Oblique: flexes and rotates the vertebral column
Transverse Abdominis: compresses abdominal contents
Rectus Abdominis: flexes and rotates the vertebral column

Muscles used in breathing:
Intercostal (internal and external): aid in breathing and moves ribs.
Diaphragm: prime mover of inspiration, flattens on constriction, increasing vertical dimensions of the thorax

Muscles of the pelvic outlet:
Levator ani: supports the pelvic visera and provides a sphincterlike action to the anal canal and vagina.
Coccygeus:  supports the pelvic visera and provides a sphincterlike action to the anal canal and vagina.
Bulbospongiousus: males: empties the urethra. in females: constricts vagina.
Ischicavernous: assists functions of the bulbiospongiousus

Muscles that move the thigh:
Illiopsoas: (Psoas Major and Iliacus): flex trunkon thigh. flex though. lateral flexion of the vertebral column.
Gluteus Maximas: complex. powerful thigh extensor. laterally rotates and abducts though.
Gluteus Minimus: abducts and medially rotates thigh. steadies pelvis.
Tenor Fasciae Latae: flexes, abducts and medially rotates the thigh.  steadies trunk.
Adductor Longus: adducts and medially rotates and flexes the thigh.
Gracillis: adducts thigh. flexes and medially rotates leg, especially while walking.

Muscles that move the leg:
Biceps Femoris: (hamstring) extends thigh, laterally rotates leg. flexes knee.
Semitendinous: extends thigh, flexes knee. laterally rotates leg.
Semimembranosus: extends thigh. flexes knee. laterally rotates leg.
Satorius: flexes, abducts and laterally rotates thigh. flexes knee.
Rectus femoris: (quad) extends knee and flexes thigh at hip
Vastus Lateralis: extends knee and stabilizes knee
Vastus Medalis: extends and stabilizes knee
Vastus Intermedius: extends knee

Muscles that move the foot:
Tibialis Anterior: prime move of dorsifexion; inverts foot. supports longitudinal arch
Extensor hallicus longus: extends hallux. dorsiflexes feet.
Soleus: plantar flexion. good for locomotion
Gastrocnemius: plantar flexes foot when knee is extended

Wednesday, June 16, 2010

A little more about muscle tissue.

Botulinum Toxin is a bacterial toxin that blocks the release of acetyl choline from synaptic vesicles.  Botulinum toxin can be found in improperly canned foods.  A tiny amount can paralyze respiratory muscles and cause death.  Even though this can be deadly it is the primary ingredient in Botox.  It can help with strabismus, blepharospasm, spasms of the vocal cords that interfere with speech, cosmetic treatment and to alleviate chronic back pain due to muscle spasms. 

Curare is a plant poison that was used on arrows and blowgun darts.  It causes muscle paralysis by blocking acetyl choline receptors, thus inhibiting sodium ion channels.  Derivatives of curare are used during surgery to relax skeletal muscles. 
Anticholinesterase can slow the of Achase and removal of acetyl choline.  This chemical can strengthen weak muscle contractions.  It is treatment for myasthenia gravis, an antidote for curare poisoning and terminate the effects of curare after surgery. 

Muscle tension is controlled by the brain.  The axons of motor neurons are branched and innervate several muscle fibers within a muscle.  A motor unit is a single motor neuron and all the muscle fibers it innervates.  Recruitment occurs when contraction of more muscle fibers by stimulating more motor units in order to generate greater tension in a muscle.  2-3 muscle fibers per motor unit power our voice muscles.  10-20 muscle fibers per motor unit power eye movement.  2000-3000 muscle fibers move our arms and legs. 
A muscle twitch is a single contraction that lasts only a fraction of a second. 
Summation occurs when a muscle contraction is increased until maximal sustained contraction is reached. 
Tetanus is the maximal sustained contraction.
Tone is a continuous slight tension maintained by motor units that take turns contracting.  Muscle tone keeps skeletal muscles firm and keep the head from slumping forward on the chest. 

Skeletal Muscle fibers vary in their amount of myoglobin, mitochondria and capillaries.  Red muscle fibers have more myoglobin, capillaries and mitochondria than white muscle cells.  Contraction and relaxation speeds vary based on how fast myosin ATPase hydrolyzes ATP.  Resistance to fatigue depends on different metabolic reactions used to generate ATP. 
Slow oxidative muscle fibers are red in color and very resistant to fatigue, but they are the least powerful and smallest in diameter.  They make ATP aerobically. 
Fast oxidative muscle fibers are pinkish in color and they are glycolytic.  They have lots of mitochondria, myoglobin and blood vessels.  They split ATP very, very fast. 
Fast glycolytic muscle fibers are white in color.  It is most often used in anaerobic activity for a short duration.  They are the largest in diameter and make ATP via glycolysis. 

Most muscles contain a mixture of all fiber types, but remember that each motor unit only powers one type of cell.  Exercise can change the characteristics of skeletal muscles fibers to some degree, but not the number of cells. 

Cardiac muscles are striated, short, quadrangular-shaped, branching fibers.  They have a single centrally located nucleus.  Cells connected by intercarlated discs with gap junctions.  They have the same arrangement of thick and thin filaments as skeletal.  Cardiac muscles have more mitochondria compared to skeletal muscle fibers, contractions last 10-15 times longer due to prolonged delivery of calcium from the sarcoplasmic reticulum and the extracellular fluid.  They are involuntary and contract by themselves or from each other.  This continuous, rhythmic activity is a major physiological difference between cardiac and skeletal muscle tissue.  Skeletal muscle depends on aerobic respiration to generate ATP.  

Anatomy of smooth muscles are usually involuntary.  The action potential spread through fibers by gap junctions.  Fibers are stimulated by neurotrasnmitters or hormones.  Myofilaments are randomly organized and have no sarcomeres.  They lack striations and transverse tubles.  Contractions of smooth muscles are initiated by calcium flow primarily from the interstitial fluid.  Calcium moves slowly out of the muscle for delaying muscle relaxation.  In smooth muscle, the regulator protein that binds calcium ions in the cytosol is calmodulin. 

Monday, June 14, 2010

Muscle tissue

As we have previously mentioned, there are three types of muscle tissue: skeletal, cardiac and smooth. When we refer to the muscle system, we generally speak specifically of the skeletal system.

As just a quick comparison of the three different types of muscle tissue...

Smooth muscle is spindle shaped and non-striated.  It surrounds our tubes and helps things move.  Smooth muscle in involuntary.  The smooth muscles contract and release slowly.

Cardiac muscle is also involuntary.  It is branched and striated and is only located on the heart.  The network of fibers contract as a unit and are self-exciting.

Skeletal muscle is striated and tubular.  It is usually attached to the skeleton and is almost completely voluntary.  Contraction and releasing occurs very quickly. 

All muscle tissue has several functions.  They move something.  They help to stabilize part of the body.  Muscles store and move substances in the body.  Maintenance of homeostasis.  

Muscle tissue also has several properties.  It is excitable (responds to chemicals released from nerve cells), conductive (ability to propagate electrical signals over membrane), contractile (ability to shorten and generate force), extensive (ability to be stretched without damaging the tissue... to a degree) and elastic (ability to return to original shape after being stretched). 

The muscular system is the voluntarily controlled muscles of the body.  Most skeletal muscles also are controlled subconsciously to some extent, such as the diaphragm.  Each muscle is an organ composed of skeletal muscle tissue and connective tissue.  Skeletal muscles are also called fibers or myofibers.

The connective tissue of muscles includes facia, perimysium, endomysium, tendons and aponeuroses. There are two types of facia, superficial (this is loose connective tissue and fat underlying the skin) and deep (dense irregular connective tissue around the muscle). Epimysium is the outermost connective tissue that surrounds the whole muscle.  It separates 10-100 fibers into fascicles.  The perimysium surrounds fascicles.  The endomysium separates individual muscle cells.  At the end of the muscle belly, a tendon is formed and attaches to the bone.  Aponeuroses are the connective tissue sheets attaching to bone or adjacent muscles. 

Intramuscular injections are used to give relatively large doses of drugs that can't be administered to the bloodstream.  If administered directly to the bloodstream, it could be extremely dangerous or fatal. 

Neurons that stimulate muscles to contract are called efferent neurons.  Muscle action depends on a rich blood supply to deliver nutrients and oxygen. 

The anatomy of a skeletal muscle consists of the whole muscle which is of the organ level.  The fascicle which is a single bundle of cells.  The muscle fiber is a single muscle cell.  You are born with all of the muscle cells you will ever have, the just get bigger when you exercise.  Muscle growth is called hypertrophy. 

The anatomy of a muscle fiber is a bit more.  The muscle cells contain most of the normal cell components.  Sarcolemma, T tubules and sarcoplasm are additional/different organelles.  The sarcomeres are the units of myofibrils.  Myofibrils are the bundles of myofilametns that contract.  There are two types of myofilaments: actin and myosin; their function and structure is wholly for muscle contractions.  Sarcoplasm reticulum is a modified endoplasmic reticulum that surrounds myofibrils and stores calcium.  A contraction of muscle is when the microfilaments slide past one another causing the muscle to shorten. 

Muscle proteins include contractile proteins and structural proteins.  Myosin is a thick filament as well as a contractile protein.  It resembles golf clubs or oars sticking off a boat.  Myosin converts ATP to energy of motion.  Actin is another contractile protein.  But instead of being thick like myosin, it is rather thin.  It provides a site where a myosin head can attach.  Tropomyosin covers the binding site for myosin on the actin strands.  Tropinin moves tropomyosin off the binding sites so that myosin can bond to it.  Structural proteins include titin which stabilizes the position of myosin at the M line and dystrophitin which links thin filaments to the sacrolemma. 

Physiology of muscle contractions:
motor neurons
action potential in muscle
role of calcium
tropopmyosin uncovers binding sites
cross bridging
role of ATP

Muscle Metabolism:
A huge amount of ATP is needed to power the contraction cycle and pump calcium into the sacroplasm.The ATP inside muscle fibers will only power contractions for a few seconds.  ATP must be produced by the muscle fiber after reserves are used up.  There are three ways that muscle fibers can do so: creatine phosphate, anaerobically and aerobically. 

Creatine phosphate is made by excess ATP.  Creatine phosphate transfers its high energy phosphate to ADP regenerating new ATP, but this is only useful for 8-15 seconds. 

Anaerobic respiration uses glucose to make ATP when creatine phosphate is used up.  The process gets glucose from the blood and glycogen from muscle fibers.  It makes 2 pyruvic acids and two ATP.  Pyruvic acid is converted to acetic acid and carried away by the blood.  This process is only good for about 30-40 seconds. 

Aerobic respiration occurs when an activity lasts longer than 30 seconds.  Aerobic respiration provides 90% of the needed ATP in activities lasting more than 10 minutes.  Pyruvic acid enters the mitochondria and is completely oxidized generating ATP, water, CO2 and heat.  Each molecule of pyruvic acid generates 36 ATP.  Muscle has two sources of oxygen, hemoglobin (from the blood) and myoglobin (from the muscle cell).  Myoglobin and hemoglobin are oxygen-binding proteins. 

Myoglobin stores some oxygen and reduces the muscle's constant need for blood supply during muscle contractions.  Muscle contractions compress blood vessels.  After exercise, heavy breathing continues to get oxygen back into the system.  Oxygen debt occurs when additional oxygen is used to restore muscle cells to resting level in three ways: the liver cells convert lactic acid into glycogen, to synthesize creatine phosphate into ATP and to replace the oxygen removed from myoglobin.

Fatigue occurs from a lowered pH, thanks to lactic acid.  Following exercise, muscle cramps are mostl ikely due to a temporary deficit of ATP.   Athletes experience less muscle fatigue because they produce less lactic acid. 

there is a little more, but that will way until after the test tomorrow.

Sunday, June 13, 2010


Joints hold bones together but permit movement.  There are three different types of contact between tissues.  Bone to bone, cartilage to bone and teeth to bone.  Arthrology is the study of joints and kinesiology is the study of motion.  Joints are classified by both structure and function.  Structural classifications are based on the presence or absence of a synovial cavity and type of connecting tissue.  There are three kinds: 1. fibrous (bones are held together by dense collagen fibers), 2. cartiliginous (joints are held together by cartilage) and 3. synovial (held together by ligaments).  Functional classification is based upon how much it can move and there are also three kinds.  1. immovable or synarthrotic, 2. slightly movable or amphiarthrotic and 3. freely moveable or diarthrotic.

Fibrous joints do not have a synovial cavity.  The articulating bones are held closely together by dense irregular connective tissue.  They permit little or no movement.  They are also sometimes called sutures (ragged edges of adjacent bones re held together by fibers).

Cartilaginous joints lack a synovial cavity as well.  There are two types.  1. synchondroses which are bones held together by hyaline cartilage that are synarthrotic and 2. symphyses that are bones held together by fibrocartilage that are amphiarthrotic.

Synovial joints have a synovial cavity that allow them to be diarthrotic.  The articular cartilage covers ends of bones to reduce friction and absorb shock.  The articular capsule has two layers that surround the joint.  Fibrous capsule is the ligaments that attach to periosteum around the bone.  The synovial membrane is the inner lining of the capsule and is loose connective tissue.  The synovial membrane secretes synovial fluid.  The synovial fluid brings nutrients to articular cartilage because cartilage is avascular.  There are two accessory ligaments: the extracapsular ligaments and the intracapsular ligaments (acl).  The menisci stabilize the joint by providing a better fit of articulating bones.  There are medial and lateral menisci of the knee: c-shaped like 2 half stadiums facing each other.  Bursae are the saclike structures of connective tissue that are lined with synovial membrane and filled with synovial fluid  They function in cushioning and reducing friction.

The types of movement at synovial (diarthrotic) joints include:
1. gliding movement: the simple movement of back and forth and side to side.
these are mostly found in intercarpal joints.  They permit mainly sliding, back and forth and twisting movements.
2. angular movement: increases or decreases the angle between articulating joints.
a. flexion: decreasing the angle between bones. ex: bending the trunk forward
b. extension: increasing the angle between bones.  ex: in anatomical position, the body is in extension.
c. hyperextension: continuation of extension beyond anatomical position.
d. abduction: movement away from the midline
e. adduction: movement toward the midline
f. circumduction: making a cone with the distal end of the bone.
3. rotation: a bone revolves around it's longitudinal axis ex: turning your head side to side to say no.
4. special movements.
a. supination: turning palms up
b. pronation: turning palms down
c. plantar flexion: standing on tippy toes
d. dorsiflexion: press soles of feet together and lift arch medially
e. eversion: press soles away from each other and press arch medially
f. depression: lovering a body region
g. elevation: raise a body region
h. protraction: move body part anteriorly
i. retraction: move protracted body part back to normal.

Types of synovial joints:
Planar joints primarily permit back and forth or side to side movement.  These include intercarpal and intertarsal joints.
Hinge joints have a spool that fits into a concave area.  They permit flexion-extension movements.  The knee and elbow are good examples.
A pivot joint is when the rounded surface of bone articulates with a ring formed by second bone and ligament.  Monoaxial since it allows only rotation around the longitudinal axis.  Examples include the proximal radioulnar joint of the hand.
Condyloid or Ellipsoidal joints are oval shaped projections that fit into an oval depression.  They are biaxial and can flex/extend or abduct/adduct.  The best example is your wrist.
A saddle joint looks like a person riding on a saddle.  Examples include the thumb joint.
The ball and socket joint has a ball that fits into a cuplike depression.  Movement is capable in all planes and rotations.  The only examples include the hip and shoulder.
A sprain is a stretch or tear of a ligament.  More serious sprains involve complete tears of one or more ligaments.  A common knee sprain involves the anterior cruciate ligament.
Strains are defined as a partially or completely torn muscle or tendon.  Patellar tendinitis or jumper's knee is a common strain that usually results from overuse.  Tendonitis is an inflammtion of the tendons and synovial membranes surrounding certain joints.

Appendicular Skeleton

The appendicular skeleton has one primary function: facilitate movement! Within the appendicular skeleton, there are 126 bones in for areas.  The upper limbs have 60, the lower limbs have 60, the pectoral girdle has 4 and the pelvic girdle has 2.

The pectoral girdle is also known as the shoulder.  There are two of them, therefore two of each bone.  The pectoral girdle is made of the scapula and the clavicle.  The clavicle is an s-shaped bone.  The medial curve is convex posteriorly, while the lateral curve is concave anteriorly. It extends from the sternum to the scapula, above the first rib.  Where the two curves meet is a common fracture site. The medial side articulates with the manubrium of the sternum forming the sternoclavicular joint.  The lateral end articulates with the acromium forming the acromioclavicular joint.  Ligaments attached to the clavicle to stabilize its position.
The scapula is also called the shoulder blade.  For the amount of work that it does, it is extremely thin.  It is triangular is shape.  It articulates with both the radius and the humerus.  It is held in place posteriorly by complex shoulder and back musculature.  The medial borders of the scapulae lie about 5 cm from the vertebral column.  The scapula has four main features.  The spine is a large process on the posterior of the scapula that ends laterally as the acromion.  The acromian is the flattened portion of the spine on the scapula.  The coracoid process is a protruding projection that provides the point of attachment for the biceps trachiae.  The gelnoid is a shallow concavity that articulates with the head of the humerus.

Each upper limb consists of 30 bones.  The humerus, ulna, radius, carpals, metacarpals and phalanges.  Joints include the shoulder, elbow, wrist, metacarpophalageal and interphalageal.  
The humerus is the largest and longest bone of the upper limb.  It articulates proximally at the scapula at the glenoid cavity and distally with the ulna and radius at the elbow.  At the proximal end of the humerus, we find a rounded head, a greater tubercle (the lateral projection, distal to the neck), lesser tubercles for muscle attachment, the deltoid tuberosity and the body.  The distal end of the humerus has 2 condyles.  The capitulum laterally articulates with the the head of the radius.  The trochlea is the medial articulation with the ulna.  Medial and lateral epichondyles are the attachment sites for muscles.  
The radius and ulna make up the forearm.  On the medial side is the ulna.  The radius is on the lateral side.  The radius turns the radio (with the thumb).  Each bone articulates with the humerus and three carpal bones.  At the proximal end of the forearm, the ulna has the olecranon process that forms the point of the elbow.  The radius head articulates with the capitulum of the humerus and radial notch of ulna tuberosity for the biceps attachment. At the distal end of the forearm, the styloid process of the ulna is the site of attachment for wrist ligaments.  The radius forms wrist joints with carpals.
Eight carpal bones bound together by ligaments form the wrist.  Five metacarpal bones are in the palm of the hand (one for each finger and the thumb).  These make up knuckles.  14 phalanges are create the fingers and the thumb.

The Pelvic girdle is also known as the hip girdle.  This area provides strong and stable support for the lower appendages.  It also allows for some flexibility.  There is less flexibility than the pectoral girdle however, because it it more stable.  There are two hip bones that are also known as coxal bones or ossa coxae.  Each hip bone is composed of three bones at birth, the illium, ischium and the pubis.  These three bones fuse at the acetabelum during childhood to form the socket for the hip joint.  The ischium is the inferior, posterior portion of the hipbone.  The ischial spine and tuberosity are located here.  It forms the obturator foramen with the pubis which is the largest foramen in the body.  The pubis is the body that is superior and inferior to ramus.  It is the area that is linked to pubic symphysis.  The illium forms the illiac crest, a site for muscle attachment.  It is anterior and superior to the iliac spine. It can be felt laterally to groin.  The greater sciatic notch is here for the sciatic nerve.  The pelvis is made of the sacrum, coccyx and 2 hip bones.  The pelvic brim is from the top of the symphysis to the sacral promontory.  The false pelvis is above the brim, while the true pelvis is below the brim.

Each of the lower limbs, like the upper limbs has 30 bones.  The femur and patella within in the thigh, the tibia and fibula are in the leg, the tarsals in the ankle. the metatarsals are the foot and the phalanges are the toes.  The joints include the hip, knee and ankle, proximal and distal tibiofibular, and metatarsophalangeal.

The femur is aka the thighbone.  It is the largest, heaviest and strongest bone in the body.  It articulates with the hip bone and tibia.  The head of the femur articulates with the acetabulum.  The tibia articulates with both the medial and lateral condyles.  The neck of the femur is a constricted region distal to the head and it is a common fracture site among the elderly.  The trochanters are a bony landmark that can only be found on the hip bone.  There are greater and lesser trochanters, linea aspera and muscle attachments.

The patella, aka the kneecap, is the only sesamoid bone in the body and is located anterior to the knee joint.  It functions to increase the leverage of the tendon of the quadriceps femoris to maintain the position of the tendon when the knee is bend and to protect the joint.

The tibia is the shin bone and does all of the weight bearing.  It is larger and medial to the fibula.  The fibula is lateral and parallel to the tibia.  The tibia has lateral and medial condyles that articulate with the femur.  The tibial tuberosity os for the patellar ligaments of the quadricep femoris.  The medial malleolus is at the ankle and is the articulation point for the talus. The fibula is not in the knee.  Its main function is for attachment of muscles.  There is a lateral malleolus at the ankle.

There are seven tarsals that make the ankle and share the weight associated with walking. Five metatarsal bones are contained in the foot.  Dancers, especially ballet, fracture their metatarsals.  The arrangement of the phalanges in the toes is the same as the phalanges of the hand and is the same as described above.  The big toe is known as the hallux.

The ankle is made of seven tarsal bones.  The talus is the ankle bone and articulates with the medial malleolus of the tibia and the lateral malleolus of the fibula.  The calcaneous is the heel bone and is the largest and strongest bone in the foot.

The bones of the foot are arranged in two arches held together by ligaments and tendons.  They enable the foot to support and distribute body weight over the hard and soft tissues and provide leverage while walking.  The arches are fully developed by about age 12-13.  Flatfoot (decline), clawfoot (elevation) and clubfoot (rotation) are caused by the medial longitudinal arches.  Arches provide yield and spring back when weight is lifted.  Longitudinal arches from heel to toe along each side and the transverse arch is across the midfoot region.

Axial Skeleton

The axial skeleton is one of the two parts of the skeletal system.  It has 80 bones that compose the skull, ribs, spine/vertebrae, sternum, ear ossicles and the hyoid bone.  The axial system can be broken down even further.  The skull has 22 bones, 8 in the cranium and 14 in the face; there is one hyoid bone, 6 auditory ossicles, 26 vertebrae, 1 sternum and 24 ribs.

The Skull
The Skull is made up of cranial and facial bones.  In general, the skull serves as a place for cavities, paranasal sinuses, mandible and suture bones.
The frontal bone is a part of the cranium.  There is only one.  It forms the forehead, roof of the orbits (eyes) and anterior cranial floor.  The coronal suture connects the frontal bone to the parietal bones.
The parietal bones are the 2nd and 3rd bones of the cranium. They form the roof of the cranium.  There are four sutures involved with the parietal bones: the first is the coronal suture that connects the parietal bones to the frontal bone.  The second is the saggital suture that connects the two parietal bones together.  The lamboid suture connects the parietals to the occipital bone.  The squamous suture connects the parietal bones to the temporal bones. 
The occipital bone is the 4th bone of the cranium.  There is only one.  It is the back of the skull and base of the cranium.  There is the foramen magnum that is the opening for the spinal cord, vertebral and spinal arteries to leave the head.  The external occipital protuberance (a projection that sticks out from the occipital bone) is the bump just above our necks.  This joins together with the axis of the vertebrae to allow us to nod our head yes.  The ligament that allows us to do this is called the ligamentum nuchae.  The lamboid suture connects the occipital bones to the parietal bones.
The temporal bones are the 5th and 6th bones of the cranium.  They are the sides of our cranium, as well as the floor.  It is also the floor and side of each orbital.  The squamous suture attaches the temporal bones to the parietal bones.  The temporal bones are the location of the external acoustic (auditory) meatus, the mastoid process (neck muscle attachment point), the styloid process (one of the tongue muscle attachment points) and the zygomatic process. 
The sphenoid bone is the 7th bone and base of the cranium, sides of the skull, floor and sides of the orbits.  It has a sella tuchica and the sphenoid sinus. 
The ethmoid bone is the 8th bone of the cranium.  It makes up the anterior portion of the cranial floor, the medial walls of the orbits.  The perpendicular plate makes our septum and is on the ethmoid bone. 

Facial Bones
There are 14 facial bones: 2 nasal, 2 maxillae, 2 zygomatic, 2 lacrimal, 2 palentine, 2 inferior nasal conchae, 1 mandible, and 1 vomer.  I'm not going to cover the palentine or lacrimal bones because we aren't going to be tested on them.
The maxillary bones are the floor of our orbits, the nasal cavity or hard palate.  A cleft plate occurs when the amxillae don't fuse together.
The zygomatic bones are the prominences of our cheeks.  They form the lateral walls and floor of our orbits.  The temporal process joins to the zygomatic process of the temporal bone.
The nasal bones make up the bridge of our nose.
The vomer is our nasal septum.  It divides the nose into left and right cavities.  If someone has a deviated septum, the septum is not directly in the middle of the nose.
The mandible is the only movable part of our skull.  It is horseshoe shaped with a flat ramus going upward at the ends.  The mandibular condyle is a fossae of the temporals.  The mandibular notch is between the condylar and coronoid processes. 
The orbits, as I've mentioned, have 7 bones that make them up.  The roof is formed by the frontal and sphenoid bones.  The lateral wall is formed by the zygomatic and sphenoid bones. The floor is the maxilla, zygomatic and sphenoid.  The medial wall is made of the maxilla, lacrimal, ethmoid and sphenoid.

The hyoid bone is the only bone in the body that does not articulate with another bone.  It is u-shaped. It is suspended by ligaments and muscle from the skull.  It helps support the tongue, and provides attachment for the tongue, neck and pharyngeal muscles.

Moving onto the Vertebral Column
The vertebral column is composed of 7 cervical vertebrae, 12 thoracic vertebrae, 5 fused vertebrae, a sacrum (5 fused vertebrae) and a coccyx (4 fused vertebrae).  Each of the four curvatures of the vertebrae make sense.  The cervical vertebrae make the cervical curvature, the thoracic vertebrae make the thoracic curvature, the lumbar curvature comes from the lumbar vertebrae and the sacrum and coccyx make up the pelvic curvature.  (Which makes sense because the top of the sacrum and the top of the pelvic girdle match up).
The vertebrae are separated by intervertebral discs.  These help absorb vertical shock.  The discs permit various movements within the column.  They are a fibrocartilagenous with a pulpy center.  When one or more of the discs are injured, the nucleus pulposes protrudes into the ring, which causes pressure to be put on the spinal nerves.  Surgically removing a disc is called laminectomy.
Every vertebrae has several parts.  Different vertebrae have different prominent parts.  The body is the weight bearing part and is anterior to the rest of the vertebrae.  The vertebral foramen is the opening for blood vessels and the spinal cord.  There are seven processes (projections).  There are two transverse processes, one spinous process and four articular processes.  The intervertebral notch forms the intervertebral foramen with the next vertebrae.  
The spinal canal is the vertebral foramen all linked together.  Intervertebral foramen allow the spinal cord to leave leave the spine.
The seven cervical vertebrae are at the top of the spine.  The first one is called the atlas.  It allows the skull to say yes.  The second vertebrae is called the axis.  It is the only one to have a dens. The dens allows the head to say no.  Cervical vertebrae 3-6 are typical vertebrae.  The 7th, vertebrae pominens is different, it has a more prominent spinous process.
Thoracic vertebrae articulate with ribs.  There are 12 of them and they have larger and stronger bodies.  Thoracic vertebrae also have longer transverse and spinous processes.  Facets and demifacets articulate from the body of the vertebrae to the head of the ribs.
Lumbar vertebrae are the largest and strongest.
The sacrum is the union of 5 vertebrae by age 30.  The median sacral crest was the spinous process.  The sacral ala is a fused transverse process.
The coccyx is the union of 4 fused vertebrae by age 30.  Caudal or epidural anesthesia is inserted into the sacral to anesthetize sacral and coccygeal nerves.

The Thorax is the extire chest.  It consists of sternum, costal cartilage, ribs and bodies of thoracic vertebrae.  The thorax is a bony cage that is flattened from front to back.   The sternum consists of the manubrium (1st and 2nd ribs); it is the sternal angle junction within the body.  The body of the sternum is the costal cartilage of ribs 2-10.  The sternum's xiphoid is at the most inferior of the sternum.  It has the xiphisternal joint and is the location for CPR as well as a connection site for abdominal muscles.
We have 24 ribs.  They increase in length from ribs 1-7.  After the 7th rib, they decrease in size.  The head and tubercle articulate with facets of the vertebrae.  The tubercle of the rib articulates with the transverse process of the vertebrae, while the head articulates with the vertebral bodies.

Friday, June 11, 2010

Bone Markings

There are two major types of bone markings. 
1. depressions and openings  (joints or allow for the passage of soft tissue)
2. processes or projections (outward growths that either form joints or serve as attachment points for connective tissue. 

The specific names and definitions of Depressions and Openings include:
Fissure: a narrow slit between adjacent parts of bones
Foramen: an opening that blood vessels, nerves and/or ligaments can travel through. 
Fossa: a shallow depression
sulcus: This is a furrow along a bone that accommodates a blood vessel, nerve or tendon. 
Meatus: tube-like opening

The specific names and definitions of Processes and Projections:
Joint forming Processes or Projections:
Condyle: a large round protuberance at the end of a bone
Facet: a smooth, flat articular surface
Head: a rounded articular projection supported on the neck of a bone

Processes that form attachment points for connective tissue:
Crest: is a prominent ridge or elongated projection
Epicondyle: the projection above (epi-) a condyle (a large round protuberance at the end of a bone)
Line (or Linea): a less prominent form of a crest
Spinous process: sharp, slender projection
Trochanter: very large projection
Tubercle: small, rounded projection
Tuberosity: larger rounded, but rough projection

Throughout the skeletal system, I'll be pointing out different bony landmarks using these terms, so remember them!