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