The Muscular System

BIO 231

Anatomy and Physiology

 

Muscle Organization

  Muscle s pull never push

  As a muscle shortens, its insertion (attachment on the movable bone) moves toward its origin (fixed or immovable point of attachment)

  Thus what one muscle (or group) does another muscle (or group) “undoes”

Muscle Organization

   Prime movers (agonist) - provides the major force for a specific movement

   Antagonists - muscle that oppose or reverse a particular movement

   Synergists - muscles that help prime movers

   Fixators - synergists that immobilize a bone or muscle origin

  There are fixator muscle from the axial skeleton to the scapula - thus only shoulder joint movements occur

Naming Muscles

   Location - name from the bone or body region

  e.g. temporalis muscle , intercostal muscles

   Shape

   e.g. Deltoid - triangular shape

   Relative size

  e.g. maximus, minimus, longus, brevis

   Direction of muscle fibers

  e.g. rectus (straight), transversus & oblique

Naming Muscles

   Number of origins

  biceps, triceps, quadriceps (2, 3 or 4  origins)

   Locations of attachments

  e.g. sternocleidomastoid - dual origin on sternum & clavicle & inserts on the mastoid process of the temporal bone

   Actions

  e.g. flexor, extensor or adductor

Arrangement of Fascicles

  Fascicle - bundle of muscle fibers segregated from the rest of a muscle by connective tissue

Muscle of Scalp

  Epicranius - main scalp muscle - bipartite

  Frontalis & occipitalis

Muscles of the Face

  Corrugator supercilii - works with obicularis oculi  - draws eyebrow together - wrinkles forehead (frowning)

  Obicularis oculi - sphincter of eyelid - surrounds rim of the orbit - blinking and squinting - draws eyebrows inferiorly

Muscles of the Face

   Zygomaticus - major & minor - raises lateral corner of the mouth - smiling

   Risorius -  inferior & lateral to zygomaticus - synergist of zygomaticus

   Lateral Labii superioris - open lips & furrounds upper lip

   Depressor anguli inferioris - draws lower lip inferiorly (pouting)

Muscles of the Face

  Depressor anguli oris - zygomaticus antagonist - draws the corner of the mouth downward and laterally - grimace

  Obicularis oris - closes & protrudes lips - kissing and whistling

  Mentalis - protrudes lower lip & wrinkles chin

Muscles of the Face

  Buccinator - draws the corner of the mouth laterlly - compresses cheek (whistling & sucking) - holds food between teeth

  Platysma - helps depress mandible - pulls lower lip back & down - downward sag of mouth - tenses skin of the neck (shaving)

Muscles of Mastication

  Masseter - prime mover of jaw closure - elevates the mandible

  Temporalis - closes jaw - elevates and retracts mandible - synergist with pterygoids in side to side movements - maintains position of mandible at rest

Muscles of Mastication

  Lateral pterygoid - protrudes mandible - sliding and side-to-side movements (grinding)

Muscles Promoting Tongue Movements (Extrinsic)

   Genioglossus - primarily protrudes the tongue - but depress the tongue Or act with others to retract the tongue

   Hyoglossus - depresses tongue & draws it side ways

   Styloglossus - retracts ( and elevates) tongue

Muscles of Swallowing

   Swallowing begins when the tongue and buccinator muscles of cheeks - push food along the roof of the mouth to the pharynx

   Next - pharynx is widened, glottis is covered with epiglottis

  Accomplished by suprahyoid muscles - they pull the hyoid bone forward toward the mandible

  The hyoid bone is  connects to the thyrohyoid membrane to the larynx - it is now pulled upward and forward - this widens the pharynx & closes off the glottis

Muscles of Swallowing

   The nasal passages are also closed off since the soft palate is elevated

  tensor & levator veli palatini

   Food is propelled through the pharynx and into the esophagus inferiorly by the pharyngeal constrictor muscles

   The infrahyoid muscle return the hyoid bone and larynx to their inferior positions after swallowing

Muscles of Swallowing

Head Movements

  Head flexors - sternocleidomastoid muscles

  Suprahyoid and infrahyoid muscles are synergists

  Lateral head movement - sternocleidomastoids and deeper neck muscles - scalenes

  Head extension - splenius

Trunk Movements

  Erector Spinae - largest group of back muscles

  Iliocostalis - extend vertebrae - maintain erect posture - bend column to one side

  Longissimus -  thoracis & cervicis - act together - extend column - bend laterally

capitis - extends the head & turns the face toward the same side

  Spinalis - extends vertebral column

Trunk Movements

   Semispinalis - extends vertebral column & head & rotates them to the same side - synergistic with sternocleidomastoid

   Quadratus lumborum - Flexes vertebral column laterally separately -  When the pair works together - lumbar spine is extended & 12th rib is fixed - maintains upright posture - acts in forced inspiration

Muscles of the Thorax: Breathing

   External intercostals - with 1st rib fixed by scalene muscles - pull ribs toward one another - elevates rib cage

   Internal intercostals - with 12th rib fixed by quadratus lumborum, muscles of posterior abd. wall & obliques - they draw ribs together & depress the rib cage - aid in forced expiration

   Diaphragm - prime mover of inspiration - medial superficial flattens on contraction

Trunk Movements

   Rectus abdominis - flex & rotate lumbar region of vertebral column - fix & depress ribs, stabilize pelvis during walking - increase intrabdominal pressure

   External oblique - most superficial - when pair contracts - aids rectus abdominus in flexing the vertebral column - compresses abdominal wall

   Internal oblique -  same as ext. oblique

   Transversus abdominus -  compresses abdominal contents

Compression of Abdominal Wall

    When all abdominal muscles contract  in unison - different activities may be effected depending on which muscles are activated simultaneously

    If all are contracted, the ribs are pulled inferiorly & abdominal contents compressed

   This pushes the viscera up against the diaphragm - forced expiration

    When all are contracted with the diaphragm and the glottis is closed

   Valsalva manuever

   Increased abdominal pressure - promotes urination, defecation, childbirth, vomiting, coughing, screaming, sneezing, and nose blowing

Pelvic Floor

    Paired muscles - levator ani & coccygeus - form pelvic floor

    Urogenetial diaphragm - triangular - pierced by the rectum, urethra & vagina in females - contains the sphincter urethrae - voluntary control of urination

    Superficial to the diaphragm are ischiocavernous & bulbospongiosus - help maintain erection  of penis  & clitoris

    More posterior - external anal sphincter

    Just anterior the anal sphincter - central tendon of the perineum

Movements of the Scapula - Anterior Thorax

    Pectoralis minor - ribs fixed - draws scapula forward - scapula fixed draws rib cage superiorly - obscured by pectoralis major - lies over it

    Serratus anterior - deep to the scapula & inferior to the pectoral muscles - lateral rib cage - prime mover to protract & hold scapula against the chest wall - rotates scapula - important in abduction & raising the arm

    Subclavius - rib 1 to clavicle - help stabilize & depress pectoral girdle

Movements of the Scapula - Posterior Thorax

  Trapezius -  most superficial - flat & triangular shape - stabilizes, raises, retracts & rotates scapula - inferior fiber depress scapula & shoulder

  Levator scapulae - back side of neck - deep to trapezius - elevates /adducts scapula with superior trap fibers - tilts glenoid cavity downward & flexes neck to side

Movements of the Scapula - Posterior Thorax

  Rhomboids - two rectangular muscles - deep to the trapezius -  act together & with middle trapezius to retract scapula (square up the shoulders) - also rotates glenoid cavity downward such as in paddling a canoe

Muscles Crossing the Shoulder Joint - Arm Movements

    Pectoralis major - fan shaped - covers upper portion of the chest - prime mover of arm flexion - rotates arm medially - adducts arm against resistance - with scapula fixed (pulls rip cage upward) - used in climbing, throwing and in forced inspiration

    Latissimus dorsi - broad triangular muscles of lower back - covered by trapezius superiorly - prime mover of arm extension - powerful arm adductor - medially rotates the shoulder - depresses the scapula  - thus involved in powerful downward movements such as striking a blow, hammering and swimming

Muscles Crossing the Shoulder Joint - Arm Movements

   Deltoid - thick multipennate muscle - forms the rounded shoulder muscle mass - prime mover of arm abduction - antagonist of the pectoralis major and latissimus dorsi - if only anterior fibers active (powerful flexion and medial rotation of the humerus) - if only posterior fibers active (effects extension and lateral rotation of the arm) - active during rhythmical arm movements

Muscles Crossing the Shoulder Joint - Arm Movements

   Subscapularis - posterior wall of axilla - chief medial rotator if the humerus - also holds head of humerus in glenoid cavity

   Supraspinatus - on posterior aspect of the scapula - deep to the trapezius - rotator cuff muscle - stabilizes shoulder joint

   Infraspinatus - partially covered by deltoid and trapezius on the scapula - helps hold humerus head in glenoid cavity

Muscles Crossing the Shoulder Joint - Arm Movements

   Teres minor - small, elongated - lies inferior to the intraspinatus - rotator cuff muscle - helps hold humerus head in glenoid cavity (just like infraspinatus)

   Teres major - thick rounded muscle - inferior to teres minor - helps form posterior wall of the axilla - posteromedially extends, medially rotates and adducts the humerus (synergist with latissimus dorsi)

   Coracobrachialis - small cylindrical muscle - flexion and adduction of humerus - synergist of pectoralis major

Muscles Crossing the Elbow Joint - Forearm Movements

  Triceps brachii - large fleshy - three headed origin -Forearm extensor

  Anconeus - short triangular muscle - merges with the triceps on the humerus - abducts ulna during forearm pronation - synergist of triceps brachii in elbow extension

Muscles Crossing the elbow Joint - Forearm Movements

  Biceps brachii -  two headed fusiform muscle - flexes elbow joint and supinates the forearm

  Brachialis - strong muscle - deep to biceps brachii - major forearm flexor - lifts the ulna as biceps lifts the radius

  Brachioradialis - superficial muscle of the lateral forearm

Muscles of the Forearm - Movement of the Wrists,Hands and Fingers

   Pronator teres - two headed - pronates the forearm and weak elbow flexor

   Flexor carpi radialis - runs diagonally across the forearm midway - powerful flexor of the wrist - abducts the hand - weak synergist for elbow flexion

   Palmaris longus - small fleshy muscle with long insertion tendon - often absent - weak wrist flexor - tenses skin  & fascia of the palm during hand movements

Muscles of the Forearm - Movement of the Wrists,Hands and Fingers

  Flexor carpi ulnaris - most medial of the above - two headed -  powerful flexor of the wrist - also adducts hand in concert with extensor carpi ulnaris - stabilizes wrist during finger extension

  Flexor digitorum superficialis - two headed - intermediate layer - flexes wrist & middle phalanges

Muscles of the Forearm - Movement of the Wrists,Hands and Fingers

   Flexor pollicis longus - partially covered by flexor digitorum superficialis - parallel the flexor digitorum profundus laterally - flexes distal phalanx of the thumb

   Flexor digitorum profundus - overlain by flexor digitorum superficialis -  slow acting flexor of any or all fingers - assists in flexing the wrist

   Pronator quadratus - deepest muscle of the forearm - prime mover of forearm pronation, acts with the pronator teres - also helps hold ulna and radius together

 Muscles of the Forearm - Movement of the Wrists,Hands and Fingers

   Extensor carpi radialis longus -  parallels brachioradialis - extends wrist in conjunction with extensor carpi radialis - abducts wrist in conjunctyion with flexor carpi radialis

   Extensor carpi radialis brevis - shortrer than above -  extends and abducts wrists - acts synergistically with extensor carpi radialis longus to steady wrist during finger flexion

Muscles of the Forearm - Movement of the Wrists,Hands and Fingers

   Extensor digitorum -  medial to Extensor carpi radialis brevis - detached portion extends to little finger (extensor digiti minimi)

   Extensor carpi ulnaris - most medial of the superficial posterior muscles (slender) - extends wrist in conjunction with extensor carpi radialis - adducts wrist with the flexor carpi ulnaris

Muscles of the Forearm - Movement of the Wrists,Hands and Fingers

   Supinator - deep at superior aspect of the elbow - assists the biceps brachii to forcibly supinate the forearm - works alone in slow supination

   Abductor pollicis longus - lateral and parallel to extensor pollicis longus - abducts and extends the thumb

   Extensor pollicis brevis & longus - deep muscle pair - extends the thumb

   Entensor indicis - tiny muscle - extends index finger & assists in wrist flexion

Muscles of the Forearm - Movement of the Wrists,Hands and Fingers

    Abductor pollicis brevis - abducts thumb

    Flexor pollicis brevis - flexes thumb

    Opponens pollicis - oposition - moves thumb to touch tip of little finger

    Adductor pollicis - adducts & helps top oppose thumb

Muscles of the Forearm - Movement of the Wrists,Hands and Fingers

    Abductor digiti minimi - abducts little finger at metacarpophalangeal joint

    Flexor digiti minimi brevis - flexes little finger at metacarpophalangeal joint

    Opponens digiti minimi - helps in opposition - brings metacarpal 5 toward thumb

Muscles of the Forearm - Movement of the Wrists, Hand and Fingers

    Lumbricals - 4 worm shaped muscles in palm - one for each finger - flex fingers at metacarpophalangeal joints - but extends fingers at the interphalangeal joints

    Plamar interossei - 4 long cone shaped muscles - adductors of the fingers - pull fingers in toward third digit - act with lumbricals to extend fingers at interphalangeal joints & flex at the metacarpophalangeal joints

    Dorsei interossei - four bipennate muscles - abduct (diverge) the fingers - extend fingers at interphlalngeal joints & flex at the metacarpophalangeal joints

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

    Iliopsoas - composed of two muscles - the iliacus & psoas major

   Iliacus - large fan shaped, more lateral - prime mover for flexing the thigh or flexing the trunk on thigh during a bow

   Psoas major - longer, thicker more medial - prime mover for flexing the thigh or flexing the trunk on thigh during a bow - also lateral flexion of vertebral column - major postural muscle

    Sartorus - straplike running obliquely across the anterior surface of the thigh (longest muscle of the body) - flexes, abducts and laterally rotates the thigh - weak knee flexor

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

    Adductors - large muscle mass - 3 muscles - medial aspect of thigh

   Adductor magnus -  triangular - anterior portion adducts and medially rotates & flexes the thigh- posterior portion is a synergist of hamstrings in thigh extension

   Adductor longus - overlies middle aspect of Adductor magnus - addcuts, flexes and medially rotates thigh

   Adductor brevis - adducts & medially rotates thigh

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

    Pectineus - short flat muscle that overlies the adductor brevis - addcuts, flexes and medially rotates the thigh

    Gracilis - long, thin & superficial- adducts thigh, flexes and medially rotates the leg

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

    Quadriceps femoris - arise from 4 separate heads - front and side of the thigh

   Rectus femoris - superficial muscle front of thigh - extends the knee and flexes thigh as hip

   Vastus lateralis - largest head - lateral aspect of thigh - extends & stabilizes knee

   Vastus medialis - inferiomedial aspect of thigh - extends knee - inferior fibers stabilize the patella

   Vastus intermedius - lies between the v. lateralis & v medialis - extends the knee

    Tensor fasciae latae - enclosed between the fascia layers of the anteriorlateral aspect of the thigh - flexes & adducts thigh

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

    Gluteus maximus - largest most superficial - major extensor of the thigh - major extensor of the thigh

    Gluteus medius - thick muscle largely covering the G. maximus - abducts & medially rotates thigh - steadies the pelvis - important in walking -  muscle of the planted side prevents the non-planted side from sagging during stepping

    Gluteus minimus -  smallest & deepest - same as G. medius

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

   Lateral rotators

  Piriformis - pyramidal muscle - inferior to G. minimus - rotates extended thigh laterally - can also assist in abduction of the thigh

  Obturator externus - flat triangular muscle -same as piriformis

  Obturator internus - same as piriformis

  Gemelius - two small muscles with common insertions and actions - same as piriformis

  Quadratus femoris - short thick muscle  - most inferior of rotators - rotates thigh laterally & stabilizes hip joint

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

   Hamstrings -  fleshy muscles of the posterior thigh

  Biceps femoris -  most lateral - extends the thigh & flexes the knee - laterally rotates the leg especially when knee is flexed

  Semitendinosus - lies medial to biceps femoris - extends the thigh at the hip - flexes the knee - with semimembranous - medially rotates the thigh

  Semimembranous - deep to the semitendinosus - extends the thigh & flexes the knee - medially rotates the leg

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

    Tibialis anterior - superficial muscle of anterior leg - prime mover of dorsiflexion; inverts foot - assists in supporting medial longitudinal arch of the foot

    Extensor digitorum longus - unipennate of anterolateral surface of the leg - prime mover of toe extension (metatarsophalangeal joints) - dorsiflexes foot

    Fibularis (peroneus) tertius - small & often fused with distal part of extensor digitorum longus - dorsiflexes & everts foot

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

    Extensor hallucis longus -  extends great toe- dorsiflexes foot

    Fibularis (peroneus) longus - overlies fibula - plantar flexes & everts foot

    Fibularis brevis - smaller deep to F. longus - plantar flexes  & everts foot

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

    Triceps surae -  refers to muscle pair that shapes the calf

   Gastrocnemius - superficial - plantar flexes the foot when knee is extended - can flex knee when foot is dorsiflexed (it crosses the knee joint)

   Soleus - broad flat muscle - deep to gastrocnemius - plantar flexes the foot - important locomotor & posture muscle during walking, running and dancing

    Plantaris - small - assists in knee flexion & plantar flexion of foot

Muscles Crossing the Hip and Knee Joints - Thigh & Leg Movements

    Popliteus - thin triangular muscle at posterior knee - flexes & rotates leg medially to unlock knee from full extension - tibia fixed rotates thigh laterally

    Flexor digitorum longus - runs partially over the tibialis posterior - plantar flexes & inverts foot - flexes toes

    Flexor hallucis longus - bipennate, lateral to inferior aspect of tibialis posterior -  plantar flexes & inverts foot flexes great toe at all joints - push off muscel during walking

    Tibialis posterior - thick flat muscle, deep to the soleus - prime mover of foot inversion - plantar flexes foot - stabliizes medial longitudinal arch of foot (as during ice skating)

Intrinsic Muscles of the Foot

    Extensor digitorum brevis - small four-part muscle of dorsum of the foot - helps extends toes at metatarsophalangeal joint

    Sole of the foot - most superficial

   Flexor digitorum brevis - bandlike muscle in middle of sole - flexes toes

   Abductor hallucis - medial to flexor digitorum brevis - abducts big toe

   Abductor digiti minimi - most medial - abducts & flexes little toe

 Intrinsic Muscles of the Foot

   Sole of the foot - second layer

  Flexor accessorius - rectangular muscle deep to flexor digitorum brevis - straightens out the oblique pull of the  flexor digitorum longus

  Lumbricals - four worm-like muscles - by pulling on extensor expansion, flex toes at metatarsophalangeal joints & extend toes at interphalangeal joint

 Intrinsic Muscles of the Foot

   Sole of the foot - third  layer

  Flexor hallucis brevis - flexes great toe at metatarsophalangeal joint

  Adductor hallucis - helps maintain transverse arch of the foot - weak adductor of great toe

  Flexor digiti minimi brevis - flexes little toe at metatarsophalangeal joint

Intrinsic Muscles of the Foot

  Sole of the foot - fourth layer

  Plantar (3) interossei - adducts toes

Dorsal (4) interossei - abducts toes