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