A&P Ch 10. The muscular system

Prime mover (agonist)

Major responsibility for producing specific movement

Antagonist

Opposes or reverses particular movement

– Prime mover and antagonist are located on opposite sides of joint across which they act

Synergist

helps prime movers

– Adds extra force to the same movement

– Reduces undesirable or unnecessary movement

Fixators

type of synergist that immobilizes bone or

muscle’s origin rather than enhancing movement of

prime movers

▪ Gives prime mover stable base on which to act

example of muscle actions and interactions

For elbow flexion:

• Prime mover—brachialis

• Synergist—biceps brachii

• Antagonist—triceps brachii

• Fixator—muscle that holds

scapula firmly in place

– Rhomboids

Pennate

Three forms

▪ Unipennate: fascicles attach only to one side of

tendon (example: extensor digitorum longus)

▪ Bipennate: fascicles insert from opposite sides of

tendon (example: rectus femoris)

▪ Multipennate: appears as feathers inserting into

one tendon (example: deltoid), strongest

Patterns of Fascicle Arrangement in Muscles

Lever Systems

– Lever: rigid bar (bone) that moves on a fixed point

called fulcrum (joint)

– Effort: force (supplied by muscle contraction) applied

to lever to move resistance (load)

– Load: resistance (bone + tissues + any added weight)

moved by the effort

Basic principle of levers

– Effort farther than load from fulcrum = lever operates

at mechanical advantage

– Effort nearer than load to fulcrum = lever operates at

mechanical disadvantage

Mechanical advantage (power lever)

load is close to fulcrum, with effort far from fulcrum

– Small effort can move large load

slower, but more stable

▪ Used where strength is a priority

Mechanical disadvantage (speed lever)

load is far from fulcrum, with effort close to fulcrum

– Load moved rapidly over large distance; offers wider

range of motion

force is lost, but speed and range of movement are gained

First-class lever

– Fulcrum is between load and

effort

– Example: seesaw, scissors

second-class lever

– Load is between fulcrum

and effort

– Example: wheelbarrow,

standing on toes

Third-class lever

– Effort is applied between fulcrum and load

– Example: tweezers, forceps, most skeletal muscles

Muscles of Facial Expression

frontalis- elevator and depression of eyebrows

Orbicularis oculi

Zygomaticus minor

Zygomaticus major

Platysma

Corrugator supercilii- furrowed brow

buccinator

Orbicularis oris

Zygomaticus major

orbicularis oris

mentalis

platysma

corrugator supercilii

orbicularis oculi

frontal belly of epicranius

Muscles Promoting Mastication

Prime movers of jaw closure: temporalis (elevation and retraction) and masseter (elevation and retraction)

▪ Chewing role: buccinator (elevation of mandible)

push food back toward pharynx, where muscles in posterior mouth and pharynx

complete swallowing process

Muscles promoting tongue movements

▪ Genioglossus (goes from tongue to chin)-

Tongue Protrusion (sticking tongue out), Tongue Depression

hyoglossus- pulls tongue back and down

Depression: Pulls the side and lower third of the tongue downward, flattening the tongue.

Retraction (Retrusion): Pulls the tongue backward into the oral cavity.

styloglossus- pulls tongue back and up

Retraction (Retrusion): Draws the tongue backward into the oral cavity and oropharynx.

• Elevation: Pulls the tongue upward and poster superiorly.

all help with swallowing

Suprahyoid muscles

– Four deep muscles involved in swallowing (move

hyoid bone and larynx)-above

▪ Form floor of oral cavity

▪ Anchor tongue

▪ Elevate hyoid bone

▪ Move larynx during swallowing

Infrahyoid muscles

– Four straplike muscles

– Depress hyoid bone and larynx during swallowing and

speaking, below

think thyroid cartilage

Muscles of the Anterior Neck and Throat Used in Swallowing

Suprahyoid

digastric (mandible to hyoid) - elevates/retracts hyoid, depresses mandible (right lateral side of neck)

stylohyoid (connects to styloid process)- hyoid elevation

Infrahyoid

thyrohyoid (thyroid cartilage to hyoid)- depresses hyoid or elevates larynx if hyoid is fixed

sternohyoid (sternum to hyoid)- depresses thyroid cartilage and larynx

Muscles of the Anterior Neck and

Throat Used in Swallowing

three stacked, fan-shaped skeletal muscles that form the circular muscular wall of the pharynx

suprahyoid squeezes food and pushes it further down

superior pharyngeal constrictor- pushes food into mpc

middle pharyngeal constrictor pushes food into ipc

inferior pharyngeal constrictor- pushes food into esophagus

Sternocleido-mastoid (2)

on lateral sides of neck-neck movement

activates and head is turned to opposite side

posterior side of neck

splenius capitus (goes to skull)

splenius cervicus (goes to cervical spine)

both turn head and help it flex

back muscles

erector spinae (split into 3)- keep spine straight and erect

iliocostalis: ilium to ribs

longissimus: runs all the way up to skull

spinalis: entire length of spine

diaphragm

breathing prime mover

exhale- pulls up

inhale- pulls down

external intercostal and internal intercostal muscles

control rib position during breathing

Muscles of the Abdominal Wall

rectus abdominus- runs straight down abs and engages in flexion

internal oblique and external oblique- run across abdominal cavity, rotation and lateral flexion

Transversus abdominius(deepest abdomen muscle)- wrapping horizontally around the torso from the ribs and spine to the pelvis like a natural corset

Muscles of the Pelvic Floor and Perineum

pelvic diaphragm

levator ani- elevates anus

coccygeus (coccyx to ischium)- form supportive part of pelvic diaphragm and stabilize pelvic floor

perineum

diamond-shaped region at the bottom of the pelvis, located between the thighs 

scapula and arm (anterior)

pectoralis minor (ribs to coracoid process of scapula)- protraction, depression, downward rotation

serratus anterior (connects to 9 ribs)- attached to scapula on back (protraction and rotation upward), stabilizes scapula

scapula and arm (posterior)

trapezius- elevation, depression, retraction of scapula

rhomboid minor and rhomboid major- retraction of scapula

latissimus dorsi (goes to arm and across back except midline)- adduction, extension, internal rotation, sometimes hyperextension

levator scapulae- elevates scapula

Muscles Crossing the Shoulder Joint (anterior)

pectoralis major- adduction and flexion

Deltoid-

• front: flexion

• lateral: abduction

• posterior: extension

coracobrachialis- flexion and adduction of upper arm, humeral head stabilization

triceps brachii- extension of forearm at elbow joint

long head of triceps-extension of shoulder

biceps brachii- flexion of elbow, supination

brachialis- pronation

brachioradialis- flexes elbow joint, supination and pronation

Muscles Crossing the Shoulder Joint (deep)

infraspinatus

teres minor

(both laterally rotate shoulder joint)

teres major- internal rotation, adduction, extension

triceps brachii- extension of forearm at elbow joint

long head of triceps-extension of shoulder

latissimus dorsi (goes to arm and across back except midline)- adduction, extension, internal rotation, sometimes hyperextension

Biceps Brachii

triceps brachii

Brachioradialis

Brachialis

rotator cuff (SITS)

originate on scapula; reinforce shoulder capsule; prevent dislocation, stabilizes humerus in glenoid facet of scapula

– Supraspinatus- arm abduction (lifting the arm out to the side)

– Infraspinatus- externally rotates shoulder joint

– Teres minor- externally rotates shoulder joint

– Subscapularis- internal rotation and adduction

flexor digitorum superficialis

flexes middle joint of second through fifth fingers (index, middle, ring, and little fingers) and wrist flexion

Flexor Pollicus Longus

deep muscle in the anterior forearm that flexes the thumb (flexion)

pronator teres and pronator quadratus

pronators

Wrist and Fingers

flexor pollicis longus- deep muscle in posterior forearm that flexes the thumb (flexion)

flexor digitorum profundus: flexing the fingers and gripping power

supinator- sits deep under the superficial skin and muscles of upper forearm, near the elbow joint, supination

pronator quadratus- Forearm Pronation: Rotates radius over ulna to turn the palm downward

supinator

deep under the superficial skin and muscles of the upper forearm, supination

Flexor Digitorum Profundus

flexing the fingers and primary gripping power

Palmaris Longus

flexes the wrist and tenses the palmar fascia, for grip

Flexor retinaculum

bracelet-like fibrous sheet on wrist where most tendons of the extrinsic muscles pass under

carpal tunnel syndrome

prolonged, repetitive motions of wrist and fingers cause tissues in the

carpal tunnel to become inflamed, swollen

–Puts pressure on median nerve of wrist that passes through the carpal tunnel along with flexor tendons

–Tingling and muscular weakness in the palm and medial side of the hand

–Pain may radiate to arm and shoulder

–Treatment: anti-inflammatory drugs, immobilization of the wrist, and sometimes surgery to remove part or all of flexor retinaculum

posterior wrist and fingers muscles

extensor digitorum: Extends the metacarpophalangeal (MCP) and interphalangeal (PIP/DIP) joints of fingers 2–5

extensor pollicis longus- Extends all joints of the thumb

Extensor Digitorum

extending the wrist. When it contracts, it pulls the tendons on the back of the hand to lift the index, middle, ring, and little fingers

Posterior Compartment - Deep Extensor Pollicis Longus

a deep forearm muscle, extends the distal phalanx of the thumb

movements of hand

muscles of hand

second lumbrical (central compartment of hand): flexion and extension simultaneously, allows to bend the knuckle while keeping the finger straight

first lumbrical- worm-like intrinsic muscle of the hand, fine motor control and precision grip (flexion and extension)

dorsal interossei (4 muscles): located in the spaces between the metacarpal bones of the hand- (Dorsal ABduct)

opponens pollicis (index finger)- Flexes, medially rotates, and opposes the 1st metacarpal toward the palm

opponens digiti mini (pinky)- Flexes and laterally rotates the 5th metacarpal to bring the pinky toward the thumb (deepens the palm)

dorsal interossei (4 muscles-DAB)

located in the spaces between the metacarpal bones of the hand

the index, middle, and ring fingers away from the middle finger's central axis, aided by the mnemonic DAB (Dorsal ABduct)

palmar interossei (PAD)

spaces between the metacarpal bones of the hand (palmar ADuct)

iliopsoas (iliacus and psoas major)

hip flexion and lateral rotation

hand muscle groups

Thenar group—form thick, fleshy mass at base of thumb

– Flexor pollicis brevis

– Opponens pollicis

• Hypothenar group—fleshy base of the little finger

– Abductor digiti minimi

– Flexor digiti minimi brevis

– Opponens digiti minimi

• Midpalmar group—hollow of palm

– Dorsal interosseous muscles (4)

– Palmar interosseous muscles (3)

– Lumbricals (4 muscles

Thigh muscles

adductor brevis: Adducts, lateral rotation and flexion of the hip

adductor longus: Adducts, flexes, and medially rotates the thigh.

adductor magnus: Powerful thigh adductor, hip extensor, and stabilizer

leg muscles (anterior)

vastus lateralis (largest and strongest): extends knee and helps stabilize patellar tracking

vastus intermedialis: Extends leg at knee joint

vastus medialis: Extends knee

all extensors

sartorius: flexor, abductor, and lateral rotator of the hip (crossing your legs)

quadriceps femoris (rectus femoris): Extends leg at knee and flexes thigh hip joint

glutes

Gluteus maximus: hip extension, lateral rotation of thigh and knee

– Gluteus medius and Gluteus minimus: abduction and medial and lateral rotation of thigh

Piriformis (also laterally rotates thigh, posterior)

biceps femoris

a two-headed muscle in the posterior compartment of the thigh, primary component of the hamstrings

flexes knee, extends hip (long head only), and laterally rotates lower leg or thigh

semitendinosus, semimembranosus

extension at thigh by hip, flex leg at the knee, and internally rotate the lower leg when the knee is bent

tibialis anterior (dorsiflexion)

Fibularis longus (on lateral side of leg)

Plantar flexion and eversion of the foot; stabilize lateral

ankle and lateral longitudinal arch of foot

posterior compartment (lower leg), goes deeper and deeper

gastrocnemius (forms visible shape of calf): plantar flexion, knee flexion, propulsion (walking, running)

soleus (deep to the gastrocnemius): plantar flexion, posture and balance

flexor hallucius longus: flexes the great toe (hallux) and stabilizes the foot during movement

flexor digitorum brevis

flexion of 4 toes