Anatomy: Major Muscles, Actions, Fiber Types & Directions

Frontalis

Raises eyebrows and helps with facial expression

temporalis

elevates and retracts mandible

sternocleidomastoid

flexes neck; rotates head

orbicularis oculi

closes eyelids

Masseter

elevates mandible and connects the skull to the jaw

Trapezius

Moves the shoulder blades upward, backward, and downward

diaphragm

Contracts and flattens to draw air into the lungs

rectus abdominus

compresses abdomen

pectoralis major

Moves the arm forward, towards the body, and rotates it inward

latissmus dorsi

Pulls the arm backward, towards the body, and rotates it inward

serratus posterior

elevates ribs during inhalation

Deltoid

Medially rotates arm

Biceps brachii

Flexes arm

Triceps brachii

Extends arm

Brachioradialis

flexes forearm

Supraspinatus

abducts arm

Infraspinatus

rotates arm laterally

teres major

rotates arm medially

teres minor

rotates arm laterally

gluteus maximus

extends thigh

tensor fasciae latae

flexes and abducts thigh

Sartorius

flexes thigh at hip joint

IT band

stabilizes hip and knee

rectus femoris and vastus lateralis

extends leg at knee

vastus medialis

extends knee, stabilizes patella

gastrocnemius and soleus

plantar flexion of foot

biceps femoris

flexes knee

Parallel

Run in the same direction, allowing for a greater range of movement and shortening. This produces less force.

convergent

Spreads out broad from origin and comes together at one tendon allowing the muscle to pull in different directions

Bipennate

Fibers on both sides of tendon. This produces the greater force but has a smaller range of movement

Circular

form rings arounding opening and they contract to close

superior

above

Inferior

below

superficial

near the surface

deep

away from the surface

medial

toward the midline

Lateral

away from the midline

Skeletal

Parallel fiber, striations, and voluntary

Cardiac

branching, striations, intercalated disks, and involuntary

Smooth

Sheets, involuntary, and has no sarcomere

Cause of striations

sacromere