Chapter 10: Skeletal Muscle System

Agonists

“prime movers”; produce a specific movement

Antagonists

oppose the agonist’s movement; ex. the triceps (posterior) are antagonists to the biceps (anterior)

Synergists

“accessory” muscles; work with the agonists; add extra force to the same movement

Fixators

immobilize bone or muscle origin rather than enhance agonist’s actions; helps with stability

Location

to what bone or body region the muscle is associated; temporalis muscle is over the temporal bone

Shape

does the muscle have a distinct shape; the deltoid muscle is shaped like a triangle, the rhomboids shaped like a rhombus

Size

maximus = biggest; minimus = smallest; longus = longer; brevis = shorter

Fiber or Fascicle Direction

Rectus = fibers run straight; transversus = fibers run at right angles; oblique = fibers run at angles to imaginary axis

Number of Origins

biceps have two origins, triceps have three

Origin

attachment to the immovable (or less movable) bone

Muscle Action

what does the muscle do?

Circular

concentric rings (orbicularis orbis)

Convergent

broad, converging toward a single tendon (pec major)

Parallel

parallel to the long axis (sartorius)

Pennate

spindle-shaped with parallel fibers (rectus femoris, deltoids)

Fusiform

large muscle belly, tapered ends near tendon

Description

where it is located relative to other muscles

Origin and Insertion Points

where the muscle attaches, often crossing a joint

Actions

what movement does the contraction cause

Innervation

what nerve supplies it with motor stimulus

Zygomaticus Major

raises lateral corners of mouth (smiling)

Orbicularis Oris

closes and protrudes lips (puckering, kissing, whistling)

Orbicularis Oculi

closes eye (blinking and squinting); pulls eyebrows inferiorly

Mentalis

wrinkles the chin; protrudes lower lip (pouty lips)

Currugator Supercili

pulls eyebrows medially and inferiorly; wrinkles eyebrows vertically (angry eyebrow)

Epicranius (occipitofrontalis)

frontal belly raises eyebrows and wrinkles forehead skin horizontally (surprise)

Platysma

tenses skin of the neck

Masseter and Temporalis

jaw closure

Medial and Lateral Pterygoids

deep muscles; grinding movements

Sternocleidomastoid

forward flex neck; laterally flex neck ipsilaterally (same side) and rotate neck contralaterally (opposite side)

Scalenes

laterally flex and rotate neck; elevate first two ribs for inspiration

Trapezius

originate on occipital bone; stabilize, elevate, retract and rotate scapula

Levator Scapulae

originate on C1-C4; elevate and retract scapula

Erector Spinae Group

3 muscles which collectively act to keep back erect and extend spinal column; all three run the length of the spine; laterally flex spinal column ispilaterally if only activated unilaterally; iliocostalis, longissimus, spinalis

Iliocostalis

most lateral, subgroups: cervicis, thoracis, lumborum

Longissimus

intermediate, subgroups: capitis, cervicis, thoracis

Spinalis

most medial; subgroups: thoracis and cervicis

Quadratus Lumborum (QL)

similar actions to erector spinae

Diaphragm

inspiration; depresses to expand thoracic cavity; contraction (depression) and relaxation (elevation) dictate respiratory rate

External Intercostals

inspiration; elevates rib cage to expand thoracic cavity

Internal Intercostals

expiration; depresses rib cage to compress thoracic cavity

Rectus Abdominis

forward flex and rotate lumbar vertebrae; stablize pelvis during walking (“6-pack” or really 8)

External Oblique

foward flex lumbar vertebrae; aid back muscles to laterally flex trunk ipsilaterally and rotate trunk contralaterally

Internal Oblique

same as external oblique

Transverse Abdominis

deepest abdominal muscle; compress abdominal contents and stabilize spine

Pectoralis Major

adducts and internally (medially) rotates shoulder

Anterior Deltoid

flexes and internally (medially) rotates shoulder

Medial Deltoid

abducts shoulder

Biceps Brachii

flexes elbow and supinates forearm

Brachialis

flexes elbow

Brachioradialis

assists in elbow flexion; stabilizes elbow

Serratus Anterior

aka “boxer’s muscle” protracts scapula

Latissimus Dorsi

extends, adducts and internally (medially) rotates shoulder

Triceps Brachii

extends elbow

Supraspinatus

abducts shoulder

Infraspinatus

externally (laterally) rotates shoulder

Teres Minor

same as infraspinatus

Subscapularis

abducts shoulder

Rhomboids

attach to medial border of scapula; stabilize and retract scapula

Pronator Teres

pronates forearm; assists with elbow flexion

Flexor Carpi Radialis

flexes and abducts wrist

Palmaris Longus

flexes wrist; tenses skin and fascia of hand during movements

Flexor Carpi Ulnaris

flexes and adducts wrist

Extensor Carpi Radialis Longus/Brevis

extends and abducts wrist

Extensor Digitorum

prime mover in finger extension and abducts (flares) fingers

Extensor Carpi Ulnaris

extends and abducts the wrist (ulna)

Iliacus

flexes hip, also flexes trunk at hip

Psoas Major

same as iliacus, also laterally flexes trunk ipsilaterally

Rectus Femoris

flexes hip and extends knee

Vastus Lateralis (VL)

extends and stabilizes knee

Vastus Medialis and Vastus Intermedius

extends knee

Sartorius

flexes, abducts and externally (laterally) rotates hip

Tensor Fasciae Latae (TFL)

flexes, abducts and internally (medially) rotates hip

Adductor Group

consists of the adductor magnus, longus, and brevis; flexes, adducts and internally (medially) rotates hip; posterior fibers assist in hip extension

Pectineus and Gracilis

flexes, adducts and internally (medially) rotates hip

Gluteus Maximus

extends, abducts and externally (laterally) rotates hip

Gluteus Medius and Minimus

abducts and internally (medially) rotates hip

Piriforms

externally (laterally) rotates hip (when hip extended); abducts hip (when hip is flexed); commonly implicated in cases of sciatica

Biceps Femoris

extends hip; flexes knee; externally (laterally) rotates knee (when knee flexed)

Semitendinosus and Semimembranosus

extends hip; flexes and internally (medially) rotates knee

Iliotibial (IT) Band

thick fascial band on lateral aspect of thigh; stems off gluteus maximus and TFL; aids pelvic stability; will become hurt when abductors are weak

Dancer’s Hip

IT band moves over great trochanter creating a “snapping” noise and inflammation

Tibialis Anterior

dorsiflexes and inverts ankle

Extensor Digitorum Longus

dorsiflexes ankle and extends toes

Extensor Hallucis Longus

dorsiflexes ankle and extends big (great) toe

Shin Splints

excess tightness or hypertrophy of anterior compartment muscles puts pressure on tibia causing pain

Fibularis Longus (peroneal)

plantar flexes and everts ankle; may aid in applying pressure to lateral arch keep foot flat on the ground

Fibularis Brevis

plantar flexes and everts ankle

Gastrosnemius

plantar flexes ankle (when knee extended); aids with knee flexion (when ankle dorsiflexed); attaches to calcaneus via calcaneal (achilles) tendon; commonly injured during ankle sprains and can rupture in “stop and go” movements involving rapid plantar flexion with knee extension

Soleus

plantar flexes ankle

Plantaris

aids in knee flexion and ankle plantar flexion

Popliteus

flexes and internally (medially) rotates knee; unlocks extended knee so that flexion can begin