Actions and Relationships for Selected Muscles

Links are given to show location and attachments of muscle. No guarantee is given as to the veracity of information. You should learn the relationships shown below.

Links: [Loyola University Medical Education] [UW Online Muscle Atlas for leg muscles]
Muscles of the head
Synergists in closing the jaw:

masseter - closes jaw

temporalis - closes jaw

Antagonist to those at left:

platysma - opens jaw

Synergists in flexing head and neck:

sternocleidomastoid - working as pair flex head and neck

Antagonists in rotation of head:

sternocleidomastoid - working independently rotate in opposite directions

Synergists in extension of head and neck:

splenius capitus - working as a pair extend and rotate head

trapezius - upper portion extends head and neck

semispinalis capitus -

longissimus capitus -

Antagonists in rotation of head:

splenius capitus - working independently rotate head in opposite directions


sternocleidomastoid muscles acting in unison flex the head and neck
Synergists in adduction of scapula :

rhomboid major and rhomboid minor - adduct (retract) and fixate scapula

trapezius - retracts and fixates scapula


levator scapulae - raises and fixates scapula
Antagonist to those at left:

serratus anterior - abducts (protracts) scapula

Synergists in abduction of arm:

supraspinatus - abducts and fixates humerus,

stabilizes shoulder as part of rotator cuff.

deltoid - abducts humerus

Antagonists to those at left:

(synergists in adduction and lateral rotation of arm))

infraspinatus - adducts and laterally rotates humerus

stabilizes shoulder as part of rotator cuff.

teres minor - adducts and laterally rotates humerus

stabilizes shoulder as part of rotator cuff.


(synergists in adduction and medial rotation of arm)

teres major - adducts and medially rotates humerus

latissimus dorsi - adducts and medially rotates humerus

pectoralis major - adducts and medially rotates humerus

subscapularis - adducts and medially rotates humerus

stabilizes shoulder as part of rotator cuff.


coracobrachialis - weakly flexes and adducts arm


Synergists in flexion of elbow:

biceps brachii - flexion of elbow

brachialis - flexion of elbow


brachioradialis - fixates arm in flexed position for lifting
Antagonist to those at left:

triceps brachii - extension of elbow

Synergists in flexion of wrist:

flexor carpi radialis - flex the wrist on the lateral side

flexor carpi ulnaris - flex the wrist on the medial side

palmaris longus - flexes wrist

Antagonists to those at left:

(synergists in extension and abduction of wrist

extensor carpi radialis longus - extends and abducts wrist

extensor carpi radialis brevis - extends and abducts wrist


extensor carpi ulnaris - extends and adducts wrist
extensor digitorum - extends the fingers Antagonists to that at left:

(synergists in flexion of fingers)

flexor digitorum superficialis -

flexor digitorum profundus -

Synergists in forced inspiration:

(They expand the ribcage and thorax)

External intercostals

pectoralis minor

diaphragm

scalenes

sternocleidomastoid

Antagonist to those at left:

(compresses the thorax)

internal intercostals

Abdominal Muscles

Synergists in forced expiration:

rectus abdominus - flexes trunk

internal oblique - rotates trunk, supports abdominal wall

external oblique - rotates trunk, supports abdominal wall

transverse abdominus - supports abdominal wall


Synergists: in flexion of torso:

iliopsoas - the psoas major and iliacus-

flexes the torso on the thigh or the thigh on the torso.

rectus abdominus - flexes trunk

Back Muscles:

erector spinae - extends trunk, antagonist to rectus abdominus and trunk flexors.

quadratus lumborum - unilaterally abducts (laterally flexes) trunk, together extend trunk on hip, stabilizes rib in forced expiration

Synergists in flexion of thigh:

iliopsoas - the psoas major and iliacus- flexes the torso on the thigh or the thigh on the torson, as in situps.

Extensor of Thigh

The gluteus maximus - extends and abducts the thigh. Important stabilizer of femur in the abducted position. Important muscle in climbing and running, but not walking

Synergists with above in abduction of thigh:

gluteus medius - abduction of thigh, important in walking to stabilize leg which is planted

gluteus minimus - abduction of thigh

piriformis - aids in abduction and stabilization of femur in acetabulum.

Synergist in abduction of thigh:

tensor fascia latae - also stabilizes knee and thigh

Synergists in extension of thigh:

See hamstrings below

Synergists in adduction of thigh:

adductor magnus - greatest thigh adductor

adductor brevis - adducts and flexes the thigh

adductor longus - adducts and flexes the thigh

gracilis - flexes the knee and adducts the thigh

Synergists in extension of knee:

Quadriceps

rectus femoris -

vastus medialis -

vastus lateralis -

vastus intermedius -

sartorius -

Antagonists to those at left:

(Synergists in flexion of knee and extension of thigh)

Hamstrings

biceps femoris  -

flex and laterally rotate the knee, extend hip on thigh

semitendinosus -flexes the knee and extends the thigh

semimembraneosus - flexes the knee and extends the thigh

Anterior Leg: (antagonist of those to right)

tibialis anterior - dorsiflexion and inversion of foot

Synergists in plantar flexion:

peroneus longus and brevis - everts and plantar flexes foot

gastrocnemius -most important plantar flexor

soleus - plantar flexes and fixates ankle

plantaris - plantar flexes ankle and flexes knee

tibialis posterior - plantar flexes and inverts foot.