muscles of the head, neck and trunk actions
infraspinatus
lateral rotation of humerus; helps hold head of humerus in glenoid cavity; stabilizes shoulder
latissimus dorsi
prime mover of arm extension; adducts and medially rotates arm; brings arm down in power stroke, as in striking a blow
pectoralis major
prime mover of arm flexion; adducts, medially rotates arm; with arm fixed, pulls chest upward (thus also acts in forced inspiration)
diaphragm
prime mover of inspiration flattens on contraction, increasing vertical dimensions of thorax; increases intra-abdominal pressure
masseter
prime mover of jaw closure; elevates mandible
serratus anterior
prime mover to protract and hold scapula against chest wall; rotates scapula, causing inferior angle to move laterally and upward; essential to raising arm; fixes scapula for arm abduction
lateral pterygoid
protracts jaw (moves it anteriorly); in conjunction with medial pterygoid, aids in grinding movements of teeth
mentalis
protrudes lower lip; wrinkles chin
external intercostals
pull ribs toward one another to elevate rib cage; aid in inspiration
rhomboids- major and minor
pull scapula medially (retraction); stabilize scapula; rotate glenoid cavity downward
levator labii superioris
raises and furrows upper lip; opens lips
zygomaticus- major and minor
raises lateral corners of mouth upward (smiling muscle)
sternocleidomastoid
simultaneous contraction of both muscles of pair causes flexion of neck forward, generally against resistance (as when lying on the back); acting independently, rotate head toward shoulder on opposite side
medial pterygoid
synergist of temporalis and masseter, elevates mandible; in conjunction with lateral pterygoid, aids in grinding movements
platysma
tenses skin of neck; depresses mandible; pulls lower lip back and down (i.e. produces downward sag of the mouth)
orbicularis oculi
various parts can be activated individually; closes eyes, produces blinking, squinting, and draws eyebrows inferiorly
epicranius- frontal belly
with aponeurosis fixed, it raises eyebrows
pectoralis minor
with ribs fixed, draws scapula forward and inferiorly; with scapula fixed, draws rib cage superiorly
depressor anguli oris
zygomaticus antagonist; draws corners of mouth downward and laterally
deltoid
acting as a whole, prime mover of arm abduction; when only specific fibers are active, can aid in flexion, extension, and rotation of humerus
digastric
acting in concert, elevate hyoid bone; open mouth and depress mandible
semispinalis (capitis, cervicis and thoracis)
acting together, extend head and vertebral column; acting independently (right vs. left) causes rotation toward the opposite side
sternothyroid
acting with sternohyoid and omohyoid depresses larynx and hyoid bone if mandible is fixed; may also flex skull
omohyoid
acting with sternohyoid and sternothyroid depresses larynx and hyoid bone if mandible is fixed; may also flex skull
sternohyoid
acting with sternothyroid and omohyoid depresses larynx and hyoid bone if mandible is fixed; may also flex skull
splenius (capitis and cervicis)
as a group, extend or hyperextend head; when only one side is active, head is rotated and bent toward the same side
internal oblique
as for external oblique
teres minor
as for infraspinatus
temporalis
closes jaw; elevates and retracts mandible
orbicularis oris
closes lips; purses and protrudes lips (kissing and whistling muscle)
transversus abdominis
compresses abdominal contents
external oblique
compresses abdominal wall; also aids muscles of back in trunk rotation and lateral flexion; used in oblique curls
thyrohyoid
depresses hyoid bone; elevates larynx if hyoid is fixed
internal intercostals
draw ribs together to depress rib cage; aid in forced expiration; antagonistic to external intercostals
risorius
draws corner of lip laterally; tenses lip; zygomaticus synergist
buccinator
draws corner of mouth laterally; compresses cheek (as in whistling); holds food between teeth during chewing
corrugator supercilii
draws eyebrows medially and inferiorly; wrinkles skin of forehead vertically
depressor labii inferioris
draws lower lip inferiorly
quadratus lumborum
each flexes vertebral column laterally; together extend the lumbar spine and fix rib 12; maintains upright posture
levator scapulae
elevates and adducts scapula; with fixed scapula, laterally flexes neck to the same side
stylohyoid
elevates and retracts hyoid bone
mylohyoid
elevates hyoid bone and base of tongue during swallowing
erector spinae (iliocostalis, longissimus and spinalis)
extend and bend the vertebral column laterally; fibers of the longissimus also extend head
trapezius
extends head; raises, rotates, and retracts (adducts) scapula and stabilizes it; superior fibers elevate scapula (as in shrugging the shoulders); inferior fibers depress it
teres major
extends, medially rotates, and adducts humerus; synergist of latissimus dorsi
epicranius- occipital belly
fixes apponeurosis and pulls scalp posteriorly
scalenes- anterior, middle and posterior
flex and slightly rotate neck; elevate ribs 1-2 (aid in inspiration)
rectus abdominis
flexes and rotates vertebral column; increases abdominal pressure; fixes and depresses ribs; stabilizes pelvis during walking; used in sit-ups and curls
supraspinatus
initiates abduction of humerus; stabilizes shoulder joint