Main Model
Muscles : 43 Sternocleidomastoid
Muscle: Sternocleidomastoid
Superior
Attachment: Lateral surface of
mastoid process
of temporal bone
and lateral half of superior nuchal line
Inferior
Attachment:
Sternal head - anterior surface of
manubrium of
sternum
Clavicular head - superior surface
of medial third of
clavicle
Innervation: Spinal accessory
nerve (CN XI,
motor); C2 and C3 nerves (pain and proprioception)
Main Action(s):
A. Unilateral contraction - tilts head to same side
(i.e., laterally flexes neck) and rotates it so
face is turned superiorly toward opposite side
B. Bilateral contraction - (1) extends neck at
atlanto-occipital joints, (2) flexes
cervical vertebrae so that chin approaches
manubrium, or (3) extends superior
cervical vertebrae while flexing inferior vertebrae
so chin is thrust forward with head kept level
C. With cervical vertebrae fixed, may elevate
manubrium and medial ends of clavicles,
assisting pump-handle action of deep respiration