Neuroanatomy Draw It To Know It

52 Neuroanatomy: Draw It to Know It

Cervical Plexus (Advanced) (Cont.)

We have completed the cervical plexus innervation of
the muscles of the anterior cervical triangle and the fl oor
of the mouth, so now let’s show how the cervical plexus
derives the majority of cranial nerve 11, the spinal acces-
sory nerve, which innervates the sternocleidomastoid
and trapezius muscles. Motor cells from the medulla to
the sixth cervical segment are responsible for the com-
plete supply of the spinal accessory nerve, but we will
only show the cervical plexus contribution, here. Show
that branches from C2–C4 ascend the spinal canal, pass
through the foramen magnum, and exit the cranium
through the jugular foramen as the spinal accessory
nerve. Th e spinal accessory nerve innervates the trape-
zius, supplied by C3 and C4, and the sternocleidomas-
toid, supplied by C2–C4. Trapezius elevates the shoulders
(most notably) and sternocleidomastoid turns the head.
Note that the trapezius receives additional innerva-
tion from cervical sources other than the spinal accessory

nerve; and therefore, in spinal accessory nerve palsy, the

trapezius muscle is partially spared.

Now, in the corner of the diagram, make a notation

that the cervical plexus also provides innervation to the

deep anterior vertebral muscles, which comprise the

anterior and lateral rectus capitis muscles (C1, C2),

longus capitis (C1, C2, C3), and longus colli (C2–C6)

muscles, and that the cervical plexus also helps innervate

the scalene and levator scapulae muscles.

As a fi nal note, keep in mind that it is the cervical

spinal ventral rami that form the cervical plexus; on the

contrary, the cervical dorsal rami supply the posterior

scalp and suboccipital region. Th e primary motor inner-

vator of this region is the suboccipital nerve and the pri-

mary sensory innervator of this region is the greater

occipital nerve. Th e dorsal ramus of C1 supplies the sub-

occipital nerve whereas the dorsal ramus of C2 supplies

the greater occipital nerve — see Drawing 5-6.^1 – 4

FIGURE 3-39 T r a p e z i u s. FIGURE 3-40 Sternocleidomastoid.

FIGURE 3-41 Levator scapulae.