The accessory nerve has one functional component. This is going to be general somatic efferent.
With respect to somatic efferent or motor control, the accessory nerve innervates two muscles.
One is the sternocleidomastoid that is now highlighted in red. The second muscle innervated by the
accessory nerve is the trapezius which is now highlighted in red. Clinical considerations for you
to remember about the accessory nerve would be that injury to this nerve could result in shoulder pain.
Individual could have difficulty or impairment of abduction at the shoulder because the trapezius would be
unable to rotate the glenoid cavity superiorly to promote abduction of the shoulder above the horizontal.
The last clinical consideration would be due to paralysis or paresis of the sternocleidomastoid muscle.
As a result, there could be weakness in the turning of the chin to the opposite side. Some causes of
these clinical considerations would be penetrating or blunt injury to the distribution of the accessory
nerve or a tumor could encroach upon that and cause a disruption of its ability to innervate
the sternocleidomastoid or the trapezius or both.