2-Minute Neuroscience: Hypoglossal Nerve (Cranial Nerve XII)

2-Minute Neuroscience: Hypoglossal Nerve (Cranial Nerve XII)

The hypoglossal nerve is a motor nerve that
controls all of the muscles of the tongue (except for one, the palatoglossus, which
is controlled by the vagus nerve). The tongue muscles consist of what are known
as intrinsic muscles, which control the shape of the tongue, and extrinsic muscles, which
act to protrude, retract, elevate, and move the tongue side to side. Healthy function of the hypoglossal nerve
is thus critical for things like eating, swallowing, and speaking. The hypoglossal nuclei are found in the medulla. Hypoglossal nerve fibers leave the hypoglossal
nuclei on each side of the brainstem and descend to travel to the same side of the tongue to
stimulate the muscles of the tongue from below, hence the term hypoglossal, which comes from
the Greek for under the tongue. There are three other branches that extend
from the hypoglossal nerve to supply various other muscles in the neck as well as the dura
mater at the back of the head. Only the fibers that supply the tongue originate
in the hypoglossal nucleus, however, and thus they are often considered the true hypoglossal
nerve. Damage to the hypoglossal nerve can cause
tongue weakness and impair tongue dexterity. It may also lead to small muscle twitches,
or fasciculations, in the tongue as well as atrophy of the tongue–especially at the tip
or borders of the organ. If the hypoglossal nerve on only one side
is damaged, then atrophy will typically be seen in the tongue muscles on that same side. If the patient is asked to protrude his or
her tongue, the tongue will often deviate toward the side of the damaged nerve. Patients with damage to only one hypoglossal
nerve, however, are often able to compensate for the deficiency of the tongue muscles on
one side. But if both nerves are damaged, the patient
may be unable to protrude the tongue at all and may experience severe problems with speech
and swallowing.

3 Replies to “2-Minute Neuroscience: Hypoglossal Nerve (Cranial Nerve XII)”

  1. Great that you also write your transcript in the description! This can help students with their tutorials and studies. Keep it up bro!

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