Hey this is Dr K from imedicalschool. Make sure to download and print the cranial nerve
map in the comments section so you can take notes as we go along. Well lets get to today's
practice question.
What cranial nerve if damaged can result in a patient losing their ability to shrug his
or her shoulders?
Is it: A) Cranial Nerve XII
B) Cranial Nerve V C) Cranial nerve VIII
D) Cranial Nerve XI E) Cranial Nerve III
Pause the video here and think about the answer. Let's go on and talk about how we figure out
the answer. Here the correct answer is D.
So let's talk about the cranial nerves. There are 12 cranial nerves in all.
Cranial nerve one is purely a sensory cranial nerve. It is responsible for recognizing smells
as a result it is known as the olfactory nerve. Cranial nerve one is located in the cribiform
plate and originates from the telencephalon. Generally damage to cranial nerve one can
occur due to head trauma but is generally less clinically relevant.
Cranial nerve two is another purely sensory nerve responsible for transmitting signals
from the retina to the brain. These signals allow us to see. The cranial nerve ends in
the lateral geniculate nucleus and eventually transported to the primary visual cortex where
they are interpreted to create the images we see.
Cranial nerve three has a mainly motor function and is called the oculomotor nerve. Cranial
nerve three originates from the anterior midbrain specifically from the edinger-westphal nucleaus
and the oculomotor nucleus. Cranial nerve three innervates the levator palpebrae superiorus,
superior rectus, medial rectus, inferior rectus, and inferior oblique. These muscles coordinate
most eye moevments. If cranial nerve three is not working then the eye appear to be looking
down and out. The reason is that the only muscle working in cranial nerve three palsy
is the lateral rectus and the superior oblique, as they are innervated by other cranial nerves.
In addition to eye movement, cranial nerve three innervates the ciliary body and the
sphincter pupillae. As a result the oculomotor nerve is responsible for pupillary constriction.
Cranial nerve four is called the trochlear nerve and originates from the trochlear nucleus
in the dorsal aspect of the midbrain. The trochlear nerve innervates the superior oblique
muscle. The superior oblique muscle is involved in intorting the eye.
Cranial nerve five is termed the trigeminal nerve. The trigeminal nerve has both sensory
and motor components arising from the pons. It has three main branches termed V1, V2,
and V3. Each of these nerves acts as sensory inputs from the face as well as innervating
muscles involved in chewing. Branch V1 is called the opthalmic nerve, V2 is called the
maxillary nerve, and V3 is called the mandibular nerve.
Cranial nerve six is the abducens nerve and originates from the fourth ventricle/pons.
It innervates the lateral rectus which moves the eye down and out. The nerve courses through
the superior orbital fissure.
Cranial nerve seven is the facial nerve that originates from the pons at the cerebropontine
angle. The facial nerve provide innervation to the muscles that allow for facial expression.
In addition it has a sensory function transmitting taste signals from the anterior 2/3 of the
tongue, as well as, providing stimulation for several salivary glands including lacrimal
glands. In terms of motor innervation the facial nerve innervates the stylohoid, digastric,
and stapedius muscles.
Cranial nerve eight is the vestibulococchlear nerve. it originates from the cerbropontine
angle. It splits into two branches. The vestibular branch is responsible for transmitting signals
that are responsible for balance. The cochlear nerve is responsible for transmitting signals
involved in hearing.
Cranial nerve nine is otherwise known as the glossopharyngeal nerve. The glossopharyngeal
nerve has both sensory and motor functions.In terms of sensory the glossopharyngeal nerve
relays taste from the posterio one third of the tongue. In addition cranial nerve nine
also innervates the parotid gland stimulates it to stimulate secretions. Finally cranial
nerve nine also stimulates the stylopharngyeus muscle. The stylopharyngeus muscle is involved
in the movement of the pharynx and larynx.
Cranial nerve ten is the very famous vagus nerve. It originates from the sulcus of the
medulla and provides motor, as well as, sensory functions. In terms of motor function it provides
innervation to the muscles that help control the larynx and pharynx. In addition the vagus
nerve provides parasympathetic innervation to much of the abdominal and thoracic viscera.
A very important function of the vagus nerve is control of the muscles that help create
our voice.
Cranial nerve eleven is the accessory nerve that serves primarily a motor function. This
nerve controls the sternocleidomastoid muscle and the trapezius muscle. These muscles are
involved in shoulder shrugging. If this nerve is damaged a patient will not be able to shrug
and may have poor head movement.
Cranial nerve twelve is the last cranial nerve and it is otherwise called the hypoglossal
nerve. The hypoglossal nerve consists mainly of motor functions. Specifically it provides
motor innervation to many muscles of the tongue and plays a role in swallowing, as well as,
articulation when talking.
Well that was a brief review of cranial nerves and a USMLE practice question. If you liked
this video give it a like, if you have any comments or questions place them down below,
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importantly subscribe. This is Dr K and I will see you next time