The Cranial Nerves
Although every effort has been made to make this document accurate, it is possible there are mistakes. I am fairly confident that everything is correct but since this document is made available as a courtesy it is your responsibility to catch any mistakes there might be (although I don't think there are any). That's it!! Have fun studying for the test.
Before we talk about the cranial
nerves I just want to review some major points. First, nerves are a collection of axons contained within the
peripheral nervous system whereas tracts are a collection of axons in the central
nervous system (i.e. the brain and spinal cord). Therefore, when we talk about the cranial nerves we are really
referring to part of the peripheral nervous system. Secondly, what makes the cranial nerves so special, after all we
have hundreds of nerves throughout the body?
The answer is that the cranial nerves are nerves that come directly off
of the brain and since we're doing a brain dissection, it is important to point
them out.
Alright, enough with the review. Let's talk about the nerves. There are 12 cranial nerves that you're
responsible for in this class (there's actually a cranial nerve zero that you
will not be responsible for). They are
numbered from 1-12 with the number of the cranial nerve increasing the more
posterior (caudal) the cranial nerve is (roughly). Make sure you know how to identify the cranial nerve on the brain
(this may be impractical for some cranial nerves; see below), know the number
of the cranial nerve, the name of the cranial nerve, and what it is responsible
for. Much of the information you need
to know is summarized immediately following the text on your sheep brain
dissection in the lab manual. Be aware
that many of the cranial nerves will be hard to identify in dissection, this
will not preclude us from asking you questions about the nerve even though we
cannot stick a pin in it. In order to
memorize the names of the cranial nerves you can learn the following mnemonic:
"On Old Olympus' Towering Top A Fin
And German Viewed Some Hopps". This will give you the first letter of the
names of the cranial nerves in numerical order. Alternatively, you can memorize the X-rated version which is
"Ooh, Ooh, Ooh, To Touch And Feel
A..."
Well...you
get the picture.
So
lets go over the cranial nerves
Cranial Nerves and Major
Functions
I
Olfactory Nerve Sensory Contains many small fibers arising in olfactory
mucous membrane and ending in the olfactory bulb. Be aware that in your brain dissections we can really only see the
termination of the olfactory nerve, the olfactory bulb, because the olfactory
nerve has been torn out.
II
Optic Nerve
Sensory
Encompases the nerve from the ganglion cells of each retina to the optic
chiasm. Be aware that your sheep brain
may contain the optic nerve, chiasm, and tract. Also know how the fibers cross in the optic chiasm.
III
Oculomotor Nerve Motor Origin in the midbrain; supplies four muscles of the eye.
IV
Trochlear Nerve Motor Motor to one eye muscle. Innervates superior oblique muscle which turns the eye downward
and laterally. This is the only cranial
nerve not shown in the pictures in the sheep brain atlas or web site. Be aware of its location traveling in the
ventral-anterior direction around the area where the cerebellum meets the
cerebral hemispheres.
V
Trigeminal Nerve Motor and Sensory Attached to the side of pons, very
large. Sensory from muscles of
mastication, skin of face and scalp, mucous membranes of mouth and nasal
cavity, cornea of eye, teeth, and dura mater.
Motor to muscles of mastication.
VI
Abducens Nerve Motor Motor to one eye muscle, turns eye laterally. This nerve arises from the trapzoid body.
VII
Facial Nerve Motor and Sensory Lateral to abducens and just behind the trigeminal; controls
most facial expression muscles and sensory from anterior two-thirds of tongue
for taste.
VIII
Auditory(also called the Vestibulocochlear) Nerve Sensory Just behind and
lateral to the facial nerve. Serves
senses of hearing and equilibrium.
IX Glossopharyngeal Nerve Motor and Sensory Arises together with vagus nerve behind and ventral to the auditory nerve. Sensory from posterior third of tongue for taste, other mouth and throat areas. Motor to salivary gland.
X Vagus Nerve Sensory and Motor Both sensory and motor for heart, stomach, blood vessels, viscera. Keep in mind what Professor Grisham talked about in regards to the James-Lange Theory and the Vegas Nerve.
XI
Spinal Accessory Nerve Motor Runs along lateral surface of medulla and spinal cord receiving
fibers along the way. Motor to muscles
of neck.
XII Hypoglossal Nerve Motor Arises in lower medulla in several more or less distinct roots. Motor to muscles of tongue.
In order
to maintain consistency, much of this information was adapted from the
Psychology 116 Lab Manual [1]. I didn't
want to include a lot of extra information that may overload your brain. There is certainly more out there to
know. If you are interested in learning
more about the cranial nerves I would recommend going to the following
link.
http://www.anatomy.wisc.edu/cn/cntable.htm
[1]
Grisham, W. (2001) Psychology 116, Psychobiology Lab Spring Quarter,
UCLA. Academic Publishing Service:Los
Angeles.