The Cranial Nerves and What They Are About

[Quixotic1]

Olfactory

Optic

Oculomotor

Trochlear

Trigeminal

Abducens

Facial

Vestibulocochlear (also Auditory)

Glossopharyngeal

Vagus

Accessory/Spinal

Hypoglossal


A little bit on the Cranial Nerves: These are a twelve sets of nerves that sprout directly off the brain and brainstem. Thus, even though they go out into the body, (like peripheral nerves do) their origins are in the white matter of the Central Nervous System. So these 12 nerves (actually 24 nerves, one on each side) are considered white matter. A lot of the common MS sites of demyelination involve the Cranial nerves. If you have read many of my posts, you'll remember that I am always mentioning that this that or the other symptom are from lesions in the Cranial nerves.

The Cranial Nerves have an wide interaction with each other to give the brain far more information and control than the nerves do alone.  They interact within the brainstem through a series of nerve hubs called nuclei (plural of nucleus).  Through these nuclei we have greater understanding of what we see, can move our eyes in complex ways, have greater balance and coordination.

CN I - is the Olffactory Nerve -

What it does - this nerve comes directly off the brain and handles the entire job of the sense of smell.
What happens when MS attacks it - Changes in sense of smell can occur in MS, from partial or complete loss of smell to alterations in smell like smelling weird things that aren't there.

CN II - the Optic Nerve -

What it does - Yep, handles the whole process of sight and vision.  As a sensory nerve, the Optic  Nerve picks up the image in light and color and carries it backwards to the brain where the information is processed by several parts of the brain.  This forms the images we see, and adds to the information that keeps us upright in space and helps us keep our balance.  The information is also used in the cerebellum to help us with fine motor and coordination.
Lesions on this nerve from MS cause the condition Optic Neuritis, symptoms include decreased vision, pain behind the eye, pain with eye movements, loss of color saturation (vivid colors become paler or more grayed out), flashes of light, loss of parts of the field of vision

CN III - the Oculomotor (eye movement) Nerve

What it does - It's a motor nerve.  This nerve handles 4 of the six muscles that allow the eyeball to move around, instead of staring straight ahead.

It also raises one of the major muscles of the upper eyelid on the same side. Alesion will cause the eyelid on the same side to droop.

It also has the function of working to control the pupil constriction to light and to close/far vision.  Lesion can change our ability to bring objects at different distances into focus.

When there is a lesion on it it can cause double vision because the affected eye cannot move in coordination with the normal eye.

The eyelid on the same side can droop

The pupil on that side may not respond as promptly to light.


CN IV - the Trochlear Nerve

This nerve handles the muscle that allows the "opposite" eye to rotate using the supeior oblique muscle. This allows fine tuning of the eye movements other than just up/down and side-to-side. It is the only cranial nerve that crosses over to direct something on the OPPOSITE side of the face.

Lesion - double vision

CN V - the Trigeminal Nerve

This is the major sensory nerve for sensation to the face and the motor nerve for chewing. The Trigeminal Nerve also handles the sensation from the sinuses, from the outside surface of the eardrum, and from the meninges.  This nerve has three main branches. ( It's name means "three roots) V1 brings sensation from the upper part of the face and eyelid, the temple and the forehead. It may reach as far as the top of the scalp.  V2 is the mid-part of the face, cheek, nose. Also the upper teeth, gums,upper lip and inner cheek. V3 handles the sensation from the lower face, lower teeth and gums, and lower lip. It extends down to and slightly beyond the jawline.

Lesion - It is responsible for the sensations of numbness, tingling and PAIN (as in Trigeminal Neuralgia) seen in MS.  There can be an alteration of sensation noted both preceeding and following an episode of TN.  A lesion may cause inability to chew effectively or fatigue with chewing.

CN VI - the Abducens Nerve - This motor nerve handles the same side eye muscle attached to the outside eyeball and allow the eye to turn laterally to the side.

CN VII - The Facial Nerve - This nerve handles most of the muscles of the face and lips and around the eye. But it is not only a motor nerve.  It is also a sensory nerve and a visceral nerve.  (A visceral nerve causes actions in an organ of the body like causing a gland to secrete or causing the bowles to have peristalsis).   It handles part of the control of the glands of the face. It also carries sensation from the ear, the middle ear and the interior of the eardrum. It handles taste for the anterior 2/3's of the tongue on the same side. When this nerve goes wonky you get a Bell's Palsy - Drooping of the side of the face, droopy eye, etc.

CN VIII - The Auditory Nerve - This is a sensory nerve responsible for Hearing and Balance (peripheral balance) Damage to this nerve can cause hearing loss and vertigo, and tinnitus.

I'll do the last 5 nerves later.  Also some neuroanatomists claim there is a Nerve #0 which is responsible for the production of pheromones.

There are uncounted mnemonics for remembering the cranial nerves and there order.  These range from odd to silly to downright slutty.

On Occasion Our Trusty Truck Acts Funny. Very Good Vehicle Any How.

On Old Olympus' Towering Tops A Friendly Viking Grew Vines and Hops

Only On Occasion, Touching The Amorous Female Virgin Goat Vacillates A Hand

OLympic OPium OCcupies TRoubled TRiathletes After Finishing VEgas Gambling VAcations Still High

Orange orangutans often try to avoid feeding angry gorillas very ancient hotdogs.

On Old Olympus' Tufted Top A Fat Armed German Viewed An Hop

Oh Once One Takes The Anatomy Final Very Good Vacations Are Heavenly  

Only Older Octogenarians That Take A Free Viagra Get Very Aroused Here

Oh, Oh, Onward Through The Airy Facade Viewing Gorgeous Vixens Acessorizing Hedgehogs



Another set of mnemonics helps to remember the nerves' purposes and to remember the types of information these nerves carry (Sensory, Motor, or Both) is thus:

Some Say Money Matters, But My Brother Says Big Brains Matter More.

Some Say Money Matters, But My Brother Says Big Boobs Matter More.

Small Ships Make Money, But My Brother Says Big Boats Make More.

Some Say Marilyn Monroe, But My Brother Says Bridgette Bardot Mmmm Mmmmm

I had been waiting to finish this, but decided a little was better than nothing.

Quix

[doublevision1]

agree, awesome post Quix.

Re; showing up on MRI, I have a large lesion on my brain stem that damaged my 6th cranial nerve and caused constant double vision for about a year.  I don't know if they isolated it on MRI to the actual nerve responsible, or,  just the brain stem, and concluded damage to that particular cranial nerve based on clinical observation.  Since my MRI report said nothing about cranial nerves I assume the latter.

Quix???

[Zacksmomi]

As ususal, awesome post.  Do lesions on these nerves generally show up on a brain MRi?
I have so man of these sx's.  I am being checked for disease after disease that causes a lot of the things you explained above.  I am seeing that it really could all be from MS.

Thanks for being you
D

[MonkeyMom4]

Thank you so much! Very informative.  =D I bookmarked this page already!