Cranial Nerves

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Nerves from the brain run from top of motor cortex, for example, down through the insular, brainstem (* pons, medulla) where they form a tract looking like a pyramid. (This is how the name 'pyramidal tract' appeared.) 90% will decussate here (switch sides) before going down the spinal cord. Cranial nerves, switch sides and synapse with LMN earlier in the brain stem than other nerves.

If there is a lesion in the upper motor neurone the patient may exhibit spasticity - where the body fails to inhibit tensing reflex.

If the lesion is in the lower motor neurone (below where nerves decussate) then they will be floppy / hypertonic.

https://www.youtube.com/watch?v=zfzgz-XN_S8

Cranial nerves are different from most spinal nerves in that they are bilaterally innervated. WHen it get to the decussaiton, it also stays on its own side, aswell as synapsing with the other side. The exception is CNVII (Facial nerve), the part that deals with the lower face only receives input from one side. Similarly with CNXII (hypoglossal) muscles of protrusion.

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Twelve nerves of Christmas song: https://www.youtube.com/watch?v=NEenJCk3EIE

Olfactory is the first cranial nerve - one has a funny kind of smell

Optic is the second cranial nerve - Two helps you see & one has a funny kind of smell.

Oculomotor is the third cranial nerve - Three up and down (eyes), two helps you see & one has a funny kind of smell.

Trochlear is the forth cranial nerve - four down and out, three up and down, two helps you see & one has a funny kind of smell.

Trigeminal is the fifth cranial nerve - Neuralgia! Four down and out, three up an down, two helps you see and one has a funny kind of smell.

Abducent is the sixth cranial nerve - Six looking sideways... Neuralgia! Four down and out, three up and down, two helps you see & one has a funny kind of smell.

Facial is the seventh cranial nerve - Seven screw your face up, six looking sideways, Neuralgia, four down and out, three up and down, two helps you see & one has a funny kind of smell.

Vestibular is the eighth cranial nerve - Eight makes you dizzy, seven screw your face up, six looking sideways, Neuralgia, four down and out, three up and down, two helps see & one has a funny kind of smell.

Glossopharyngeal is the ninth cranial nerve - Nine very tasty, eight makes you dizzy, seven screw your face up, six looking sideways, neuralgia, four down and out, three up and down, two helps you see, and one has a funny kind of smell.

Vagus is the tenth cranial nerve - Ten makes you chunder, nine very tasty, eight makes you dizzy, seven screw your face up, six looking sideways, Neuralgia, four down and out, three up and down, two helps you see and one has a funny kind of smell.

Accessory is the eleventh cranial nerve, Eleven shrug your shoulders, ten makes you chunder, nine very tasty, eight makes you dizzy, seven screw your gace up, six looking sideways, Neuralgia, four down and out, three up and down, two helps you see and one has a funny kind of smell.

Hypoglossal is the twelfth cranial nerve - Twelve stick your tongue out, elven shrug your shoulders, ten makes you chunder, nine very tasty, eight makes you dizzy, seven screw your face up, six looking sideways, neuralgia! Four down and out, three up and down two helps you see and one has a funny kind of smell.