Cranial Nerves Anatomy

Okay, so this is a tutorial on the cranial nerves. So cranial nerves are nerves that emerge directly from the brain. And you've got 12 pairs of cranial nerves, and they're a part of the peripheral nervous system. So all 12 pairs are part of the peripheral nervous system except cranial nerve number 2, which actually emerges, which is kind of like an extension of the brain. So it's not technically a peripheral nerve. So in this tutorial we're going to go through the 12 cranial nerves. We're going to look at where they originate from in the brain, and we'll talk a little

bit about their function. So the cranial nerves have lots of different functions. You've got somatic and visceral components. They've got motor components, and there's some nerves which have special sensory components. So components to do with the special senses like smell, vision, hearing, balance, and taste. So if I just rotate the model of the brain round, you can see, so we're looking at the base of the brain, and you can see all these nerves emerging from the brain. So the first two nerves actually emerge from the telenecephalon and diencephalon.

But the rest of the nerves, nerves 3 to 12, emerge from the brainstem. So that's the midbrain, the pons, and the medulla. So the nerves are sort of numbered from 1 to 12, from kind of top to bottom, if you like. So I'm just going to run through a list of the nerves. So we've got the olfactory nerve, number one, optic, ocular motor, trochlear, trigeminal, abducent, facial, vestibulococular, glossopharyngeal, vagus, accessory, and hyperglossal nerves. So they've got kind of strange names, but there is a mnemonic from remembering these.

So I'll give you the clean version, which is o-o-o, to touch and feel very good velvet, R-heaven. So the dirty version is what probably most people are taught, and it involves touching and feeling other things. So you can use your imagination there. So there's also a mnemonic for remembering the function of the cranial nerves. So this is some, say, marry money, but my brother says big boobs matter more. So S is sensory, M, motor, B is both, so sensory and motor. So keep these mnemonics in mind when we go through the nerves.

So we'll start with cranial nerve number one, which is the olfactory nerve. And this nerve is responsible for olfaction, so the sense of smell. So there are receptors in the nasal cavity which pick up the sense of smell, and the nerves pass through the nasal cavity up through the cribriform plate of the ethmoid bone, and synapse on this olfactory bulb. So you can see this projection along the base of the brain. So this is called the olfactory bulb, and the olfactory nerves synapse onto this olfactory bulb.

So I've just switched over to this model, and you can see these little nerves coming up to synapse onto the olfactory bulb. So if we just take a quick look at the cribriform plate, we're looking at a side of the skull here. So we're going to rotate the skull around and look at the interior of the skull. So we're looking from a superior view at the inside of the skull. So this is the anterior part, and the cribriform plate lies here. So it's not shown clearly here, but the olfactory bulb runs along the cribriform

plate. There are little holes in the cribriform plate called foramina where the olfactory nerves pass through. So if I just rotate the model around, you can see these olfactory nerves passing up through the foramina to synapse onto the olfactory bulb. So next we've got the optic nerve, and you can see these two nerves on either side, these big nerves coming here, and you can see they cross at this area called the optic chiasm. So the optic nerve, nerve number two, is responsible for vision, so it carries sensory information

from the retina to the brain. So the third nerve is the ocular motor nerve. So now we're coming, this is the first nerve that originates from the brainstem. So you can see its origin here in the interpeduncular fossa. So you can see these two pillars, these are called cerebral peduncles, and these are part of the midbrain. So the ocular motor nerve originates anteriorly on the midbrain in the floor of the interpeduncular fossa. So you can see the ocular motor nerve originating here. And this nerve is responsible for innovating muscles that move the

eye, so extraocular muscles. And it also innovates the pupillary sphincter. So nerve number four is called the trochlear nerve. So if we just zoom in a little bit to the brainstem, and I'll just remove the cerebellum, and I'll remove the cerebral hemispheres, so it just makes things a little bit more clear. So we've just seen the ocular motor nerve here originating in the interpeduncular fossa. And if we rotate the model around to look at the dorsal surface of the midbrain, we can see the trochlear nerves originating.

So the trochlear nerve is another nerve which is involved with movements of the eye. So it only innovates one eye muscle called the superior oblique muscle. So it originates on the dorsal midbrain and it winds around the sides of the cerebral peduncles. So the lower margin of the cerebral peduncle. So next we've got the trigeminal nerve. So you can see this big fat nerve coming off the side of the pons on the middle cerebellum peduncle. So this is the trigeminal nerve. So you can see it here originating laterally on the pons on the middle

cerebellum peduncle. So the cerebellum peduncle is a bit which connects the pons to the cerebellum. So I'll just rotate around so you can see that a bit more clearly. So you can see the big trigeminal nerve coming off the side of the pons.

So this nerve is responsible for sensation from the face. And if you just follow the nerve along you can see this big bulge. So this is the trigeminal ganglion. So this is a group of cell bodies of the sensory neurons. And then it splits into three branches. So if I just zoom in a bit you can see these three nerves coming off. So you've got three branches of the trigeminal nerve. You've got the ophthalmic maxillary and mandibular nerves. So that's just worth remembering. So as well as providing sensation from the face,

the trigeminal nerve is responsible for the innovating the muscles of mastication. We just rotate the model around again so we're looking anteriorly at the brainstem. Just follow the brainstem down. We can see this nerve here originating at the border between the pons and the medulla. So this nerve is called the abducent nerve. And this is another nerve involved in innovating the extraocular muscles of the eye. So it innovates one muscle of the eye called the lateral rectus muscle. So we've now talked about three nerves responsible for innovating extraocular.

Oculomotor nerve, the trochlear nerve and now the abducent nerve. So this originates at the border between the pons and the medulla. So if we just rotate the model again looking latchly, if we follow the brainstem latchly, we've got two nerves here. And this part of the brainstem is called the cerebellopontine angle. So just above the olive of the medulla, you've got this nerve here called the facial nerve. So this originates at the cerebellopontine angle above the olive. And it's responsible for muscles of facial expression. And it receives taste from the anterior two thirds of the tongue.

And it also has secretomotor function to the sliver glands and the lacomal gland. So just latch on to this nerve. We've got the vestibulococular nerve, which also originates in the cerebellopontine angle. And this nerve is responsible for hearing and balance. So it has two branches. The vestibular part is responsible for balance and the cochlear part is responsible for hearing. And then just below it, we've got this nerve here, which is called the glossopharyngeal nerve. And this originates just dorsal to the olive. So you can see its position here just behind the olive on the lateral margin of the medulla.

So this nerve is responsible for taste from the posterior third of the tongue. So remember the facial nerve was responsible for taste from the anterior two thirds. The glossopharyngeal nerve is responsible for taste from the posterior third. So it's responsible for taste and it's got this secretomotor function to the parotid gland. And it is also responsible for innervating muscles in the throat and carrying sensation from various areas in the throat. So that's nerve number nine, the glossopharyngeal nerve. And nerve number 10 originates just below it. And this is the vagus nerve.

So this originates in the posterior lateral sulcus of the medulla. So just behind the olive and just below where the glossopharyngeal nerve originates. So the vagus nerve innovates lots of laryngeal and pharyngeal muscle. And it innovates almost all of the abdominal and thoracic viscera. So next we've got the accessory nerve. So this is nerve number 11. And this nerve has cranial and spinal roots. So it's got, so this is this nerve here. It isn't shown sort of, it's not best illustrated by this model, but you can see it's sort of, it's got a lower origin and an upper origin.

So it's got a cranial and spinal root. So this muscle is responsible for innovating the sternocleidomastoid and the trapezius muscles. And finally we've got the 12th nerve. So this is the hypoglossal nerve. So you can see it here. So this sits between the pyramids of the medulla. So these are the medullary pyramids. And it sits between these pyramids and the olive. So you can see that here, the hypoglossal nerve. And this nerve is responsible for innovating the muscles of the tongue. So those are the 12 cranial nerves.

You've got mnemonics remembering them and you've seen sort of where they originate on the brain stem and the brain.