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 a part of the peripheral nervous system, except cranial nerve number
2, which actually emerges from, 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 around, 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 actually emerge from the telencephalon 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 nerves.
So you've got the olfactory nerve, number 1, optic, oculomotor, trochlear, trigeminal,
abducent, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, and hypoglossal nerves.
So they've got kind of strange names, but there is a mnemonic for remembering these.
So I'll give you the clean version, which is "Oh, oh, oh, to touch and feel very good
velvet, ah, 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 functions of the cranial nerves.
So this is some "Some say marry money, but my brother says big boobs matter more", so
"S" is sensory, "M" is 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 1, 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, the 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 on to this olfactory bulb.
So I've just switched over to this model, and you can see these little nerves, coming
up to synapse on to the olfactory bulb.
So if we just take a quick look at the cribriform plate, we're looking at a side view of the
skull here, so we're going to rotate the skull round 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 and there are little holes
in the cribriform plate, where the olfactory nerves pass through.
So if I just rotate the model round, you can see these olfactory nerves passing up through
the foramina, to synapse on to 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 that they cross at this area called the optic chiasm,
so these nerves, the optic nerve, nerve number 2 is responsible for vision, so it carries
sensory information from the retina to the brain.
So the third nerve is the oculomotor 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 sort of pillars,
these are called cerebral peduncles, and these are part of the midbrain.
So the oculomotor nerve originates anteriorly on the midbrain, in the floor of the interpeduncular
fossa.
So you can see the oculomotor nerve originating here.
And this nerve is responsible for innervating muscles that move the eye, so extraocular
muscles, and it also innervates the pupillary sphincter.
So nerve number 4 is called the trochlear nerve.
So if we just zoom in a 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 oculomotor nerve here, originating in the interpeduncular fossa,
and if we follow the, if we rotate the model round 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 innervates one eye muscle, called the superior oblique muscles.
So it originates on the dorsal midbrain, and it winds round the sides of the cerebral peduncles,
so the lower margins of the cerebral peduncle.
So next we've got the trigeminal nerve, so this, so you can see this big fat nerve coming
off the side of the pons on the middle cerebellar peduncle, so this is the trigeminal nerve,
so you can see it here, originating laterally on the pons, on the middle cerebellar peduncle.
So the middle cerebellar peduncle is the bit which connects the pons to the cerebellum.
So I'll just rotate round so you can see that more clearly, so you can see the big trigeminal
nerve coming off the side of the pons.
So this nerve is responsible for sensation to 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 neurones, and then it splits into three branches, so if
I 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 innervating the muscles of mastication.
So if we just rotate the model around again, so we're looking anteriorly at the brainstem,
just follow the brainstem down, we can see this 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 muscle, sorry nerve, involved in innervating the extra-ocular muscles of the
eye.
So it innervates one muscle of the eye called the lateral rectus muscles.
So we've now talked about three muscles, sorry three nerves responsible for innervating extra-ocular...
oculomotor nerve, 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 laterally, if we follow the brainstem laterally,
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 salivary glands and the lacrimal glands.
So just lateral to this nerve, you've got the vestibulocochlear 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 the muscles in the throat, and carrying sensation from various areas
in the throat.
So that's nerve number 9, the glossopharyngeal nerve, and nerve number 10 originates just
below it, and this is the vagus nerve, so this originates in the postero-lateral sulcus
of the medulla, so just behind the olive, and just below the, just below where the glossopharyngeal
nerve originates.
So the vagus nerve innervates lots of laryngeal and pharyngeal muscle, and it innervates 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, it's this nerve here, it isn't shown sort of, it's not best illustrated by
this model, but you can see its sort of, it's got a lower origin and an upper origin, so
it's got a cranial and spinal root.
So this nerve is responsible for innervating the sternocleidomastoid and the trapezius
muscles.
And finally we've got the 12th nerve, so this is the hypoglossal nerve, and 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 innervating the muscles of the tongue.
So those are the 12 cranial nerves, you've mnemonics for remembering them and you've
seen sort of where they originate from on the brainstem and the brain.