hello all this is dr. Alsup and we are going to talk about how to locate cranial nerves and
numerous different views including an inferior view of the brain the actual cranial base with
the dura on and how they exit the skull and lastly we're gonna talk about a brainstem model so we can
get an idea of the origins of these cranial nerves so let's get started we are starting
with an inferior view of the brain and hopefully we're getting used to this view at this point now
how this was cut we can only see a few cranial nerves but let's talk about the ones that we can
see here you can see part of the olfactory tracts which are associated with cranial nerve one the
bold the olfactory bulbs have been cut on this particular dissection these are located on the
inferior portions of the frontal lobe so this is the frontal lobes right here we're looking
at an inferior view they're going to be lateral to the anterior extensions of the anterior cerebral
artery so fairly closely associated with those now you can also see a bit of the optic nerves
and the optic chiasm right in this region here these are going to be medial to to the anterior
cerebral arteries as well as the internal carotid artery so here's your anterior cerebral and here
your icas or internal carotid the chiasm is where some fibers from the retina decussate or
cross which is super important for a binocular vision you can see some of the cut oculomotor
nerves here closely associated with two arteries the superior cerebellar which is the smaller one
and the posterior cerebral which is going to be the larger one so any nerve that is between
these two arteries you're going to identify as the ocular motor nerve or cranial nerve three you can
see a bit of the abducens nerve abducens nerves right here on the inferior surface of the ponds
and lastly at least on this side on this region right here you can see the accessory nerve or
cranial nerve 11a sending from the spinal cord and its close relationship to the posterior inferior
cerebellar artery or pica which you can see right there so that nerve that's going to be a sending
from the spinal cord is your accessory nerve all right so let's work through a few slides
showing most of the cranial nerves and how they're actually exiting through the skull it is important
to note in this particular and these particular dissections that we're going to see in these next
few slides the dura mater is still present so the foramina that we are going to talk about will
look different very different than what it would look like on dry bone with the dura removed so if
you see right here just kind of a hint this is your jugular foramen think about how different
that looked on the the dry skulls that we have been looking at so we really need to be able to
identify these regions with the dura and without in order to get a good understanding of these
areas so we're gonna start anteriorly and move posteriorly oops excuse me all right so you
can see the optic nerves or portions of the optic nerves right here so that is going to be cranial
nerve two they're going to be just superior to your internal carotid arteries or your cut
internal carotid arteries right there you know that the solid structures are going to be nerve
because nerves are going to be solid they're going to be consisting of collections of axons whereas
the artery would not be solid it would be hollow individual in this dissection because no blood
is going to be flowing through so the these are going to be the internal carotid arteries these
are the optic nerves the oculomotor nerve so here is one of your oculomotor nerves this one
actually was cut a little bit more distally so the oculomotor nerve is located on the lateral
wall of the sella turcica and you know you're in that sella turcica region because I can see
a little bit of the pituitary gland right here and also the internal carotid arteries will be
closely associated with that region so these are cranial nerve three same thing over here alright
both the root of the trigeminal nerve which you can see clearly here it's a little bit of it over
here as well as the trochlear nerve or cranial nerve four can be found in association with the
dura on the petrous part of the temporal bone now the trochlear nerve would be right about here ish
if present it is considerably more difficult to locate on a dissection which makes sense because
it is the smallest cranial nerve so not quite as easy to locate but you can clearly see the
trigeminal nerve right there alright moving on the abducens nerve or cranial nerve 6 is
going to be found on the clivus or the basilar or basal or part of the occipital bone so here
are your two abducens nerves now note that this is not where it is exiting the skull this is just
a close relationship to this part of the bone it will actually exit the skull and head to the
orbit via the superior orbital fissure after traversing the lumen of the cavernous sinus
on its way to the lateral rectus muscle so it has quite a ways to go but this relationship with this
basal or part of the occipital bone is something that will help you identify this nerve the facial
and vestibular cochlear nerves will enter the internal acoustic meatus so I am circling around
the internal acoustic meatus the facial nerve is eventually going to exit the internal acoustic
meatus or the petrous part of the temporal bone but the vestibulocochlear will head toward
the inner ear so enters this region and never exits it's really impossible to tell which one
is which here and we wouldn't ask you for that on the practical but the vestibulocochlear is a
little larger so we've kind of separated on this image this would be the facial the smaller one
here and then this kind of collection right here would be vestibulocochlear or cranial nerve eight
alright let's identify the last four cranial nerves from this view recall that the
glossopharyngeal the vagus and accessory nerves will exit the skull via the jugular foramen or
the jugular foramina and if we're talking about both with its neighbor the internal jugular vein
and this jugular foramen is going to be in this region right here so like I said very different
than from what it looks like on the dry bone without the dura intact so similar to what we
had at the internal acoustic meatus it's really difficult to tell which one is which in this
region so we would not ask you to identify the glossopharyngeal or the vagus here because it's
really impossible to tell or it's not as clear but you can tell which one is the accessory
nerve and this is because the accessory nerve will ace in through the foramen magnum before
it heads to the jugular foramen to exit the skull so if you have a nerve that is traversing both of
these foramina both the foramen magnum and the jugular foramen you know you're looking at the
accessory nerve lastly the hypoglossal nerve will exit through the hypoglossal canals so
with dura still present it sometimes looks like different nerves but these are really just accents
of the hypoglossal nerve so these right in this region are both parts of the hypoglossal nerve so
anything deeper in the frame and magnum region where no we're heading towards the hypoglossal
canal is really more superior lateral to the framin magnum lastly let's look at a brainstem
model as this will give us some good indications of where these cranial nerves will originate from
because most originated from the brainstem the optic nerve however does not originate from the
cranial nuclei of the brainstem but you can see right in this region the optic chiasm as well as
the optic nerves so this would be cranial nerve two moving to the midbrain region there are going
to be two cranial nerves which will originate here you will have the oculomotor nerves so these are
both ocular motor nerves right here this is going to be larger and more oriented towards the midline
whereas the trochlear nerve these are going to be smaller and it's really the only cranial nerve
that exits the brain dorsally so you can kind of see it's sneaking in from that direction here so
these are your trochlear nerves for cranial nerves originated from the pons and this will be cranial
nerves five six seven and eight six six through eight will be more closely associated with the
inferior portions of the pons very close to the medulla oblongata whereas trigeminal is going
to be your largest cranial nerve it's a fairly distinctive and it's large trunk will be on the
lateral sides of the pons here the abducens will be located right here they are going to be more
medially located whereas the facial and vestibular cochlear are going to be pretty closely associated
facial is going to be the smaller one so this would be facial and then this larger one right
here is going to be the best stimulate cochlear or cranial nerve eight cranial nerves nine ten
and twelve will originate on the medulla oblongata the glossopharyngeal nerve is the more superiorly
located so this is going to be glossopharyngeal and this will be the vagus of vagus and
glossopharyngeal are pretty closely associated to one another whereas the hypoglossal is going
to be more medially and in fear we position so these are going to be the hypoglossal nerves
lastly the accessory nerve we remember this one traditionally was referred to
as the spinal accessory it is going to come off the spinal cord so inferior to or distal to the
medulla oblongata so this is going to be the accessory alright so we have really explored
how we are going to identify the cranial nerves and many different views we will be seeing many
of these in close association with their target organs and subsequent sessions to kind of add
on to what we know about their origins from this session I apologize if you've heard any
dog barking in the background somebody must be delivering a package but I want you to I
want to thank you for your time and attention and always feel free to reach out with any questions