in this segment we're going to talk more about the specifics of the midbrain the midbrain is the most
cranial of the three parts of the brainstem and it's continuous with the diencephalon now
the diencephalon is all things that we'll talk more about that when we talk about the central
the cortex and the gray matter deep within the cortex but for now what I want you to know is
it's the thalamus and it's right here it's a bilateral structure and we talked a little bit
about the thalamus when we talked about sensory systems because that's a place where all of your
senses are going to relay before they go up to the cortex so the midbrain is continuous with
the diencephalon and you can see that here in the dorsal and then here in the ventral aspects the
other things that I want to draw your attention to are again the crus cerebri which remember are
those motor fibers as they come from the posterior aspect of the posterior internal capsule and as
and then they go through the pons and then they become the pyramids in the in the medulla and to
new structures that I haven't really talked too much about yet and that is the tectum and the
tectum is just means four and what you have are two superior and two inferior colliculi and the
colliculi there's two on each side and so two total of fourths hence tectum the superior and
inferior colliculi are involved with auditory and visual relays and some of the coordinating
of your audio and visual reflexes which is more complicated than even I have got all the logistics
down on yet but I'm working on it so I'm not going to really talk about those in this series
of lectures but I do want you to know that those landmarks are there and that they're prominent and
they're easy to see so in the next section next slide you can actually see the tectum here here
are those two superior and two inferior colliculi just colliculus just means little bump so if you
section through the the midbrain you'll see two different levels are two different areas that are
of note and these include the the level of the superior colliculus and the inferior colliculus
another important landmark that you'll see is remember we talked about the fourth ventricle
which is on top of the pons and underneath the cerebellum and we talked about how the lateral
ventricles drained into the third ventricle the third ventricle drains into the fourth and the
the passageway between the third and the fourth is the cerebral aqueduct and that is right here right
in the heart of the midbrain again we can see our crew cerebri right here our superior and inferior
colliculus and our cerebral aqueduct there are two cranial nerves that are associated with the
midbrain and those are cranial nerves 3 which is here on the midline and 4 now the reason that 4 is
all the way out here is because for cranial nerve 4 is very strange it is the only cranial nerve
that starts dorsally and then wraps around the other direction all of the other cranial nerves
exit from the ventral aspect of the brainstem only the trochlear and I don't know why exits from the
dorsal aspect and wraps around so it's a little bit odd but that's the way it is you if you've
been counting you know that we're only up to 10 cranial nerves and you probably already know that
there are 12 cranial nerves 1 & 2 don't really attach to the brainstem so cranial nerve one
olfactory is way up in front and it doesn't make it to the brainstem at all but you can see cranial
nerve 2 and it is right here so there is your optic nerve it's usually can be seen coming up
from under the brain from the eyeball which is out in here we'll talk more about the optic and the
olfactory nerves when we talk about our cranial nerves a special sense in the next segment we'll
talk a little bit about areas of the brainstem that don't fall into any of these specific cranial
nerve categories so we'll talk a little bit in the next segment about the reticular formation