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so things that can go wrong during
cerebellar development include the
Chiari malformation now curie
malformation has a variety of subtypes
but the main thing to remember is that
there's too little space in the
posterior cranial fossa
so the cerebellum normally fits in that
post your cranial fossa very nicely but
with too little space it has to go
somewhere and in type 1 and type 2
Chiari malformation the cerebellum
partially herniates inferiorly through
the foramen magnum in particular the
cerebellar tonsils tend to extend down
the foramen magnum and they put pressure
on the medulla that's located anterior
to it now that pressure on the medulla
can result in difficulty with organizing
your respiratory and heart activity
because your parasympathetic
cardiorespiratory nucleus is located
just in that area so this is tied to
some problems with regulating breathing
and heartbeat in addition having that
pressure can back up the flow of
cerebral spinal fluid causing
hydrocephaly or even Sereno Miglia which
is going to be a cyst that develops in
the central canal of the spinal cord as
fluid is unable to exit the central
canal it builds up and create a cyst in
the upper cervical region and again that
is cyrene Amelia now another problem
involving the cerebellum is called dandy
Walker malformation and it's a series of
problems that basically boil down to
there being two little cerebellum a
genesis of the cerebellar vermis the
midline region of the cerebellum can
result in an expansion of the fourth
ventricle if there's no cerebellum there
then the space that it used to occupy
will now be filled with spinal fluid of
the fourth ventricle and as that fluid
builds up it's going to cause a
ballooning of the dura mater
that's just superior to where the
cerebellum is going to be located so
altogether that's known as dandy Walker
malformation
and this can result in postnatal
hydrocephaly and has a variety of other
problems that need to be diagnosed
radiologically and this is a fairly good
example of what that's going to look
like in sagittal cross-section
proceeding further superiorly we're
going to now enter the midbrain and just
like before it's easy to get confused by
all the nuclei present in the midbrain
but try to think of whether they're
motor or sensory and it'll make a little
more sense early on the ALR plate sends
some sensory nuclei very far dorsally to
become the superior and inferior
colliculus and the basal plate sends
some motor nuclei inferior or pardon me
ventrally to become the substantial
so we take a look at the inferior
portion of the midbrain or the
mesencephalon and we can see the
inferior colliculus which is tied to
sensory activity of hearing it's a relay
for hearing and other sensory activity
coming from the vestibular and cochlear
nuclei then we have some motor nuclei
located inferior to that in particular
the trochlear nucleus is found in the
inferior midbrain and the substantia
is present very far ventrally
close to the motor fibers coming from
the brain down to the spinal cord the
crus cerebri go a little further up and
it looks very much the same take a look
at this picture and this picture they
look very similar one thing that
distinguishes the superior brain partly
a superior midbrain from the inferior
midbrain is that we have a superior
colliculus for visual activity relay and
we've got the oculomotor nucleus for
moving the eyes but we have one more
motor nucleus located in between the
substantia and the ocular motor
this is called the red nucleus and it's
a motor nucleus that's very important in
some animals is a little bit less
pronounced in humans but that nucleus is
still present and we move a little
further up and we come to the
diencephalon or the flam ik nuclei this
is where that easy breakdown of LR and
basal
played somewhat breaks down and we have
an epithalamus or pineal gland
developing off the very most very
superior most portion of the ALR plate
the thalamic nuclei which receive a
great deal of sensory information from
all over the body developed from the ALR
plate and the hypothalamus develops from
the basal plate now if you remember what
the hypothalamus does it directs a lot
of our very basic motor activity our
basic drives of appetite wakefulness
thermal regulation are all located in
the hypothalamus so you can think of it
as a type of motor nucleus but it's a
bit more sophisticated than just an easy
motor versus sensory breakdown so the
hypothalamic nuclei are going to be
present there whereas the thalamic
nuclei are present coming from the ALR
plate just above that hypothalamic
sulcus
now the cerebral cortex is going to have
its own lecture altogether we're gonna
talk really quickly though about a small
portion of the hypothalamus that blebs
downward and meets a very strange
structure called Rath keys pouch Rath
keys pouch is a little actually called
ballooning of the epithelium of the oral
cavity and it stretches upward to meet a
down growth an infant Divya ylim of the
diencephalon and this weird two-part
structure is going to form our pituitary
gland so Rath Keyes pouch grows up from
the oral cavity the infundibulum goes
down from the diencephalon and
eventually the rathke's pouch completely
disassociates from the oral cavity and
wraps around the infundibulum and this
is going to be our pituitary gland and
the anterior lobe of the pituitary gland
is from rathke's pouch oral epithelium
whereas the posterior lobe and
infundibulum are coming from the
diencephalon so very strange embryologic
development creating that single gland
from two separate sources and finally
the pituitary gland sits inside a little
saddle of bone called the sella turcica
completely separate from the oral
cavity but interestingly if you need to
do a pituitary surgery you will actually
somewhat replicate its pathway of
migration by going through the upper
nasal pharynx to crack through that bone
and get to the pituitary by following
more or less the original pathway of
Raffi's pouch now let's take a step back
we've discussed how the LR plate gives
rise to sensory and the basal plate to
motor neurons when we think about the
cranial nerves 1 through 12 and there
are extreme complexity one thing that
can help make sense of them is the fact
that any motor activity of a cranial
nerve must be tied to a derivative of
the basal plate likewise any sensory
activity associated where the cranial
nerve has to be tied to a nucleus
originating from the LR plate so if you
look at where those plates originate and
where the final sensory and motor nuclei
are located in the brainstem it can help
make sense of where the different nuclei
are located when you're trying to look
through a cross-sectional image and
localize a lesion inside the brainstem
now the sensory ganglia that are
associated with core nerves 5 7 9 and 10
originate from the same place that the
posterior root ganglia originate they
come from neural crest cells that
migrate and then extend axons out to the
skin or other sensory structures and
back into the central nervous system to
inform the brain about what they're
sensing so Crean under five is going to
be innovating the face kearney nerve 7
part of the ear and taste for the tongue
and crew nerves 9 and 10 innovating the
pharynx palate larynx and other
structures inside the head now we've
left out
cranial nerves 1 2 & 8 there are very
special structures that are going to be
giving rise to the olfactory the optic
and vestibular cochlear apparatus in
particular and we're going to have
separate discussions on each one of
those because they're very special in
the way that they develop take a step
back into the lowest part of the body
initially our spinal cord extends all
the way to
very tip of our developing vertebral
canal and during early development as
those spinal nerve roots come out they
just immediately exit the inter
vertebral foramina that are associated
with them but for some reason as we grow
our spinal cord does not grow at a
corresponding length and it remains
tethered to the base of the sacrum and
coccyx but the whole cord extends
leaving behind a small little cord of
material called the filum terminale II
and the cord quote-unquote ascends it
doesn't literally move upward but it
does not elongate as quick as the rest
of the body so as it gets pulled more
superiorly we wind up with the nerve
roots being stretched out behind it and
that creates a structure called the
cauda equina that translate as horse
translates to horse's tail and it really
does look like a horse's tail you have a
variety of nerve roots filling the space
inside the vertebral canal and then
exiting at their designated spinal level
you generally find the tip of the spinal
cord the conus medullaris located at
about the l1 to l2 region in most mature
people but by the time we're born it is
already ascended quite a long way and if
we have to do a spinal tap on someone
we're generally going to aim to enter
the canal at some place below l1 so that
we're not going to risk hitting the
actual cord but can push those nerve
roots out of the way and pull cerebral
spinal fluid out of the nearby space all
right thank you very much and I'll see
you at the next talk
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