So as i mentioned in the very beginning of this lecture, the cerebellar cortex has about
50 percent of the brains neurons. we couldn't fit them all in this illustration but they
are in the granule cel layer.
so the cerebellar cortex has 3 layers. an outer molecular layer, and intermediate purkinje
cell layer, and an inner granule cell layer.
This is where the cells are really really dense.
the molecular layer doesn't have a lot of neurons in it, it mostly has the dendritic
arbor, all of the dendrites that are extending from this giant purkinje cell and heres another
one and another one and of course they live in the purkinje cell layer.
the purkinje cells are amazing.
they extend this huge dendritic arbor, but what is fascinating is that they are in one
plane, so its only 2D, its not 3D like most dendritic arbors.
Its 1D, and these purkinje cells all across the layer have different orientations of their
dendritic arbors.
That difference in dendritic arbor orientation is going to determine which of these granule
cells here are going to synapse with it so you can see these granule cells send an axon
up into the molecular layer and it goes along the edge here and synapses on the purkinje
neurons.
the cerebellar cortex gets information from the brainstem and spinal cord and areas of
the brainstem concerning balance and areas of the spinal cord that have to do with the
position of your muscles in space.
All of this info comes into the cortex via the middle and inferior peduncles and some
of the the fibers synapse directly on the purkinje cells and some synapse on the granule
cells that will then synapse on the purkinjes.
The purkinjes then take all of this info and send it back out down to the deep grey matter
of the cerebellum.
so info comes into the cerebellum, goes up to the cortex, up to a purkinje cell and back
down to the cerebellar white matter to synapse in one of these deep cerebellar nuclei. in
this particular section, you can see the dentate. this is the dentate nucleus of the cerebellum.
The dentate nucleus and the other deep nuclei of the cerebellum are the part of the cerebellum
that sends info out to the motor cortex via the superior peduncle.
So info in through the middle and inferior, going through some complex circuitry up in
the cerebellar cortex, output of the cortex to the deep cerebellar nuclei, then back out
to the motor cortex.
That is how the cerebellum can keep tabs on your spinal cord and brainstem and inform
your motor cortex about how what you're doing is actually matching up with what you think
you're doing.
So in summary, what i want you to know about the cerebellum is i want you to be able to
describe its gross anatomy, so hemispheres, lobes, and other main areas.
What are the cerebellar peduncles and how many are there, names, what type of fibers
travel in each one.
When it comes to the cerebellar cortex, how many layers, their names, and what's going
on in each layer.
And when it comes to the cerebellum talking to the rest of the nervous system, how does
this info leave, what is the last stop in the cerebellar train before it goes out, and
how does it go out.
If you can understand those things, then you are ready for the assessment.