NEUROANATOMY NOTES 08/06/99
Profesor: Dr. Martinez Sandoval
He draws a picture of the brainstem and the cerebellum. He draws a sagittal section. This region of the
cerebellum is the vermis, and we see the right hemisphere. The position is posterior to the pons and
medulla. The anterior surface of the cerebellum will be this one to this point. This surface forms the roof
of this cavity that you knew as the 4th ventricle. The 4th ventricle or cavity has a dorsal surface or roof.
There is a dorsal surface of the pons. This is a roof because the brainstem is not vertical. This position you
would say this is the ventral or anterior surface, and posterior or dorsal portion, if it was vertical. Instead,
since its at an angle, its called an anterioinferior surface and posteriorsuperior surface or roof.
He shows us pictures of the cerebellum. Then you can see the remaining part, known as the cerebellar
hemisphere. This being anterior and this being posterior, with right and left sides, of course we have our
midline. So the cerebellum has right and left part or halves. However, there are three main divisions of the
cerebellum. The central part can be seen here, or vermal region. So in this view, that we showed in the
beginning, this is the entire vermal region. Now this vermal region, is extremely important because it
receives in general, the information from the limbs. The unconscious propioception from the limbs will be
projected to the cerebellum by tracts to cells that lie in the vermis.
The second region is paravermal. It is on the side of the midline. So paravermal on the side of the vermis.
This region will be associated with some special nuclei that is related with muscular coordination. And this
same function but more precise and important control will be the third part known as the lateral or
hemispheric region. This is the main region that will control the muscular coordination. The paravermal
helps a little. The anterior view of the cerebellum is where you see a structure with two parts: 1) nodulus,
the central part. This central part is connected by a small stalk with 2) flocculus which is a lateral part
located on each side of the nodulus. Yesteday we noted that the floccularnodular nerve maintains the
equilibrium. This is the part of the cerebellum that deals with vestibular nuclei, and then the vestibulospinal
tract that will control posture and balance of the body.
In this superior view, you can see a line, a deep fissure, or sulcus, called the primary fissure. The primary
fissure divides anatomically the cerebellum into the anterior and posterior lobe. So now you have an
anterior lobe and a posterior lobe and a flocculonodular lobe. But try to think there are different divisions.
Finally in addition to that, if you see again the anterior view of the cerebellum, be careful of these two small
parts, the most inferior projections of the cerebellum. In the anterior view you can see the two most inferior
projections of the cerebellum, known as cerebellar tonsils, or the amygdala of the cerebellum. If you were
to project these tonsils in the lateral view, you go back to this first figure. You will see the tonsils here, in
the small regions at the inferior portion, and increase of pressure on the brain will push this region down
into the foramen magnum. The first part of the cerbellum that will begin to enter through the foramen, will
be the cerebellar tonsil. This is the dorsal surface of the medulla. This is the posterior surface. So when
youdo that the tonsil is advancing and finally is compressed against the dorsal surface of the medulla. That
is when the patient may die easily because of cardiac arrest.
So now the cerebellum in this medial view, you can see that the cerebellum is connect to the midbrain via
the superior cerebellar peduncles. This enters the midbrain. The cerebellum will also be connected with
the pons, via the middle cerebellar peduncle. And the cerebellum is connected with the medulla through the
restiform body or the inferior cerebellar peduncle. Now please understand that the main difference between
the three pedunculi, is that the middle cerebellar peduncle, the inferior one, contain two types of axons, to
and from the cerebellum. But the superior cerebellar peduncle has afferent and efferent. The middle
cerebellar peduncle usually only has the afferent fibers to the cerebellum. And the inferior cerebellar
peduncle also will contain afferent and efferent fibers to the cerebellum. All incoming fibers except one, to
the cerebellum, such as these ones, or these ones, or these ones, are known as mossy fibers. From different
sources are nuclei in the medulla. Some comes from the midbrain, spinal cord, medulla, etc. So most of
these fibers are mossy fibers, except one type, and this exception are called climbing axons. These axons
have the origin in the inferior olive located in the pons. What is the function of the superior olive? We saw
that yesterday? Auditory. The inferior olive is for the cerebellar functions. So all axons from the inferior
olive are known as climbing fibers. So, just imagine that the cerebellum receives from different sources
such as the reticular nuclei, and you can apply that if i have the mossy fibers, well, lets suppose reticular
nuclei, well, youwill say reticular cerebellar, reticular nuclei from the midbrain or the pons or the medulla.
Trigeminal nuclei will send info to the cerebellum. You will have also the dorsal spinal cerebellar tracts
through the inferior peduncle. We have ventral spinal cerebellar via the superior cerebellar peduncle, or
restiform body. So any nuclei may send information to the cerebellum. Just look at the nucleus, and its
tract is named after its nucleus. All these fibers are mossy. And only the ones originated in the inferior
olive will be climbing fibers.
Now what is the importance of this? If you have the view. Here is the inferior cerebellum. Look at the
climbing axons, and you can see that these axons enter the cerebellum, and very rapidly, the axon will reach
and becomes mixed in the synaptic connections with the most beautiful neurons of the brain, the very
popular beautiful Purkinje cells. That's why they're called "climbing" cells, because they climb their way to
the Purkinje fibers. So now the Purkinje cell body lies here, and the axon of the Purkinje neuron will send
efferent information out of the cerebellar cortex. By definition, Purkinje neuron is the sole neuron that
sends information out from the cerebellar cortex. The only one. Now you can see examples of the mossy
fibers. So now mossy fibers, in general, you can see one example here. Lets take this axon. Now you will
see that the axons very rapidly reaches the synaptic connections with the granular cells. So in order for you
to understand the different types of cells. You will say that the cerebellar cortex is divided into two part:
grey and white matter. The grey matter is made up of three layers: superficial, middle, and deep. In the
deep layer, you will find the most abundant of all cerebellar cells, granular types of cells. The granular cell
aside that its the most abundant of all types of cells in the cerebellum, it is the only cell that is excitatory in
function. The granular cells are excitatory. And from the different types of cells in the cerebellum, the
granular cell is the only excitatory, while the other types are inhibitory. The granular cells send axons that
descend and divide like a T-shaped structure, and this T-shaped type of axon is the so-called parallel axons.
And you can see with these horizontally guided axons, the granular cell can make other connections with
other types of cells within the cerebellar cortex. It can be Purkinje neuron, stellate cell, or basket cell, that
lie in the cerebellar cortex. Now don't learn what is the position of the cells. No, no, no, just know that the
granular cell is in the deepest layer, but most important it is excitatory cells while others are inibitory.
Which of the following is not a cerebellar cell? Golgi, Stellate, Purkinje, Granular, Basket. All of these are
cerebellar cells.
Suppose you have an axons going to this cerebellar cells. So the axons reaches the synpatic connection with
this large purkinje neuron. Or you can see the collaterals making the syaptic connections with the golgi
cells. Or there will be collateral axons to make synaptic connections with the Golgi cell. Or another
collateral to make connections with this other golgi cell. So it doesn't matter how you send information
fromthe granular cell to which ever cell. Or from granular to stellate, and stellate to golgi. Now you can
see the axons of golgi cell. Now lets take this out. Not because it will leave the cortex, no, no, no, this
arrow will mean one important characteristic of golgi cell. it doesn't matter what type of coordination. the
granular cell will be inhibited directly by golgi cells. You may have other connections, but most important
inhibition of the granular cells is via the golgi type of neurons. So granular cells, different type of
connections at the end, reaching the golgi cell, which is the only one that can inhibit the granular fiber.
The Purkinje neuron is the only nerve that sends fibers out of the cerebellar cortex. These fibers will reach
different targets. So now you have here, the cerebellum (he draws). Let suppose that this is a horizontal
section, and we have a superior view. He is showing us a little transverse slice, and he shows the purkinje
neurons which lie in the middle of the cerebellar cortex. Inside the white matter, you have nuclei in the
central part of the cerebellum, called nucleus fastigii (right and left). Then immediately lateral to this, the
nucleus globosus (right and left). Also is the emboliform nucleus. Then the most important will be the
cerebellar dendate nucleus. This resembles, slightly like the inferior olivary, because it is a folded type of
nucleus. He doesn't care about asking you about the fastigii, globosus, emboliform, but you should be
aware of the dendate nucleus of the cerebellum. There connections with the cerebellum called the superior
cerebellar peduncle leaving the cerebellum reaching the midbrain structures. Well, in the examination, the
superior cerebellar peduncle is called the brachium conjunctivum. This superior cerebellar peduncle
continues to the midbrain. We need to take one simple cell from the dendate nucleus of the cerebellum, the
rubral and dendato axons or cerebellar rubral axons. These reach the midbrain. The red nucleus cells will
give origin to fibers that travel a little ventral in the midbrain, and immediately they will cross in the ventral
part of the midbrain, before descending. So this crossing of the fibers form a decussation that you will
name, forrel's decusation or Ventral tegmental decusation of Forrel. This is the origin of the rubrospinal
tract, the red nucleus, axons crossing and then descending. Dendato axons, from the dentate nucleus, will
ascend, but now these axons will, lets say take out of this, and now lets send them both to the thalamus. So,
since this is only one segment, we are ascending more, and that is why it is out, superiorly, in order to reach
the thalamus. And we said that the nucleus ventralis lateralis. And these two nuclei are the main targets of
the cerebellum to the thalamus. From these nuclei, you will send info to the cerebral cortex. What areas?
Motor areas of the brain? MII, 6, 4. So the execution of the movement will be ordered. The nucleus
fastigii is connected primarily with the flocculonodular part, however the fastigii and globosus transmit their
axons through this system that we just mentioned, but don't worry about them. We will ask you about
dendate rubral, dendato thalamic.
Lets summarize. Corticospinal: voluntary mov. Corticobulbar: voluntary mov CN's. Corticopontine, and
pontocerebellar. What type of axons are in the pontocerebellar? Mossy. All type of axons coming to the
cerebelllum are mossy, except climbing from the inferior olive. So now the purkinje cell will receive the
connection via cell pathways. The purkinje cell to the dendate nucleus, then to rubral, then to the thalamus.
A lesion of any of these neurons will cause muscle incoordination. So if you destroy the corticopontine,
muscular incoordination. If you destroy any part of the cerebellum you hav muscular incoordination. Same
with lesions in the red nucleus.
The lesion of the cerebellum of course will be different things. Intention tremor which means that when you
want to perform something, you will begin to tremor. This is a sheet of paper. This is dysmetria.
Adiadocokinesis is the inability to perform. Language problems. You will pronounce complete words, but
will sound wrong because can't control tongue movements. If you are told to walk a straight line and then
walk backwards, they can't do it in a straight line. This is called the Star sign. Deviation will occur
depending on the site of the lesion of the brainstem.
Point 2.
Difference between the lesion in the anterior versus posterior cerebellum. I know that everyone should
know that flocculo system will give you problems with vision. Monday before 12.