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Introduction
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What’s up.
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Meditay here.
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Let’s continue the anatomy of the Central Nervous System.
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In this segment, we’ll cover the anatomy of the Cerebellum
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So the central nervous system consists of two parts: the encephalon and the spinal cord.
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The encephalon is then further divided into specific parts.
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We have the brainstem, which consists of the Medulla, Pons, and the Midbrain of the mesencephalon.
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We have the Cerebellum back here, then the diencephalon and the telencephalon.
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Our focus in this video is going to be the Cerebellum.
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So in this video, we’re first going to cover the topography of the Cerebellum.
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Then we’re gonna talk about the functions of it.
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After that, we’ll go ahead and take a look at the external surface, and then make a cross-section
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and look at the internal surface of the Cerebellum.
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Basically covering the gray matter nuclei and the white matter tracts.
Topography of the Cerebellum
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Alright, so we can start by replacing this picture with a more realistic one.
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From here, we’re able to see Pons, Medulla, Cerebellum, and the Spinal Cord.
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And if we remove half of the cerebral hemisphere, we’ll see the rest of the brainstem, which
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is the Midbrain.
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So the Cerebellum mainly lies *behind* Pons and the Midbrain, as you see here.
Functions of the Cerebellum
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Now, what are the functions of the cerebellum?
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When you’re walking, the Cerebellum continuously receives unconscious proprioception from muscles
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and joints, as well as receiving information from different senses.
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Based upon that, it sends out motor fibers that regulate all the muscle contractions
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necessary to perform your movements smoothly.
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So by doing that, it coordinates your balance and posture.
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It regulates the tone of your muscles by passively contracting the muscles to ensure joint stability.
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And it also smoothens voluntary movements of muscles.
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So when you write.
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Here most of the fibers come from the cerebral cortex since this is a voluntary movement.
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But these movements are able to be smooth and precise by the Cerebellum engaging its
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fibers into the muscles necessary to stabilize the movements.
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So these are the top three functions the Cerebellum has.
External Structures of the Cerebellum
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Let’s now finally understand the actual anatomy of it by looking at the external structures.
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So here’s a posterior view of the Cerebellum.
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If we isolate the Cerebellum and the brainstem, you’ll be able to see the rest of the Cerebellum.
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The Cerebellum consists of two hemispheres on either side and a vermis in the middle.
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And if you look closely at the surface of the Cerebellum, you’ll see grooves and bumps
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on it.
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These grooves are called sulci of the Cerebellum.
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And between them, you’ll see the Folia of the Cerebellum, which are the small bumps
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between the sulci.
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You’ll also be able to see some deeper grooves on the surface, which we call fissures.
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The first one is a very prominent one called Primary Fissure,
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And this fissure marks the separation between the Anterior Lobe of the Cerebellum and the
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Posterior Lobe of the Cerebellum.
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So this is a posterior view, but if you look at the cerebellum from an anterior view as
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well, you’ll see another deep fissure, called Posterolateral fissure which separates the
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posterior lobe from the flocculonodular lobe.
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It’s kind of a tongue twister, but it consists of two parts.
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The Nodular part and the floccular part.
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That’s why we call it the Flocculonodular lobe.
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From the anterior view of the cerebellum, we can also see the Cerebellar Peduncles.
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The cerebellar peduncles connect the Cerebellum with the brainstem.
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So if we remove the Cerebellum, you’ll find the cerebellar peduncles here on the anterior
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view of the brainstem.
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So again, this is Pons, This is the Medulla, and this is the Mesencephalon.
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On either side of the brainstem, you’ll see the cerebellar peduncles, which contain fibers
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that run between the Cerebellum and all three parts of the brainstem.
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The inferior cerebellar peduncle contains fibers that go to the Medulla.
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The middle cerebellar peduncle contains fibers that go to Pons.
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The superior cerebellar peduncle contains fibers that go to the Midbrain.
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So that was the main external anatomical structure of the Cerebellum.
Internal Structures of the Cerebellum
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Let’s now take the Cerebellum and give it a good slice like this.
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And then look at it from this perspective.
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We’ll see this.
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So this is a scheme I made in order to make it easier to understand the internal structures
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of the Cerebellum.
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We can see the two hemispheres of the Cerebellum on either side and the Vermis of the Cerebellum
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in the middle.
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Vermis literally means worm because it looks like a worm between the hemispheres.
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Alright.
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Let’s first add the white matter of the Cerebellum so that it’s easier to distinguish the grey
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matter from the white matter.
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Remember, White matter contains myelinated nerve fibers, so when we talk about white
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matter, we mainly talk about tracts.
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Gray Matter contains nuclei of neurons, so when we talk about the gray matter, we mention
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nuclei.
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Let’s first go through the Gray matter of the Cerebellum and then do the white matter.
Gray Matter of the Cerebellum
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So the gray matter of the Cerebellum is mainly located at the surface and forms the cortex
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of the Cerebellum of the cerebellar cortex.
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It’s a dense cortex that consists of three layers with nuclei.
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The Cerebellum is also going to have gray matter within the actual Cerebellum in between
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the fibers of the white matter.
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And the first one is the dentate nucleus, which takes part in the unconscious coordination
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of your muscles through the corticopontine tract.
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I’ll show you later in this video when we go through the tracts.
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Then we have the fastigial nucleus.
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And one thing it’s responsible for is, remember the inner ear consists of the cochlea and
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the vestibulum?
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The vestibular system has these semicircular canals that sense the movements of the head,
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whether it’s horizontal movement or vertical or angular movement.
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They will stimulate the vestibular nerve, which will travel towards the vestibular neurons
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of Pons, where two things will happen.
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One.
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It will send a vestibulospinal tract towards your muscles to maintain a balance.
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But from the vestibular nuclei, a vestibulocerebellar tract will also go to the Cerebellum and synapse
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with the fastigial nucleus.
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This is to engage the Cerebellum in helping with balance and posture.
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Because remember, the Cerebellum is the master of unconscious proprioception, and It knows
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exactly where your arm is and where your legs are all the time.
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So that is this one.
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Next, there are the globose nucleus and the emboliform nucleus.
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Remember when we talked about the spinal cord, there were the anterior and the posterior
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spinocerebellar tracts?
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The fibers from the posterior spinocerebellar tract will go directly to the Cerebellum through
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the inferior cerebellar peduncle, and fibers from the anterior spinocerebellar tract will
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go up through Pons and the Midbrain, and then to the Cerebellum through the superior cerebellar
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peduncle, to then synapse with the emboliform and the globose nuclei.
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These are sensory fibers for unconscious proprioceptive sensation.
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They will give sensory input about posture and joints and then provide stability by passively
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contracting the muscles around the joints.
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It also provides sensory input from the surrounding area, which is a part of the feedforward control.
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So that is the grey matter of the Cerebellum.
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Take a mental picture of this, and let’s go over and do the white matter.
White Matter of the Cerebellum
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The white matter of the Cerebellum consists of tracts.
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But one thing that is very characteristic for the Cerebellum is the white matter branching
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out towards the cortex to resemble branches of a tree.
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We call this the tree of life, or arborvitae.
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And it’s very prominent.
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If you look at the Cerebellum, these beautiful branching patterns are very characteristic
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for the Cerebellum, as you see here.
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It resembles the branching of a tree, and because the Cerebellum has crucial functions
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in our body, it’s called the tree of life.
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So the white matter contains tracts that go in and out of the Cerebellum.
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And they do that through these peduncles.
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The superior peduncle between the Midbrain and the Cerebellum, the middle cerebellar
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peduncle between Pons and the Cerebellum, and the inferior cerebellar peduncle, between
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the Medulla and the Cerebellum.
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To visualize this in an easier way, I’ve made this scheme that shows the Cerebellum here
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in green.
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And we can see the superior cerebellar peduncle, the middle cerebellar peduncle, and the inferior
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cerebellar peduncle going between the Cerebellum and the brainstem.
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I’ve also divided this model into two sides.
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The right side will show fibers that enter the cerebellum, called afferent fibers, or
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sensory fibers.
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And the left side will illustrate fibers that leave the cerebellum, called efferent fibers,
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or motor fibers.
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The first tract t is a tract we mentioned earlier.
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So from the vestibular system of the inner ear, we got the Vestibular nerve going towards
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the vestibular nuclei of the rhomboid fossa, in Pons.
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Some fibers from the vestibular nuclei will pass posteriorly, and then through the inferior
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cerebellar peduncle, towards the Cerebellum.
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And remember, the vestibular system is for balance.
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So that is this one.
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The next tract is also one we mentioned earlier.
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And that is the spinocerebellar tracts that receive information about unconscious proprioception.
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So if we add the CNS to illustrate.
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The posterior spinocerebellar tract will enter the Cerebellum through the inferior peduncle.
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And the anterior spinocerebellar tract will ascend up through Medulla and Pons and the
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Midbrain, ad then through the superior peduncle and into the Cerebellum.
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So again, posterior spinocerebellar through the inferior peduncle.
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And the anterior spinocerebellar through the superior peduncle.
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Next is a tract you hear about a lot when you study the central nervous system.
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So here we have a cross-section of Pons and the Medulla Oblongata.
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Sensory fibers from the lower part of your body will go to the spinal cord and from the
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Gracile Fascicle.
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Fibers from the upper part of your body will go to your spinal cord and form the Cuneate
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Fascicle, which is lateral to the gracile fascicle
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These two fibers will go up and synapse with the Cuneate nucleus and the gracile nucleus
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of the Medulla, as you see here.
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And then, from here, two things will happen.
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Fibers will cross internally as the internal arcuate fibers and then ascend as the medial
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lemniscus.
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Or they will leave the brainstem as the external arcuate fibers through the inferior cerebellar
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peduncle.
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And that is another tract we can add to this scheme, the external arcuate fibers.
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Then there are fibers that originate from the olivary nucleus of the medulla.
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These fibers cross the Medulla and then go through the inferior cerebellar tract towards
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the Cerebellum.
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Then there is the corticopontine tract.
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This tract includes the frontopontine fibers, parietopontine fibers, temperopontine fibers,
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and occipitopontine fibers.
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Basically, all the fibers coming from the different lobes of the cerebral cortex to
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the Pons are grouped as the corticopontine tract.
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They will descend to Pons and synapse with the pontine nuclei.
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And then they go from the Pontine nuclei to the Cerebellum.
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So here are the pontine nuclei.
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They cross Pons and go through the middle peduncle to the Cerebellum.
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From the Cerebellum, fibers go up towards the nucleus ruber in the Midbrain, as you
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see here.
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As the cerebellorubral tract or the Dentatorubral tract because they synapse with the dentate
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nucleus of the Cerebellum.
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And then from the red nucleus, the tract will descend as a rubrospinal tract.
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Notice that none of the corticopontine tracts came from the pyramidal cells of the primary
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motor cortex.
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They came from all other regions of the cerebral cortex.
White Matter of Medulla (Descending Tracts)
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That means that this is an extrapyramidal tract, so this tract engages the Cerebellum
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in coordinating and helping with smooth and precise voluntary movements.
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So that was all I had for the anatomy of the cerebellum.
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If you found this video helpful, don’t forget to like, comment, share, whatever you find
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convenient.
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And I hope this was helpful.
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