Anatomy of the cerebellum

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Introduction0:00–1:17

The word cerebellum translates to little brain, not because it's the brain of a tiny animal or baby. But rather because the fact that the cerebellum looks like a smaller version of the human cerebrum.
Very simply the cerebellum assist with coordinating and adjusting voluntary movement. It plays a major role in posture, balance, maintenance of muscle tone and coordinating skilled voluntary motor activities, things like riding a bicycle or for the more adventurous walking, a tightrope.
In order for the cerebellum to undertake these functions, it has to be in constant communication with the cerebral cortex.
It also sends and receives signals to many other structures in the central and peripheral nervous systems, processing information about current movement and positional states in order to help refine correct and improve the motion.
Now, the cerebellum sits in the posterior part of the cranium called the posterior cranial fossa. And it's covered by the tentorium, cerebelli which separates the cerebellum from the occipital and temporal lobes of the brain.
Anterior to the cerebellum lies the fourth ventricle pons and medulla oblongata just like the cerebrum. The cerebellum consists of two hemispheres.

Cerebellar hemispheres1:17–1:35

These two hemispheres are connected by a narrow ridge in the middle called the vermis. From an inferior view parallel to the vermis.
There are two distinguishable lobules called the cerebellar tonsils. The cerebellum can be divided into three lobes, the anterior lobe, the posterior lobe and the flocculonodular lobe.

Lobes1:35–3:03

From a superior view, we can identify the anterior lobe functionally referred to as a spinocerebellum, which is responsible for the regulation of muscle tone and adjusting ongoing movements.
Posterior to the anterior lobe is a v shaped primary fissure from a superior view and posterior to this primary fissure is the posterior lobe functionally referred to as a cerebro cerebellum or pontocerebellum, which contains a horizontal fissure separating the superior and inferior surface of the cerebellum.
The cerebral cerebellum is the largest part of the cerebellum and is responsible for assisting in planning and programming of skilled or fine motor movements.
Looking at the cerebellum from an anterior view, the posterior lobe is bounded by the posterolateral fissure. This fissure separates the posterior lobe from the third lobe of the cerebellum called the flocculonodular lobe or functionally referred to as the vestibulo cerebellum.
The floccular nodular lobe is responsible for the maintenance of posture and balance. The floccular nodular lobe is named such because it contains a central part of the vermis called the nodule as well as two lateral flocculi.
If we continue to view the cerebellum from the anterior aspect, we can see bundles of dense white matter that attach the cerebellum to the brainstem.

Cerebellar peduncles3:03–3:59

These white matter stalks are called cerebellar peduncles and consist of superior, middle and inferior divisions. They contain efferent and afferent axons that signal back and forth between the cerebellum and the central nervous system.
The superior cerebellar peduncle connects the cerebellum with the midbrain. The middle cerebellar peduncle connects with the pons and the inferior cerebellar peduncle attaches to the medulla, oblongata, afferent fibers to the cerebellum can be found within all three cerebellar peduncles.
But the majority of afferent signals use inferior and middle peduncles for passage, efferent signals from the cerebellum.
However, travel mainly through the superior peduncle on a sagittal section. The cerebellum looks similar to the cerebrum in that the cortex is folded, creating ridges with small sulci in between the difference.

Sagittal section3:59–4:46

However, is that in the cerebellum, the cortical ridges are thinner, smaller and organized into more parallel layers which are called folia.
These folia not only increase the surface area but enable the large area of cortex to fit into a smaller space just like the cerebrum.
The folio contained an external gray matter layer called the cerebellar cortex and a subcortical white matter region deep to the external gray matter.
As we see the shape of this white matter within the folia creates a tree like arrangement or branching pattern referred to as an Arbor vitae or tree of life.

Deep cerebellar nuclei4:46–5:26

On a transverse section of the cerebellum, we can see four clusters of deep gray matter nuclei buried deep within the subcortical white matter these deep cerebellar nuclei or intracerebral nuclei contain multipolar neurons that receive signals from the cerebellar cortex and other parts of the nervous system.
And their axons contribute to the formation of the three cerebellar peduncles from lateral to medial. These deep cerebellar nuclei consists of the dentate and bulliform globose and fastigial nuclei.
To remember these remind yourself in order to have a healthy cerebellum, you don't eat greasy foods. In addition to having anatomical divisions, the cerebellar cortex can also be divided into three functional regions that are positioned longitudinally.

Functional regions5:26–6:41

The most lateral and largest functional region is a lateral zone. The lateral zone send signals to the dentate nucleus, the largest of the deep cerebellar nuclei.
And together they assist in planning and programming movements medial to the lateral zone is an intermediate zone, also known as a paramedian or paravermal zone.
The intermediate zone sends signals to the emboli form and globose nuclei collectively, these two nuclei are known as the interpose nuclei and are usually referred to together as they both work in the intermediate zone.
Finally, most medial and occupying the cortex of the vermis is a third functional zone. The median or vermal zone, the median zone will send signals to the fastigial nucleus which is the most medial of the deep cerebellar nuclei located within the vermis and next to the roof of the fourth ventricle.
The intermediate and median zones along with their deep cerebellar nuclei are involved in modulating motor execution of lateral and medial descending motor pathways respectively.

Quiz6:41–7:00

Let's take a quick break and see if you can identify the lobes of the cerebellum as well as the functional zones and deep cerebellar nuclei.

Afferent pathways7:00–7:14

Now, let's have a look at the afferent pathways which bring information to the cerebellum to be processed. And the efferent pathways which leave the cerebellum to help coordinate motor activity.
Afferent pathways generally originate from the spinal cord and brainstem. The cerebral cortex and the vestibular system starting with the afferent pathways from the spinal cord to the cerebellum.

Ventral spinocerebellar pathway7:14–8:20

Let's look at the ventral or anterior spinocerebellar pathway. First, it carries proprioceptive information from muscle spindles, golgi tendon organs and joint receptors of the lower extremities.
Then the afferent fibers enter the spinal cord where they synapse with spinal border cells located in lamina seven of the spinal cord gray matter.
From here, the majority of these axons cross to the contralateral side of the spinal cord and form the ventral spinal cerebellar pathway which ascends in the white matter of the spinal cord to the brainstem.
Here, the axons cross back over and enter the cerebellum through the superior cerebellar peduncle to reach the cerebellar cortex.
The signals on the ventral spinocerebellar pathway cross over the neural axis and then cross back. So it's often referred to as a double crosser.

Dorsal spinocerebellar pathway8:20–9:02

Next is the dorsal or posterior spinocerebellar pathway. This pathway contains fibers that receive proprioceptive information from muscle spindles, golgi tendon organs and joint receptors mainly found in the trunk and lower extremities.
This information enters the spinal cord from peripheral nerves and the signal synapses on Clark's nucleus or Clark's column, also known as nucleus dorsalis.
Instead of crossing over. After they synapse, the axons ascend in the ipsilateral white matter of the spinal cord to the brainstem where they then enter the cerebellum through the inferior cerebellar peduncle to reach the cerebellar cortex.
The final afferent pathway that carries proprioceptive information from the extremities is called the cuneocerebellar pathway.

Cuneocerebellar pathway9:02–9:37

The axons in this pathway receive proprioceptive information from muscle spindles, golgi tendon organs and joint receptors within the upper limb and upper thorax signals within this pathway synapse in the external or accessory cuneate nucleus located in the medulla.
The axons travel ipsilaterally through the inferior cerebellar peduncle to reach the cerebellar cortex. Let's now move on to the afferent pathways from the cerebral cortex to the cerebellum which include the corticopontocerebellar, cerebral olivocerebellar and cerebro reticulocerebellar pathway.

Pathways from cerebral cortex to cerebellum9:37–10:23

Talk about your tongue twisters. Ok.
Now, these pathways originating in the cerebral cortex signal through brainstem structures to reach the cerebellum and allow for these areas to communicate to further regulate and modify voluntary movements.
For example, the initiation planning and timing of motor activities. This information is important to the cerebellum to know so that it can take part in making the appropriate adjustments and modifications to that plan for synergy and overall motor coordination.
The corticopontocerebellar pathway is important in relaying motor commands of the cortex and begins with the afferent fibers arising from the cerebral cortex of the frontal temporal parietal and occipital lobe.

Corticopontocerebellar pathway10:23–11:02

These fibers signal through the corona radiata and internal capsule to synapse on pontine nuclei. Then the signals are sent along transverse fibers called pontocerebellar fibers.
The crossover and enter the middle cerebellar peduncle to terminate in the cortex of the contralateral cerebellar hemisphere.

Cerebro-olivocerebellar pathway11:02–11:29

The cerebral olivocerebellar pathway also begins in the cerebral cortex of the four lobes and sends its fibers through the corona radiata and internal capsule where the fibrous synapse in the inferior olivary nuclei.
After synapsin, these fibers cross the midline and travel to the inferior cerebellar peduncle to synapse with the contralateral cerebellar hemisphere.

Cerebro-reticulocerebellar pathway11:29–11:59

The cerebro reticulocerebellar pathway also arises from the cerebellar cortex, however, mainly from the sensory motor cortical regions associated with the parietal lobe.
The axons descend in the same way as the previous two pathways and snaps at the nuclei of the reticular formation located in the pons of medulla.
These fibers then travel through the middle and inferior cerebellar peduncles to terminate in the cerebellar hemisphere of the ipsilateral side.
Finally, the last major system to provide afferent information to the cerebellum is the vestibulo cerebellar pathway. It plays a key role in the maintenance of balance, posture, body position and coordination of eye movements.

Vestibulocerebellar pathway11:59–13:21

This pathway begins by receiving sensory input regarding motion from the semicircular canals of the inner ear as well as body position relative to gravity from the saccule and utricle via the vestibular nerve, a portion of the vestibulo cochlear cranial nerve.
During their course afferent fibers of the vestibular nerve either signal straight through the inferior cerebellar peduncle to the ipsilateral cerebellar cortex or the synapse.
First in the vestibular nuclei of the brainstem. Before signaling to the cerebellum.
Together, these afferent fibers reach the cerebellar cortex of the floccular nodular lobe to be processed. The vestibulo cerebellar pathway gathers visual input as well.
These afferent fibers originate from the superior colliculus and the primary visual cortex. And the visual information is relayed through the superior cerebellar peduncle to reach the floccular nodular lobe.

Quiz13:21–13:42

Ok. Now, that was a lot to take in.
Let's take a quick quiz and see if you can identify the afferent tongue twisters. I mean pathways from the brain to the cerebellum on this image.

Efferent pathways 13:42–14:23

So now that we've discussed the major afferent pathways of the cerebellum, what does the cerebellum do with all of the information it's received?
Well, the cerebellum processes this information and the cerebellar cortex relays a movement modification message to the deep cerebellar nuclei which then sends signals along different afferent fibers to places such as the vestibular nuclei, thalamus, red nucleus, reticular formation, cerebral cortex and the spinal cord.
In doing so, the cerebellum plays a continuous role in maintaining posture, balance and modifying adjusting and coordinating movements of the body.
The first efferent pathway we're going to discuss is a vestigial vestibular pathway which is responsible for regulating extensor muscle.

Fastigial vestibular pathway14:23–15:12

Tone fibers originate in the vestigial nucleus of the cerebellum and travel through the inferior cerebellar peduncle to synapse on the lateral vestibular nuclei.
From here, some efferent fibers form the vestibulo spinal tracts which signal the motor neurons of the spinal cord that control antigravity musculature that helps maintain posture.
Other Effient fibers will form the medial longitudinal fasciculus which transmits information to the motor nuclei of cranial nerves, 34 and six to modify and control movements of the eye.
Another important efferent pathway of the cerebellum is a dentatothalamic pathway which is responsible for modifying ipsilateral motor activity.

Dentatothalamic pathway15:12–16:00

This pathway begins in the dentate nucleus of the cerebellum where fibers cross the midline and travel through the superior cerebellar peduncle to the contralateral ventrolateral nucleus of the thalamus, the fiber synapse in the thalamus.
And from there, the signal continues through the internal capsule and corona radiata to reach the primary motor cortex. Once here, the information is relayed to motor pathways such as the corticospinal tract.
And this is how the cerebellum influences and modulates motor activity of descending motor pathways. Next, there's a globose emboliform RR pathway which also influences ipsilateral motor activity.

Globose-emboliform-rubral pathway16:00–16:30

These efferent fibers begin in the globose and emboliform nuclei travel across the midline through the superior cerebellar peduncle and synapse with the contralateral red nucleus.
This pathway influences motor activity of the rubrospinal tract which acts on proximal flexor musculature of the upper limb.

Fastigial reticular pathway16:30–16:55

Finally, we have the fastigial reticular pathway where inferent signals originate in the fastigial nucleus, travel through the inferior cerebellar peduncle and then synapse with neurons in the reticular formation.
These signals provide modulatory information to the medial and lateral reticulospinal tracts which collectively are involved in regulation of muscle tone and posture.
All right, that's a quick recap. The cerebellum is located in the posterior cranial fossa below the occipital and temporal lobes and ventral to it is the fourth ventricle pons and medulla oblongata.

Review16:55–19:21

It has two hemispheres which are connected by the vermis and is divided into three lobes. The primary fissure divides anterior and posterior lobes.
While the posterior lateral fissure separates the posterior lobe from the floccular nodular lobe from an anterior view. The cerebellum is connected to the rest of the central nervous system via the superior, middle and inferior cerebellar peduncles.
Looking at a cross section of the cerebellum. It's composed of gray matter folds with white matter within that form folia.
The four deep gray matter nuclei are the dentate emboliform globose and fastigial nuclei. The cerebellar cortex can be divided into three functional zones.
The median which helps to adjust medial descending motor pathways to include those that act on axil mula, the intermediate or paramedian zone which assists in adjusting lateral descending motor pathways that include those that act on appendicular musculature and the lateral zone that works on planning and evaluating movements major afferent pathways from the spinal cord to the cerebellum include the ventral spinocerebellar pathway.
The dorsal spinocerebellar pathway and the cuneocerebellar pathway. Major afferent pathways from the brain to the cerebellum include the cortico ponto cerebellar pathway.
The cerebral olivocerebellar pathway and the cerebral reticulocerebellar pathway. The vestibulo cerebellar pathway gathers information from the semicircular canals, inner ear, superior colliculi and primary visual cortex to help maintain balance, posture, body position and coordinate eye movements.
And finally, the efferent pathways from the cerebellum include the vestigial vestibular pathway. The dentatothalamic pathway, the globose emboliform rubral pathway and the vestigial reticular pathway.