CEREBELLUM – DIVISIONS & FUNCTIONS

Pyramidal cells

Cellular component of cerebellum

• Purkinje cells
• Granule cells
• Mossy fibers
• Climbing fibers ti 
• Interneurons

1. Golgi cells
2. Lugaro cells
3. Stellate cells
4. Basket cells

Ans. is. B. Motor planning [REF: Ganong 22″^d ed p. 221]

Metancephalon

Cerebellum is the largest part of hind brain situated in the posterior cranial fossa beneath the tentorium cerebelli. It plays an important role in control of muscle tone and co-ordination of muscle movement.

The cerebellum controls the same side of the body (ipsilateral side).
Cerebellar nuclei are present within the grey matter of the cerebellum. There are four pairs of nclei they are;

• Nucleus dentatus
• Nucleus globosus
• Nucleus fastigii
• Nucleus emboliformis 

Lateral portion of cerebellar hemisphere is called cerebrocerebellum or neocerebellum. It interacts with the motor cortex in planning and programming movements.

• Ataxia of extremities, asynergy
• Dysmetria
• Dysdiadochokinesia
• Intentional tremor
• Rebound phenomenon

• Loss of equilibrium
• Nystagmus

• Truncal ataxia and drunken gait

C i.e. Cerebellar nuclei

B. i.e. Deep cerebellar nuclei 

B. i.e. Medulla

B. i.e. Medulla

Three paired cerebellar peduncles connect cerebellum to the brainstem

The cerebellar peduncles are named according to their position relative to the vermis as

• Superior cerebellar peduncle
• Middle cerebellar peduncle
• Inferior cerebellar peduncle

A. i.e. Flocculus; B i.e. Nodules; C i.e. Uvula

– Middle Cerebellar Peduncle transmits ponto cerebellar (afferent) tract; it has no efferent tract. Anterior spinocerebellar tract is in superior crebellar peduncle, whereas, posterior spinocerebellar tract is in inferior peduncle.(Mn- Anterior in Superior and Posterior in Inferior”).

Vestibulo cerebellar (mossy) fibers arise from vestibular nerve/ganglion (1°) and nucleus (2° fibers). These fibers terminate in granular layer of nodule, uvula, vermis (ipsilaterally = 1°) and flocculus (all bilaterally = 2°)

D i.e. Purkinje cells

Purkinje cells are amongst the biggest neurons in the body. Their axons are the only output from the cerebellar nucleiQ from where they are projected to other part viz, thalamus, brainstem,Q.

Granule cells are excitatoryQ

B i.e. Co- ordination C i.e. Planning of motor movements

Cerebellar lesions are associated with intentional tremorsQ whereas, resting tremors occur in lesions of basal gangliaQ.

–   The afferent input to the cerebellum is excitatory and comes through – Climbing fibers and mossy fibers

The output is through purkinje cells and deep cerebellar nuclei. The output of purkinje cell is inturn inhibitory to deep cerebellar nuclei. It is interesting that the output of deep cerebellar nuclei to the thalamus and brain stem is always excitatoryQ Thus almost all the cerebellar circuitry seems to be concerned solely with modulating or timing the excitatory output of the deep cerebellar nuclei to the brain stem & thalmusQ

D i.e. Cerebellum

C i.e. Mossy fibres inhibit Purkinje cells

D i.e. Smoothens and coordinates ongoing movement

Cerebellum smoothens & coordinates ongoing movement in motor performance this is the reason why lesion of cerebellum causes:  – Ataxia (lack of coordination of movement)

– Asynergia (lack of coordination b/w different group of muscles)

– Astasia (Unsteady voluntary movement).

Ans. B: Equilibrium

From a functional point of view, the cerebellum is divided into three parts:

• The nodulus in the vermis and the flanking flocculus in the hemisphere on each side form the flocculonodular lobe, or vestibulocerebellum. This lobe, which is phylogenetically the oldest part of the cerebellum, has vestibular connections and is concerned with equilibrium.
• The rest of the vermis and the adjacent medial portions of the hemispheres form the spinocerebellum, the region that receives proprioceptive input from the body as well as a copy of the “motor plan” from the motor cortex. By comparing plan with performance, it smoothes and coordinates movements that are ongoing. The vermis projects to the brainstem area concerned with control of axial and proximal limb muscles, whereas the hemispheres project the brainstem areas concerned with control of distal limb muscles.
• The lateral portions of the cerebellar hemispheres are called the cerebrocerebellum, or neocerebellum. They are the newest from a phylogenetic point of view, reaching their greatest development in humans. They interact with the motor cortex in planning and programming movements.

Ans. is ‘c’ i.e., Cerebellum

Cerebellum, through its connection with the red nucleus influences the activity of brainstem reticular formation and thereby gamma motor neuron activity.

Through its connections with the vestibular nucleus and vestibulospinal tract, cerebellum influnences the activity of alpha motor neurons.

Thus, normal cerebellar function is essential for the maintenance of normal muscle tone and posture.

The cerebellum seems to play crucial roles in walking as well as maintaing a standing posture.

Cerebellar vermis plays an important role in maintenance of standing postuk.

Basal ganglia is also involved in maintaining posture by acting as relay center for extrapyramidal pathways. But its role is not as important.

Ans. is ‘c’ i.e., Planning of movements

Functional divisions of cerebellum

* From the functional point of view the cerebellum is divided into three parts : ‑

1) Vestibulocerebellum (flocculonodular lobe)

* This division contains flocculus, and nodulus, i.e., flocculonodular lobe. 

* It receives afferent from the vestibular apparatus and sends efferents to the vestibular nuclei directly without projecting on deep nuclei. 

* It works with vestibular apparatus to : –

 – Modulate muscular activity so as to achieve postural equilibrium or balance.

 – Coordinate movements of the eyes with movements of the head, i.e., vestibulo-ocular reflex.

2) Spinocerebellum

* It consists of the vermis and the adjacent medial portion of cerebellar hemisphere. 

* It receives proprioceptive information from the body as well as a copy of the “Motor plan” from the motor cortex.

* By comparing plans, it smoothens and coordinates movements that are ongoing.

3) Cerebrocerebellum (neocerebellum)

* It is the large lateral portion of the cerebellar hemisphere. 

* They are the newest from a phylogenetic point of view and therefore also called neocerebellum. 

* They interact with the motor cortex in planning and programming movements.

Ans. is ‘d’ i.e., All of the above 

• The two main inputs to the cerebellar cortex are climbing fibers and mossy fibers, which are excitatory.
• The climbing fibers come from a single source, the inferior olivary nuclei and directly projects to the primary dendrites of a purkinje cell.