Cerebellum

Question 1

The cerebellum (or small brain) lies in the posterior cranial fossa. In an adult, the weight of the cerebellum is about 150 g. It is separated from the pons and medulla by the ____________________.

Answer 1

4th ventricle

Question 2

Define the term, peduncle.

Answer 2

It is a collection of different tracts.

Question 3

What are some of the gross anatomical parts of the cerebellum?

Answer 3

✔ Hemispheres
✔ Tonsils
✔ Flocculus
✔ Vermis
✔ Nodule (the anteroinferior part of the vermis that joins the 2 flocculi)
✔ [Video (6 mins)] [Diagram]

Question 4

Flocculonodular lobe
1. Functional classification
2. Phylogenetic subdivision
3. Nucleus contained in the anatomical lobe?
4. Function
5. Nucleus mentioned in number 3 give efferents to?

Answer 4

1. Vestibulocerebellum (receives afferent from the vestibular nuclei, which enter through the inferior cerebellar peduncle)
2. Archicerebellum
3. Fastigial nucleus
4. it is concerned with the maintenance of equilibrium, tone and posture of trunk muscles
5. • to vestibular nuclei
   • to reticular formation of the medulla
   • to thalamus
   • to midbrain (red nucleus, central grey matter-nucleus of Darkschewitsch)
   • to visceral centres in brainstem
   • to medial accessory and main inferior olivary nuclei

Question 5

Vermis and tonsils.
1. Functional lobe
2. Phylogenetic lobe
3. Nucleus contained in the anatomical lobes?
4. Functions
5. Nucleus mentioned in number 3 give efferents to?

Answer 5

1. Spinocerebellum [afferents are from the spinal cord]
2. Paleocerebellum
3. Emboliform and globose nuclei
4. it is concerned with tone, posture and cude movements of the limbs
5. • to red nucleus
   • to thalamus
   • to reticular formation
   • to pontine nuclei
   • to dorsal accessory olivary nucleus

Question 6

Cerebellar hemispheres.
1. Functional lobe
2. Phylogenetic lobe
3. Nucleus contained in it
4. Functions
5. Nucleus mentioned in number 3 gives efferents to?

Answer 6

1. Cerebrocerebellum [afferents enter here through the middle cerebellar peduncle]
2. Neocerebellum
3. Dentate nucleus
4. • Motor planning
   • Motor learning
5. • to thalamus
   • to red nucleus
   • to oculomotor nucleus
   • to inferior olivary nucleus
   • to reticular formation

Question 7

State the afferents and efferents for each cerebellar peduncle.

Answer 7

Superior cerebellar peduncle
AFFERENT FIBERS: Anterior spinocerebellar tract, Tectocerebellar fibres, Trigeminocerebellar fibres, Ceruleocerebellar fibres, Hypothalamocerebellar fibres
EFFERENT FIBERS: Cerebellorubral fibres, Dentatorubral, dentatothalamic fibres, Cerebello-olivary fibres, Cerebelloreticular fibres
[PRO TIP: The deep cerebellar nuclei give efferents that pass through superior cerebellar peduncle e.g. dentatothalamic, dentatorubral etc.]

Middle cerebellar peduncle
AFFERENT: Pontocerebellar fibres, Reticulocerebellar fibres, Seratogenic fibres
EFFERENT: None

Inferior cerebellar peduncle
AFFERENT: Posterior spinocerebellar fibres, Olivocerebellar fibres, Parolivocerebellar fibres, Cuneocerebellar fibres (posterior external arcuate fibres), Anterior external arcuate fibres, Vestibulocerebellar fibres, Reticulocerebellar fibres
EFFERENT: Cerebellovestibular fibres, Cerebelloreticular fibres, Cerebello-olivary fibres

Question 8

Discuss ataxia as one of the signs and symptoms produced by cerebellar lesions.

Answer 8

Inability to maintain the equilibrium of the body, while standing, or while walking, is referred to as ataxia. This may occur as a result of the interruption of afferent proprioceptive pathways (sensory ataxia). Lack of proprioceptive information can be compensated to a considerable extent by information received through the eyes. The defects mentioned are, therefore, much more pronounced with the eyes closed (Romberg’s sign positive).

Further notes:
Disease of the cerebellum itself, or of its efferent pathways, results in more severe disability. Coordination of the activity of different groups of muscles is interfered with, leading to various defects. The person is unable to stand with his/her feet close together: the body sways from side to side and the person may fall. While walking, the patient staggers and is unable to maintain progression in the desired direction. Visual input adds little improvement in cerebellar lesions.

Question 9

Discuss asynergia as one of the signs and symptoms produced by cerebellar lesions.

Answer 9

This is refers generally to a lack of coordination of muscles such that one is unable to combine the various components of a movement to create fluid motion. Movements are jerky and lack precision. For example, the patient finds it difficult to touch his nose with a finger, or to move a finger along a line.

Question 10

Discuss dysarthria as one of the signs and symptoms produced by cerebellar lesions.

Answer 10

Incoordination of the muscles responsible for the articulation of words leads to characteristic speech defect: staccato speech/scanning speech.

Question 11

Discuss nystagmus as one of the signs and symptoms produced by cerebellar lesions.

Answer 11

This refers to a condition whereby the eyes are unable to fix their gaze on an object for any length of time. Attempts to bring the gaze back to the same point result in repeated jerky movements of the eyes.

Question 12

Discuss asthenia as one of the signs and symptoms produced by cerebellar lesions.

Answer 12

The muscles are soft and tire easily. Joints may lack stability (flail joints).

Question 13

What symptoms appear when the dentate nucleus or the superior cerebellar peduncle (which carries fibres from the dentate nucleus) is damaged?

Answer 13

Intention tremors and staggering.
[Intention tremor video]

Further notes:
~ Intention tremors: Intention tremors are a type of tremor that occurs during a purposeful, voluntary movement. They are characterized by involuntary, rhythmic muscle contractions that typically worsen as the movement proceeds. This means that the tremor increases in intensity upon reaching a target. (e.g. you tremble as you stretch to pick up a pen that you fell, and the amount of trembling increases as you continue stretching to pick it up)
~ It’s important to note that while both intention and essential tremors are characterized by muscle oscillations, they are different. Intention tremors are slower, zigzag-like movements which are evident when intentionally moving towards a target, whereas an essential tremor is a neurological disorder that can lead to tremors without accompanying intentional movements. However, individuals with essential tremor may often experience intention tremors as well.

Question 14

For understanding (you may rate it a 5, but from this you can pick up some things of importance): Cerebellum and learning. For example, why is net practice so important prior to playing cricket matches at an international level?

Answer 14

• The cerebellum, particularly the neocerebellum, is concerned with learned adjustments that make coordination easier when a given motor task is performed over and over.
• As a task is being learned, activity in the brain shifts from the prefrontal areas to the basal nuclei and the cerebellum.
• The basis of the learning in the cerebellum is through the input via the inferior olivary complex (the only climbing fibre input).
• Climbing fibre activity is increased when a new movement is being learned, and selective lesions of the olivary complex abolish the ability to produce long-term adjustments in certain motor responses.
• During motor learning, climbing fibre activation produces a large, complex spike in the Purkinje cell and this spike produces a long-term modification of the pattern of mossy fibre input to that particular Purkinje cell. This is especially so, when there is a mismatch between an intended movement and the movement that is actually executed.
• Therefore, climbing fibres act as error signals, and teaching signals that induces synaptic modification in parallel fibre-Purkinje cell synapses.

Question 15

Describe the arterial supply of the cerebellum.

Answer 15

1. Superior cerebellar artery: A branch of basilar artery supplies the superior surface of the cerebellum.
2. Anterior inferior cerebellar artery: A branch of basilar artery supplies the anterior part of the inferior surface of the cerebellum.
3. Posterior inferior cerebellar artery: A branch of vertebral artery supplies the posterior part of the inferior surface of the cerebellum.
4. [Diagram: blood supply of cerebellum] [Circle of Willis for reference]

Question 16

A 35-year-old man complained of tinnitus and vertigo, decreased lacrimation in the left eye, and asymmetry of face with deviation of angle of mouth to the right side. Magnetic resonance imaging (MRI) examination revealed a tumour in the cerebellopontine angle.
A. On which side would the tumour be?
B. Explain the anatomical basis of all the symptoms mentioned above.

Answer 16

A. Left side; the facial nerve does not decussate
B. Involvement of left vestibulocochlear nerve
results in tinnitus and vertigo; involvement of left facial nerve results in decreased lacrimation in the left eye and deviation of angle of the mouth to the right side due to unopposed pull of right side facial muscles.

Question 17

A 10-year-old female child showed intention tremors, hypotonia and severe ataxia. She was diagnosed to have Friedrich’s ataxia (hereditary cerebellar degeneration). Specify the functional part of cerebellum that is affected to cause
A. Intention tremors
B. Ataxia

Answer 17

A. Cerebrocerebellum
B. Vestibulocerebellum

Question 18

Briefly discuss climbing fibres of the cerebellum. (origin, which cerebellar peduncle, connections and role)

Answer 18

They originate from the inferior olivary nucleus located in the medulla oblongata. They ascend through the pons and enter the cerebellum via the inferior cerebellar peduncle, where they form synapses with the deep cerebellar nuclei and Purkinje cells. Each climbing fibre synapses with 1-10 Purkinje cells, but each Purkinje cell receives input from only one climbing fibre. The climbing fibers provide very powerful excitatory input to the Purkinje cells and play a crucial role in motor learning. The climbing fibres form the olivocerebellar and par-olivocerebellar tracts.

Question 19

Briefly discuss mossy fibres of the cerebellum.

Answer 19

All fibres entering the cerebellum, other than through olivocerebellar and par-olivocerebellar tracts, end as mossy fibres. Mossy fibres originate from the vestibular nuclei (vestibulocerebellar), pontine nuclei (pontocerebellar), and spinal cord (spinocerebellar) and enter the cerebellum via the middle and inferior cerebellar peduncles to terminate in the granular layer of the cortex within the glomeruli. Before terminating, they branch profusely within the granular layer, each branch ends in an expanded terminal called a rosette.
[Diagram: Layers of the cerebellar cortex]

Question 20

Briefly explain Romberg’s test. Give examples of lesions that may result in a positive Rhomberg’s sign.

Answer 20

~ This is a neurological test used to evaluate balance and proprioception.
~ The test involves the patient standing with their feet together and arms at their side or crossed in front of them. The patient is first observed with their eyes open, and then with their eyes closed.
~ A positive Romberg sign is observed when a patient, who is able to maintain balance with their eyes open, loses balance when their eyes are closed.
~ This suggests that the patient is relying on vision to maintain balance due to a deficit in proprioception.
~ Examples of conditions that can cause a positive Romberg sign include: (1) posterior cord syndrome (Posterior spinal artery infarction), (2) hemisection of the spinal cord (Brown Sequard syndrome), (3) cerebellar lesions

Question 21

Name the subdivisions of the inferior cerebellar peduncle.

Answer 21

Juxtarestiform body, restiform body

Further notes:
☞ The inferior cerebellar peduncle is composed of a larger part, the restiform body, and a smaller portion, the juxtarestiform body. ☞ The restiform body is the large ridge on the dorsolateral aspect of the medulla rostral to the level of the obex. This bundle contains mainly fibers that arise in the spinal cord or medulla. ☞ The juxtarestiform body is located in the wall of the fourth ventricle. This bundle is composed primarily of fibers that form reciprocal connections between the cerebellum and vestibular structures.

[Cadaveric image of the cerebellum showing the cerebellar peduncles]