Cerebellum

Question 1

Which 3 parts of the brain control gross and fine motor skills?

Answer 1

1. Cerebral Cortex - Controls movements of muscles & execution of movements
2. Cerebellum - Monitors muscles during movement
3. Basal Ganglia - Controls position & voluntary movement

Question 2

Describe the basal ganglia and cerebellar circuits and their connections to the cerebral cortex and Lower Motor Neurons

Answer 2

Cerebral Motor Cortex sends signals to lower motor neurons via the corticospinal tract which influence the actions of the muscles.

However, the extent of the neurons sent are influenced by signals that are sent to the basal ganglia and cerebellum, which return modulatory signals to the cerebral motor cortex that then modify the signals sent to the Lower Motor Neurons and Muscles
- Cerebral Cortex –> Basal Ganglia –> Cerebral Cortex
- Cerebral Cortex –> Pons –> Cerebellum –> Cerebral Cortex

Returning signals from the cerebellum to the cerebral cortex is excitatory;
Returning signals from the basal ganglia to the cerebral cortex is inhibitory

Question 3

Where is the cerebellum located in the cranial cavity?

Answer 3

Posterior Cranial Fossa, below the occipital lobe & behind the brainstem

Question 4

What separates the occipital lobe and the cerebellum?

Answer 4

The Tentorium Cerebelli

Question 5

What are 3 arteries that supply the cerebellum? Identify the origins of these arteries

Answer 5

1. Superior Cerebellar Artery (SCA)
2. Anterior Inferior Cerebellar Artery (AICA)
3. Posterior Inferior Cerebellar Artery (PICA)

Question 6

Name the connection between the cerebellum and the brainstem. How may this structure be subdivided further?

Answer 6

Cerebellar Peduncles.
- Inferior: Carries information from the spinal cord to the cerebellum
- Middle: Carries information from the cerebral cortex to the cerebellum
- Superior: Carries information from the cerebellum to the cerebral cortex

Question 7

How are the two hemispheres of the cerebellum connected?

Answer 7

Vermis, and a deep groove called the vallecula inferiorly

Question 8

What are the 3 lobes of the cerebellum?

Answer 8

1. Flocculonodular Lobe
2. Anterior Lobe
3. Posterior Lobe

Question 9

What divides the anterior lobe from the posterior lobe?

Answer 9

Primary Fissure

Question 10

What makes up the grey matter of the cerebellum?

Answer 10

1. Cerebellar Cortex
2. Deep Nuclei
   - Dentate Nuclei
   - Interposed Nuclei
   - Fastigial Nuclei

Question 11

What is the function of the deep nuclei?

Answer 11

The fastigial nucleus is involved in controlling posture and balance,

while the globose and emboliform nuclei are involved in controlling limb movements.

The dentate nucleus is the largest of the deep nuclei and is involved in controlling fine movements of the limbs, including finger and hand movements.

Question 12

Histologically, what are the two layers that the cerebellar cortex consists of?

Answer 12

1. Molecular Layer
2. Granule Cell Layer

Question 13

What are the main types of neurons involved in cerebellar circuits? within these neurons, what types of axons are there?

Answer 13

1. Purkinje Cells
2. Granule Cells
3. Mossy Fibres
4. Climbing Fibres
5. Parallel Fibres

Question 14

Describe the stages of transmission of signals from the cerebral cortex to the cerebellum, and then back to the cerebral cortex? make reference to the neurons and axons involved.

Answer 14

1. Sensory and motor information from various regions of the brain, including the cerebral cortex, is transmitted to the cerebellum via mossy fibers. These fibers synapse with granule cells in the granular layer of the cerebellar cortex.
2. Granule cells process the incoming information and send their axons, called parallel fibers, to the molecular layer of the cerebellar cortex, where they synapse with the dendrites of Purkinje cells.
3. Purkinje cells integrate the information from multiple parallel fibers and climbing fibers that synapse with their dendrites. Purkinje cells send their axons, called Purkinje cell fibers, to the deep cerebellar nuclei.
4. The deep cerebellar nuclei receive input from Purkinje cells and send output to various regions of the brain, including the thalamus and brainstem. The output from the deep cerebellar nuclei influences motor and cognitive functions.

EXTRA SIGNALS:
Climbing fiber input: Climbing fibers, which originate from the inferior olivary nuclei, synapse with the Purkinje cells in the cerebellar cortex. Climbing fibers provide a strong excitatory input to Purkinje cells and play a crucial role in motor learning and adaptation.

Question 15

From medial to lateral, what are the 3 zones of the cerebellum?

Answer 15

Vermis
Para-vermal
Lateral Hemispheres

Question 16

What are the functional subdivisions of the cerebellum?

Answer 16

1. Vestibulo-Cerebellum: Flocculonodular Lobe
2. Spino-Cerebellum: Vermis + Paravermis
3. Cerebro-Cerebellum (Neocerebellum): Lateral Hemisphere

Question 17

For the vestibulo-cerebellum:
a) function
b) location
c) afferents
d) efferents

Answer 17

a) involved in vestibular reflexes and postural maintenance
b) flocculonodular lobe
c) from the vestibular nuclei
d) to the vestibular nuclei, from there projects to the spinal cord via vestibulospinal tract (regulates axial musculature) and to the nuclei of CN 3, 4, 6 (coordination of eye movements [vestibulo-ocular reflex])

Question 18

For the spino-cerebellum:
a) function
b) location
c) afferents
d) efferents

Answer 18

a) integration of sensory input with motor commands to produce adaptive motor coordination (adjusts on-going movement)
b) Vermis & Paravermis
c) From spinocerebellar tracts
d) to vestibular and red nuclei, and thence to the spinal cord (from the deep nuclei [fastigial & interposed nuclei])
- interposed nuclei through superior cerebellar peduncle, decussate, rubrospinal tract which decussates back to original sid
- fastigial nuclei via inferior cerebellar peduncle to vestibular nucleus on same side, then form vestibulospinal tract

Question 19

For the cerebro-cerebellum:
a) function
b) location
c) afferents
d) efferents

Answer 19

a) planning and timing of movements + cognitive functions of the cerebellum
b) lateral part of cerebellar hemispheres
c) from cerebral cortex (cortico-pontine –> ponto-cerebellar fibres)
d) to the thalamus and thence back to the cortex (via dentate nucleus)
- dentate nuclei via superior cerebellar peduncle, decussate, go to ventrolateral nucleus of thalamus; then via internal capsule and corona radiata to the cerebral cortex
(bear in mind the corticospinal tract would decussate as it moves from cerebral cortex to muscles, so dentate nucleus actually controls muscle activity on same side of body

Question 20

How would damage to the flocculonodular lobe of the cerebellum present?

Answer 20

Loss of equilibrium, hence an altered walking gait with a wide stance that indicates difficulty in balancing

Question 21

How would damage to the cerebrocerebellum present?

Answer 21

1. Hypotonia (decreased muscle tone)
2. Dysarthria (problems with speech articulation)
3. Dysmetria (problems judging distances or ranges of movement)
4. Dysdiadochokinesia (inability to perform rapid alternating movements)
5. Impaired check reflex or rebound phenomenon
6. Tremors (involuntary movement caused by alternatingf contractions of opposing muscle groups

Question 22

What is the basal ganglia?

Answer 22

A group of subcortical nuclei

Question 23

What is the function of the basal ganglia?

Answer 23

Responsible for motor control, and motor learning, executive functions, behaviours and emotions

Question 24

What are symptoms of basal ganglia damage?

Answer 24

1. Problems controlling speech, movement, and posture
   - i.e., parkinsonism

Question 25

Describe the path of cerebellar afferent fibres from the cerebral cortex?

Answer 25

1. Corticopontocerebellar Pathway
   - From frontal, parietal, temporal, occipital lobes of the cerebral cortex
   - Descend through corona radiata and internal capsule
   - Terminate on pontine nuclei
   - Transverse fibres of pons cross midline and enter opposite cerebellar hemisphere via middle cerebral peduncle
2. Cerebro-olivocerebellar Pathway
   - From frontal, parietal, temporal, occipital lobes of the cerebral cortex
   - Descend through internal capsule and corona radiata
   - terminates bilaterally on the inferior olivary nuclei
   - fibres cross the midline and enter the opposite cerebellar hemisphere via the inferior cerebral peduncle; as climbing fibres
3. Cerebroreticulocerebellar Pathway
   - from sensorimotor areas
   - descend to terminate on the reticular formation and on opposite side in the pons and medulla
   - cells in reticular formation give rise to reticulocerebellar fibres that enter the cerebellar hemisphere on the same side through inferior and middle cerebellar peduncles

Question 26

Describe the cerebellar afferent fibres from the spinal cord? What sort of information does each pathway bring back?

Answer 26

1. Anterior Spinocerebellar Tract
   - from posterior root ganglion to nucleus dorsalis (clarke column)
   - most decussate, some remain ipsilateral, rise up as AST
   - fibres enter the cerebellum via superior cerebellar peduncle
   - terminates as mossy fibres in the cerebellar cortex

– Muscle joint info from upper and lower limbs

2. Posterior Spinocerebellar Tract
   - from posterior root ganglion to nucleus dorsalis (clarke column)
   - Ascend as the posterior spinocerebellar tract to the medulla oblongata on ipsilateral side
   - enters cerebellum via inferior cerebellar peduncle, terminates as mossy fibres in the cerebellar cortex

– muscle joint info from trunk and lower limb

3. Cuneocerebellar Tract
   - From nucleus cuneatus of medulla oblongta, enter cerebellar hemisphere on same side through inferior cerebellar peduncle
   - fibres terminate as mossy fibres in the cerebellar cortex

– muscle joint info from upper limb and thorax

Question 27

Describe the afferent fibres from the vestibular nerve

Answer 27

Vestibular afferents to vestibular nuclei in brainstem, then to cerebellum thru inferior cerebellar peduncle on same side

terminate as mossy fibres in the flocculonodular lobe of cerebellum