L22 - Cerebellum

Question 1

Function of Cerebellum?

Answer 1

Sensorimotor integration:
regulatory influence on muscular activity&raquo_space; coordination and control of movements

also contributes to cognitive processes

Question 2

Divide the anatomical lobes of the cerebellum?

Answer 2

Anterior, Posterior, Flocculonodular lobes (from Nodulus and Folcculus nodes)

10 lobes in total

Question 3

Connection between cerebellum and brainstem?

Answer 3

Superior, Middle, Inferior cerebellar peduncle

Superior = output
Middle and inferior = input

Question 4

Divide the cerebellum into saggital zones, function of these zones and nuclei that resides in each zone.

Answer 4

1) Medial zone (vermal cortex) = Fastigial nucleus
2) Intermediate zone (intermediate cortex) = globose nucleus, emboliform nucleus, Interposed nuclei
3) Lateral zone (hemispheri cortex) = Dentate nucleus

1 + 2 = Spinocerebellum
3 = Cerebrocerebellum

Vestibulocerebellum = flocculonodular lobe

Question 5

List 5 cells types in cerebellum.

Answer 5

• Purkinje cells
• Golgi, Stellate, Basket cells
• Granule cells

Question 6

Function of Purkinje cells in cerebellum?

Answer 6

Receive direct and indirect input from climbing fibers and mossy fibers

Only cortical output neuron (GABAnergic)
Project to mainly inhibit subcortical/ deep cerebellar nuclei + some end in vestibular nuclei

Question 7

Function of the lateral zone of cerebellum?

Answer 7

Contains 2 dentate nuclei:

For projection through superior cerebellar peduncle to thalamus to motor/ pre-motor cortex for motor planning

Question 8

Function of the vermal cortex of cerebellum?

Answer 8

Vermal cortex = medial zone

Contains 2 fastigial nuclei:
Project through superior cerebellar peduncle to:
1) Medial descending pathway for motor execution
2) Vestibular nuclei for balance and eye movement

Question 9

List the inhibitory interneurons in the cerebellum? Function?

Answer 9

Basket, Golgi, Stellate cells

Regulatory interneurons (GABA neurotransmitter = inhibitory) of Purkinje cells

Question 10

Describe the excitatory input to the cerebellum and the cells involved?

Answer 10

Two inputs reach the cerebellar cortex via excitatory fibers:

1) Direct pathway: Climbing fibers from inferior olive (visual, audio, vestibular signals)&raquo_space; Inferior cerebellar peduncle
» Deep cerebellar nuclei and directly to Purkinje cells

2) Indirect pathway:
Mossy fibers from spinal cord/ brainstem (visual, audio, vestibular)&raquo_space; Inferior cerebellar peduncle&raquo_space; Granule cells fibers&raquo_space; Parallel fibers at the top of cerebellar cortex&raquo_space; Purkinje cell dendritic trees

Question 11

Describe the 2 modes of signal spread in the parallel fibers at the top of cerebellar cortex?

Answer 11

1) 1-dimensional spread: focal mossy inputs excite on-beam P cells + inhibit subcortical, brainstem cells

2) 2-dimensional spread: focal mossy inputs excite on-beam basket cells, stellate cells
» transverse fibers spread inhibition to neighboring off-beam P-cells
» dis-inhibit neighboring subcortical, brainstem cells (more excited)

Question 12

Where do signals from the subcortical cerebellar nuclei end up?

Answer 12

a. first to thalamus: then to the cerebral cortex

b. brainstem nuclei (e.g. red nucleus, vestibular nuclei and reticular formation).

Question 13

List the 3 cerebellar functional units? **

Answer 13

• Spinocerebellum
• Cerebrocerebellum
• Vestibulocerebellum

Question 14

Function of the Vestibulocerebellum?

Answer 14

a) Control of vestibulospinal reflex (postural movements via the axial motor system).
b) Coordination of vestibulo-ocular reflex.

Question 15

Input and output of vestibulocerebellum?

Answer 15

Input: vestibular nucleus, spinal cord, reticular formation

Processing: Vermal cerebellum + Vestibulocerebellum

Output:
1) Vermal cerebellum&raquo_space; lateral vestibulospinal tract

2) Vestibulocerebellum&raquo_space; reticulospinal tract

Question 16

Function of the Spinocerebellum? What tracts are involved

Answer 16

ERROR-DETECTOR:

COMPARING the command signals (intended action) originated from the cerebral cortex [cortico-ponto-cerebellar circuit]

with updated feedback from actual execution of the motor action [spinocerebellar tract]

> > correct mistakes during the course of movements

Question 17

Divide the spinocerebellum into 2 zones and their respective function?

Answer 17

Error-detection and update from spinocerebellar tract

a) Medial corticonuclear zone - Control both postural and voluntary movements of axial and proximal body parts
b) Intermediate corticonuclear zone - Coordinate voluntary movements of distal body parts by executing moment-to-moment course corrections

Question 18

Describe how the medial corticonuclear zone of the spinocerebellum exerts control? (3 tracts: 2 descending, 1 ascending))

Answer 18

Origin: Vermis (fastigial nucleus), send fibers to:

i) descending vestibulospinal tract
ii) Descending reticulospinal tract (can loop back to vermis via spinocerebellar pathway or mossy fibers)
iii) ascending thalamocortical projection, acting on medial descending motor system&raquo_space; proximal and truncal muscles

Question 19

Describe how the Intermediate corticonuclear zone of the spinocerebellum exerts control? (2 pathways)

Answer 19

Error detection and moment-to-moment control

1) Direct: via Rubrospinal tract&raquo_space; spinal cord
2) Indirect: via thalamocortical projections&raquo_space; corticospinal tract of lateral descending motor system

Question 20

Which saggital zone makes of the cerebrocerebellum?

Answer 20

lateral corticonuclear zone

Question 21

Function of cerebrocerebellum?

Answer 21

1) Converts movement designs from association cortex [cerebro-cerebellar tract] to movement programs

> > > sent to premotor cortex (area 6) for subsequent execution of goal-directed* voluntary movements* (i.e. voluntary oculomotor control)

2) Non-motor cognition

Question 22

Sequence of pathway through the cerebrocerebellum?

Answer 22

Association cortex
» Pontine relay nuclei&raquo_space; Mossy fibers&raquo_space; Dentate nuclei&raquo_space; thalamus&raquo_space; pre- motor cortex&raquo_space; corticospinal tract in spinal cord

or directly from dentate nucleus to rubrospinal tract in spinal cord

Question 23

List 4 pathological manifestations of cerebellar lesion?

Answer 23

Ataxia

Intention tremor

Hypotonus

Nystagmus

Question 24

Define the mechanism of ataxia caused by cerebellar lesion? How to test?

Answer 24

Errors in rate, range, force, direction of voluntary movements

due to Decomposition of movement and Asynergia (out of sync/ smoothness)

Tests:

1) Finger to nose test
2) Tandem steps test (unsteady gait)
3) Scanning, slurred speech

Question 25

How can the type of tremor be used to ddx area of brain damage?

Answer 25

Intention tremor associated with cerebellum lesion

vs. unintentional tremor associated with basal ganglia disorder
v. s Resting tremor associated with parkinosnism
v. s. physiological tremor = normal

Question 26

Define nystagmus and which part of the cerebellum is affected?

Answer 26

Nystagmus: alternate slow, fast eye movements

vestibulocerebellum: Purkinje cells normally exert inhibitory influence onto vestibule-ocular neural network

Question 27

List some forms of ataxia?

Answer 27

• Decomposition of movement/ Asynergia (cannot combine various components of a movement to create fluid motion)
• Dysmetria (e.g. finger-nose-finger test)
• Unsteady / uncoordinated posture, gait (clinical test: tandem steps)
• Adiadochokinesis (cannot perform rapidly alternating muscular movements)
• Asthenia (abnormal physical weakness / lack of energy)
• Scanning / slurred speech

Question 28

What is the function of Globose and Emboliform nucleus in the intermediate zone of cerebellum?

Answer 28

Sensory discrimination

Question 29

Where is visual and auditory input processed in the cerebellum?

Answer 29

Medial zone/ vermal cortex

Question 30

SUmmarize the input tracts into the 4 saggital zones of the cerbellum?

Answer 30

Medial = Trigeminal, spinal , vestibular (visual and auditory and vestibular)

Intermediate = Spinal, trigeminal

Lateral = Corticopontine input from association cortex

Flocculonodular/ Vestibulocerebellum= vestibular input and corticopontine input

Question 31

What excites the inhibitory interneurons in the cerebellum?

Answer 31

Stellate = excited by mossy fibers and granule cells

Basket = excited by climbing fibers from infeiror olive

> > both inhibit Purkinje cells