Week 5

Question 1

Structure of cerebellum?

Answer 1

3 lobes (Anterior, posterior and flocculonodular)

3 functional subdivisions

3 pairs of peduncles

3 pairs of deep nuclei

3 cortical layers

Question 2

Functions of the cerebellum?

Answer 2

Coordinates movement, maintains posture and balance, and enables motor learning.

Integrates sensory and motor information for smooth execution of movements.

Question 3

Location of cerebellum?

Answer 3

Posterior of the brainstem

Question 4

Consequences of cerebellar damage?

Answer 4

Causes severe movement disruption

Can lead to ataxia which is the abnormal execution of multi-jointed voluntary movements, characterized by lack of coordination and is caused by strokes, MS or tumours etc.

Question 5

Gross anatomy of the cerebellum?

Answer 5

Cerebellar peduncles - Superior, Middle, Inferior

Cerebellar cortex -Cerebrocerebellum, Spinocerebellum, Vestibulocerebellum

Deep cerebellar nuclei -
Dentate nucleus, Interposed nucleus, Fastigial nucleus

Question 6

Cerebellar peduncles?

Answer 6

The cerebellum is connected to the dorsal aspect of the brainstem by 3 symmetrical
pairs of peduncles:

Superior peduncle
* No inputs
* Outputs to motor cortex (via thalamus) and
red nucleus

Middle peduncle
* Inputs from motor cortex (via pons)
* No outputs

Inferior peduncle
* Inputs from inferior olivary nucleus, spinal
cord and vestibular nuclei
* Outputs to reticular formation (brainstem),
spinal cord and vestibular nuclei

Question 7

Cerebellar cortex subdivisions?

Answer 7

Cerebrocerebellum
Spinocerebellum
Vestibulocerebellum

Question 8

Spinocerebellum?

Answer 8

Comprises the vermis and
intermediate cortex
Regulates body and limb movements
Somatic sensory inputs exhibit somatotopy:

Vermis: Input(s) spinal cord carrying sensory info from trunk and head
Output(s): Fastigial nucleus to medial descending
reticulospinal and vestibulospinal tracts, Motor execution

Intermediate cortex:
Input(s): Spinal cord, carrying sensory information from the limbs
Output(s): Interposed nucleus to lateral descending
corticospinal and rubrospinal tracts, Motor planning

Question 9

Vestibulocerebellum?

Answer 9

Also known as the flocculonodular lobe -
Oldest evolutionary part of cerebellum

Only region of the cerebellar cortex to
bypass the deep cerebellar nuclei

Regulates balance and eye movements

Input(s): Vestibular nucleus, from semicircular canals
and otolith organs

Output(s): Vestibular nucleus, to axial and proximal muscles, limb extensors, and head/eye muscles

Question 10

Cerebrocerebellum?

Answer 10

Largest, involved in motor planning.

Input(s): Pons, from motor cortex (via thalamus)
Inferior olive, from motor cortex (via red
nucleus) and spinal cord

Output(s): Dentate nucleus, to motor cortex (via
thalamus)

Question 11

Deep cerebellar nuclei components?

Answer 11

Dentate
Interposed
Fastigial

Question 12

Dentate Deep cerebellar nuclei ?

Answer 12

Most lateral nucleus

Located in cerebrocerebellum

Output is to motor cortex via superior peduncle and thalamus

Question 13

Interposed Deep cerebellar nuclei ?

Answer 13

Located in intermediate cortex
(spinocerebellum)

Output is to red nucleus via superior peduncle

Question 14

Fastigial Deep cerebellar nuclei ?

Answer 14

Most medial nucleus

Located in vermis (spinocerebellum)

Output is to reticular formation and vestibular
nucleus via inferior peduncle

Question 15

Cerebellar circuitry elements?

Answer 15

Mossy fibres (granule layer) - Mossy fibres are the primary neurons that carry information into the cerebellum. Activate granule cells and cerebellar nuclei

Granule cells (granule layer) - attach to parallel fibres which synapse with dendrites of Purkinje cells

Climbing fibres (granule layer) - excites Purkinje cells directly (but can also inhibit via interneurons).
Originates in the inferior olive.
Believed to sense error signals to elicit learning

Purkinje cells (Purkinje cell layer) - cell body with vast dendritic tree with inhibitory function, inhibits cerebellar nuclei, modulating motor output

Parallel fibres (molecular layer)

Question 16

Overall Function of the Basal Ganglia?

Answer 16

The basal ganglia modulate strategic aspects of movement, including initiation, termination, and scaling of motor activity.

They influence premotor cortical activity indirectly through the cortico-basal ganglia-thalamic loop.

They have no direct connections to the spinal cord but are essential for integrating cortical input and motor planning.

Question 17

Cerebellum Connections?

Answer 17

Connections only to sensorimotor
areas of cerebral cortex (via
thalamus)

Receives input from brainstem and
spinal cord

Involved almost exclusively with movement

Question 18

Basal Ganglia Connections?

Answer 18

Widespread reciprocal connections to cerebral cortex (via thalamus)

Not just involved in movement

Behaviour and emotion

Question 19

Gross anatomy of Basal Ganglia?

Answer 19

The basal ganglia is a
collection of 5 nuclei

1. Caudate
2. Putamen
3. Globus pallidus
   * Internal (GPi)
   * External (GPe)
4. Subthalamic nucleus (STN)
5. Substantia nigra
   * Pars compacta (SNc)
   * Pars reticulata (SNr)

Caudate and putamen are part of the striatum

Question 21

Basal Ganglia Gross anatomy inputs/outputs?

Answer 21

Input(s):
Striatum (caudate and putamen)

Receives direct and indirect (via thalamus) connections from cerebral cortex

Output(s):
GPi and SNr

Provide tonic inhibitory output to thalamus

Question 22

Basal Ganglia internal connections?

Answer 22

Striatum projects to:
a) Globus pallidus (striato-
pallidal pathway)
b) Substantia nigra (striato-
nigral pathway)

STN forms indirect pathway
between GPe and SNr

GPi and SNr are the output
centre of the basal ganglia
and send inhibitory signals to the thalamus

Question 23

Basal Ganglia feedback loop?

Answer 23

Basal ganglia receives excitatory input from cerebral cortex which then sends inhibitory signals to the thalamus, in turn SUPPRESSING motor cortical activity

Excessive basal ganglia input results in slow movement and reduced input results in
enhanced movement

Question 24

What is the transcortical loop?

Answer 24

A 3 stage loop involving the cerebral cortex, basal ganglia and thalamus.

1. Striatum (putamen) receives vast
   array of inputs from the cerebral
   cortex (motor and sensory)
2. Output from GPi and SNr project to
   thalamus (inhibitory signal)
3. Inhibited thalamus projects to motor
   cortex, thus suppressing movement

Question 25

Direct motor pathway?

Answer 25

Involves two inhibitory
synapses resulting in disinhibition, thereby
facilitating movement

Question 26

Indirect motor pathway?

Answer 26

Involves excitation of the
inhibition, thereby supressing movement

Question 27

Key Features of (In)Direct motor pathways?

Answer 27

The basal ganglia exert a tonic inhibitory output to the thalamus.

Neurotransmitters involved:
Glutamate (excitatory): Open arrows.
GABA (inhibitory): Filled arrows.
Dopamine (mixed effects): Mixed arrows

STN is a relay from the striatum (input) to the
GPi/SNr (output), forming an indirect motor
pathway

Question 28

Dopamine’s Role in motor pathways?

Answer 28

Excites the direct pathway via D1 receptors and inhibits the indirect pathway via D2 receptors, collectively facilitating movement.

Question 29

Differences Between Basal Ganglia Diseases?

Answer 29

Parkinson’s Disease: Hypokinetic

Caused by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNc).
Overactive indirect pathway suppresses movement.
Symptoms: Bradykinesia, rigidity, tremor, postural instability.

Huntington’s Disease: Hyperkinetic

Results from striatal atrophy, reducing activity in the indirect pathway.
Underactive indirect pathway facilitates excessive movement.
Symptoms: Uncontrolled, jerky movements (chorea).