L09: Cerebellum & Basal Ganglia

Question 1

What makes up the basal ganglia?

Answer 1

Striatum (putamen, caudate nucleus & nucleus accumbens sometimes)
Globus pallidus (interna + externa)
Subthalamic nucleus
Substantia nigra (reticulata + pars compacta)

Question 2

What is the function of th basal ganglia?

Answer 2

Regulates cortical activity by intergrating sensory + motor info for smooth, coordinated movement.
INITIATES MOVEMENT

Question 3

Where does basal ganglia recieve input from?

Answer 3

Sensroy & motor areas, pre frontal cortex + parts of brain involving emotion (hippocampus, amygdala etc.)

Question 4

Where does basal gangla output go to?

Answer 4

Thalamus - then relayed back to cortex (esp area 6)

Question 5

What is ‘normal’ basal ganglia outflow?

Answer 5

Inhibitory to the thalamus, via GABA - done by Snr & GPi

Question 6

What are the different pathways within the basal ganglia ?

Answer 6

Direct: facilitates intended action
Indirect: supresses competing actions
Balance between both influences thalamus

Question 7

What is the role of the substantia nigra?

Answer 7

Contains dopaminergic neurones involved in rewarding behaviour. Pars compacta modulates direct & indirect pathways

Question 8

Describe the direct pathway within BG

Answer 8

• cortex stimulates striatum
• striatum inhibits SNr + GPi via GABA
• causes DISINHIBITION of thalamus (hence activation)
• thalamic feedback to cortex promotes movement

Question 9

How does dopamine influence the direct pathway?

Answer 9

Dopamine excites GABAnergic neurones (via D1 receptors) in striatum –> increased inhibition of SNr + GPi hence greater thalamic activity

Question 10

Describe the indirect pathway within BG

Answer 10

• cortex stimulates striatum
• Striatum inhibits GPe via GABA (GPe usually inhibits STN)
• inhibiton of GPe hence –> activation of STN
• STN allowed to stimulate SNr + GPe
• SNr + GPe can therefore INHIBIT thalamus to supress movement

Question 11

Action of dopamine on the indirect pathway?

Answer 11

Acts of D2 receptors within striatum to inhibit GABAnergic neurones
Hence reduces inhibtion of GPe
Reversal of indirect pathway hence facilitates movements

Question 12

What causes motor dysfunction?

Answer 12

Imbalance between direct & indirect pathways

Question 13

Examples of hypokinetic + hyperkinetic disorders?

Answer 13

Hypo: Parkinsons
Hyoer: Hemibalism, huntingtons, tardive dyskinesia

Question 14

What are the functional components of the cerebellum?

Answer 14

Spino, vestibulo + cerebro-cerebellum

Question 15

Describe the actions of the spino-cerebellum

Answer 15

Spino-cerebellum: sensory input from spinal cord, output to RF + red nucleus –> motor cortex to control posture (axial muscles)

Question 16

Describe the actions of the vestibulo-cerebellum

Answer 16

vestibular nuclei project to flocculonodular lobe which relays back to vestibular nuclei to control balance + eye movement, input from vestibular ear

Question 17

Describe the actions of the cerebro-cerebellum

Answer 17

inputs from proprioceptors used to judge quality of movement compared to intented movement, output back to M1 via dentate nucleus + venterolateral thalamus for error correction

Question 18

What is the functions of the cerebellum?

Answer 18

Controls muscle tone, sensorimotor coordination, motor learning + involved with posture + balance
Controls unconscious motor movements
Comparator between intended + actual movement

Question 19

What is the result of damage to the spino-cerebellum?

Answer 19

hypotonia, ataxia, intention tremor (can’t stop + change direction)

Question 20

What is the result of damage to the vestibulo-cerebellum?

Answer 20

slow saccades (movement of eyes between 2 points), nystagmus (rapid involuntary movements of eyes), ataxia

Question 21

What are the functional layers of cerebellum?

Answer 21

molecular layer, purkinje cell, granule cell layer, white matter

Question 22

Which way to impulses travek within cerebellum?

Answer 22

From deep cerebellar nuclei up to purkinje cells

Question 23

Function of the cerebellar peduncles?

Answer 23

Superior: connects cerebellum to midbrain = provides feedback to cerebrum
Middle: conveys impulses FROM cerebrum –> cerebellum
Inferior: connects cerebellum to medulla + spinal cord (inputs from vestibulo & proprioception, output motor fibres)