Motor control: Role of the cerebellum and basal ganglia

Question 1

What mechanisms is the cerebellum closely involved with?

Answer 1

Brainstem mechanisms, which are involved with unconscious motor control

Question 2

What are the functions of the cerebellum?

Answer 2

Control of muscle tone, motor learning, and sensorimotor coordination.

Question 3

What is the role of the basal ganglia?

Answer 3

Responsible for integration of sensory and motor information.

Question 4

Do the cerebellum and basal ganglia project beyond the brain?

Answer 4

No, they do not project down to the spinal cord.

Question 5

What makes the cerebellum unique?

Answer 5

The cerebellar cortex is densely packed with neurons that receive and process information, outputting to the deep cerebellar nuclei.

Question 6

What are the 3 functional and anatomical components of the cerebellum?

Answer 6

Spino-cerebellum, vestibulo-cerebellum, and cerebro- (ponto-) cerebellum.

Question 7

What is the function of the spino-cerebellum and what does it allow?

Answer 7

Receives sensory input from the spinal cord and directs output to the motor cortex, allowing control over axial musculature and posture.

Question 8

What is the function of the vestibulo-cerebellum and what does it allow?

Answer 8

Receives input from and provides output to the vestibular nucleus, playing a role in control over posture/balance and eye movement.

Question 9

What is the function of the cerebro-cerebellum and what does it allow?

Answer 9

It is an intracerebral motor loop that adjusts ongoing movements by comparing intended movements with actual movements.

Question 10

If a patient presents with ataxia, what functional components would you expect to see damaged?

Answer 10

Spino-cerebellum, cerebro- (ponto-) cerebellum, and vestibulo-cerebellum.

Question 11

If a patient presents with dysmetria, what functional components would you expect to see damaged?

Answer 11

Spino-cerebellum and cerebro- (ponto-) cerebellum.

Question 12

If a patient presents with hypotonia, what functional components would you expect to see damaged?

Answer 12

Spino-cerebellum.

Question 13

If a patient presents with slow saccades & nystagmus, what functional components would you expect to see damaged?

Answer 13

Vestibulo-cerebellum.

Question 14

If a patient presents with dysarthria, what functional components would you expect to see damaged?

Answer 14

Cerebro- (ponto-) cerebellum.

Question 15

Describe Purkinje fibers and their role.

Answer 15

Final destination of afferent pathways in the cerebellar cortex, releasing GABA to coordinate movement.

Question 16

Describe granule cells and their role.

Answer 16

Receive excitatory input from mossy fibers in pontine nuclei.

Question 17

What layers are the different cell types in the cerebellum arranged in?

Answer 17

Molecular layer, Purkinje cell layer, granule cell layer, and white matter.

Question 18

What are the inputs to the cerebellar cortex?

Answer 18

Climbing fibers from the inferior olive and mossy fibers from brainstem nuclei.

Question 19

What are the cerebellar cortex outputs?

Answer 19

Only Purkinje cells output from the cerebellar cortex, providing inhibitory output.

Question 20

What do deep cerebellar nuclei receive?

Answer 20

Direct excitatory input from climbing fibers and mossy fibers, and inhibitory input from Purkinje cells.

Question 21

How is the function of deep cerebellar nuclei (DCN) unique?

Answer 21

They can compare input from mossy and climbing input to detect error signals.

Question 22

What happens once the DCN have made a comparison?

Answer 22

It can decide to send a compensatory signal if needed.

Question 23

What is the main function of the cerebellum?

Answer 23

To act as a comparator, a timer, and a regulator.

Question 24

What do coordinated movements leading to meaningful behavior require?

Answer 24

Integration of sensory cues that inform the animal of its environment and body state.

Question 25

Describe the 'motor plan' that the cerebellum contains.

Answer 25

It compares intended movement with actual movement using sensory feedback.

Question 26

What are the basal ganglia?

Answer 26

A group of associated subcortical nuclei, often referred to as the 'dark basement of the brain.'

Question 27

Describe how the basal ganglia are organized.

Answer 27

Linked together in a loop pathway, integrating info from the cortex and feeding back via thalamus.

Question 28

What happens if the basal ganglia are damaged?

Answer 28

Results in movement disorders.

Question 29

Describe the function of the basal ganglia.

Answer 29

Involved in integration of sensory and motor information, crucial for voluntary movement.

Question 30

What is the difference between the basal ganglia and cerebellum function?

Answer 30

Basal ganglia ensure correct movements are initiated and maintained, while cerebellum guarantees smooth and coordinated movements.

Question 31

What is the cortico-basal ganglia-cortical loop?

Answer 31

A neural circuit involving connections between the cortex, basal ganglia, thalamus, and back to the cortex.

Question 32

What is the input to the basal ganglia?

Answer 32

Input comes from the cortex.

Question 33

What is the output of the basal ganglia?

Answer 33

Outputs to ventrolateral thalamus, which then feedbacks to the cortex.

Question 34

What is associated with increased activity in the basal ganglia output?

Answer 34

GABA, which has an inhibitory effect.

Question 35

Describe the loop in a resting situation.

Answer 35

Cortex feeds into BG, leading to inhibitory outflow to thalamus, resulting in no movement.

Question 36

Describe the loop when you want to move.

Answer 36

Prefrontal cortex sends excitatory signal to BG, switching off inhibitory outflow, allowing thalamus activation.

Question 37

What are the main structures of the basal ganglia?

Answer 37

Striatum, subthalamic nucleus, globus pallidus, and substantia nigra.

Question 38

What is the striatum made up of?

Answer 38

Caudate nucleus, putamen, and nucleus accumbens.

Question 39

What is the globus pallidus made up of?

Answer 39

External segment (GPe) and internal segment (GPi).

Question 40

What makes up the substantia nigra?

Answer 40

Reticulata (SNr) and pars compacta (SNc).

Question 41

Where does inhibitory outflow from the basal ganglia directed to the thalamus come from?

Answer 41

The internal segment of GP and the substantia nigra reticulata, which are GABAergic neurons.

Question 42

What is the basic circuit of the basal ganglia?

Answer 42

The basic circuit includes the cortex at the top, basal ganglia in grey, and red indicating GABAergic neurons.

Question 43

What neurotransmitter does the cortex use to send excitatory input into the striatum?

Answer 43

Glutamate

Question 44

What are the two major areas the striatum relays cortical input to?

Answer 44

SNr and GPi

Question 45

What pathways are present in the internal organization of the basal ganglia?

Answer 45

Direct pathway to SNr and GPi; Indirect pathway to output stations via GPe and STN.

Question 46

What is the role of dopamine in the basal ganglia pathways?

Answer 46

Dopamine is a key modulator released from the SNc.

Question 47

What is the output type of the cortex?

Answer 47

Excitatory

Question 48

What is the output type of the striatum?

Answer 48

Inhibitory

Question 49

What is the output type of the globus pallidus?

Answer 49

Inhibitory (both external & internal)

Question 50

What is the output type of the substantia nigra reticular?

Answer 50

Inhibitory

Question 51

What is the output type of the substantia nigra pars compacta?

Answer 51

Dopamine - depends on receptor (D1 = excitatory, D2 = inhibitory)

Question 52

What is the output type of the subthalamic nucleus?

Answer 52

Excitatory

Question 53

What is the output type of the thalamus?

Answer 53

Excitatory

Question 54

What does the direct pathway serve to do?

Answer 54

Promote movement by increasing inhibition to SNr/GPi, freeing the thalamus to excite the cortex.

Question 55

What receptors does dopamine act on in the direct pathway?

Answer 55

D1 receptors on striato-GPi/SNr neurons.

Question 56

What is the effect of dopamine on the direct pathway?

Answer 56

Increases inhibition which decreases BG outflow and facilitates movement.

Question 57

What is the purpose of the indirect pathway?

Answer 57

To suppress movement.

Question 58

What happens to BG outflow when the indirect pathway is activated?

Answer 58

BG outflow is increased.

Question 59

What receptors does dopamine act on in the indirect pathway?

Answer 59

D2 receptors on striato-GPe neurons.

Question 60

What is the effect of dopamine on the indirect pathway?

Answer 60

Acts in an inhibitory manner.

Question 61

When will motor dysfunction occur?

Answer 61

If there is an imbalance between the direct and indirect pathways.

Question 62

What disorders are associated with imbalance in basal ganglia pathways?

Answer 62

Hypokinetic disorders (e.g., Parkinson's disease) and hyperkinetic disorders (e.g., Huntington's disease, Hemiballism, Tardive Dyskinesia).

Question 63

What are the characteristic symptoms of Parkinson's disease?

Answer 63

Tremor, bradykinesia, rigidity.

Question 64

How much does Parkinson's disease affect the population?

Answer 64

0.1% of the population under 50; > 50 years old, 1%.

Question 65

What type of disorder is Parkinson's disease?

Answer 65

A progressive disorder with early movement symptoms leading to dementia, depression, and bladder disturbance.

Question 66

What is the average survival time after diagnosis of Parkinson's disease?

Answer 66

15 years

Question 67

What is used as the pathological landmark to diagnose Parkinson's disease?

Answer 67

Lewy bodies, confirmed post-mortem.

Question 68

How is Parkinson's disease treated?

Answer 68

Treatment aims to control symptoms by replacing dopamine.

Question 69

What is the main drug used to treat Parkinson's disease?

Answer 69

L-DOPA, a dopamine precursor.

Question 70

What does L-DOPA do?

Answer 70

Offsets loss of dopaminergic transmission and reduces dopamine breakdown or reuptake.

Question 71

What other treatment can be used for Parkinson's disease?

Answer 71

Deep brain stimulation.

Question 72

What are some problems associated with L-DOPA treatment?

Answer 72

Effectiveness diminishes over 2-5 years due to disease progression, leading to increased L-DOPA dose frequency and movement abnormalities.

Question 73

What are the symptoms of Huntington's disease?

Answer 73

Excessive choreiform movement, uncontrollable rapid motor patterns, later stages include psychiatric disturbance and dementia.

Question 74

What are the causes of Huntington's disease?

Answer 74

Autosomal dominant disorder with a prevalence of about 1 in 15,000, peak onset age 40-45 years.

Question 75

What is the primary pathology of Huntington's disease?

Answer 75

Loss of striatal output neurons in the indirect pathway, leading to increased excitation of GPe and overactive thalamocortical pathway.

Question 76

How is Huntington's disease treated?

Answer 76

Drug treatments for symptomatic relief, including Tetrabenazine, Chlorpromazine, and Baclofen.

Question 77

What is the cause and effect of Hemiballismus?

Answer 77

Cause: damage to STN (usually due to stroke). Effect: involuntary violent flailing movements of limbs (contralateral).

Question 78

What is the cause and effect of Tardive Dyskinesia?

Answer 78

Cause: increased DA receptor sensitivity due to long-term exposure to antipsychotic drugs. Effect: uncontrolled movement, especially of facial and trunk muscles.