Motor Modulation - Basal Ganglia

Question 1

the basal ganglia and cerebellum modulate motor input by influencing upper motor neurons to……?

Answer 1

• improve movement efficiency
• coordinate timing between muscle groups to produce fluid movements
• making movements adaptable in real time

Question 2

what is the basal ganglia and its function?

Answer 2

a group of nuclei which function to
- select and initiate a collection of relevant movements for a given task
- inhibit competing movements for that task

Question 3

why do lesions of the basal ganglia cause disturbances in initiation of a movement?

Answer 3

due to planning bc the BG neurons fire before a movement happens

Question 4

the basal ganglia acts on the motor cortex via the …?

Answer 4

thalamus

Question 5

when movement is needed what happens to the basal ganglia neurons?

Answer 5

they are transiently relieved from being tonically inhibited at rest

Question 6

when the neurons of basal ganglia are stimulated, what pathways are activated?

Answer 6

direct pathway
indirect pathway

Question 7

explain the direct pathway

Answer 7

• go signal
• disinhibited (releases inhibition)
• thalamic neurons that could stimulate wanted motor programs can now fire

Question 8

explain the indirect pathway

Answer 8

• stop signal
• reinforces inhibition
• thalamic neurons that could stimulate unwanted motor programs will not fire

Question 9

what are the basal ganglia brain nuclei?

Answer 9

• caudate
• putamen
• globus pallidus
• subthalamic nucleus

Question 10

what is the basal ganglia brainstem nuclei?

Answer 10

substantia nigra

Question 11

what is input nuclei and what does it include?

Answer 11

• nuclei of the basal ganglia that receives the initial stimulus from the cerebral cortex
• includes the striatum (caudate and putamen collectively)

Question 12

what is the main input nucleus for motor movement?

Answer 12

putamen

Question 13

what is output nuclei and what does it include?

Answer 13

• delivers the final signal to the thalamus provided via a segment of the globus pallidus

Question 14

what are the two segments of the globus pallidus ?

Answer 14

internal and external segment

Question 15

what is the function of the internal segment of the globus pallidus ?

Answer 15

output motor information via direct and indirect pathways

Question 16

what is the function of the external segment of the globus pallidus ?

Answer 16

modulates projections to the subthalamic nucleus via indirect pathway only

Question 17

what does the globus pallidus internal segment have high levels of?

Answer 17

tonic inhibitory activity acting to inhibit the thalamus in a resting state

Question 18

what is a modulatory nuclei and what are the three in the basal ganglia?

Answer 18

nuclei that communicate only with other nuclei in the BG either to reinforce or inhibit their signals
- globus pallidus external
- subthalamic nucleus
- substantia nigra

Question 19

what is happening in the direct pathway at REST?

Answer 19

the ability of the thalamus to excite the cortex to initiate a motor program is INHIBITED by the tonic action of the globus pallidus internal

Question 20

what could cause a motor program to be activated in the direct pathway?

Answer 20

• stimulation of the cerebral cortex OR substantia nigra
  causes the striatum to be stimulated which inhibits the GPi, freeing the thalamus to be able to stimulate the cortex

Question 21

explain why hypokinetic syndromes like Parkinson’s Disease occur

Answer 21

• striatal neurons are hyper-polarized and need multiple excitatory inputs to reach firing threshold
• the loss of stimulatory drive from the substantia nigra causes the inability of the striatum to reach threshold

Question 22

Parkinson’s Disease is associated with the degeneration of what?

Answer 22

dopaminergic neurons in the substania nigra

Question 23

neurodegeneration normally affects what neurons?

Answer 23

direct pathway neurons causing loss of the go signal

Question 24

how would you increase inhibitory drive to the thalamus ?

Answer 24

provide greater stimulus to the GPi through the subthalamic nucleus which enhances the inhibitory drive of the GPi and causes inhibition of the thalamus

Question 25

which nuclei tonically inhibits the subthalamic nucleus ?

Answer 25

Globus pallidua external

Question 26

what neurons can inhibit the globus pallidus external causing the subthalamic nucleus to fire?

Answer 26

striatum

Question 27

explain the indirect pathway

Answer 27

• striatum is excited by cortical neurons and inhibits the globus pallidus external
• GPe cannot inhibit the subthalamic nucleus anymore
• subthalamic nucleus stimulates GPi which inhibits the thalamus
• thalamus inhibited = no unwanted movement

Question 28

what causes Huntington’s Disease and what does it result in?

Answer 28

• degeneration of neurons in the striatum
• results in unwanted movements like chorea (writhing and twisting movements) and rigidity

Question 29

Huntington’s disease is a genetic disorder revolving around what chromosomal mutation?

Answer 29

chromosome 4 mutates such that an abnormally large number of CAG repeats occurs

Question 30

how is the indirect pathway modulated?

Answer 30

by the neurons of the substantia nigra inhibiting the striatum

Question 31

neurons of which brain nuclei use dopamine as a neurotransmiter?

Answer 31

substantia nigra

Question 32

striatal neurons associated with the direct pathway have which type of receptor?

Answer 32

D1 dopamine receptor that depolarizes a cell in response to dopamine

Question 33

striatal neurons associated with the indirect pathway have which type of receptor?

Answer 33

D2 dopamine receptor that hyperpolarizes a cell in response to dopamine

Question 34

the D1 and D2 dopamine receptors of the striatal neurons allows for what?

Answer 34

both excision of the direct pathway and inhibition of the indirect pathway