The Basal Nuclei And Motor Control

Question 1

What are the basal nuclei

Answer 1

A collection of nuclei deep to the white matter of cerebral cortex
Also called cerebral nuclei
Masses of gray matter
Are embedded in white matter

Question 2

What are the basal nuclei composed of

Answer 2

Caudate nucleus
Putamen
Globus pallidus
Subthalamic nucleus
Substantia Nigra

Question 3

Much of the output of the basal nuclei which is mediated through the …… is to ….. the …… to the cerebral cortex

Answer 3

Thalamus is to reduce or dampen the excitatory input to the cerebral cortex

Question 4

The basal nuclei provide a …….. off which ….. can be made

Answer 4

Postural platform off which purposeful movement can be made

Question 5

When discharge patterns of BN are excessive, there is…

Answer 5

An abnormal slowing of movements

Question 6

If there is a reduced output….

Answer 6

Abnormal involuntary movements occur at periods of rest (dyskinesia)

Question 7

Basal nuceli encode for

Answer 7

Decision to move, direction of movement, amplitude of movement, motor expression of emotions

Question 8

Input to the basal nuclei

Answer 8

Input to the striatum
Putamen - micromary motor area, secondary motor areas primary somatosensory area
Caudate nucleus - association areas, frontal eye fields, limbic system

Question 9

Input enables…

Answer 9

BN to integrate info from multiple sources

Question 10

Out put from the basal nuclei

Answer 10

Output from the globus pallidus interna (medial)
Via GABA-ergic neurons
To the thalamus
Thalamus under tonic inhibiton
Overall output from thalamus is excitatory to the cortex
Strength of thalamic signal dependent on GPi

Question 11

Output from BN is …

Answer 11

Highly regulated

Question 12

Balance of ……. To the thalamus

Answer 12

Inhibitory and excitatory pathways to the thalamus

Question 13

Thalamus is under …… and BN either ……

Answer 13

Tonic inhibiton and basal nuclei either increase or decrease this inhibiton

Question 14

Caudate nucleus

Answer 14

GABA - inhibitory

Question 15

Putamen

Answer 15

GABA - inhibitory

Question 16

Globus pallidus interna and externa

Answer 16

GABA - inhibitory

Question 17

Subthalamic nucelus

Answer 17

Glutamate - Excitatory

Question 18

Substantia nigra

Answer 18

Dopamine
Excitatory and inhibitory

Question 19

Describe the basal nuceli circuit

Answer 19

• Striatum receives input from cortical areas inputs are roughly topographical (multiple parallel circuits)
• GPi/SNr are the major output nuclei
• Output is inhibitory
• Gpi/SNr neurons have high baseline firing rates (baseline = inhibition)
• Gpi/SNr input from the striatum is focal and inhibitory, whereas input from the STN is diffuse and excitatory
• Direct vs. indirect striatal pathways have opposing effects (inhib. vs. excit.)
• Output of thalamus is primary to motor areas

Question 20

What are the 2 internal circuits of the basal nuclei

Answer 20

Direct pathway and indirect pathway

Question 21

Describe the direct pathway and how it influences the thalamus

Answer 21

The wiring in this circuit releases the thalamus from its tonic inhibiton leading to more excitation of the cortex and in turn more cortical output

Question 22

Describe the indirect pathway and how this influences the thalamus

Answer 22

The wiring in this circuit inhibits the output from the thalamus leading to less excitation of the cortex and in turn less cortical output
The indirect pathwa suppresses superfluous behaviours that are not related to targeted behaviour

Question 23

Indirect and direct pathway together …

Answer 23

Influence the thalamus and ultimately streamline behavioural output

Question 24

Describe SNc involvement in direct pathway

Answer 24

SNc sends dopaminergic connections to Putamen, that synapse onto excitatory D1 receptors. This effect is similar to excitation by cortex
This excites the inhibitory connections from putamen to Gpi and SNr, high, in turn releases VL from inhibiton to allow cortex excitation

Question 25

Describe the overall direct pathway

Answer 25

1. Excitatory projections from the cortex to the striatum synapse with the inhibitory neurons 2. Inhibitory Enron’s project directly to the GPi 3. From the GPi, inhibitory neurons project to the thalamus 4. Inhibiton of the inhibiton releases the tonic inhibitory of the thalamus resulting in increased output 5. The thalamus then sends excitortatory fibres to the cortex 6. STN provides tonic stimulation to the SN, influencing output from the SN 7. SN enhances the excitatory input from the cortex

Question 26

Describe the indirect pathway overall

Answer 26

1. Excitatory projections from the cortex to the stratum synapse with inhibitory neurons 2. Dopaminergc neurons inhibit (via D2 receptors) excitatory cholinergic Interneurons in the striatum 3. Inhibitor neurons project to the GPe 4. From the GPe, an inhibitor projection goes to the STN 5. The STN in turn sends an excitatory projection to the globus pallidus internal segment (GPi). This excites the inhibitory neurons in the GPi 6. This excitation of the inhibition by the STN projection increases he tonic inhibition of the thalamus 7. The thalamus then sends excitatory fibres to the cortex

Question 27

Parkinson’s disease and pathways

Answer 27

Decr output of the SNc dopaminergic projections Decrease inhibiton in direct pathway Increase excitation in indirect pathway Net effect: more inhibiton of thalamus and therefore less excitatory input to motor cortex

Question 28

What happens in Parkinson’s - direct pathway

Answer 28

Less excitation from SNc to putamen Less inhibiton of GPi and SNr More tonic inhibiton of VL Less excitation of cortex

Question 29

What happens in Parkinson’s - indirect pathway

Answer 29

Less dopamine released on inhibitory D2 receptors more inhibiton from putamen to GPe Less inhibiton from GPe to STN More excitation from STN to GPi and SNR More inhibiton from GPi and SNR to VL of thalamus Less excitation of cortex

Question 30

What happens in Huntington’s disease

Answer 30

Cell loss in the striatum that seems to affect the indirect pathway disproportionately Net effect: less inhibiton of the thalamus and therefore excessive excitation of the motor cortex