5.1 Basal Ganglia

Question 1

What is the function of the basal ganglia?

Answer 1

• Planning and controlling motor movement/intensity of movement
• Gates proper initiation of movement

Question 2

What are the two components of the striatum?

Answer 2

• Caudate nucleus
• Putamen

Question 3

What are the four principal structures of the basal ganglia?

Answer 3

1. Striatum
2. Globus pallidus
3. Substantia nigra
4. Subthalamic nucleus

Question 4

Describe the shape of the caudate nucleus. What are its three components?

Answer 4

• C-shaped (c for caudate)
• 3 parts: head, body, tail

Question 5

Why is the striatum named the striatum?

Answer 5

Named after the stripes created by cellular bridges between the putamen and the caudate nucleus

Question 6

What are the components of the lentiform nucleus?

Answer 6

• Putamen
• Globus pallidus

Question 7

What are the two divisions of the substantia nigra?

Answer 7

Dorsal: pars compacta
Ventral: pars reticulata

Question 8

What is the major input structure to the basal ganglia? Where does IT recieve input from?

Answer 8

• Major input structure is striatum
• Recieves glutamatergic input from cortex and dopaminergic input from pars compacta of substantia nigra

Question 9

What type of neurons are most abundant in the striatum? What neurotransmitter do they release, and does this make them excitatory or inhibitory?

Answer 9

• Medium spiny neurons
• Release GABA
• Therefore, inhibitory

Question 10

What are the two output nuclei of the basal ganglia?

Answer 10

• SNr (ventral)
• GPi

Question 11

Which of the following have a high/zero tonic firing rate: striatal medium spiny neurons, globus pallidus, and SNr

Answer 11

MSN: zero
Globus Pallidus: high
SNr: high

Question 12

Which thalamic nuclei do GPi and SNr disinhibit upon MSN activation in the striatum?

Answer 12

Ventral anterior and ventral lateral nuclei (VA and VL)

Question 13

True or false: since we are constantly moving around slightly, almost all basal ganglia activity is at a tonic level

Answer 13

• False
• Most of it is transient; only Globus Pallidus and SNr are tonic

Question 14

What are the four channels that the thalamus excites when disinhibited by the basal ganglia?

Answer 14

• Motor loop (motor control)
• Oculomotor loop (regulation of eye movements)
• Prefrontal loop (frontal-lobe dependent cognition)
• Limbic loop (emotional/motivational regulation)

Question 15

Considering the basal ganglia, do the direct/indirect pathways promote/inhibit motor function?

Answer 15

Direct: promotes
Indirect: inhibits

Question 16

What are the two kinds of dopamine receptors? Which is excitatory/inhibitory?

Answer 16

D1: excitatory
D2: inhibitory

Question 17

Dopaminergic receptors are G coupled receptors. Signal transduction via these receptors stimulates the production of a secondary messenger known as…

Answer 17

cyclic AMP (cAMP)

Question 18

Describe, with mention of dopamine receptors, the balance between the two sources of input to the indirect pathway of the basal ganglia

Answer 18

• Glutamatergic input from the cortex is excitatory
• Due to D2 receptor expression, dopaminergic input from SNc is inhibitory

Therefore: net effect depends on which input is greater

Question 19

True or false: neurons from the GPe have a high tonic firing rate, and are GABAergic/inhibitory

Answer 19

True (read that again)

Question 20

Are the neurons from the subthalamic nucleus in the basal ganglia excitatory or inhibitory?

Answer 20

Excitatory

Question 21

Which of dopamine/glutamate promote/prevent activity in the indirect pathway of the basal ganglia?

Answer 21

Glutamate promotes, dopamine prevents

Question 22

Outline the direct pathway of the basal ganglia

Answer 22

• Glutamate and dopamine from cortex/SNc excite mesium spiny neurons in striatum
• These MSNs inhibit inhibitory neurons in the GPi
• This disinhibits the thalamus, leading to movement

Question 23

Describe the indirect pathway of the basal ganglia (assuming glutamate is greater than dopamine)

Answer 23

• Dopamine inhibits MSNs, and glutamate excites
• MSNs inhibit inhibitory neurons in the GPe
• Inhibitory neurons in the GPe no longer inhibit excitatory nuclei in the subthalamic nuclei
• STN nuclei promote GABAergic neurons in GPi/SNr
• This inhibits the thalamus, preventing motor movement initiation