The Basal Ganglia

Question 1

Basic components of the basal ganglia.

Answer 1

5 interconnected subcortical nuclei: the putamen, caudate nuclei, globus pallidus, subthalamic nuclei and the substantia nigra.

Question 2

What two components make up the ventral striatum?

Answer 2

The caudate nucleus and the putamen.

Question 3

What is another name for the ventral striatum?

Answer 3

Nucleus accumbens

Question 4

Name the major input nuclei of the basal ganglia.

Answer 4

The striatum: the caudate nucleus and putamen.

Question 5

In what way are the caudate nucleus and the putamen fused together?

Answer 5

Partially fused together (ventrally) by mini strips of tissue forming bridge btw each. Are separated dorsally by the corticospinal tract.

Question 6

From where does the BG receive inputs?

Answer 6

From the motor cortex, sensory cortex, association cortex and the limbic system.

Question 7

What sort of motor information is sent to the BG?

Answer 7

Receives info from the primary motor cortex about the intended motor command to be sent to the spinal cord.

Question 8

What sort of sensory information is sent to the BG?

Answer 8

Visual, auditory, olfactory info etc. informing BG about safety of surroundings. Some info is raw, some is sent via sensory integration in parietal lobe.

Question 9

What sort of motivational / emotional inputs does the BG receive?

Answer 9

Info regarding hunger, thirst, temperature, fear stimuli?

Question 10

What sort of info regarding memory is sent to the BG?

Answer 10

Info regarding mvmts / actions made in the past to inform decision re current mvmt.

Question 11

How does the BG deal with all of the incoming info? (5)

Answer 11

Each piece of info will be weighted differently according to how relevant it is to the current situation. BG somehow integrates all of this info and determines whether motor action should or shouldn’t be carried out / is appropriate given the current internal / environmental conditions.

Question 12

What is the major output nuclei of the BG?

Answer 12

The internal globus pallidus

Question 13

What 4 substances mediate transmission within the BG?

Answer 13

Dopamine, substance P, GABA and dynorphin.

Question 14

What kind of input does the striatum receive and from what location?

Answer 14

An excitatory input from the motor cortex.

Question 15

What type of output signal does the BG send out and where to?

Answer 15

An inhibitory one to the motor cortex via the thalamus.

Question 16

Describe the direct pathway of the BG.

Answer 16

(1) Motor cortex excites striatum.
(2) Striatum decides to release motor beh. and sends inhibitory input to the int. segment of the globus pallidus.
(3) Inhibitory input onto thalamus is lessened, increasing thalamic output to motor cortex.
(4) Allows motor behaviour to be generated.

Question 17

Which pathway (direct or indirect) results in the generation of mvmt?

Answer 17

Direct

Question 18

Which pathway, (direct or indirect) prevents the release of motor action?

Answer 18

Indirect

Question 19

Describe the indirect pathway of the BG.

Answer 19

(1) Motor cortex excites striatum.
(2) Striatum decides NOT to release motor beh. so inhibits the ext. segment of the globus pallidus.
(3) Inhibition of subthalamic nucleus is lessened
(4) Subthalamic nuclei’s excitation of the internal globus pallidus increases
(5) The inhibition of the int. globus pallidus on the thalamus increases, decreasing thalamic output to the cortex
(5) Prevents motor behaviour from being generated

Question 20

Where do dopaminergic inputs arise from within the BG?

Answer 20

The substantia nigra.

Question 21

What class of receptors does dopamine act on in the direct circuit?

Answer 21

D1 receptors

Question 22

What class of receptors does dopamine act on in the indirect circuit?

Answer 22

D2 receptors

Question 23

Does dopamine increase or decrease the activity of the direct circuit?

Answer 23

Increases activity of direct circuity

Question 24

Does dopamine increase or decrease the activity of the indirect circuit?

Answer 24

Reduces activity of indirect circuit

Question 25

What kind of function does dopamine perform on the BG circuits?

Answer 25

Neuromodulatory function.

Functionally altering the synaptic connections btw BG neurons.

Question 26

How does dopamine increase the activity of the direct circuit of the BG?

Answer 26

It increases the level of cAMP so increases the striatum’s inhibition of the internal globus pallidus, strongly disinhibiting the thalamus and increasing its excitatory input into the motor cortex.

Question 27

How does dopamine reduce the activity of the indirect circuit of the BG?

Answer 27

Lessens the inhibition of the ext. globus pallidus via the striatum. Increases the inhibitory input of the ext. globus pallidus onto the subthalamic nucleus, decreasing subthalamic nucleus’ excitation of the int. globus pallidus, and decreases the int. globus pallidus’ inhibition of the thalamus , increasing thalamic output.

Question 28

Ultimately, what circuit does dopamine bias activity towards?

Answer 28

Biases activity towards the direct circuit and away from the indirect circuit. Increases likelihood of mvmt behaviours being released.