Module 2: Basal Ganglia

Question 1

what does the cortex connect to, and with what kind of connection

Answer 1

excitatory connection to the caudate and putamen

Question 2

what connections does the caudate and putamen have

Answer 2

to substantia nigra pars compacta, and inhibitory connection to globus pallidus and substantia nigra pars reticulata

Question 3

what connection does the substantia nigra pc have

Answer 3

to caudate and putamen

Question 4

what connections do the globus pallidus and substantia nigra pr have

Answer 4

inibitory to subthalamic nucleus and inhibitory to thalamus

Question 5

what connections does the subthalamic nucleus have

Answer 5

excitatory to globus pallidus and substantia nigra pr

Question 6

what connection does the thalamus have

Answer 6

excitatory to cortex

Question 7

how do we know that the basal ganglia is involved in motor control

Answer 7

postmortem exam of brains of individuals with motor diseases reveals pathology of basal ganglia nuclei

Question 8

striatum components

Answer 8

caudate and putamen

Question 9

what kind of input does the striatum receive

Answer 9

glutamatergic input via the corticostriatal pathway

Question 10

what are the only cortical areas that do not project to the striatum?

Answer 10

primary auditory and visual cortex

Question 11

what kind of synapses does the substantia nigra make

Answer 11

dopaminergic synapses at the base of spines
- this modulates the cortical input

Question 12

where do inhibitory synapses occur

Answer 12

near cell soma

Question 13

where do local circuit neurons synapse

Answer 13

on the cell soma of medium spiny neurons

Question 14

where do cortical pyramidal neurons synapse

Answer 14

onto dendritic spines of striatal medium spiny neurons

Question 15

are medium spiny neurons usually active or silent

Answer 15

silent

Question 16

are the inhibitory globus pallidus and substantia nigra pr neurons usually active or inactive

Answer 16

usually spontaneously active
- due to persistant sodium currents, T-type calcium currents, and hyperpolarization-activated currents

Question 17

what happens when medium spiny neurons aren’t silent

Answer 17

their inhibitory GABAergic shuts down the spontaneous firing of the palladial and SNpr neurons

Question 18

what happens when striatum is at rest?

Answer 18

globus pallidus is tonically active and inhibiting the VA/VL complex of thalamus, which leads to no excitation of upper motor neurons in cortex

Question 19

what happens when the striatum is excited

Answer 19

the globus pallidus is transiently inhibited and the VA/VL complex of thalamus is disinhibited so other inputs can excite it, leading to the excitation of the upper motor neurons in the cortex

Question 20

what are the brain connections that encode for the disinhibition of eye movement?

Answer 20

the caudate and putamen have an inhibitory connection to the SNpr which has an inhibitory connection to the superior colliculus

Question 21

what happens to the motor neurons in the eye when they are not scanning the environment

Answer 21

they are tonically inhibited

Question 22

what happens to the eyes prior to a saccade

Answer 22

the tonic discharge of reticulata neurons drops
- opens the ‘gate’ for eyes to move

Question 23

what happens if you inject muscimol to shut down the SNpr in eye movements?

Answer 23

it disinhibits the superior colliculus, and the eyes can no longer fixate (moving constantly)

Question 24

how can you cause spontaneous irrepressible saccades

Answer 24

intranigral injection of muscimol to act as an agonist at GABA receptors, and is inhibitory

Question 25

true or false: injecting muscimol into the SNpr mimics the action of medium spiny neuron firing

Answer 25

true

Question 26

true or false: injecting muscimol into the SNpr mimics the action of globus pallidus neurons firing

Answer 26

false

Question 27

true or false: injecting muscimol into the SNpr helps the eyes fixate

Answer 27

false

Question 28

true or false: injecting muscimol into the SNpr activates the thalamus

Answer 28

false

Question 29

what function does dopamine have

Answer 29

neuromodulatory
- doesn’t directly trigger a channel to open

Question 30

what characteristic do DA receptors have

Answer 30

metabotropic

Question 31

what does DA bind to

Answer 31

D1 and D2 type dopamine receptors on medium spiny neurons

Question 32

what does DA do when bound to D1 receptors

Answer 32

facilitates neuronal firing

Question 33

is dopamine a neurotransmitter?

Answer 33

no
- doesn’t directly allow ions to enter through it, but rather modulates other ion channels that do via G-proteins)

Question 34

what does DA do when bound to the D2 receptor

Answer 34

inhibits activity

Question 35

where is the D1 receptor located

Answer 35

on the membrane of the medium spiny neurons of the caudate/putamen

Question 36

what is the main function of dopamine

Answer 36

facilitates activation of the direct pathway to excite the thalamus

Question 37

what happens when msns projecting to the GPe fire?

Answer 37

they inhibit the GPe, which no longer inhibits the GPi, providing even stronger inhibition of the thalamus, decreasing movement

Question 38

what is the indirect pathway modulated by

Answer 38

inhibitory DA input (D2 receptors) specifically to the striatal msn that project to the GPe

Question 39

what happens when DA binds to D2 receptors on the MSNs that project to the GPe?

Answer 39

it makes it less likely that they will fire; now GPe is not inhibited; it inhibits the GPi, disinhibiting the thalamus and increasing movement

Question 40

what is the net effect of DA on both pathways

Answer 40

to increase movement

Question 41

what is the function of the indirect pathway when activated

Answer 41

to suppress undesired movements

Question 42

what happens to the DA neurons in the SNpc in Parkinson’s

Answer 42

they degenerate