Basal Ganglia

Question 0

Neurone populations

Answer 0

Striatum (putamen and caudate)
Globus pallidus internus and externus (GPi and GPe)
Substantia nigra (SN)
Subthalamaic nucleus (STN)

Question 1

What is the basal ganglia

Answer 1

System of separate but inter related neurone populations within brain
Interact with part of cerebral cortex that initiates movement
Responsible for fine tuning initiation, control and termination of movements
Through loop of inhibitory and excitatory signals (direct and indirect pathways)

Question 2

Direct pathway

Answer 2

Upon initiation of movement, frontal lobe sends excitatory signal to striatum via glutamate
Striatum sends inhibitory signals to GPi and SN pars reticula
Normally GPi and SNpr inhibit the thalamus- they are inhibited so the thalamus is dis-inhibited
Thalamus sends message to cortex allowing movement to take place
Motor cortex sends message down spinal cord for movement

Question 3

Dopamine effect on direct pathway

Answer 3

Dopamine secreted by SN pars compacta
Secreted onto parts of striatum, and interacts with d1 receptors on these cells, causing them to be more active
Striatum activated, so GPi doesnt inhibit thalamus therefore movement allowed to take place
Increases propensity towards movement

Question 4

Indirect pathway

Answer 4

Initiation of movement, frontal lobe sends excitatory signal to striatum
In indirect, striatum sends inhibitory signal via GABA to GPe
Normally, GPe indirectly inhibits GPi
So when GPe is inhibited it is releasing GPi to send inhibitory signals to thalamus
Causes thalamus to stop sending excitatory signals to motor cortex
Decrease in movement

Question 5

Indirect inhibition of GPi

Answer 5

Message relayed from Gpe to GPi via STN
GPe usually inhibits STN so when GPe is inhibited it releases STN from inhibition
STN sends excitatory signals to GPi
GPi more active, inhibiting thalamus

Question 6

Dopamine effect on indirect pathway

Answer 6

Secreted by SN and binds to d2 receptors on striatum
Causes striatal neurones to decrease inhibitory message to GPe
GPe free to carry out normal response and inhibit GPi
Thalamus dis-inhibited
More movement

Question 7

Precursors for direct and indirect pathways

Answer 7

Direct - dynorphin

Indirect - enkephalin

Question 8

What kind of neurones are in striatum

Answer 8

Medium spiny neurones

Question 9

Which parts of thalamus does GPi send to?

Answer 9

Ventral anterior and ventral lateral nuclei of the dorsal thalamus