Anatomy and function of the basal ganglia

Question 1

BASAL GANGLIA ANATOMY

i) what is the main function of the basal ganglia?
ii) what three structures is it composed of?
iii) which structure is not technically part of the BG but has densley interwoven function
iv) label structures A-G

Answer 1

i) acts as a filter
ii) made of caudate, globus pallidus and putamen
iii) the thalamus

iv) A - caudate nucleus
B - putamen
C - thalamus
D - Globus pallidus
E - substantia nigra
F - sub thalamic nucleus
G - hypothalamus

Question 2

TERMINOLOGY

i) what two structures if the globus pallidus split into?
ii) what is the pallidum?
iii) which two structures make up the lentiform nucleus
iv) which three structures make up the corpus striatum? what is this divided by?
v) what is the neostriatum aka dorsal striatum?

Answer 2

i) pars externa and pars interna
ii) pallidum = GP internal and external
iii) lentiform nuc = putamen and GP

iv) corpus striatum = caudate + putamen + pallidum
- divided by the internal capsule

v) neostriatum = caudate + putamen

Question 3

BASAL GANGLIA - INTERFACE WITH THE CORTEX

i) what happens to movement plans that come into the BG?
ii) where does information go after the BG? what does this structure then do to signal back to the cortex?

Answer 3

i) movement plans are filtered in the BG

ii) BG > thalamus
- thalamus then sends movement signals back to the cortex

Question 4

BASAL GANGLIA LOOPS

name loops A-D

Answer 4

A = motor loop
B = oculomotor loop
C = prefrontal loop
D = limbic loop

Question 5

THE DIRECT PATHWAY

i) what does it facilitate?
ii) what is NT A between cortex and striatum?
iii) what is NT B between the striatum and the GPi
iv) are the outputs from GPi to the thalamus inhibitory or excitatory?
v) what does inhibition of the GPi cause in relation to movement? explain

Answer 5

i) movement
ii) Glutamate
iii) GABA
iv) GPi to thalamus are inhibitory
v) inhibition of GPi causes movement as there is disinhibition of the thalamus so it can therefore send excitatory impulses to the cortex

Question 6

THE INDIRECT PATHWAY

i) what does it cause?
ii) what is NT A between cortex and striatum? what is NT B between striatum and GPe?
iii) when the GPe is stimulated by the striatum is there increased or decreased activity?
iv) does the GPe normally inhibit or activate the STN?
v) does the STN inhibit or activate the GPi normally?
vi) what effect does the GPi have on the thalamus? what does this ultimately cause?

Answer 6

i) inhibtion of movement

ii) A = glutamate
B = GABA

iii) striatum inhibits GPe = decreased activity
iv) GPe normally inhibits the STN
v) the STN excites the GPi normally
vi) GPi inhibits the thalamus therefore decreases its activity and it cant signal to the cortex so this decreases movement

Question 7

THE HYPERDIRECT PATHWAY

i) what does it do?
ii) does it pass through the BG?
iii) where do signals pass to from the cortex? what does this cause?
iv) does the STN activate or inhibit the GPi? and what does this cause?
v) give an example of a situation that this may be activated in?

Answer 7

i) pauses movement - emergency brakes
ii) no it bypasses the BG
iii) cortex straight to the STN which causes rapid activation of the STN
iv) STN activates the GPi which inhibits the thalamus therefore pausing movement
v) may happen when crossing road and a car suddenly comes towards you

Question 8

which movement pathway is this?

Answer 8

hyperdirect

Question 9

PATHWAYS SUMMARY

i) cortex > striatum = excite or inhib?
ii) output from striatum = excite or inhib?
iii) thalamus > cortex = excite or inhib
iv) what does inhibition of the thalamus cause?

Answer 9

i) excite
ii) inhib
iii) excite
iv) inhibition of thalamus causes prevention of movement

Question 10

STRIATUM NEURONS AND DOPAMINE

i) which structure releases DA to the basal ganglia?
ii) what type of neurons are found in the striatum and have specialised DA receptors? where do they project to?
iii) which type of receptors to neurons in the direct pathway have? what happens when DA stimulates these?
iv) which type of receptors to neurons in the indirect pathway have? what happens when DA stimulates these?

Answer 10

i) substantia nigra

ii) medium spiny neurons are found in the striatum and have different DA receptors
- project to the globus pallidus

iii) direct pathway = D1 receptors
- DA stimulation will ramp up medium spiny neuron excitation

iv) indirect pathway = D2 receptors
- DA stimulation will dampen down MSN excitation

Question 11

STRIATAL NEURONS AND ACH

i) which type of striatal neurons use ACH? do they project out of the striatum?
ii) what effect does Ach have on direct D1 receptors?
iii) what effect does Ach have on indirect D2 receptors
iv) what is the effect of Ach in relation to DA?
v) which way does Ach tip the balance for movement?

Answer 11

i) striatal interneurons use Ach and they dont project out the striatum
ii) Ach dampens excitation at D1 receptors
iii) Ach increases excitation at D2 receptors
iv) Ach opposes the effects of DA
v) Ach tips the balance in favour of movement prevention

Question 12

PATHWAY BALANCE

I) what does the balance of activity beftween the two medium spiny neuron populations determine?

ii) which two NTs regulate this balance
iii) what else can influence this?

Answer 12

i) determines the likelihood of a movement taking place
ii) regulated by DA and Ach
iii) also influenced by cortical inputs to the striatum