anatomy and function of the basal ganglia Flashcards
Outline the anatomy of the basal ganglia
caudate nucleus: the most superior aspect of the basal ganglia
putamen: sits inferiorly to the caudate nucleus
globus pallidus: sitting behind the putamen and on the medial edge
thalamus: sitting behind the globus pallidus and it isn’t technically part of the basal ganglia.
describe the function of the basal ganglia
to interface with the cortex to perform a filtering function for your movements
input into the basal ganglia first come into the striatum which is the caudate and putamen together and inputs go into the pallidum and goes to the thalamus which releases signals back out into the cerebral cortex and a loop system is created to filter motor function.
What is glutamate and GABA
glutamate: a primary excitatory neurotransmitter in the brain
inhibitory: a primary excitatory neurotransmitter in the brain
Outline the direct pathway through the basal ganglia and how it ensures perfect movement control
depends on the balance of NTM
first, a plan comes from the cortex to the striatum via glutamatergic excitatory connections. Then we go from striatum to pallidum and the link comes specifically to the internal segment in the direct pathway. The link is inhibitory in nature and GABA is used.
next stage of the pathway is an output from the internal segment of the pallidum to the thalamus which is also inhibitory and we get double inhibition.
describe the double inhibition in the direct pathway
the striatum inhibits the GPi which inhibits the thalamus but due to being inhibited in itself, GPi can no longer have an inhibiting effect on the thalamus. this means the thalamus is now active which sends a signal back to cortex due to being excitatory and promotes the production of movement.
Outline the indirect pathway through the basal ganglia
this pathway is used when you need to not move
from the cortex, there are excitatory signals to striatum but in another part of the striatum and it synapses onto the external globus pallidus, the output is into the subthalamic nucleus and now there is double inhibition.
because GPe is being inhibited the inhibitory effect on STN is reduced and now it can excite GPi which then sends inhibitory signals to the thalamus and because it’s being inhibited no signals are being sent back to the cortex and as a result, no movement is made.
Pathways summary
cortex —-> striatum are excitatory
striatum outputs —> inhibitory
thalamus—> cortex excitatory
the inhibition of thalamus prevents movement
reducing inhibition of thalamus facilitates movement
What is the function of the substantia nigra
The key regions of the brain that releases dopamine to the striatum. More activity in the direct and less in the indirect pathway.
Outline the role acetylcholine in movement
there is a small population of interneurons in striatum and they tune up and modulate the actions in that area, acetylcholine decreases the activity of dopamine, more activity in the indirect pathway and less in the direct.
