Task 2 - the Basal Ganglia Flashcards
(14 cards)
What is the main function of the basal ganglia?
Decides what movement to make and which not to make
What are the inout zones of the basal ganglia?
Caudate and putamen = striatum
–> throuhg medium spiny neurons
What are the output zones of the basal ganglia?
Globus pallidus and substantia nigra
–> also through medium spiny neurons
What are these medium spiny neurons?
Dominate in the striatum (95%) and interact to some degree through local GABAergic collaterals that activate GABA channels.
The MSNs have a very high convergance. Why is that?
Because the dorsal striatum has approx. 100 million neurons, whereas globus pallidus only about 700000
Where do MSNs project to?
To Substantia Nigra, Pars reticulata and Globus pallidus
What is the influence of Substantia nigra and Pars reticula?
When they get signals, they influence the head and eye movement
Explain direct pathway for initiation of movement
Cortex → activates Medium spiny neurons → inhibition of internal segment of globus pallidus → disinhibition (i.e. release of inhibition) of VA/VL thalamus → initiation of movement
What is the role of the substantia nigra and subthalamic nucleus in the direct pathway?
When STN sends excitatory signals to Substantia nigra, the latter ine send dopamine projections to the D1 receptors in the MSNs going from striatum to Globus Pallidus and therefore inhibiting it much more
–> the help create finer movements
Explain the indirect pathway for inhibition of unwanted movement
Medium spiny neurons (Dorsal striatum) → inhibits external segment (the lateral part) of the globus pallidus → inhibitory signals to (1) internal segment of globus pallidus and (2) subthalamic nucleus (of ventral thalamus)
Activity in subthalamic nucleus also comes from cerebral cortex → excitatory (glutamate-based) activation of Globus pallidus and Substantia nigra → activation of globus pallidus internal segment (to inhibit Va/VL thalamus)→ suppression of movement that is not directed by the cortex
What is hypokinesia?
Reduced dopamine innervation of the striatum. The consequences are difficulties initiating different motor patterns
What is hyperkinesia?
Enhanced striatal dopamine activity. The consequences are unintended activation of motor conductances.
What is an example of hypokinesia?
Parkinson’s desease
What is an example of hyperkinesia?
Huntington’s disease
