Basal ganglia Flashcards
(13 cards)
What is the primary function of the direct pathway in the basal ganglia?
The direct pathway facilitates movement by disinhibiting the thalamus, which increases excitatory input to the primary motor cortex
What neurotransmitter does the cerebral cortex use to excite the striatum?
Glutamate (excitatory neurotransmitter)
Which dopamine receptor subtype is primarily involved in the direct pathway, and what effect does dopamine have on it?
The D1 receptor; dopamine excites D1-expressing medium spiny neurons, enhancing the direct pathway and facilitating movement
In the indirect pathway, what happens to the activity of the subthalamic nucleus (STN) when the globus pallidus externus (GPe) is inhibited?
The STN is disinhibited (its activity increases) because it is normally inhibited by the GPe.
What role does dopamine play in the indirect pathway via D2 receptors?
D2 receptors are located on indirect pathway neurons in the striatum.
Activated by dopamine from the substantia nigra pars compacta (SNc).
Inhibitory (Gi-coupled) — they reduce activity of indirect pathway neurons.
Result: Decreased inhibition of movement → facilitates motor activity.
In Parkinson’s disease: less dopamine → less D2 activation → increased movement suppression.
Describe the overall effect of the indirect pathway on movement.
The indirect pathway suppresses movement by increasing inhibition of the thalamus, leading to decreased excitation of the motor cortex
What neurotransmitter and receptor are involved in the inhibitory projection from the striatum to the globus pallidus?
GABA is the inhibitory neurotransmitter, acting on GABA receptors
How does loss of dopamine in Parkinson’s disease affect the direct and indirect pathways?
Loss of dopamine reduces stimulation of the direct pathway (via D1 receptors), making it less active, and reduces inhibition of the indirect pathway (via D2 receptors), making it overactive. This results in excessive inhibition of the thalamus and decreased movement (hypokinesia)
Which neuropeptides are co-expressed with D1 and D2 receptor-expressing medium spiny neurons?
D1 MSNs co-express substance P and dynorphin
D2 MSNs co-express enkephalin
Explain how disinhibition of the thalamus occurs in the direct pathway.
In the direct pathway, the striatum inhibits the GPi, which normally inhibits the thalamus. Inhibiting the GPi reduces its inhibitory output to the thalamus, thus disinhibiting the thalamus, allowing it to excite the motor cortex
Huntington’s is an autosomal dominant disease caused by mutation in HTT gene causing neurotoxic aggregates of huntingtin to form. What part of basal ganglia degenerates in Huntington’s?
These neurotoxic huntingtin aggregates cause degeneration of corpus striatum (caudate nucleus + putamen)
what causes dystonia in huntingtons?
Dystonia in Huntington’s is caused by degeneration of striatal neurons, especially in the INDIRECT pathway of the basal ganglia.
This leads to reduced inhibition of the thalamus, resulting in abnormal and excessive activation of the motor cortex, which causes involuntary muscle contractions and abnormal postures.
In Parkinson’s, what happens to the D1 and D2 receptors?
In Parkinson’s disease, the degeneration of dopaminergic neurons in the SNc leads to:
Reduced D1 receptor stimulation: Diminished activation of the direct pathway, leading to less movement facilitation.
Reduced D2 receptor stimulation: Less inhibition of the indirect pathway, resulting in increased movement suppression
