S2 Basal Ganglia Flashcards
What is the primary function of the basal ganglia?
To provide a feedback mechanism to the cerebral cortex for the initiation and control of the motor response.
Anatomically, what are the four parts to the basal ganglia?
Their subdivisions?
Caudate nucleus, lentiform nucleus, amygdala, claustrum.
Lentiform nucleus = putamen + globus pallidus.
Functionally, what are the five parts to the basal ganglia?
Caudate nucleus. Putamen. Globus Pallidus (interna + externa) Sub thalamus. Substantia nigra (pars compacta, pars reticulata).
What does the Pars compacta contain?
Melanin.
Dopamine.
What is the Pars reticulata functionally part of?
Globus pallidus interna.
Together, the caudate nucleus and the putamen are known as the…
Striatum.
What is the function of the direct pathway?
Facilitate movements that are appropriate and necessary.
What is the function of the indirect pathway?
Inhibits unwanted behaviour and movement.
Very simplified: inhibits extensors to allow flexors to contract.
Describe the direct pathway:
Excitatory neurone from the cortex to the striatum.
This increases the effect of inhibitory neurons from striatum to Globus pallidus interna.
This decreases the inhibitory action of the neurone to the thalamus, allowing the thalamus to EXCITE the cortex.
Describe the indirect pathway:
Excitatory neurone from the cortex to the striatum.
This increases the effect of inhibitory neurons from striatum to Globus pallidus externa.
This decreases the inhibitory action of the neurone to the Subthalamus.
New neurone excites the GPi, which increases the inhibition the GPi provides to the thalamus.
Inhibition of the thalamus means cortex is INHIBITED.
What is the role of the substantia nigra pars compacta?
How?
INITIATE movement. Releases dopamine.
Excites direct pathway via D1 receptors at striatum.
Inhibits indirect pathway via D2 receptors at striatum.
What happens with damage to the substantia nigra pars compacta?
Can’t initiate movement.
What happens after damage to the basal ganglia?
Contralateral slow movement, poor initiation, rigidity and tremor.
What is the most common disease of the basal ganglia?
Disruption of nigrostriatal input - Parkinson’s.
What are the two physiological mechanisms for hyperkinetic movement disorders? (Huntington’s)
Degeneration of sub thalamic nucleus.
Degeneration of inhibitory fibres from stratum to globus pallidus.
Both result in a lack of an indirect pathway.
