neuro exam (basal ganglia)

What is the main role of the basal ganglia in motor control?

To modulate upper motor neurons for smooth initiation and execution of movement (not direct control of lower motor neurons).

Does the basal ganglia have direct connections to lower motor neurons?

No — it influences movement indirectly by modulating upper motor neurons via feedback loops.

Name the four major motor components of the basal ganglia.

Striatum, Globus Pallidus, Subthalamic Nucleus, Substantia Nigra.

What structures make up the striatum?

Caudate nucleus, putamen, nucleus accumbens

What are the two parts of the globus pallidus?

External (GPe) and internal (GPi) segments.

What are the two divisions of the substantia nigra?

Pars compacta (dopaminergic) and pars reticulata (GABAergic, functionally like GPi).

What is the basal ganglia’s role in movement selection?

It facilitates intended movements while suppressing competing or unwanted ones.

What happens to the firing rate of basal ganglia neurons during movement?

It changes during initiation, performance, and cessation — reflecting movement control.

How is the basal ganglia involved in learning?

It supports procedural learning and habit formation by signaling reward and prediction errors.

Which structure signals “error” or reinforcement learning?

The striatum (specifically the ventral and dorsal regions)

From where does the striatum receive most of its input?

From all association cortices via the corticostriatal pathway.

What type of neurons are medium spiny neurons (MSNs)?

GABAergic inhibitory projection neurons (≈80–95% of striatal neurons).

Where do MSNs project to?

Putamen → Globus pallidus

Caudate → Substantia nigra.

What is the main neurotransmitter used by the basal ganglia network?

GABA (inhibitory). Glutamate is excitatory input

dopamine is modulatory.

What does “disinhibition” mean in the basal ganglia?

Inhibiting an inhibitory neuron → allows movement initiation (thalamus released from tonic inhibition).

What is the effect of the direct pathway?

Disinhibits the thalamus → facilitates movement.

What is the effect of the indirect pathway?

Increases inhibition of thalamus → suppresses movement.

Which receptors does dopamine act on, and what is its net effect?

D1 (stimulates direct) and D2 (inhibits indirect) → both promote movement overall.

What are three hallmark motor symptoms of basal ganglia disorders?

Tremor/involuntary movement, abnormal posture/tone, and slowness (bradykinesia).

What are the two main types of movement dysfunctions?

Hypokinesia (reduced movement, e.g., Parkinson’s) and hyperkinesia (excess movement, e.g., Huntington’s).

What causes Parkinson’s disease?

Loss of dopaminergic neurons in substantia nigra pars compacta → decreased activation of the direct pathway.

What causes Huntington’s disease?

Degeneration of striatal neurons in the indirect pathway → excessive movement (chorea).

If the GPi and SNr are tonically active, what happens when the striatum inhibits them?

Thalamus is disinhibited → movement is initiated.

If dopamine release decreases (e.g., in Parkinson’s), how are pathways affected?

Direct pathway underactive (↓ movement), indirect pathway overactive (↑ inhibition) → bradykinesia.

What would happen if the subthalamic nucleus is damaged (e.g., hemiballismus)?

Decreased excitatory drive to GPi → reduced inhibition of thalamus → hyperkinetic movements.

Besides motor control, what other functions involve the basal ganglia?

Emotion (via limbic loop), memory, and motivation through nucleus accumbens.