Motor control - Striatum

11 important questions on Motor control - Striatum

What is the circuit of the extrapyramidal system?

Neocortex -> striatum -> globus pallidus -> a thalamic nucleus -> (pre)motor cortex -> 2nd motor neurons/interneurons

Which neurotransmitters are used in the extrapyramidal circuit?

GABA (inhibitory)
Glutamate (excitatory)

Which two subcircuits excist in the extrapyramidal system?

To the substantia nigra (from striatum)
To the subthalamic nucleus (from the pallidum)
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Which NT are used in the subcircuit from the striatum to the substantia nigra?

GABA (inhibitory)
Dopamine (in this case excitatory)

Which NT are used in the subcircuit from the globus pallidus to the subthalamic nucleus?

GABA (-)
Glutamate (+)

What is the function of the globus pallidus in the striatal circuit?

It is the gate of the whole system. If the pallidum is active, all other inputs will not reach the thalamic nucleus. The globus pallidus is inhibited by the striatum, which results in less inhibition of the thalamic nucleus and other signals can pass to the motor cortex.

What happens when the subthalamic nucleus is defect?

The pallidum is not active enough (pallidum hypoactive). That means the gate is not present / less present and other inputs will reach the thalamic nucleus (thalamic nucleus hyperactive) and thus is the (pre)motor cortex overstimulated.

What is the result of a defect in the subthalamic nucleus?

Hyperkinetic disorders

- Ballism -> finging movements of extremities, throwing/kicking like
o Subthalamic nucleus defect at one side = hemiballism
o Dissapears over night, because there is no tone of the muscles
o Hemiballism can largely dissappear spontaneously
§ Other subthalamic nucleus takes over the control (plasticity of brain)

What is the function of the substantia nigra?

It excites the striatum. The striatal neurons are very stable and therefore hard to excite by the cortex. The dopaminergic excitation lowers the threshold, which increases the thalamic drive of the MC. 

What if the dopaminergic neurons in the substantia nigra degenerate?

The striatum is less excited. This means that the striatum cannot be excited by the cortex and the continously inhibition of the pallidum dissapears. The pallidum becomes hyperactive and the (pre)motor cortex is understimulated

What is the result if the substantia nigra degenerates?

This results in hypokinetic disorders.
- Parkinsons’ disease

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