Basal Nuclei and Ganglia Function

Study Notes

Basal nuclei are a collection of masses of gray matter situated within each cerebral hemisphere.
They play an important role in the control of posture and voluntary movement.
They have no direct input or output connections with the spinal cord.

The basal ganglia are functionally closely related to the subthalamic nuclei, the substantia nigra, and the red nucleus.
The basal ganglia consist of the caudate nucleus, the lentiform nucleus, and the amygdaloid nucleus.

The caudate nucleus is a large C-shaped mass of gray matter that lies lateral to the thalamus.
It consists of a head, body, and tail, which terminates anteriorly in the amygdaloid nucleus.

The amygdaloid nucleus is situated in the temporal lobe close to the uncus.
It is considered part of the limbic system and can influence the body's response to environmental changes through its connections.

The lentiform nucleus is a wedge-shaped mass of gray matter consisting of a darker lateral portion (putamen) and an inner lighter portion (globus pallidus).
It is related laterally to the external capsule, which separates it from the claustrum.

The claustrum is a thin sheet of gray matter separated from the lateral surface of the lentiform nucleus by the external capsule.
Its function is unknown.

The basal ganglia have three primary functions: starting movement, stopping movement, and modulating movement.
They modify the motor plan and send it back to the motor cortices.
The motor cortices decide the voluntary movement of a muscle and send information to the lower motor neurons.

The basic components of the basal ganglia are the caudate nucleus, putamen, globus pallidus, thalamus, ventral anterior nucleus, ventral lateral nucleus, subthalamic nucleus, and substantia nigra.

The direct pathway involves the thalamus sending action potentials to the motor cortex, which results in increased motor activity.
The nigrostriatal pathway amplifies the direct pathway by releasing dopamine, which binds to D1 receptors, increasing stimulation of the striatum.

The nigrostriatal pathway releases dopamine, which binds to D1 receptors, increasing stimulation of the striatum.
This results in increased action potentials towards the globus pallidus internus, increased GABA released, and decreased action potentials towards the thalamus.

The indirect pathway involves the motor cortex sending glutamatergic neurons to the striatum, which becomes hyperactive and sends action potentials towards the globus pallidus externus.
The globus pallidus externus releases GABA, which inhibits the subthalamic nucleus, resulting in decreased action potentials towards the globus pallidus internus.
The globus pallidus internus then sends decreased action potentials towards the thalamus, resulting in decreased GABA released and increased stimulation of the thalamus.