Definition :
They are masses of grey matter that lie in each cerebral hemisphere deep to the floor of lateral ventricle. Radiating commissural and projection fibers pass between these nuclei.
Types of nuclei :
1. Corpus striatum :
- Caudate nucleus: it is C-shaped having head, body, and tail.
- Head: is continuous with putamen of the lentiform nucleus. It bulges into the anterior horn of the lateral ventricle.
- Body: curves forming part of the floor of the body of lateral ventricle.
- Tail: lies in the roof of inferior horn of lateral ventricle. It is continuous with amygdaloid nuclei.
- Lentiform nucleus: it is like a biconvex lens that enclosed between both internal and external capsules. It is divided into: lense form
- Globus pallidus: medially.
- Putamen: laterally.
N.B:
- Neostriatum = caudate nucleus + putamen of lentiform.
- Paleostriatum = globus pallidus.
Functions :
They are concerned with motor activities:
- subconscious control of skeletal muscle tone and coordination of learned movement patterns.
- Prepare the body posture to suit the movement.
Mechanism of function:
- They alter the motor commands from the cerebral cortex by feed back loop.
- Information from cerebral cortex arrives at caudate nucleus and putamen (neostriatum).
- Then processing occurs in these nuclei and in globus pallidus.
- Most of output of basal nuclei leaves the globus pallidus and synapses in the thalamus.
- Nuclei of thalamus project the information to appropriate areas of the cerebral cortex.
2. Other nuclei :
- Amygdaloid nuclei: they are part of the limbic system.
- Claustrum: a band of grey matter that lies lateral to lentiform nucleus, and separated from it by the external capsule. It is separated from grey matter of the insula by the extreme capsule.