Extrapyramidal System

A collection of nerve fibres connecting two masses of grey matter within the central nervous system is referred to as a tract, system or pathway. They are often referred to as fasciculi (bundles) or lemnisci (ribbons).

Tracts may be ascending or descending, and are usually named after the masses of grey matter they interconnect. Therefore, a pathway that originates in the cerebral cortex and descends to terminate in the spinal cord is referred to as a corticospinal tract, while a tract ascending from the spinal cord to the thalamus is called the spinothalamic tract.

The extrapyramidal pathway or system is an important part of the motor system of the body and can also be described as the descending motor pathway, whose fibres pass through the tegmentum rather than the medullary pyramid. The extrapyramidal pathway is actively involved in the initiation and selective activation of movements, along with their coordination.

Major contribution in the extrapyramidal motor system are the nuclei of the basal ganglia. Other structures which are involved include substantia nigra, red nucleus, subthalamic nucleus, mesencephalic reticular formation and the cerebellum. The extrapyramidal system is also often described as the motor-modulation system.

The term “extrapyramidal” is to distinguish between the effects of basal ganglia diseases and those of damage to the “pyramidal” system, even though there is an intertwine of a functional relationship between the two systems. Extrapyramidal system is polysynaptic in nature with many synapses within the brainstem.