24. Define the terms grey and white matter, fasciculus,tract, commissure, pathway, chiasm, decussation,nucleus, ganglion and cortex.

Define grey matter

the darker tissue of the brain and spinal cord, consisting mainly of nerve cell bodies and branching dendrites. Non-myelinated

Define White matter

The paler tissue of the brain and spinal cord, consisting mainly of nerve fibres with their myelin sheaths.

Define fasciculus

A bundle of nerve fibres/axons

Define Tract

A bundle of axons within the CNS travelling together

Define comissure

A bundle of nerve fibres connecting the left and right side of the brain

Define Pathway

A route taken by nerve signals through the nervous system

Define chiasm

A place where nerve fibres cross, usually forming an X shaped crossing

Define decussation

When nerve fibres cross from one side to another

Define ,nucleus

A collection of neurone cell bodies inside the CNS

Define , ganglion

A collection of neurone cell bodies outside the CNS

Define Cortex

Outer layer of grey matter covering the brain especially the cerebral hemisphere