Grey matter

Grey matter (or gray matter) is a major component of the  central nervous system, consisting of nerve cell bodies, glial cells (astroglia and oligodendrocytes), capillaries, and short nerve cell extensions/processes (axons and dendrites).

Composition
Grey matter is composed of unmyelinated neurons as opposed to white matter (myelinated neurons). It has a grey brown color which comes from the capillary blood vessels and the neuronal cell bodies.

Distribution
Grey matter is distributed at the surface of the cerebral hemispheres (cerebral cortex) and of the cerebellum (cerebellar cortex), as well as in the depth of the cerebral (thalamus; hypothalamus; subthalamus, basal ganglia - putamen, globus pallidus, nucleus accumbens; septal nuclei), cerebellar (deep cerebellar nuclei - dentate nucleus, globose nucleus, emboliform nucleus, fastigial nucleus), brainstem (substantia nigra, red nucleus, olivary nuclei, cranial nerve nuclei) and spinal white matter (anterior horn, lateral horn, posterior horn).

Function
The function of grey matter is to route sensory or motor stimulus to interneurons of the CNS in order to create a response to the stimulus through chemical synapse activity. Research has shown that the amount of gray matter in a brain is positively correlated with human intelligence. (Andreason & Others, 1994)

Grey matter structures (cortex, deep nuclei) process information originating in the sensory organs or in other grey matter regions. This information is conveyed via specialized nerve cell extensions (long axons), which form the bulk of the cerebral, cerebellar, and spinal white matter.