The formation of the spinal nerve from the dorsal and ventral roots. (Grey matter labeled at center right.)
Grey matter or gray matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and myelinated as well as unmyelinated axons), glial cells (astroglia and oligodendrocytes), synapses, and capillaries. Grey matter is distinguished from white matter, in that grey matter contains numerous cell bodies and relatively few myelinated axons, while white matter is composed chiefly of long-range myelinated axon tracts and contains relatively very few cell bodies. The color difference arises mainly from the whiteness of myelin. In living tissue, grey matter actually has a very light grey color with yellowish or pinkish hues, which come from capillary blood vessels and neuronal cell bodies.
Grey matter is distributed at the surface of the cerebral hemispheres (cerebral cortex) and of the cerebellum (cerebellar cortex), as well as in the depths of the cerebrum (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).
Grey matter is also present in the spinal cord. It travels down the spinal cord in three grey columns. The grey matter in the spinal cord is distributed in an "H" shape. The forward-facing tip is called the anterior horn, and the tip facing the back is called the posterior horn). The grey matter on the left and right side is connected by the gray commissure. The grey matter in the spinal cord consists of interneurons, as well as cell bodies.
Grey matter undergoes development and growth throughout childhood and adolescence.
Grey matter contains most of the brain's neuronal cell bodies. The grey matter includes regions of the brain involved in muscle control, and sensory perception such as seeing and hearing, memory, emotions, speech, decision making, and self-control. 
The grey matter in the spinal cord is split into three grey columns.
- The anterior grey column contains motor neurons. These synapse with interneurons and the axons of cells that have travelled down the pyramidal tract. These cells are responsible for the movement of muscles.
- The posterior grey column contains the points where sensory neurons synapse. These receives sensory information from the body, including fine touch, proprioception, and vibration. This information is sent from receptors of the skin, bones, and joints through sensory neurons whose cell bodies lie in the dorsal root ganglion. This information is then transmitted in axons up the spinal cord in spinal tracts, including the dorsal column-medial lemniscus tract and the spinothalamic tract.
- The Lateral grey column is the third column of the spinal cord.
The grey matter of the spinal cord can be divided into different layers, called Rexed laminae. These describe, in general, the purpose of the cells within the grey matter of the spinal cord at a particular location.
Interneurons present in the grey matter of the spinal cord
Rexed laminae groups the grey matter in the spinal cord according to its function.
Volume and cognition in elderly people
Significant positive correlations have been found between grey matter volume in elderly persons and measures of semantic and short-term memory. No significant correlations with white matter volume were found. These results suggest that individual variability in specific cognitive functions that are relatively well preserved with aging is accounted for by the variability of grey matter volume in healthy elderly subjects.[non-primary source needed]
Volume associated with bipolar disorder
Some structural differences in grey matter may be associated with psychiatric disorders. There was no difference in whole-brain grey matter volume between patients with bipolar I disorder and healthy controls. Subjects with bipolar I disorder had smaller volumes in the left inferior parietal lobule, right superior temporal gyrus, right middle frontal gyrus, and left caudate. Only the volume of the right middle frontal gyrus was correlated with duration of illness and the number of episodes in patients.[non-primary source needed]
Effects of smoking
Older smokers lose grey matter and cognitive function at a greater rate than non-smokers. Chronic smokers who quit during the study lost fewer brain cells and retained better intellectual function than those who continued to smoke.[unreliable medical source]
In the current edition of the official Latin nomenclature, Terminologia Anatomica, substantia grisea is used for English grey matter. The adjective grisea for grey is however not attested in classical Latin. The adjective grisea is derived from the French word for grey, gris. Alternative designations like substantia cana  and substantia cinerea  are being used alternatively. The adjective cana, attested in classical Latin, can mean grey, or greyish white. The classical Latin cinerea means ash-colored.
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