White matter of spinal cord

At a glance

English

White matter of spinal cord

Latin (TA2)

Substantia alba medullae spinalis

System

Brain and spinal cord

Region

Whole body

Side

Single, on the midline

About the white matter of spinal cord

In a cross-section the spinal cord is oval, flattened from front to back, with a central butterfly of grey matter surrounded by a thick mantle of white matter. The grey matter holds nerve cell bodies in three columns and encloses the central canal, a narrow channel filled with cerebrospinal fluid that continues upward into the fourth ventricle. The white matter owes its pale colour to the myelin wrapping its axons; it contains almost no cell bodies.

Two midline grooves mark the cord. Behind is the shallow posterior median sulcus, carried inwards by a thin septum; in front is the deeper anterior median fissure, which holds the anterior spinal artery. The dorsal and ventral rootlets enter and leave along lines on each side, and together with these grooves they divide the white matter of each half into three funiculi: posterior, lateral and anterior. In front of the central canal a narrow band, the anterior white commissure, carries fibres from one side to the other.

Each funiculus contains bundles of fibres, or tracts, with particular jobs. The posterior funiculus carries fine touch, vibration and position sense in the gracile and cuneate fasciculi. The lateral funiculus contains the lateral corticospinal tract for voluntary movement, the spinocerebellar tracts and the lateral spinothalamic tract for pain and temperature. The anterior funiculus carries the anterior corticospinal, vestibulospinal and anterior spinothalamic tracts. Short propriospinal fibres next to the grey matter link one segment to another.

The amount of white matter increases towards the top of the cord, because more fibres join ascending tracts and more descending fibres are still present. Diseases that strip myelin, such as multiple sclerosis, and compression of the cord by disc or tumour, produce symptoms that follow the layout of these tracts, which is why the pattern of weakness and sensory loss can locate a lesion.

Function and supply

Function

Conducts ascending sensory signals to the brain, descending motor and autonomic commands to the grey matter, and short links between segments of the cord.

Blood supply

The anterior spinal artery supplies the anterior and lateral funiculi deep to the surface; the posterior spinal arteries supply the posterior funiculi; a surface network, the arterial vasocorona, feeds the outermost rim.