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The function of the white matter in the spinal cord is to convey information from the nervous systems to the brain, or from the brain to the systems. The spinal cord is made up of grey matter and white matter. The grey matter is in the middle of the spinal cord, with four horns branching off from each corner that make it resemble the letter H, and surrounded by white matter. The four horns are called the dorsal horn, the lateral horn, the intermediate column, and the ventral horn column. Both white and gray matter contain nerve fiber bundles, called neurons, that convey impulses between the peripheral nervous system and the central nervous system.
The white matter contains neurons that carry the nerve impulses. These neurons are covered in a myelin sheath. The cord links the brain with the rest of the body, via the central nervous system, and sends the information along these nerve fibers to make the body function properly.
The fiber bundles contained in the white matter are called axons. They are coated with myelin, which is mostly lipid tissue filled with capillaries that insulates the axons and helps to speed them along. The fiber bundles contained in the grey matter are called dendrites and are covered with synapses. Axons are grouped into tracts that carry similar information.
Some tracts carry information from the white matter in the spinal cord to the brain and are called ascending tracts. These tracts are responsible for informing the brain what the fingers or other body parts feel. Other tracts travel from the brain to the other parts of the body and are called descending tracts. They might give orders for the muscles to move, or for the internal organs to perform their functions. It is the neurons' function in the spinal cord to convey the information that is either ascending up the tracts, or descending down the tracts.
The grey matter provides the communication between the central nervous system and the peripheral nervous system, which inclues the nerves outside the spinal column that serve other areas of the body. The neurons in the grey matter are unmyelinated, so they travel slower than the myelinated axons in the white matter.