The spinal cord is a long, nearly cylindrical bundle of nervous tissue which is part of the Central Nervous System and continuous with the medulla oblongata. The spinal cord is composed of myelinated axons which extend from the cerebral cortex, forming its external white matter, and neurons bodies that are clustered together in the center in an H-like pattern of grey matter. Encapsulated in the vertebral column, the spinal cord has two functions: it transmits nervous signals between the brain and the rest of the body and independently controls numerous reflexes and central pattern generators.
The spinal cord is 45 cm long in men and 43 cm long in women, is enlarged in the cervical and lumbar regions. The spinal cord white matter envelops the grey matter, which has an H-like appearance. The spinal cord is divided into 31 segments as 31 pairs of spinal nerves (right and left pairs) branch out of each segment. Each nerve has a ventral (anterior), and a dorsal (posterior) root; the latter can be distinguished by the presence of an oval swelling, the spinal ganglion, which contains numerous nerve cells. 6–8 motor nerve rootlets spring from right and left ventro lateral sulci in an orderly manner. Nerve rootlets get together to form nerve roots. Likewise sensory nerve rootlets form off right and left dorsal lateral sulci and form sensory nerve roots. The ventral (motor) and dorsal (sensory) roots combine to form spinal nerves(mixed; motor and sensory), one on each side of the spinal cord.
The spinal cord is divided into cervical, thoracic, lumbar and sacral regions, corresponding with the attachments of the different groups of nerves. There are 8 pairs of cervical spinal nerves, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.