The nerve fibres and cell bodies of the afferent and efferent neurons of the CNS are located in the spinal cord. It is organised segmentally. From cranial to caudal these segments are:
The coccygeal segment (pars coccygealis medullae spinalis) is only rudimentary in humans. It is represented by segment Co1. In the cervical and lumbar segments the spinal cords shows a macroscopically visible increase in diametre due to an increased number of neurons in these segments. These two parts are called intumescentia cervicalis and intumescentia lumbosacralis.