Axons in the central nervous system, including those of the upper motor neurons, transmit information up and down the spinal cord to connect the brain above to most of the peripheral axons that are connected to the limbs and torso. The peripheral axons of each dermatome and myotome are attached to their level of the spinal cord via the spinal nerves. Each level of the spinal cord has peripheral axons connecting horizontally at that level, as well as vertical axons connecting the brain above to all the spinal cord levels below.
A spinal cord abnormality is called myelopathy. Myelopathy may involve somatosensory, upper motor neuron, or autonomic dysfunction for parts of the limbs or torso connected to the affected spinal cord levels, as well as for all the levels below the lesion if they are disconnected from the brain above. For example, a lesion about halfway up the spinal cord may cause abnormalities of both legs and the lower torso, while a lesion near the top of the spinal cord may affect all four limbs and the entire torso. Common autonomic abnormalities of myelopathy involve loss of control of urination and defecation.
Next:
Introduction to Neurology 