ABSTRACT
A cross-sectional diagram of the spinal cord can be marked with an approximate line dividing sensory and motor functions (Fig. 3). Structures dorsal to the central canal are more likely to be involved in the conduction and processing of sensory information, whereas structures ventral to the central canal are more likely to be involved in motor functions. Where spinal nerves enter and emerge from the spinal cord, one can see their dorsal and ventral roots. The dorsal root of a spinal nerve carries fibers that conduct sensory information, and the ventral root carries fibers that conduct motor information. Just before the dorsal root enters the spinal cord, there exists a small swelling or ganglion. This is the dorsal root ganglion (DRG), containing the cell bodies of those neurons that have processes extending out to the periphery, and ending in a specialized sensory receptor. These neurons are known as primary sensory neurons. The cells in the DRG also have processes that extend towards the spinal cord. Some of these processes enter the dorsal horn of spinal cord gray matter and synapse with the cell bodies of second-order sensory neurons. Others ascend to the medulla before synapsing with the cell bodies of other second-order sensory neurons (Fig. 3). After synapses between primary and second-order sensory neurons have been made, decussation (crossing over) of fibers occurs (see below for the implications of this).
