Physiology of the Spinal Cord

Abstract

Using a microelectrode, it is a straightforward procedure to record the responses of single neurons within the spinal cord gray matter to stimulation of primary afferents (Willis and Coggeshall, 2004). Interneurons in the dorsal horn can be distinguished from afferent axons by their response properties and by the configuration of their action potentials. For example, interneurons can generally be activated by a number of different types of sensory receptors, whereas a primary afferent fiber would belong to just a single kind of sense organ. The extracellular action potentials of interneurons are predominantly negative (Fig. 2.1A), whereas those of afferent axons are chiefly positive in sign (because they are usually recorded just outside an internode and only rarely outside a node of Ranvier). Intracellular recordings from dorsal horn interneurons reveal postsynaptic potentials in response to stimulation of primary afferent fibers (Fig. 2.1B, upper trace). In the ventral horn, a motor neuron can be identified by antidromic activation following stimulation of its motor axon.