Chapter 20 - Autonomic Function in the Isolated Spinal Cord

Abstract

This chapter reviews the autonomic function in the isolated spinal cord. The autonomic nervous system is divided into the parasympathetic and sympathetic nerves. Efferent neuronal cells of the autonomic nervous system that are located in either the brain stem or the spinal cord are termed as preganglionic neurons. These cells project preganglionic fibers that synapse upon postganglionic neurons located in various ganglia and plexuses outside the central nervous system (CNS). The postganglionic neuron, in turn, projects a postganglionic fiber to a specific target organ or effector tissue. Cardiac preganglionic sympathetic neurons in humans are found in spinal cord segments T-l to T-4, whereas the preganglionic neurons for the peripheral vasculature are found mainly in spinal cord segments T-l to L-2. A small proportion of the neurons in the IML column are interneurons. The cholinergic sympathetic preganglionic neurons (SPNs) innervate the adrenal medulla or noradrenergic neurons in sympathetic ganglia, which, in turn, innervate blood vessels and the heart. The heart is also innervated by three branches of the vagus nerve: (1) superior cervical cardiac, (2) inferior cervical cardiac, and (3) thoracic cardiac. Preganglionic efferent parasympathetic axons in these branches form synapses with neurons in the ganglia of the cardiac plexus.