ORGANIZATION AND FUNCTION The autonomic nervous system (ANS) functions largely below the level of consciousness and controls visceral functions. The major differen- ces between the somatic and autonomic nervous systems are given in Table II.1. Like the somatic nervous system, the ANS consists of afferents, centre and efferents. Autonomic afferents Most visceral nerves are mixed nerves and carry nonmyelinated visceral afferent fibres as well. The cell bodies of these afferent fibres are located in the dorsal root ganglion of spinal nerves and in the sensory ganglia (e.g. nodose ganglion of vagus) of cranial nerves. They mediate visceral pain as well as cardiovascular, respiratory and other visceral reflexes. Central autonomic connections There are no exclusively autonomic areas in the CNS; considerable intermixing and integration of somatic and autonomic innervation occurs. The highest seat regulating autonomic functions is in the hypothalamus—posterior and lateral nuclei are primarily sympathetic while anterior and medial nuclei are primarily parasympathetic. Many autonomic centres (pupillary, vagal, res- piratory, etc.) are located in the mid-brain and the medulla in relation to the cranial nerves. The lateral column in the thoracic spinal cord contains cells which give rise to the sympathetic outflow. Autonomic efferents The motor limb of the ANS is anatomically divided into sympathetic and parasympathetic. Many organs receive both sympathetic and parasympathetic innervation and TABLE II.1 Differences between somatic and autonomic nervous system Somatic Autonomic 1. Organ supplied Skeletal muscles All other organs 2. Distal most synapse Within CNS Outside CNS (in ganglia) 3. Nerve fibres Myelinated Pregang.—myelinated Postgang.—non-myelinated 4. Peripheral plexus formation Absent Present 5. Primary efferent transmitter Acetylcholine Acetylcholine, Noradrenaline 6. Effect of nerve section on Paralysis and atrophy Activity maintained, no atrophy isko samjhao achese notes b banana