Slide 1

AUTONOMIC NERVOUS SYSTEM Autonomic or visceral effectors—tissues to which autonomic neurons conduct impulses (that is, cardiac and smooth muscle and glandular epithelial tissue) Composed of two divisions—the sympathetic system and the parasympathetic system Autonomic conduction paths Consist of two-neuron relays (that is, preganglionic neurons from the central nervous system to autonomic ganglia, synapses, postganglionic neurons from ganglia to visceral effectors) In contrast, somatic motor neurons conduct all the way from the CNS to somatic effectors with no intervening synapses Slide 2

AUTONOMIC NERVOUS SYSTEM Sympathetic nervous system Structure Dendrites and cell bodies of sympathetic preganglionic neurons are located in the gray matter of the thoracic and upper lumbar segments of the spinal cord Axons leave the spinal cord in the anterior roots of spinal nerves, extend to sympathetic or collateral ganglia, and synapse with several postganglionic neurons whose axons extend to spinal or autonomic nerves to terminate in visceral effectors A chain of sympathetic ganglia is in front of and at each side of the spinal column Functions Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and strong emotions (anger, fear, hate, or anxiety) Group of changes induced by sympathetic control is called the fight-or-flight response Slide 4

AUTONOMIC NERVOUS SYSTEM Parasympathetic nervous system Structure Parasympathetic preganglionic neurons have dendrites and cell bodies in the gray matter of the brainstem and the sacral segments of the spinal cord Parasympathetic preganglionic neurons terminate in parasympathetic ganglia located in the head and the thoracic and abdominal cavities close to visceral effectors Each parasympathetic preganglionic neuron synapses with postganglionic neurons to only one effector Function—dominates control of many visceral effectors under normal, everyday conditions Slide 5

AUTONOMIC NERVOUS SYSTEM Autonomic neurotransmitters Cholinergic fibers—preganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons release acetylcholine Adrenergic fibers—axons of sympathetic postganglionic neurons release norepinephrine (noradrenaline) Autonomic nervous system as a whole Regulates the body’s automatic functions in ways that maintain or quickly restore homeostasis Many visceral effectors are doubly innervated (that is, they receive fibers from parasympathetic and sympathetic divisions and are influenced in opposite ways by the two divisions) Slide 6