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Lecture # 17 Friday February 22, 2001 Outline • Autonomic nervous system • Structure of ANS • Functions of ANS Autonomic Nervous System (ANS) • Part of the PNS • Regulated mainly by hypothalamus and brain stem • Main input to ANS comes from autonomic sensory neurons e.g.: • receptors for body temp., osmotic pressure • Autonomic motor neurons regulate smooth muscle, cardiac muscle and glands Two divisions of ANS • Sympathetic • Parasympathetic • Most organs have “dual innervation” • Together both divisions maintain homeostasis Autonomic motor pathway • Preganglionic neuron (cell body in CNS) - myelinated axon • Synapse (ACh) with • Postganglionic neuron (cell body in autonomic ganglia in PNS) • Synapse (ACh or NE) w/effector Remember • Somatic motor neuron always EXCITES effector organ • Autonomic postganglionic neuron can either excite or inhibit effector organ Sympathetic Division • aka thoracolumbar division • Responds to E-situations • Innervates fight-or-flight response • Examples Parasympathetic Division • aka craniosacral division • Responsible for rest-and-digest activities • “paradoxical fear” in response to NO-WIN situations ANS neurotransmitters • All preganglionic neurons secrete ACh at synapse • All postganglionic parasympathetic neurons secrete ACh at neuroeffector junction • Most postganglionic sympathetic neurons secrete ACh at neuroeffector junction • All neurons that secrete ACh = CHOLINERGIC neurons • ACh is inactivated by AChE • Most postganglionic sympathetic neurons secrete NE = ADRENERGIC neurons • Slow inactivation by enzymes linger in synaptic cleft Autonomic/visceral reflexes • Same components as somatic reflex arc • Two effector neurons • Always polysynaptic • E.G.: pupillary reflex, swallowing reflex Examples of dual innervation • Sympathetic: excitatory: increase HR, increased blood flow; increased breathing inhibitory: reduce digestion activities • Parasympathetic: inhibitory: excitatory: HR, blood flow digestion activities Higher levels of autonomic control • Integration of smell, tastes, changes in temperature, erotic stimuli, anticipation • Biofeedback or mind over matter can influence autonomic functions
