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Chapter 15.docx

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University of Toronto Scarborough
Biological Sciences
Ted Petit

Chapter 15 The Autonomic Nervous System • Basics - Input 1. general visceral sensory neurons a. e.g., chemoreceptors sensing blood gases, mechanoreceptors sensing organ stretch - Output 1. general visceral motor neurons a. excite or inhibit their effectors (cardiac and smooth muscle, glands) 2. two neuron pathway from CNS to effector organ a. preganglionic fiber has cell body in CNS, synapses with postganglionic fiber in a ganglion, postganglionic fiber innervates effector organ b. sympathetic division 1) preganglionic fibers originate in thoracic and lumbar regions of spinal cord 2) preganglionic fibers are short, synapse in a sympathetic chain ganglion lying along the vertebral column, release ACh (some pass through the chain and synapse later in a collateral ganglion closer to the effector organ) 3) postganglionic fibers are long, terminate on effector organ and release norepinephrine (NE) c. parasympathetic division 1) preganglionic fibers originate in brain stem or sacral spinal cord 2) preganglionic fibers are long, synapse in terminal ganglia in or near effector organs, release ACh 3) postganglionic fibers are short, end on the effector organ, release Ach - Dual innervation 1. most visceral organs are innervated by both sympathetic and parasympathetic fibers 2. generally have opposite effects 3. can be excitatory or inhibitory depending on the organ innervated 4. both systems are usually partially active a. sympathetic or parasympathetic tone, or tonic activity 5. when one division increases its rate of sending signals and the other decreases, it's called dominance a. sympathetic dominance 1) increase in blood flow to skeletal muscles (vessels dilate) 2) heart beats fa
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