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Anatomy Chapter 7.docx

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Biological Sciences
Connie Soros

Chapter 7 PNS: Efferent Division • Basics - autonomic nervous system 1. involuntary 2. innervates cardiac and smooth muscle, glands - somatic nervous system 1. voluntary 2. innervates skeletal muscle - two neurotransmitters 1. acetylcholine (ACh) 2. norepinephrine (NE) • ANS - all pathways have a 2 neuron chain extending from CNS to the innervated organ 1. preganglionic fiber has cell body in CNS, synapses with postganglionic fiber in a ganglion, postganglionic fiber innervates the effector organ 2. sympathetic a. preganglionic fibers originate in thoracic and lumbar regions of the spinal cord b. preganglionic fibers are short, synapse in a sympathetic chain ganglion along the spinal cord (release ACh) (1) some pass through the ganglion and synapse later in collateral ganglion nearer to the innervated organ c. postganglionic fibers are long, terminate on effector organ (release NE) 3. parasympathetic a. preganglionic fibers originate in brain stem or sacral spinal cord b. preganglionic fibers are long, synapse in terminal ganglia in or near effector organs (release ACh) c. postganglionic fibers are short, end on the effector organ (release ACh) - fibers releasing ACh called cholinergic fibers, fibers releasing NE called adrenergic fibers - postganglionic fibers terminate in many swelling called varicosities, which release nt over a large area of the organ (influence whole organs) - dual innervation 1. most visceral organs innervated by both sympathetic and parasympathetic fibers 2. generally have opposite effects 3. either can be excitatory or inhibitory depending on which organ 4. both systems usually partially active a. called sympathetic or parasympathetic tone, or tonic activity 5. when one increases its rate of firing and the other decreases it is called dominance a. sympathetic dominance results in increase of oxygen/nutrient rich blood flow to skeletal muscles (vessels dilate), heart beats faster and more forcefully, blood pressure increases, respiratory airways dilate, glycogen and fat stores broken down, digestive and urinary activities inhibited, pupils dilate, sweating b. parasympathetic dominance results in normal resting functions like digestion and urinary function being increased, while inhibiting sympathetic activities 6. allows precise control over body functions 7. exceptions... a. innervated blood vessels (most arterioles and veins) have only sympathetic fibers (regulated by increasing/decreasing rate from tonic level) b. most sweat glands have only sympathetic fibers, and postganglionic fibers release ACh c. salivary glands have dual innervation, but both stimulate secretion - role of adrenal gland 1. an endocrine gland with cortex and medulla 2. adrenal medulla secretes hormones when stimulated by sympathetic preganglionic fibers a. NE and epinephrine released (reinforce
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