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BIOB33H3 Lecture Notes - Preganglionic Nerve Fibers, Postganglionic Nerve Fibers, Adrenal Medulla

Biological Sciences
Course Code
Connie Soros

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Chapter 7 PNS: Efferent Division
- 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)
- 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
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