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BIOB34H3 Lecture Notes - Preganglionic Nerve Fibers, Postganglionic Nerve Fibers, Paravertebral Ganglia

Biological Sciences
Course Code
Ted Petit

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Chapter 15 The Autonomic Nervous System
- 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
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
a. sympathetic dominance
1) increase in blood flow to skeletal muscles (vessels dilate)
2) heart beats faster and more forcefully
3) blood pressure increases (most vessels constrict)
4) respiratory airways dilate
5) stored nutrients are broken down
6) digestive and urinary activities are inhibited
7) pupils dilate
8) sweating
b. parasympathetic dominance
1) inhibits sympathetic activities (e.g., heart rate and blood pressure decrease)
2) normal resting functions like digestive and urinary activities increase
Details of Autonomic Anatomy
- rami communicantes
1. white rami
a. branch from thoracic and first few lumbar nerves
b. contain sympathetic preganglionic fibers
2. gray rami
a. branch from sympathetic chain ganglia back to a nerve
b. contain sympathetic postganglionic fibers
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