Autonomic Nervous System Overview

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A set of vocabulary flashcards covering key terms and concepts related to the autonomic nervous system, its divisions, pathways, neurotransmitters and physiological effects.

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30 Terms

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Autonomic Nervous System (ANS)

Visceral motor portion of the peripheral nervous system that controls involuntary activity of cardiac muscle, smooth muscle and glands.

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Visceral Motor Division

Branch of the PNS that provides autonomic (involuntary) motor control to internal organs.

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Sympathetic Division

Thoracolumbar branch of the ANS that prepares the body for “fight or flight.”

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Parasympathetic Division

Craniosacral branch of the ANS that promotes “rest and digest” functions.

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Fight-or-Flight Response

Physiological changes (e.g., ↑ heart rate, pupil dilation, bronchodilation) produced by sympathetic activation during emergency, exercise, excitement or embarrassment.

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Rest-and-Digest Response

Parasympathetic state that conserves energy by lowering heart rate & blood pressure while stimulating GI activity.

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Thoracolumbar Outflow

Sympathetic preganglionic fibers exiting the spinal cord between T1 and L2.

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Craniosacral Outflow

Parasympathetic preganglionic fibers arising from brainstem nuclei and sacral spinal nerves S2–S4.

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Preganglionic Neuron

First motor neuron in an ANS pathway; cell body in CNS, myelinated axon synapses in an autonomic ganglion.

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Postganglionic Neuron

Second motor neuron in an ANS pathway; cell body in a ganglion, unmyelinated axon reaches the effector.

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Autonomic Ganglion

Cluster of neuron cell bodies in the PNS where pre- and post-ganglionic neurons synapse.

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Two-Neuron Chain

Characteristic ANS arrangement consisting of one preganglionic and one postganglionic neuron to reach an effector.

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Cholinergic Fiber

Nerve fiber that releases acetylcholine as its neurotransmitter.

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Adrenergic Fiber

Nerve fiber that releases norepinephrine (or epinephrine) as its neurotransmitter.

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Acetylcholine (ACh)

Neurotransmitter released by all ANS preganglionic neurons, all parasympathetic postganglionic neurons and somatic motor neurons.

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Norepinephrine (NE)

Primary neurotransmitter released by most sympathetic postganglionic neurons.

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Preganglionic Fiber Length (Sympathetic)

Typically short fibers that synapse in ganglia located near the spinal cord.

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Preganglionic Fiber Length (Parasympathetic)

Typically long fibers that synapse in ganglia located within or near target organs.

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Hypothalamus (ANS Control)

Highest autonomic integration center in the brain; regulates sympathetic and parasympathetic activity subconsciously.

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E Situations

Emergency, Exercise, Excitement, and Embarrassment—conditions that heighten sympathetic dominance.

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Effector Organs of ANS

Cardiac muscle, smooth muscle, glands and adipose tissue under involuntary control.

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Somatic Nervous System

PNS division that provides voluntary motor control of skeletal muscles via single heavily myelinated neurons.

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Ganglion (PNS)

General term for a cluster of neuron cell bodies located outside the central nervous system.

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Adrenergic Receptors

Alpha (α1, α2) and Beta (β1, β2) receptors on effectors that bind norepinephrine or epinephrine.

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Muscarinic Receptors

G-protein coupled receptors (M1–M5) on target organs that respond to acetylcholine released by parasympathetic postganglionic fibers.

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Nicotinic Receptors

Ligand-gated ion channels on all postganglionic neurons and skeletal muscle that bind acetylcholine.

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Sympathetic Effect on Heart Rate

Increases rate and strength of cardiac contractions.

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Parasympathetic Effect on Airways

Constricts bronchioles, reducing airway diameter.

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Blood Vessel Distribution (Sympathetic)

Constricts vessels to GI tract & kidneys while dilating vessels to heart, liver and adipose tissue.

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Pupillary Response in ANS

Sympathetic activation dilates pupils (mydriasis); parasympathetic activation constricts pupils (miosis).