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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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Autonomic Nervous System (ANS)
Visceral motor portion of the peripheral nervous system that controls involuntary activity of cardiac muscle, smooth muscle and glands.
Visceral Motor Division
Branch of the PNS that provides autonomic (involuntary) motor control to internal organs.
Sympathetic Division
Thoracolumbar branch of the ANS that prepares the body for “fight or flight.”
Parasympathetic Division
Craniosacral branch of the ANS that promotes “rest and digest” functions.
Fight-or-Flight Response
Physiological changes (e.g., ↑ heart rate, pupil dilation, bronchodilation) produced by sympathetic activation during emergency, exercise, excitement or embarrassment.
Rest-and-Digest Response
Parasympathetic state that conserves energy by lowering heart rate & blood pressure while stimulating GI activity.
Thoracolumbar Outflow
Sympathetic preganglionic fibers exiting the spinal cord between T1 and L2.
Craniosacral Outflow
Parasympathetic preganglionic fibers arising from brainstem nuclei and sacral spinal nerves S2–S4.
Preganglionic Neuron
First motor neuron in an ANS pathway; cell body in CNS, myelinated axon synapses in an autonomic ganglion.
Postganglionic Neuron
Second motor neuron in an ANS pathway; cell body in a ganglion, unmyelinated axon reaches the effector.
Autonomic Ganglion
Cluster of neuron cell bodies in the PNS where pre- and post-ganglionic neurons synapse.
Two-Neuron Chain
Characteristic ANS arrangement consisting of one preganglionic and one postganglionic neuron to reach an effector.
Cholinergic Fiber
Nerve fiber that releases acetylcholine as its neurotransmitter.
Adrenergic Fiber
Nerve fiber that releases norepinephrine (or epinephrine) as its neurotransmitter.
Acetylcholine (ACh)
Neurotransmitter released by all ANS preganglionic neurons, all parasympathetic postganglionic neurons and somatic motor neurons.
Norepinephrine (NE)
Primary neurotransmitter released by most sympathetic postganglionic neurons.
Preganglionic Fiber Length (Sympathetic)
Typically short fibers that synapse in ganglia located near the spinal cord.
Preganglionic Fiber Length (Parasympathetic)
Typically long fibers that synapse in ganglia located within or near target organs.
Hypothalamus (ANS Control)
Highest autonomic integration center in the brain; regulates sympathetic and parasympathetic activity subconsciously.
E Situations
Emergency, Exercise, Excitement, and Embarrassment—conditions that heighten sympathetic dominance.
Effector Organs of ANS
Cardiac muscle, smooth muscle, glands and adipose tissue under involuntary control.
Somatic Nervous System
PNS division that provides voluntary motor control of skeletal muscles via single heavily myelinated neurons.
Ganglion (PNS)
General term for a cluster of neuron cell bodies located outside the central nervous system.
Adrenergic Receptors
Alpha (α1, α2) and Beta (β1, β2) receptors on effectors that bind norepinephrine or epinephrine.
Muscarinic Receptors
G-protein coupled receptors (M1–M5) on target organs that respond to acetylcholine released by parasympathetic postganglionic fibers.
Nicotinic Receptors
Ligand-gated ion channels on all postganglionic neurons and skeletal muscle that bind acetylcholine.
Sympathetic Effect on Heart Rate
Increases rate and strength of cardiac contractions.
Parasympathetic Effect on Airways
Constricts bronchioles, reducing airway diameter.
Blood Vessel Distribution (Sympathetic)
Constricts vessels to GI tract & kidneys while dilating vessels to heart, liver and adipose tissue.
Pupillary Response in ANS
Sympathetic activation dilates pupils (mydriasis); parasympathetic activation constricts pupils (miosis).