Chapter 9 – Autonomic Nervous System (ANS) Vocabulary

These vocabulary flashcards cover the essential terminology and concepts from Chapter 9 on the Autonomic Nervous System, including neuron types, divisions, neurotransmission, receptor subtypes, pharmacology, and functional regulation of target organs.

Autonomic Nervous System (ANS)

Motor system that controls involuntary effectors—cardiac muscle, smooth muscle, and glands—via sympathetic and parasympathetic divisions.

Somatic Motor Neuron

Neuron with a cell body in the spinal cord that sends a single axon to a skeletal-muscle effector.

Preganglionic Neuron

First autonomic neuron; cell body in brainstem or spinal cord, axon synapses within an autonomic ganglion.

Postganglionic Neuron

Second autonomic neuron; cell body in an autonomic ganglion, axon innervates the effector organ.

Autonomic Ganglion

Cluster of neuronal cell bodies where preganglionic and postganglionic neurons synapse; located in head, neck, abdomen, or alongside spinal cord.

Thoracolumbar Division

Another name for the sympathetic division; preganglionic neurons emerge from T1–L2 spinal segments.

Paravertebral (Sympathetic Chain) Ganglia

Linked sympathetic ganglia running parallel to the spinal cord where many sympathetic synapses occur.

Convergence (ANS)

Several preganglionic neurons synapsing on a single postganglionic neuron.

Divergence (ANS)

One preganglionic neuron synapsing with multiple postganglionic neurons at different levels.

Mass Activation

Simultaneous activation of most sympathetic pathways, preparing the body for “fight-or-flight.”

Collateral (Prevertebral) Ganglia

Sympathetic ganglia (celiac, superior/inferior mesenteric) located anterior to the spinal column; receive splanchnic nerves.

Splanchnic Nerves

Preganglionic sympathetic fibers that bypass the paravertebral chain to synapse in collateral ganglia.

Adrenal Medulla

Inner adrenal region acting as a modified sympathetic ganglion; releases epinephrine and norepinephrine during mass activation.

Sympathoadrenal System

Functional unit of sympathetic nerves plus adrenal medulla hormone release.

Craniosacral Division

Another name for the parasympathetic division; preganglionic neurons arise from brainstem and S2–S4 spinal levels.

Terminal Ganglion

Parasympathetic ganglion located within or very near the target organ; gives rise to short postganglionic fibers.

Fight-or-Flight Response

Physiological changes (↑ heart rate, ↑ blood glucose, blood shunted to muscles) produced by sympathetic activation.

Rest-and-Digest Response

Parasympathetic actions that conserve energy, slow heart rate, and enhance digestive activity.

Cholinergic Synapse

Synapse that releases acetylcholine (ACh); characteristic of all autonomic preganglionic fibers and most parasympathetic postganglionic fibers.

Adrenergic Synapse

Synapse that releases norepinephrine; typical of most sympathetic postganglionic neurons.

Catecholamines

Family of adrenergic neurotransmitters, primarily norepinephrine and epinephrine.

Varicosity

Swelling along a postganglionic autonomic axon that releases neurotransmitter ‘en passant.’

Sympathomimetic Drug

Medication that mimics sympathetic (adrenergic) stimulation; e.g., phenylephrine, albuterol.

Agonist (Pharmacology)

Drug that binds to a receptor and promotes the natural neurotransmitter’s effect.

Antagonist (Pharmacology)

Drug that blocks a receptor and inhibits the neurotransmitter’s effect.

α1-Adrenergic Receptor

Adrenergic receptor subtype producing vasoconstriction, pupil dilation, and sphincter contraction when stimulated.

β1-Adrenergic Receptor

Receptor subtype primarily in the heart; stimulation increases heart rate and contractility.

β2-Adrenergic Receptor

Receptor subtype causing bronchodilation and skeletal-muscle vessel dilation when activated.

Nicotinic Receptor

Ligand-gated ACh receptor in autonomic ganglia and skeletal muscle; blocked by curare.

Muscarinic Receptor

G-protein–coupled ACh receptor in visceral organs; can be excitatory (M3, M5) or inhibitory (M2); blocked by atropine.

Dual Innervation

Condition in which an organ receives both sympathetic and parasympathetic fibers, usually with opposing actions.

Organs Without Dual Innervation

Structures (adrenal medulla, arrector pili muscles, sweat glands, most blood vessels) that receive only sympathetic fibers.

Varied ANS Tone

Balance of continuous (tonic) sympathetic and/or parasympathetic activity regulating organ function.