Chapter 15 – Autonomic Nervous System

Vocabulary flashcards summarizing key terms, structures, neurotransmitters, receptors, and functional concepts of the autonomic nervous system.

Somatic Nervous System

Motor system that uses a single neuron from CNS to voluntary skeletal muscle; always excitatory.

Autonomic Nervous System (ANS)

Involuntary motor system with two-neuron chains (pre- and post-ganglionic) to smooth muscle, cardiac muscle, and glands; maintains internal homeostasis.

Sympathetic Division

Branch of ANS arising from T1–L2 lateral horns; prepares body for "fight or flight" and produces widespread effects.

Parasympathetic Division

Branch of ANS arising from brainstem nuclei & S2–S4 spinal cord; promotes "rest & digest" activities with localized effects.

Enteric Nervous System

Network of nerve plexuses in the GI tract wall capable of independent reflex control of digestion.

Preganglionic Neuron

First ANS neuron with cell body in CNS; axon projects to an autonomic ganglion and releases ACh.

Postganglionic Neuron

Second ANS neuron with cell body in an autonomic ganglion; axon extends to effector organ.

Ganglion

Cluster of neuronal cell bodies in PNS; site of synapse, neurotransmitter storage, release, and degradation in ANS.

Cholinergic Neuron

Neuron that secretes acetylcholine; includes all preganglionic neurons and parasympathetic postganglionic neurons.

Adrenergic Neuron

Neuron that secretes norepinephrine (or epinephrine); typically sympathetic postganglionic fibers.

Acetylcholine (ACh)

Primary neurotransmitter of all preganglionic ANS neurons, parasympathetic postganglionic neurons, and somatic motor neurons.

Norepinephrine (NE) / Epinephrine

Catecholamine neurotransmitters released by most sympathetic postganglionic neurons and the adrenal medulla.

Cholinergic Receptor

Membrane receptor that binds ACh; subdivided into nicotinic and muscarinic types.

Muscarinic Receptor

Metabotropic cholinergic receptor on all parasympathetic effectors and some sympathetic effectors; may be excitatory or inhibitory.

Adrenergic Receptor

Receptor that binds NE or epinephrine on sympathetic targets; subdivided into α and β classes.

Alpha (α) Receptor

Adrenergic subtype that generally produces excitatory responses such as vascular smooth-muscle constriction.

Fight or Flight Response

Physiological state produced by sympathetic activation—elevated heart rate, dilated bronchi, decreased GI motility, etc.

Rest and Digest Response

Physiological state produced by parasympathetic activation—lowered heart rate, enhanced digestion, glandular secretion.

Chain (Paravertebral) Ganglia

Linked sympathetic ganglia running alongside the vertebral column; primary synapse sites for thoracolumbar outflow.

Collateral (Prevertebral) Ganglia

Sympathetic ganglia located anterior to vertebral column (e.g., celiac, superior mesenteric) supplying abdominal organs.

Terminal Ganglia

Parasympathetic ganglia located near or within effector organs where pre- and post-ganglionic neurons synapse.

Lateral Horn

Gray matter region in T1–L2 spinal segments housing sympathetic preganglionic cell bodies.

Agonist

Drug or ligand that binds a receptor and triggers a physiological action.

Antagonist

Substance that binds a receptor and blocks or diminishes the action of an agonist or endogenous ligand.

Effectors (ANS)

Organs regulated by ANS—smooth muscle, cardiac muscle, and glands.

Beta Receptor

A type of adrenergic receptor that responds to catecholamines like epinephrine and norepinephrine, playing a key role in the autonomic nervous system.