Autonomic Nervous System (ANS) Overview

Vocabulary flashcards covering major terms, pathways, neurotransmitters, and physiological effects of the autonomic nervous system.

Autonomic Nervous System (ANS)

A division of the peripheral nervous system that controls involuntary functions of cardiac and smooth muscle and glands.

Somatic Nervous System

Nerve system that controls voluntary skeletal muscle movement through a single-neuron pathway using acetylcholine (ACh).

Sympathetic Nervous System

Branch of the ANS that prepares body organs for "fight or flight"—excitation, action, or emergency situations.

Parasympathetic Nervous System

Branch of the ANS that promotes "rest and digest" functions—energy conservation and nutrient processing.

Fight-or-Flight Response

Physiological changes driven by sympathetic nerves, such as increased heart rate, dilated pupils, and elevated blood glucose.

Rest-and-Digest Response

Parasympathetic-mediated state marked by slowed heart rate, stimulated digestion, and bladder contraction.

Dual Innervation

Most visceral organs receive input from both sympathetic and parasympathetic nerves, enabling opposite effects (on/off control).

Craniosacral Outflow

Origin of parasympathetic nerves from cranial nerves III, VII, IX, X and sacral spinal cord segments S2-S4.

Thoracolumbar Outflow

Origin of sympathetic nerves from thoracic (T1-T12) and lumbar (L1-L2) spinal cord segments.

Acetylcholine (ACh)

Neurotransmitter released by all preganglionic ANS neurons and postganglionic parasympathetic neurons; excites or inhibits depending on receptor.

Norepinephrine (NE)

Primary neurotransmitter of most postganglionic sympathetic neurons; typically excites cardiac muscle and inhibits digestive organs.

Adrenal Medulla

Sympathetically controlled gland that secretes epinephrine and norepinephrine into the bloodstream during stress.

Pupil Dilation

Sympathetic effect that increases light entry by enlarging the pupil.

Pupil Constriction

Parasympathetic effect that decreases light entry by narrowing the pupil.

Bladder Relaxation

Sympathetic action allowing urine storage by relaxing detrusor muscle.

Bladder Contraction

Parasympathetic action promoting urination by contracting detrusor muscle.

Two-Neuron Pathway

ANS route comprising a preganglionic neuron (CNS to ganglion) and a postganglionic neuron (ganglion to organ).

Preganglionic Neuron

First neuron in the ANS pathway; cell body in CNS, releases ACh onto ganglionic neuron.

Postganglionic Neuron

Second neuron in the ANS pathway; cell body in autonomic ganglion, releases ACh (parasym.) or NE (symp.) onto target organ.

Excitation, Embarrassment, Emergency, Exercise

"4 E’s" mnemonic summarizing conditions activating sympathetic nerves.

Digestion, Diuresis, Defecation, Decreased Heart Rate

"4 D’s" mnemonic summarizing functions enhanced by parasympathetic nerves.