Autonomic and Somatic Nervous System – Key Vocabulary

Vocabulary flashcards covering key anatomical, physiological and chemical concepts of the autonomic and somatic nervous systems, neurotransmission and adrenergic pharmacology.

Autonomic Nervous System (ANS)

Peripheral nervous system division that involuntarily regulates heart rate, blood pressure, respiration, digestion and sexual arousal; includes sympathetic, parasympathetic and enteric divisions.

Sympathetic Division

ANS branch originating from thoracic-lumbar spinal cord that prepares the body for stress (fight-or-flight) by increasing heart rate, blood pressure and blood flow to muscle.

Parasympathetic Division

ANS branch arising from cranial and sacral regions that conserves energy and supports “rest-and-digest” functions such as digestion and waste elimination.

Enteric Division

Intrinsic ‘brain of the gut’ that independently controls gastrointestinal motility, secretion and microcirculation; modulated by both sympathetic and parasympathetic input.

Endocrine System

Network of glands that send long-distance chemical signals via hormones in the bloodstream to coordinate nearly every cell, organ and function.

Central Nervous System (CNS)

Comprises brain and spinal cord; integration center for incoming (afferent) and outgoing (efferent) neural information.

Peripheral Nervous System (PNS)

All neural tissue outside the CNS; subdivided into afferent (sensory) and efferent (motor) divisions.

Efferent Neuron

Nerve fiber that carries impulses away from the CNS to peripheral effector tissues.

Afferent Neuron

Sensory nerve fiber that conveys information from peripheral receptors to the CNS.

Reflex Arc

Neural circuit beginning with a sensory receptor and ending with a motor effector, allowing rapid, unconscious responses.

Somatic Nervous System

Efferent system under voluntary control; a single myelinated neuron runs from CNS directly to skeletal muscle.

Preganglionic Neuron

First efferent neuron of the ANS; cell body in CNS, axon synapses in an autonomic ganglion.

Postganglionic Neuron

Second ANS neuron; cell body in ganglion, unmyelinated axon terminates on effector organ.

Ganglion

Cluster of neuronal cell bodies in the PNS acting as a relay between pre- and postganglionic fibers.

Adrenal Medulla

Modified sympathetic ganglion that releases epinephrine (≈85%) and norepinephrine (≈15%) into blood when stimulated by preganglionic acetylcholine.

Fight-or-Flight Response

Sympathetic activation plus adrenal epinephrine release producing global physiological changes to confront stress.

Rest-and-Digest

Parasympathetic dominance during restful states, promoting digestion, energy storage and elimination.

Dual Innervation

Condition in which most organs receive both sympathetic and parasympathetic fibers, often with opposite effects.

Local Mediator

Chemical released by cells that acts on neighboring cells and is rapidly destroyed (e.g., histamine, prostaglandins).

Hormone

Signal molecule secreted by endocrine cells into the bloodstream to reach distant target tissues.

Neurotransmitter

Chemical released from nerve terminals upon depolarization that binds receptors on adjacent cells to convey a neural signal.

Receptor (Membrane)

Protein recognition site that binds a specific messenger and initiates a cellular response; most are located on the cell surface.

Second Messenger

Intracellular molecule (e.g., cAMP, IP3, DAG) generated after receptor activation to amplify and propagate the signal.

Adenylyl Cyclase System

Gs-protein–linked pathway that converts ATP to cAMP, a common second messenger for adrenergic signals.

Calcium/Phosphatidylinositol System

Gq-protein–linked pathway activating phospholipase C to produce IP3 and DAG, increasing intracellular Ca²⁺.

Cholinergic Neuron

Nerve fiber that releases acetylcholine as its neurotransmitter.

Adrenergic Neuron

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

Acetylcholine (ACh)

Primary transmitter at all autonomic ganglia, parasympathetic postganglionic-effector synapses, adrenal medulla, and neuromuscular junction.

Norepinephrine (NE)

Main sympathetic postganglionic neurotransmitter; also released from adrenal medulla and adrenergic neurons in CNS.

Epinephrine (Adrenaline)

Hormone produced in adrenal medulla from NE; circulates to activate adrenergic receptors throughout the body.

Tyrosine Hydroxylase

Rate-limiting enzyme converting tyrosine to DOPA in catecholamine synthesis.

Dopamine β-Hydroxylase

Enzyme in synaptic vesicles that converts dopamine to norepinephrine.

Reserpine

Drug that blocks the vesicular amine transporter, preventing NE storage in adrenergic vesicles.

Guanethidine

Agent that blocks the release of norepinephrine from adrenergic nerve terminals.

Monoamine Oxidase (MAO)

Mitochondrial enzyme that oxidatively degrades recaptured norepinephrine inside adrenergic neurons.

Catechol-O-Methyltransferase (COMT)

Postsynaptic enzyme that metabolizes catecholamines in the synaptic space to O-methylated products.

α1-Adrenoceptor

Adrenergic receptor whose activation causes vasoconstriction, increased peripheral resistance, and bladder sphincter contraction.

α2-Adrenoceptor

Presynaptic and postsynaptic receptor that inhibits norepinephrine release and decreases insulin secretion.

β1-Adrenoceptor

Receptor predominantly in heart; stimulation increases heart rate, myocardial contractility and renin release.

β2-Adrenoceptor

Receptor mediating bronchodilation, vasodilation in skeletal muscle, uterine relaxation and increased glycogenolysis.

GABA (γ-Aminobutyric Acid)

Major inhibitory amino-acid neurotransmitter in CNS; deficits linked to seizures and anxiety.

Serotonin

Indolamine neurotransmitter involved in mood, sleep and cognition; alterations associated with depression and anxiety disorders.

Dopamine

Catecholamine neurotransmitter essential for motor control, reward and cognition; imbalance linked to Parkinson’s disease and schizophrenia.

Histamine

Biogenic amine acting as neurotransmitter and local mediator involved in allergic responses and gastric secretion.