Nervous System: Pain Pathways and Autonomic Nervous System

A comprehensive vocabulary review set covering pain reception, visceral reflexes, and the structure and function of the sympathetic and parasympathetic nervous systems.

Pain

A sensory mechanism that warns the body of actual or potential tissue damage.

Mast Cell

A type of white blood cell that produces and releases histamine during inflammation.

ATP (in pain signaling)

An intracellular energy molecule normally found in mitochondria; when detected outside damaged cells, it acts as a pain signal.

Endogenous

Chemical substances generated or created inside the body, derived from 'endo' (within) and 'genus' (beginning or created).

Pain Threshold

The stimulus intensity required to initiate an action potential (around $-55\,\text{mV}$) and send a pain signal to the brain, which is generally uniform across individuals.

Pain Tolerance

An individual's personal perception and endurance of pain, which varies based on genetics, pain metabolism, and prior experience.

Visceral Pain

Pain originating in internal organs felt as aching, gnawing, or burning, typically triggered by stretching, ischemia, or chemical irritants.

Ischemia

A condition in which tissues do not receive adequate oxygen.

Referred Pain

Pain perceived at a different location than its actual internal source because somatic and visceral pain fibers travel along the same nerve pathway.

Interneuron

A neuron within the spinal cord that acts as an integration center between sensory and motor neurons during a reflex.

Somatic Nervous System

The voluntary motor division whose motor neuron cell bodies reside in the ventral horn and send single axons via the ventral root to skeletal muscle using stimulatory acetylcholine.

Autonomic Nervous System (ANS)

The involuntary division of the nervous system that regulates smooth muscle, cardiac muscle, and glands via a two-neuron pathway extending from the central nervous system.

Sympathetic Nervous System

The 'fight or flight' division of the autonomic nervous system that originates in the thoracic and lumbar regions and generally accelerates physiological functions.

Parasympathetic Nervous System

The 'rest and digest' (or rest and repose) division of the autonomic nervous system that originates in the brain and sacral region and generally slows down physiological functions.

Preganglionic Neuron

The first neuron in the autonomic two-neuron chain, having its cell body in the central nervous system and projecting its axon to an autonomic ganglion.

Adrenergic Fibers

Autonomic nerve fibers that synthesize and release the neurotransmitter norepinephrine.

Nicotinic Receptors

A class of cholinergic receptors located on all autonomic postganglionic neurons, adrenal medullary hormone-producing cells, and skeletal muscle cells that are always stimulatory.

Muscarinic Receptors

Cholinergic receptors located on target effector cells that can produce either stimulatory or inhibitory responses depending on the tissue.

Adrenal Medulla

The interior portion of the adrenal gland located atop each kidney that secretes epinephrine and norepinephrine upon sympathetic stimulation.

Sympathetic Tone (Vasomotor Tone)

The continuous, baseline state of partial blood vessel constriction maintained by sympathetic signaling to regulate systemic blood pressure.

Parasympathetic Tone

The continuous basal activity of parasympathetic fibers that maintains a reduced heart rate and sustains baseline digestive and urinary tract functions.