Autonomic Nervous System and Reflexes

Vocabulary flashcards covering the components of reflex arcs, the structural and chemical differences between the somatic and autonomic nervous systems, sympathetic and parasympathetic pathways, and central autonomic regulation.

Unipolar Neuron

A sensory neuron characterized by a T-shaped structure that transmits signals from the peripheral nervous system into the central nervous system.

Reflex

A rapid, involuntary, and autonomic reaction to a stimulus that requires only a few neurons and occurs without conscious awareness or voluntary control.

Reflex Arc

The neural pathway that mediates a reflex response, composed of a receptor, sensory neuron, integration center (such as the spinal cord), motor neuron, and effector.

Monosynaptic Reflex

A fast reflex pathway consisting of only two neurons (a sensory neuron directly synapsing with a motor neuron) with no interneurons involved.

Polysynaptic Reflex

A more complex reflex pathway that involves one or more interneurons between the sensory neuron and motor neuron within the integration center.

Somatic Motor Pathway

A motor pathway composed of a single, uninterrupted, and always myelinated motor neuron extending from the central nervous system directly to skeletal muscle.

Autonomic Nervous System (ANS)

The involuntary division of the peripheral nervous system that utilizes a two-neuron chain to regulate cardiac muscle, smooth muscle, and glands.

Sympathetic Nervous System

The autonomic division that drives the 'fight or flight' response, originating from spinal cord segments $T1$ to $L2$ (thoracolumbar region).

Parasympathetic Nervous System

The autonomic division that controls 'rest and digest' (or repair) activities, originating from cranial nerves (CN III, VII, IX, and X) and sacral spinal segments $S2$ to $S4$.

Dual Innervation

An arrangement where a visceral organ receives nerve fibers from both the sympathetic and parasympathetic divisions.

Antagonistic Control

A control mechanism where sympathetic and parasympathetic divisions exert opposing effects on the same organ to maintain homeostasis.

Autonomic Ganglion

A cluster of nerve cell bodies outside the central nervous system where preganglionic neurons synapse with postganglionic neurons.

Preganglionic Neuron

The first neuron in the autonomic motor pathway; its cell body resides in the brain or spinal cord, and its axon is always myelinated.

Postganglionic Neuron

The second neuron in the autonomic motor pathway; its cell body lies in an autonomic ganglion, and its unmyelinated axon extends to the effector tissue.

Sympathetic Trunk

A chain of interconnected ganglia located lateral to the spinal column that allows preganglionic fibers to ascend or descend to different spinal levels.

White Ramus (White Ramus Communicans)

The communicating branch carrying myelinated preganglionic sympathetic axons from the spinal nerve into a sympathetic ganglion.

Gray Ramus (Gray Ramus Communicans)

The communicating branch through which unmyelinated postganglionic sympathetic axons exit the sympathetic ganglion to rejoin a spinal nerve.

Vagus Nerve (Cranial Nerve X)

A cranial nerve providing extensive parasympathetic innervation to thoracic and abdominal organs, featuring exceptionally long preganglionic axons.

Oculomotor Nerve (Cranial Nerve III)

A cranial nerve carrying both somatic motor fibers to eye muscles and parasympathetic fibers that control pupillary constriction.

Adrenal Medulla

A modified sympathetic ganglion whose endocrine cells secrete epinephrine and norepinephrine directly into the bloodstream upon sympathetic stimulation.

Acetylcholine (ACh)

The neurotransmitter released by all somatic motor neurons, all autonomic preganglionic neurons, and parasympathetic postganglionic neurons.

Norepinephrine (NE)

The primary neurotransmitter released by sympathetic postganglionic neurons onto visceral effector organs.

Hypothalamus

The main integration center in the brain for the autonomic nervous system, containing control centers for blood pressure, hunger, thirst, and water balance.

Baroreceptor Reflex

An autonomic homeostatic reflex that detects blood pressure changes via arterial stretch receptors in the carotid and aorta and adjusts vessel diameter accordingly.

Vasodilation

The relaxation of vascular smooth muscle that widens blood vessels, resulting in decreased blood pressure.