Motor Division of the Peripheral Nervous System

Vocabulary flashcards covering key terms and definitions from the lecture on the Motor Division of the Peripheral Nervous System, including autonomic branches, neurotransmitters, receptors, and somatic neuromuscular junction physiology.

Parasympathetic Branch

The rest-and-digest branch of the visceral motor division that dominates during routine, quiet day-to-day activities.

Sympathetic Branch

The fight-or-flight branch of the visceral motor division that dominates during stressful emergency situations and exercise.

Homeostasis

The active maintenance of a constant internal environment by cells, tissues, and organs organized in negative feedback systems.

Antagonistic Control

A regulatory mechanism in which most internal organs are innervated by both autonomic branches, where one branch is excitatory and the other is inhibitory.

Preganglionic Neuron

The first neuron in an autonomic pathway that originates in the central nervous system and terminates in an autonomic ganglion.

Postganglionic Neuron

The second neuron in an autonomic pathway that has its cell body in an autonomic ganglion and projects its axon to the target tissue.

Autonomic Ganglion

A peripheral cluster of nerve cell bodies where preganglionic autonomic neurons synapse with postganglionic autonomic neurons.

Vagus Nerve (CN X)

The major parasympathetic tract originating in the medulla that contains about $75\%$ of all parasympathetic fibers and innervates multiple internal organs.

Divergence

An autonomic pathway pattern where one presynaptic preganglionic neuron branches to synapse with an average of $8$ or $9$ postsynaptic postganglionic neurons.

Cholinergic Receptors

Receptors that bind acetylcholine, categorized into ionotropic nicotinic receptors and G protein-coupled muscarinic receptors.

Adrenergic Receptors

G protein-coupled membrane receptors that bind catecholamines (norepinephrine and epinephrine), classified into $\alpha$ and $\beta$ subtypes.

Varicosities

Swollen regions along the distal axons of postganglionic autonomic neurons that synthesize, store, and release neurotransmitters across target tissue.

Neuroeffector Junction

The synapse between a postganglionic autonomic neuron's varicosities and its target tissue.

Monoamine Oxidase (MAO)

An enzyme located in the mitochondria of varicosities that degrades and metabolizes norepinephrine.

Adrenal Medulla

The inner neurosecretory core of the adrenal gland that acts as a modified sympathetic ganglion releasing epinephrine into the circulation.

Chromaffin Cell

A modified postganglionic sympathetic neuron within the adrenal medulla that secretes the neurohormone epinephrine directly into the bloodstream.

Somatic Motor Pathway

An efferent pathway consisting of a single neuron originating in the central nervous system that directly innervates skeletal muscle with excitatory signals.

Neuromuscular Junction (NMJ)

The functional synapse between a somatic motor neuron axon terminal, the synaptic cleft, and the motor end plate of a skeletal muscle fiber.

Motor End Plate

A specialized region of the muscle fiber membrane opposite the axon terminal containing high concentrations of nicotinic acetylcholine receptors.

Acetylcholinesterase (AChE)

An enzyme present in the synaptic cleft of cholinergic synapses that rapidly deactivates acetylcholine into acetyl and choline.

DHP Receptor

A voltage-gated protein in the T-tubule membrane that changes conformation during an action potential to open calcium release channels in the sarcoplasmic reticulum.

Rigor State

The state in cross-bridge cycling where the myosin head is tightly bound to actin at a $45^\circ$ angle prior to ATP binding.

Sympathomimetic Agents

Drugs that enhance sympathetic activity by binding to adrenergic receptors or increasing norepinephrine release.

Sympatholytic Agents

Drugs that decrease sympathetic activity by blocking adrenergic receptors.