Human Physiology: Peripheral Nervous System and Autonomic Regulation

Comprehensive vocabulary flashcards covering the structure, divisions, reflexes, autonomic pathways, neurotransmitters, and receptor actions of the peripheral nervous system.

Central Nervous System (CNS)

The major division of the nervous system consisting exclusively of the brain and spinal cord.

Peripheral Nervous System (PNS)

The division of the nervous system composed of nerves and ganglia located outside the central nervous system.

Sensory Neurons (Afferent)

Neurons that conduct action potentials from sensory receptors toward the central nervous system.

Motor Neurons (Efferent)

Neurons that conduct impulses outward from the central nervous system to effector organs such as muscles and glands.

Somatic Motor Neurons

Motor neurons that have cell bodies in the spinal cord and a single neuron extending to skeletal muscle effectors for voluntary and reflex motor control.

Autonomic Motor Neurons

A two-neuron efferent system in the PNS that provides involuntary control over smooth muscle, cardiac muscle, and glands.

Oligodendrocytes

Glial supporting cells that form myelin sheaths around axons within the central nervous system.

Astrocytes

CNS glial supporting cells characterized by extensions at capillaries and extensions in close proximity to axons at synapses.

Microglia

Phagocytic glial supporting cells found within the central nervous system.

Ependyma

An epithelial glial layer that lines the ventricles of the brain and the central canal of the spinal cord.

Schwann Cells

Supporting glial cells responsible for producing myelin sheaths around axons in the peripheral nervous system.

Satellite Cells

Supporting glial cells that support neuron cell bodies located within the ganglia of the peripheral nervous system.

Interneurons (Association Neurons)

Neurons located entirely within the CNS that receive sensory information, integrate and analyze information, and stimulate motor neurons.

Distribution of Spinal Nerves

The 31 pairs of spinal nerves organized into 8 cervical pairs, 12 thoracic pairs, 5 lumbar pairs, 5 sacral pairs, and 1 coccygeal pair.

Corticospinal Pathways

Descending motor pathways descending from upper motor neurons in the primary motor cortex, undergoing decussation in the medulla, and traversing lateral or ventral corticospinal tracts to synapse on lower motor neurons in the spinal cord.

Synaptotagmin

A cytoplasmic sensor protein in axon terminals that binds $Ca^{2+}$, forming a complex that stimulates SNARE-mediated fusion and exocytosis of synaptic vesicles.

Somatic Reflex

Fast, involuntary motor responses that occur when action potentials travel through a somatic reflex arc to stimulate skeletal muscle.

Somatic Reflex Arc

The neural circuit underlying a somatic reflex, composed of a sensory receptor, sensory neuron, integrating center (gray matter in CNS), somatic motor neuron, and effector (skeletal muscle).

Stretch Reflex (Knee Jerk)

A monosynaptic reflex where stretching of a muscle spindle sensory receptor activates a sensory neuron, which directly excites an efferent motor neuron to contract the same muscle while inhibiting antagonist muscles.

Reciprocal Innervation

The reflex mechanism characterized by the simultaneous stimulation of motor neurons to an agonist muscle and interneuron-mediated inhibition of motor neurons to the antagonist muscle.

Spinal Reflex

Reflexes whose neural circuits are processed entirely within the spinal cord without sending signals to or receiving signals from the brain.

Autonomic Reflex Arc

A visceral reflex pathway whose downstream effectors are smooth muscle, cardiac muscle, or glands rather than skeletal muscle.

Preganglionic Neuron

The first neuron in the autonomic motor pathway, having its cell body located in the brain or spinal cord and synapsing within an autonomic ganglion.

Postganglionic Neuron

The second neuron in the autonomic pathway, having its cell body located in an autonomic ganglion and projecting its axon to terminate on involuntary effectors.

Sympathetic Division (Thoracolumbar Division)

The division of the autonomic nervous system whose preganglionic neurons originate from the T1 to L2 spinal cord segments.

Paravertebral Ganglia

A connected chain of sympathetic ganglia running parallel to the spinal cord where preganglionic fibers often synapse with postganglionic neurons.

Sympathetic Divergence

A neural arrangement where a single preganglionic neuron branches and synapses on several postganglionic neurons located at different ganglion levels.

Sympathetic Convergence

A neural arrangement where multiple preganglionic neurons from different spinal cord levels converge and synapse on a single postganglionic neuron.

Collateral Ganglia

Sympathetic ganglia located outside the sympathetic chain (including celiac, superior mesenteric, and inferior mesenteric ganglia) innervated by splanchnic nerves that exit below the diaphragm.

Adrenal Medulla

A modified sympathetic ganglion innervated directly by preganglionic sympathetic neurons that secretes epinephrine and norepinephrine into circulation as part of mass activation.

Parasympathetic Division (Craniosacral Division)

The autonomic division whose preganglionic neurons arise from the brain (cranial nerves III, VII, IX, X) or sacral spinal cord (S2–S4).

Terminal Ganglia

Parasympathetic ganglia situated in or near effector organs that give rise to very short postganglionic neurons.

Cholinergic Synaptic Transmission

Synaptic transmission utilizing acetylcholine ($\text{ACh}$), which occurs at all autonomic preganglionic synapses, all neuromuscular junctions, and most parasympathetic postganglionic synapses.

Adrenergic Synaptic Transmission

Synaptic transmission using norepinephrine ($\text{NE}$) as the primary neurotransmitter, characteristic of most sympathetic postganglionic terminals.

Alpha ($\alpha$) Adrenergic Receptors

Adrenergic receptors (subtypes $\alpha_1$ and $\alpha_2$) that are more sensitive to norepinephrine than to blood epinephrine.

Beta ($\beta$) Adrenergic Receptors

Adrenergic receptors (subtypes $\beta_1$ and $\beta_2$) that exhibit greater sensitivity to circulating blood epinephrine than to norepinephrine.

Alpha-1 ($\alpha_1$) Adrenergic Effect

Stimulates contraction of radial iris muscles to dilate pupils, vasoconstriction of skin and visceral arterioles, and contraction of gastrointestinal sphincters.

Beta-1 ($\beta_1$) Adrenergic Effect

Primarily stimulates the heart to increase heart rate at the sinoatrial node and increase myocardial contraction strength.

Beta-2 ($\beta_2$) Adrenergic Effect

Promotes smooth muscle relaxation, resulting in bronchodilation of lung airways, vasodilation of skeletal muscle arterioles, and relaxation of gastrointestinal walls.

Nicotinic ACh Receptors

Ligand-gated cation channels for $Na^+$ and $K^+$ located in autonomic ganglia and neuromuscular junctions that invariably cause depolarization and excitation.

Muscarinic ACh Receptors

G-protein-coupled receptors in visceral organs stimulated by postganglionic parasympathetic $\text{ACh}$, which can trigger excitation (depolarization) or inhibition (hyperpolarization, such as slowing heart rate).