Fundamentals of the Nervous System: Anatomy, Neurophysiology, and Neural Circuits

Vocabulary practice flashcards covering the anatomical subdivisions, neuroglial cells, electrical principles, resting membrane potential, graded and action potentials, synaptic transmission, and circuit architectures of the nervous system.

Central Nervous System (CNS)

The structural and functional division of the nervous system consisting of the brain and spinal cord, which functions as the primary integration and processing center.

Peripheral Nervous System (PNS)

The division of the nervous system consisting of all nervous tissue outside the CNS, including cranial nerves, spinal nerves, and ganglia.

Somatic Sensory Receptors

Sensory receptors that monitor skeletal muscles, joints, body position, and the skin surface, providing sensations of touch, pressure, pain, temperature, and proprioception.

Visceral Sensory Receptors

Sensory receptors that monitor internal conditions within cardiovascular, respiratory, digestive, urinary, and reproductive organs.

Somatic Nervous System (SNS)

The somatic motor division of the PNS that conveys efferent commands specifically to skeletal muscle effectors.

Autonomic Nervous System (ANS)

The visceral motor division of the PNS that regulates smooth muscle, cardiac muscle, glands, and adipose tissue, consisting of sympathetic and parasympathetic divisions.

Astrocytes

Abundant glial cells in the CNS that establish the blood-brain barrier, regulate the extracellular chemical environment, mop up leaked $K^+$ ions, recycle neurotransmitters, and communicate via calcium waves through gap junctions.

Satellite Cells

Glial cells in the peripheral nervous system that surround, cushion, and protect neuron cell bodies located within ganglia.

Schwann Cells

Neuroglial cells that wrap around nerve fibers in the peripheral nervous system to form insulating myelin sheaths.

Node of Ranvier

A myelin sheath gap along an axon where the axolemma is exposed to extracellular fluid and contains high concentrations of ion channels.

Lipofuscin

A brownish pigment byproduct of lysosomal activity that accumulates in aging neurons and can impede intracellular axonal transport in disorders such as Alzheimer's, ALS, and Parkinson's disease.

Multipolar Neuron

The most common structural class of neurons in the body and CNS, possessing multiple dendrites and a single axon, with its trigger zone situated at the axon hillock.

Unipolar (Pseudounipolar) Neuron

A structural class of sensory neurons found predominantly in the PNS with cell bodies in dorsal root ganglia, featuring a single process and a trigger zone located adjacent to the sensory receptors.

Resting Membrane Potential (RMP)

The voltage difference measured across the plasma membrane of a non-signaling excitable cell, typically $-70\,\text{mV}$ in neurons, reflecting a more negative charge inside relative to the outside.

Ohm's Law

The physical law governing electrical relationships, stating that current ($I$) equals voltage ($V$) divided by resistance ($R$), represented as $I = \frac{V}{R}$ or $V = I \times R$.

Leakage Channels

Non-gated ion channels in the plasma membrane that remain open continuously, permitting the passive diffusion of ions down their electrochemical concentration gradients.

Chemically Gated (Ligand-Gated) Ion Channels

Transmembrane channels that open or close in response to the specific binding of a chemical messenger, such as a neurotransmitter.

Voltage-Gated Ion Channels

Ion channels that open or close in response to direct fluctuations in the electrical potential across the cell membrane.

Sodium-Potassium Pump ($\text{Na}^+\text{-K}^+$ Pump)

An ATP-dependent active transport protein that maintains chemical gradients across the plasma membrane by pumping $3\,\text{Na}^+$ ions out of the cell and $2\,\text{K}^+$ ions into the cell.

Depolarization

A shift in membrane potential toward $0\,\text{mV}$, during which the cytoplasmic interior of the cell becomes less negative (more positive) compared to resting potential.

Hyperpolarization

An increase in membrane potential where the cell interior becomes more negative than the resting potential (moving toward $-90\,\text{mV}$), decreasing cellular excitability.

Graded Potential

A short-distance, decremental electrical signal occurring on dendrites and cell bodies whose amplitude is directly proportional to stimulus intensity and diminishes over time and distance.

Action Potential (AP)

A rapid, all-or-none reversal of membrane potential along an axon that propagates long distances without decaying, moving from $-70\,\text{mV}$ up to $+30\,\text{mV}$.

Threshold

The critical membrane potential (typically $-55\,\text{mV}$) that must be reached at the axon trigger zone to open voltage-gated $Na^+$ channels and ignite an action potential.

Absolute Refractory Period

The interval during an action potential from the opening of the $Na^+$ activation gates until the resetting of the inactivation gates, during which another action potential cannot be generated under any circumstances.

Relative Refractory Period

The phase following the absolute refractory period when $Na^+$ channels are reset to closed and voltage-gated $K^+$ channels remain open, requiring an exceptionally strong stimulus to trigger an action potential.

Continuous Conduction

The relatively slow wave of action potential propagation along unmyelinated axons, where voltage-gated channels regenerate the potential at each contiguous segment of axolemma.

Saltatory Conduction

The rapid form of impulse propagation in myelinated axons where electrical signals jump from one node of Ranvier to the next, conducting approximately $30\times$ faster than continuous conduction.

Synapse

A specialized functional junction that mediates information transfer between a presynaptic neuron terminal and a postsynaptic effector cell across the fluid-filled synaptic cleft.

Excitatory Postsynaptic Potential (EPSP)

A local graded depolarization of the postsynaptic membrane driven by neurotransmitter-gated influx of $Na^+$ ions that shifts membrane potential toward $0\,\text{mV}$.

Inhibitory Postsynaptic Potential (IPSP)

A local graded hyperpolarization of the postsynaptic membrane caused by neurotransmitter-induced outflow of $K^+$ or inflow of $Cl^-$, driving the membrane potential toward $-90\,\text{mV}$.

G Protein-Coupled Receptor (GPCR)

A transmembrane receptor that operates through indirect signaling, activating intracellular G proteins that stimulate adenylate cyclase to convert ATP into the second messenger cAMP.

Neuronal Pool

A functional cluster of interconnected neurons consisting of an input fiber, a central discharge zone where neurons receive ample synapses to reach threshold, and a peripheral facilitated zone where neurons are primed.

Diverging Circuit

A neural circuit organization in which one incoming presynaptic fiber synapses with multiple downstream neurons, amplifying a single input signal into many outputs.

Converging Circuit

A neural circuit configuration where multiple incoming presynaptic pathways funnel signals onto a single postsynaptic neuron, concentrating information from distinct sources.

Reverberating Circuit

An oscillating neural circuit where chain neurons send axon collaterals back to stimulate upstream neurons, producing continuous, repetitive output patterns.

Parallel After-Discharge Circuit

A neural circuit pattern where an incoming signal triggers parallel chains of differing lengths that converge on a single output cell, delivering a prolonged burst of impulses.