Neurophysiology: Resting Potential, Action Potentials, and Synaptic Transmission

Vocabulary practice flashcards covering resting membrane potentials, action potential generation and propagation, saltatory conduction, graded potentials, and synaptic transmission.

Neurophysiology

The study of the specialized life processes that allow neurons to use chemical and electrical signals to process and transmit information.

Polarization

The state of a resting neuron possessing a difference in electrical charge between the inside and the outside of the cell membrane.

Anion

A negatively charged ion, such as chloride ($\text{Cl}^-$) or intracellular organic proteins ($\text{A}^-$).

Cation

A positively charged ion, such as sodium ($\text{Na}^+$), potassium ($\text{K}^+$), or calcium ($\text{Ca}^{2+}$).

Phospholipid Bilayer

A semipermeable double layer of fatty molecules forming the cell membrane around the entire neuron (soma, dendrites, and axon) that freely permits water, oxygen, and carbon dioxide to cross.

Ion Channels

Membrane-spanning proteins that allow specific ions to pass into and out of the cell.

Leak Channels

Ion channels that stay open constantly, such as potassium ($\text{K}^+$) leak channels that grant neurons selective permeability.

Gated Channels

Ion channels in the cellular membrane that open and close in response to specific signals, such as changes in voltage or the binding of ligands.

Selective Permeability

The characteristic of the neuronal membrane that allows potassium ($\text{K}^+$) to enter and leave the cell freely through leak channels while restricting sodium ($\text{Na}^+$).

Resting Membrane Potential

The electrical potential difference across the cell membrane when a neuron is not producing an impulse, typically measuring between $-65\,\text{mV}$ and $-70\,\text{mV}$.

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

An active transport protein requiring $\text{ATP}$ that continually pushes $3\,\text{Na}^+$ ions out of the cell and pulls $2\,\text{K}^+$ ions in to maintain resting potential and osmotic balance.

Diffusion

The spontaneous movement of particles from areas of high concentration to areas of low concentration along a concentration gradient.

Electrostatic Pressure

The physical force causing ions to move toward oppositely charged areas and repel like charges along an electrical gradient.

Depolarization

A decrease in membrane potential where the interior of the cell becomes less negative and moves closer to $0\,\text{mV}$.

Hyperpolarization

An increase in membrane potential where the interior of the cell becomes more negative and moves farther below zero.

Threshold

The critical membrane potential (approximately $-40\,\text{mV}$ to $-55\,\text{mV}$) required to trigger an action potential by opening voltage-gated sodium channels.

Action Potential

A brief, all-or-none electrical impulse originating just after the axon hillock characterized by rapid depolarization, a positive overshoot to around $+30\,\text{mV}$ or $+40\,\text{mV}$, repolarization, and hyperpolarization.

All-or-None Property

The physiological rule stating that an action potential fires at full size or not at all; pushing a neuron past threshold does not increase the amplitude or speed of the impulse.

Absolute Refractory Period

The period immediately following an action potential during which voltage-gated $\text{Na}^+$ channels are inactivated and no stimulus can fire another action potential.

Relative Refractory Period

The time period following an action potential during which $\text{K}^+$ channels are still closing and outward flow of $\text{K}^+$ leaves the cell hyperpolarized, requiring a stronger-than-normal depolarizing stimulus to reach threshold.

Saltatory Conduction

The rapid mechanism of impulse propagation along myelinated axons in which electrical current spreads passively beneath myelin and the action potential actively regenerates at each node of Ranvier.

Node of Ranvier

An exposed gap between adjacent segments of myelin where voltage-gated $\text{Na}^+$ channels are concentrated to rebuild and propagate the action potential.

Local Anesthetics

Substances such as Novocain and Xylocaine that attach to voltage-gated sodium channels and block them, preventing $\text{Na}^+$ influx and eliminating the transmission of pain signals.

General Anesthetics

Compounds that open $\text{K}^+$ channels wider than normal, causing increased potassium outflow that keeps neurons hyperpolarized and suppresses brain activity.

Graded Potential

A local change in membrane potential at dendrites or the cell body that varies in size based on stimulus strength and decays passively as it travels.

Excitatory Postsynaptic Potential (EPSP)

A local, graded depolarization that makes the inside of a postsynaptic neuron slightly less negative, pushing it closer toward the firing threshold.

Inhibitory Postsynaptic Potential (IPSP)

A local, graded hyperpolarization that makes the inside of a postsynaptic neuron more negative, pushing it farther away from threshold.

Spatial Summation

The integration and combination of postsynaptic potentials arriving simultaneously from multiple different synapses or locations across the neuron.

Temporal Summation

The integration and stacking of postsynaptic potentials that arrive at the exact same synapse in rapid succession before previous potentials have decayed.

Exocytosis

The cellular process triggered by $\text{Ca}^{2+}$ influx wherein synaptic vesicles fuse with the presynaptic terminal membrane to discharge neurotransmitters into the synaptic cleft.

Synaptic Vesicle

A small membrane-bound sac inside the axon terminal that stores neurotransmitter molecules prior to release.

Kiss and Run

A process of transmitter release under low $\text{Ca}^{2+}$ concentration where a vesicle partially fuses with the membrane, releases a portion of its content, and reforms into a vesicle without undergoing full membrane integration.

Ionotropic Receptor

A fast-acting, ligand-gated ion channel that directly opens upon neurotransmitter binding to allow ions through and instantly generate an EPSP or IPSP.

Metabotropic Receptor

A slow-acting receptor protein that does not contain an ion pore, but instead activates G proteins and second messenger pathways to indirectly regulate ions and induce structural changes in the synapse.