Omsi - Neurophys - Key Terms

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action potential

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The electrical signal conducted along axons (or muscle fibers) by which information is conveyed from one place to another in the nervous system.

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active transport

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The movement of a substance against its concentration gradient (from low to high concentration).

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depolarization

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The displacement of a cell's membrane potential toward a less negative value.

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electrochemical equilibrium

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The condition in which no net ionic flux occurs across a membrane because ion concentration gradients and opposing transmembrane potentials are in exact balance.

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equilibrium potential

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The membrane potential at which a given ion is in electrochemical equilibrium.

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Goldman equation

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A mathematical relationship that predicts the equilibrium potential across a membrane that is permeable one or more ions.

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hyperpolarization

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The displacement of a cell's membrane potential toward a more negative value.

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ion channel

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Integral membrane protein possessing pores that allow certain ions to diffuse across cell membranes, thereby conferring selective ionic permeability.

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Nernst equation

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A mathematical relationship that predicts the equilibrium potential across a membrane that is permeable only to one ion.

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overshoot phase

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The peak, positive-going phase of an action potential, caused by high membrane permeability to a cation such as Na+ or Ca+2

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receptor potential

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The membrane potential change elicited in receptor neurons during sensory transduction.

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resting membrane potential

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The inside-negative electrical potential that is normally recorded across all cell membranes.

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rising phase

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The initial, depolarizing, phase of an action potential, caused by the regenerative, voltage-dependent influx of a cation such as Na+ or Ca+2.

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synaptic potential

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An alteration in the membrane potential of a cell resulting from activation of a synaptic input.

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threshold potential

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The level of membrane potential at which an action potential is generated.

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undershoot

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The final, hyperpolarizing phase of an action potential, typically caused by the voltage-dependent efflux of a cation such as K+.

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activation

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The time-dependent opening of ion channels in response to a stimulus, typically membrane depolarization.

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conduction velocity

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The speed at which an action potential is propagated along an axon.

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inactivation

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The time-dependent closing of ion channels in response to a stimulus, such as membrane depolarization.

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membrane conductance

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The reciprocal of membrane resistance. Changes in membrane conductance result from, and are used to describe, the opening or closing of ion channels.

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membrane permeability

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The quality of cell membranes which permits the passage of solvents and solutes into and out of cells.

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multiple sclerosis

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A chronic progressive nervous disorder involving loss of myelin sheath around certain nerve fibers.

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myelin

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The multilaminated wrapping around many axons formed by oligodendricytes or Schwann cells.

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myelination

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Process by which glial cells wrap axions to form multiple layers of glial cell membrane that increase axonal conduction velocity.

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nodes of Ranvier

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Periodic gaps in the myelination of axons where action potentials are generated.

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passive current flow

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Current flow across neuronal membranes that does not entail the action potential mechanism.

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refractory period

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The brief period after the generation of an action potential during which a second action potential is difficult or impossible to elicit.

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saltatory conduction

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Mechanism of action potential propagation in myelinated axons; so named because action potentials "jump" from one node of Ranvier to the next due to generation of action potentials only at these sites.

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tetraethylammonium ions

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A quaternary ammonium compound that selectively blocks voltage-sensitive K+ channels; eliminates the delayed K+ current measured in voltage clamp experiments.

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tetrodotoxin

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An alkaloid neurotoxin, produced by certain puffer fish, tropical frogs and salamanders, that selectively blocks voltage-sensitive K+ channels; eliminates the initial Na+ current measured in voltage clamp experiments.

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voltage clamp technique

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A method that uses electronic feedback to control the membrane potential of a cell, simultaneously measuring transmembrane currents that result from the opening and closing of ion channels.

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ATPase pump

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Membrane pump that uses the hydrolysis of ATP to translocate ions against their electrochemical gradients.

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channelopathies

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Diseases caused by disturbed function of ion channel subunits or the proteins that regulate them. These diseases may be either congenital (often resulting from a mutation or mutations in the encoding genes) or acquired (often resulting from autoimmune attack on an ion channel).

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cyclic nucleotide gated channel

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An ion channel that opens in the presence of cyclic nucleotides.

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electrogenic pump

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A pump that is capable of generating an electrical current; usually applied to membrane transporters that create electrical currents while translocating ions.

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inactivation

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The time-dependent closing of ion channels in response to a stimulus, such as membrane depolarization.

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ion exchanger

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Membrane transporters that translocate one or more ions against their concentration gradient by using the electrochemical gradient of other ions as an energy source.

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ion selectivity

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The ability of a ion transporter to allow one type of ion (K+) while prohibiting others (Na+, Cl-, etc.)

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ligand-gated ion channel

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Term for a large group of nerotransmitter receptors that combine receptor and ion channel functions into a single molecule.

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macroscopic current

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Ionic currents flowing through large numbers of ion channels distributed over a substantial area of membrane.

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microscopic current

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Ionic currents flowing through single ion channels.

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mutagenesis

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An event capable of causing a genetic mutation.

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Na+ pump

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A type of ATPase transporter in the plasma membrane of most cells that is responsible for accumulating intracellular K+ and extruding intracellular Na+.

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mutagenesis

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Capable of causing a genetic mutation

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ouabain

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Cardiotonic that blocks sodium channel electrogenic pumps.

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pore

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A structural feature of membrane ion channels that allows ions to diffuse through the channel.

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selectivity filter

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The portion of a channel complex that is responsible for the selective permeability to ions.

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voltage-gated

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Term used to describe ion channels whose opening and closing is sensitive to membrane potential.

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X-ray crystallography

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A technique in which the patterns formed by the diffraction of X-rays on passing through a crystalline substance yield information on the lattice structure of the crystal, and the molecular structure of the substance