Also found in: Dictionary, Thesaurus, Legal, Encyclopedia, Wikipedia.
existing and ready for action, but not active.
electric tension or pressure.
action potential see action potential.
after-potential the period following termination of the spike potential.
auditory evoked potential in electroencephalography, changes in waves in response to sound; see also brainstem auditory evoked potential.
brainstem auditory evoked potential that portion of the auditory evoked potential that comes from the brainstem; abnormalities can be analyzed to evaluate comas, to support diagnosis of multiple sclerosis, and to detect early posterior fossa tumors.
cognitive event--related p's a diagnostic study that uses electroencephalographic equipment and a computer dedicated to analyze brain wave P300; this wave is a measure of the brain's active cognitive processing of information. The patient is instructed to complete a task that requires attention and information processing. A recording of brain wave activity as well as information related to cognitive function is produced.
diastolic potential the transmembrane potential of the cell during electrical diastole.
maximal diastolic potential the most negative level attained during the cardiac cycle by the cell membrane of a fiber that does not have a constant resting potential, occurring at the end of phase 3 of the action potential. In pacemaker cells this is a point of hyperpolarization.
membrane potential the electric potential that exists on the two sides of a membrane or across the wall of a cell.
resting potential (resting membrane potential) the difference in potential across the membrane of a cell when it is at rest, i.e., fully repolarized. In cardiac physiology this occurs during electrical diastole in pacemaker cells and continuously in nonpacemaker cells.
spike potential the initial, very large change in potential of the membrane of an excitable cell during excitation.
threshold potential the transmembrane potential that must be achieved before a membrane channel can open; it differs among the various cardiac membrane channels.
the potential inside a cell membrane, measured relative to the fluid just outside; it is negative under resting conditions and becomes positive during an action potential.
Synonym(s): transmembrane potential
Etymology: L, membrana + potentia
the difference in electrical polarization or charge between two sides of a membrane or cell wall. Also called electric potential gradient.
membrane potentialElectrical potential due to the differences in the concentrations of ions on either side of a semipermeable membrane.
membrane potentialCardiology The voltage difference between the inside and outside of resting excitable–neurons and muscle, not-yet depolarized cells
mem·brane po·ten·tial(mem'brān pŏ-ten'shăl)
The potential inside a cell membrane, measured relative to the fluid just outside; it is negative under resting conditions and becomes positive during an action potential.
membrane potentialThe difference in millivoltage between one side of a membrane and the other.
membrane potentialthe potential difference between the two sides of a cell membrane. see NERVE IMPULSE.
a thin layer of tissue that covers a surface, lines a cavity, or divides a space or organ.
a thin tissue barrier through which gases are exchanged between the alveolar air and the blood in the pulmonary capillaries.
complement components C5-C9 which form in terminal stage of either of the complement pathways and lead to cell lysis.
the lower boundary of the scala media of the ear.
a thin layer of basement membrane between the outer layer of stratified epithelium and the substantia propria of the cornea.
the inner layer of the choroid, separating it from the pigmented layer of the retina.
a mechanism in the cell membrane of epithelial cells in the intestinal mucosa which facilitates the rapid transport of for example glucose, into the cell and thus into the bloodstream.
plasma membrane (below).
the middle of the three membranes on the outside of the yolk of the hen egg.
the membrane connecting the thyroid cartilage to the cricoid cartilage. It is extensive in the horse and surgical incision through it allows access to the interior of the larynx.
the posterior lining membrane of the cornea; it is a thin hyaline membrane between the substantia propria and the endothelial layer of the cornea.
tympanic membrane (below).
those that protect the embryo or fetus and provide for its nutrition, respiration and excretion; the yolk sac (umbilical vesicle), allantois, amnion, chorion, decidua and placenta.
the outermost of the three membranes on the outside of the yolk of the hen egg.
a membrane similar to the pseudomembrane; fibrinous exudates readily loosened from underlying tissue, as in croupous or pseudomembranous inflammation.
one of the perforated elastic sheets of the tunica intima and tunica media of arteries.
see fetal membranes. See also extraembryonic membranes (above).
the strong, fibrous support layer in a joint capsule.
see henle's membrane.
1. a membrane between the outer root sheath and inner fibrous layer of a hair follicle.
3. a homogeneous eosinophilic membrane lining alveolar ducts and alveoli, frequently found at necropsy in premature human infants. See also hyaline membrane disease.
a fibrous lamina connecting the under-surface of the tongue with the hyoid bone.
the membrane connecting the shaft of the fibula to the tibia.
one that constitutes the border of some tissue or structure.
the membrane covered with epithelium that lines many tubular organs of the body.
see membrana nictitans.
1. either of the membranes, inner and outer, comprising the nuclear envelope.
2. nuclear envelope.
the olfactory portion of the mucous membrane lining the nasal fossa.
the innermost of the three layers on the outside of the yolk in the hen egg.
the membrane that separates the fetal from the maternal blood in the placenta.
the membrane that encloses a cell; it is composed of phospholipids, glycolipids, cholesterol and proteins. The primary structure is a lipid bilayer. Phospholipid molecules have an electrically charged 'head' that attracts water and a hydrocarbon 'tail' that repels water; they line up side by side in two opposing layers, with their heads on the inner or outer surface of the membrane and their tails in the core, from which water is excluded. The other lipids affect the structural properties of the membrane. Proteins embedded in the membrane transport specific molecules across the membrane, act as hormone receptors, or perform other functions.
of a cell is the voltage difference across the cell membrane resulting from the differential concentrations of sodium and potassium on either side of the membrane. The resting potential, for example in a nerve cell, is altered by the temporary opening of the sodium channels in the membrane during an action potential, allowing a redistribution of the ions.
the large number of proteins attached to a cell membrane. They include integral proteins, called also intrinsic, which are embedded in the phospholipid bi-layer of the cell membrane, and peripheral proteins, called also extrinsic, because they are loosely bound and can readily be extracted without damage to the cell membrane.
a vascular membrane which occupies the pupil in the embryo stage, completely covering the anterior surface of the lens but subsequently disappears. See also persistent pupillary membrane.
the thin anterior wall of the cochlear duct, separating it from the scala vestibuli.
tympanic membrane, secondary.
one permitting passage through it of some but not all substances.
see serous membrane (below).
the membrane lining the walls of the body cavities and enclosing the contained organs; it consists of mesothelium lying upon a connective tissue layer and it secretes a watery fluid.
the membrane on the outside of the soft contents of the hen egg and just inside the shell. It consists of two membranes close together, with an air cell in between.
see synovial membrane.
transport of electrolytes across semipermeable membranes with the aid of a transporter.
the trilaminar structure of all cellular membranes (such as the plasma membrane, nuclear membranes, mitochondrial membranes, endoplasmic reticulum, lysosomes) as they appear in electron micrographs. The biochemical structure is a lipid bilayer.
the membrane comprising the wing of the bat.
the membrane investing the yolk of the hen egg; it includes (from the inside out) the perivitelline, the continuous and the extravitelline membranes.
1. existing and ready for action, but not active.
2. electric tension or pressure.
see action potential.
the period following termination of the spike potential.
see membrane potential.
the potential difference across the membrane of a normal cell at rest.
the initial, very large change in potential of an excitable cell membrane during excitation.
a net negative charge.