Glossary of Physiology Terms
There are
20 glossary search results for:
volt
Definition:
The difference in electrical potential between two points.
Definition:
All-or-nothing is usually used when describing the
action potential. It refers to the well-known observation that an action potential always occurs in its full size (i.e., full magnitude of voltage change).
Many physiologists use
all-or-nothing and
all-or-none interchangeably.
See also:
Important Features of the Neuronal Action Potential
Definition:
An integral membrane protein which contains a pore through which ions, water, or polar molecules permeate. For any given channel, the pore is usually very selective for the particular ion or molecule. For example, sodium (Na
+) channels are very selective for Na
+ over other cations.
The channel pore may be constitutively open, or it may be gated to the open state by various stimuli such as chemical ligands, voltage, temperature, or mechanical stimulation of the membrane.
Definition:
Electrophysiology is the study of the electrical properties of biological macromolecules, cells, tissues, and organs. Electrical signals such as voltage and/or current are generally measured. Examples include measuring changes in the membrane voltage of excitable cells (e.g., neurons, muscle cells, and some endocrine cells) during an
action potential. The current carrried by ions as they permeate the pore of ion channels can also be measured - both at the single-channel level (single-channel current), as well as the macroscopic current resulting from the activity of a population of channels. As another example, electrical measurements may involve recording voltage changes at the surface of the skin that result from the activity of skeletal muscles (electromyogram, EMG), cardiac myocytes (electrocardiogram, ECG), or neurons in the brain (electroencephalogram, EEG).
Definition:
The Hodgkin cycle represents a positive feedback loop in neurons, where an initial membrane depolarization from the resting value (∼ −70 mV) to the threshold value (∼ −50 mV) leads to rapid depolarization of the membrane potential to approach the equilibrium potential for Na
+ (
VNa ≈ +60 mV). The voltage-gated Na
+ channels of neurons are responsible for the Hodgkin cycle.
See the
figure depicting the Hodgkin cycle.
See also:
Important Features of the Neuronal Action Potential
Definition:
Lidocaine is a local anesthetic and an antiarrhythmic drug. It is a commonly used local anesthetic for minor surgery and in dental procedures. Lidocaine is also used topically to relieve itching, burning, and pain from skin inflammations.
Lidocaine's mechanism of action is to block fast voltage-gated Na
+ channels of neurons and cardiac myocytes.
Other names used for lidocaine are xylocaine and lignocaine.
See also:
Pharmacological Inhibition of Na+ and K+ ChannelsOther resources:
Lidocaine (Wikipedia)
Definition:
The voltage difference across a cell plasma membrane.
The membrane potential is generally inside negative with respect to the outside, where the outside potential is generally set as the reference value. In electrically excitable cells, the value of the membrane potential can be positive (inside with respect to the outside) during electrical activity (i.e., during action potentials).
Related glossary terms/phrases:
Resting membrane potentialSee also:
Resting membrane potential
Definition:
Neurotoxins are chemical molecules that have an adverse effect on neuron function and, thus, disrupt the normal function of the nervous system. Neurotoxins could be small molecules or peptides and can be derived from a variety of invertebrate and vertebrate animals, as well as plant species.
The following is a short list of some examples of neurotoxins:
α-Bungarotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.
Chlorotoxin: A peptide neurotoxin that inhibits chloride channels.
α-Conotoxin: A peptide neurotoxin that inhibits the nicotinic acetylcholine receptor.
δ-Conotoxin: A peptide neurotoxin that inhibits voltage-gated sodium channels.
w-Conotoxin: A peptide neurotoxin that inhibits N-type voltage-gated calcium channels.
Picrotoxin: Inhibits GABA
A receptor chloride channels.
Tetrodotoxin: Inhibitor of neuronal voltage-gated sodium channels.
Definition:
The voltage difference across a cell plasma membrane in the resting or quiescent state. It is also simply referred to as the resting potential (
Vrest). The value of the resting membrane potential varies from cell to cell. Depending on the cell type, it can range from −90 mV to −20 mV.
For example,
Vrest is −90 mV in skeletal and cardiac muscle cells as well as in astrocytes. In a typical neuron,
Vrest is approximately −70 mV. In many non-excitable cells,
Vrest ranges from −60 to −50 mV. In photoreceptors,
Vrest is about −20 mV.
See also:
Resting membrane potential
Definition:
A rectangular signal waveform used in physiological studies to perturb (i.e., challenge) the system under study. The response of the system to the pulse is then studied carefully to learn about how the system responds to challenges.
Examples include pulses of voltage or current in electrophysiological experiments. Other examples include pulses of light, pressure, temperature, ligand, etc.
A square-wave pulse is defined by the amplitude and duration of the pulse, as well as by the frequency at which the pulse is applied to the system under study.
See also:
Neuronal Action Potential - IntroductionOther resources:
Square wave (Wikipedia)
Abbreviation:
TEA
Definition:
An inhibitor of voltage-gated potassium (K
+) channels.
TEA is a quaternary ammonium
cation (positively charged ion). It is also commonly used as a cation replacement for sodium (Na
+) in physiological buffers used in ion replacement experiments.
See also:
Pharmacological Inhibition of Na+ and K+ Channels
Definition:
The membrane voltage that must be reached in an excitable cell (e.g., neuron or muscle cell) during a depolarization in order to generate an action potential. At the threshold voltage, voltage-gated channels become activated. Threshold is approximately −50 to −40 mV in most excitable cells.
Related glossary terms/phrases:
Sub-thresholdSupra-thresholdSee also:
Neuronal Action Potential - Introduction
Posted: Sunday, March 31, 2013
Last updated: Friday, August 28, 2015