Glossary of Physiology Terms – N
Newly synthesized or in the process of being synthesized
An equation used to calculate the equilibrium potential (Veq.
) of an ion. The equilibrium potential for an ion is also referred to as the Nernst potential for that ion. It is the membrane potential at which no net movement of the ion in question occurs across the membrane.
is the equilibrium potential, R
is the universal gas constant
is the temperature in Kelvin, z
is the valence of the ionic species, F
is the Faraday's constant
, and [X
are the extracellular and intracellular, respectively, concentrations of the ion in question.
See also:Resting Membrane Potential - Nernst Equilibrium PotentialDerivation of the Nernst Equation
Net flux represents the amount of substance moved in or out of the cell. It is the mathematical difference between influx and efflux.
Net flux = Influx − Efflux
Similar to influx and efflux, net flux is reported as a rate. It is the net amount of substance that moves through a given area of the plasma membrane per unit time.
Related glossary terms/phrases:FluxInfluxEffluxUnidirectional flux
Neurohormones are chemical messenger molecules that are released by neurons, but enter the bloodstream where they travel to distant target sites within the body. Therefore, neurohormones share characteristics with both neurotransmitters
. Similar to neurotransmitters, neurohormones are released by neurons. Similar to hormones, neurohormones travel in the bloodstream.
Two well-known examples of neurohormones are oxytocin and the antidiuretic hormone (also referred to as vasopressin).
Related glossary terms/phrases:HormoneNeurotransmitter
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:
receptor chloride channels.Tetrodotoxin:
Inhibitor of neuronal voltage-gated sodium channels.
Chemical messenger molecules released by neurons into the synaptic cleft.
Neurotransmitter molecules may be small molecules such as glutamate, γ
-aminobutyric acid (GABA), acetylcholine, dopamine, norepinephrine, serotonin (5-hydroxytryptamine), and glycine. These are referred to as classic neurotransmitters. A neuron generally releases only one type of small classic neurotransmitter.
Neurotransmitters may also be peptide molecules, such as substance P, opioids, and somatostatin. These are referred to as neuropeptides.
Gas molecules, such as nitric oxide (NO), may also act as neurotransmitters.
Posted: Saturday, March 9, 2013
Last updated: Sunday, February 7, 2016