| excitable cell | <cell biology, physiology> A cell in which the membrane response to depolarisations is nonlinear, causing amplification and propagation of the depolarisation (an action potential). Apart from neurons and muscle cells, electrical excitability can be observed in fertilized eggs, some plants and glandular tissue. Excitable cells contain voltage gated ion channels. (18 Nov 1997) |
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| excitable gap | A short period in the cycle of the atrioventricular or intraventricular conduction allowing passage of an impulse which at other times would be blocked in transit. Synonym: excitable gap. (05 Mar 2000) |
| excitant | <physiology> An agent or influence which arouses vital activity, or produces increased action, in a living organism or in any of its tissues or parts; a stimulant. Source: Websters Dictionary (01 Mar 1998) |
| excitation | <physics, psychology> An act of irritation or stimulation or of responding to a stimulus, the addition of energy, as the excitation of a molecule by absorption of photons. Origin: L. Excitatio, citare = to call (18 Nov 1997) |
| excitation contraction coupling | <physiology> Name given to the chain of processes coupling excitation of a muscle by the arrival of a nervous impulse at the motor end plate to the contraction of the filaments of the sarcomere. The crucial link is the release of calcium from the sarcoplasmic reticulum and the analogy is often drawn between this and stimulus secretion coupling, that also involves calcium release into the cytoplasm. (18 Nov 1997) |
| excitation radiation | <radiobiology> Line radiation (at characteristic frequencies / wavelengths) as a result of the promotion of electrons or other constituent particles of a larger system to excited states, and the subsequent de-excitation of these states by radiative transitions. (09 Oct 1997) |
| excitation spectrum | Fluorescence produced over a range of wavelengths of the exciting light. (05 Mar 2000) |
| excitation wave | A wave of altered electrical conditions that is propagated along a muscle fibre preparatory to its contraction. (05 Mar 2000) |
| excitator | <physics> A kind of discarder. Origin: L, one who rouses. Source: Websters Dictionary (01 Mar 1998) |
| excitatory | Tending to produce excitation. (05 Mar 2000) |
| excitatory amino acid | <biochemistry> The naturally occurring amino acids L glutamate and L aspartate and their synthetic analogues, notably kainate, quisqualate and NMDA. They have the properties of excitatory neurotransmitters in the CNS, may be involved in long-term potentiation and can act as excitotoxins. at least three classes of EAA receptor have been identified, the agonists of the N type receptor are L aspartate, NMDA and ibotenate, the agonists of the Q type receptor are L glutamate and quisqualate, agonists of the K type are L glutamate and kainate. All three receptor types are found widely in the CNS and particularly the telencephalon, N and Q type receptors tend to occur together and may interact, their distribution is complementary to the K type receptors. The ion fluxes through the Q and K receptors are relatively brief, whereas the flux through the N type is longer and carries a significant amount of calcium. Additionally the N type receptor is blockaded by magnesium near the resting potential and thus shows voltage gated ion channel properties, leading to a regenerative response, this is why N type receptors have been linked to long-term potentiation. Invertebrate glutamate receptors may not have the same properties as those described above. (18 Nov 1997) |
| excitatory amino acid agents | Drugs used for their actions on any aspect of excitatory amino acid neurotransmitter systems. Included are drugs that act on excitatory amino acid receptors, affect the life cycle of excitatory amino acid transmitters, or affect the survival of neurons using excitatory amino acids. (12 Dec 1998) |
| excitatory amino acid agonists | Drugs that bind to and activate excitatory amino acid receptors. (12 Dec 1998) |
| excitatory amino acid antagonists | Drugs that bind to but do not activate excitatory amino acid receptors, thereby blocking the actions of agonists. (12 Dec 1998) |
| excitatory amino acids | Endogenous amino acids released by neurons as excitatory neurotransmitters. Glutamic acid is the most common excitatory neurotransmitter in the brain. Aspartic acid has been regarded as an excitatory transmitter for many years, but the extent of its role as a transmitter is unclear. (12 Dec 1998) |