| twitch | 1. The act of twitching; a pull with a jerk; a short, sudden, quick pull; as, a twitch by the sleeve. 2. A short, spastic contraction of the fibres or muscles; a simple muscular contraction; as, convulsive twitches; a twitch in the side. 3. <veterinary> A stick with a hole in one end through which passes a loop, which can be drawn tightly over the upper lip or an ear of a horse. By twisting the stick the compression is made sufficiently painful to keep the animal quiet during a slight surgical operation. Source: Websters Dictionary (01 Mar 1998) |
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| twitch grass | <botany> See Quitch grass. Source: Websters Dictionary (01 Mar 1998) |
| twitch muscle | <physiology> Striated muscle innervated by a single motoneuron and having an electrically excitable membrane that exhibits an all or none response (c.f. Tonic muscle): in mammals almost all skeletal muscles are twitch muscles. Physiologists often divide muscles into fast and slow twitch types, the fast twitch muscles being associated with fast motor units. (18 Nov 1997) |
| isometric | 1. Of equal dimensions. 2. In physiology, denoting the condition when the ends of a contracting muscle are held fixed so that contraction produces increased tension at a constant overall length. Compare: auxotonic, isotonic, isovolumic. Origin: iso-+ G. Metron, measure (05 Mar 2000) |
| isometric chart | A chart or graph that displays three dimensions on a plane surface. (05 Mar 2000) |
| isometric contraction | Muscular contractions characterised by increase in tension without change in length. (12 Dec 1998) |
| isometric contraction period | The time between closure of the atrioventricular valves and opening of the semilunar valves. (05 Mar 2000) |
| isometric exercise | Exercise consisting of muscular contractions without movement of the involved parts of the body. (05 Mar 2000) |
| isometric period of cardiac cycle | That period in which the muscle fibres do not shorten although the cardiac muscle is excited and the pressure in the ventricles rises, extending from the closure of the atrioventricular valves to the opening of the semilunar valves (isovolumic constriction) or the reverse (isovolumic relaxation). (05 Mar 2000) |
| isometric relaxation | Decrease in tension of a muscle while the length remains constant due to fixation of the ends. (05 Mar 2000) |
| isometric relaxation period | Early ventricular diastole beginning with closure of the aortic and pulmonic valves and preceding opening of the atrioventricular valves. (05 Mar 2000) |
| isometric ruler | A calibrated scale for eliminating distortion in the measurement of plane surfaces. (05 Mar 2000) |
| isometric tension | Tension generated in a muscle without contraction occurring: cross bridges are being re formed with the same site on the thin filament and the tension (in striated muscle) is proportional to the overlap between thick and thin filaments. (18 Nov 1997) |
| isometric traction | Traction in which the length of the limb does not change. (05 Mar 2000) |