The muscle generates heat, even when It is resting An additional amount of heal is produced. when it contracts For The present discussion,

Vgreus ways, (v) repetitive stimuli causa (atigue of the muscle Exact cause of faligue is debatable, but probably wines in the isolated muscle from the 'general latigue'. (iv) The foice generated by the muscle is variable and depends upon several factors, notably on rls relaxed length, the load and recruitment, (VI) the efficiency of the muscle also varies from time to time and depends on the relaxed length and bad. THERMAL PROPERTIES OF THE SKELETAL MUSCLE Thermal changes AV Hill made the funoamental works which were later extende d enormously with the help of modern instruments (which can record very small temperature changes accurately in a time scale). The present day conception is staled below. The muscle generates heat, even when It is resting An additional amount of heal is produced. when it contracts For The present discussion, only this additional neat [henceforth referred simply as heat) will to considered" (A) In case of a single Lwitah. The heal evolve in several phases and named accordingly. The phases are, (i) activation heat (ii) shortening heal, (in) heat for the work done and (Iv) recovery heat, (i) Activation heat, (also called the initial heat) is liberated before the actual contraction of the muscle. It Is due lo mostly, The hear liberated white Ga++ ens are released from the L system (n) Shortening heal is The heal liberated in the next phase, when the muscle e actually shortening... This heal may be due To movements of The cross bridges and myofilaments. (iii) Heat for the work done, (better known as the Fenn effect) aspens upon the work done If more work is dane more heat of this type is liberated Ultimately speaking, more work done means moie expenditure of ATP Therefore Fenn effect oan be retold in another way Fenn effect says more work done causes more expenditure of ATP (iv) Recovery heal is released when the muscle is recovering From the effects of contraction and is due to various chemical processes aimed towards the resynthesis of the chemicals broken down during the contraction(B) in case of an isometric and letanlcally comraGling muscle. The heal evolved is called •maintenance heat1 its cause is complicated and mostly obscure Born In 1686, Sir Archibald Vlvin HUE shared a Nobel Prize with Olio Meyerhoff the great German biochemist) in 1922 In he researches on thermal changes of muscle during is contraction, Hill was ably assisted by William HarTree Incioentally, Harliee firsl published his paper on the muscle heat production al the age of 50 and while he was 71 he switched on to researches on the structure of atom. Considering that Hartree started his life as a teacher In engineering department, this, to say the least, is unusual AV Hill. came to Calcutta after the 2nd World War and was vanously associated with The then Cateullan physiogets. ELECTRICAL PROPERTIES Most of the issues have been discussed previously; therefore, only a summary is given: 1 At rest, the muscle fiber is polarized, e, the interior is - ve with respect to the exterior. The value of This resting membrane potential 15 about - 90 mV. 2 When the molor nerve liber to the muscle is stimulated an action potential develops and propagates with un diminished intensity any reaches the neuromuscular junction to cause a release of the ACh. the chemical transmitter. 3 ACh causes envelopment of end plate potential fl=PPi In the motor end plate. 4. The EPP, in turn causes development of a single action potential. (AP) on the sarcotemma. The AP travels both ways and eventually causes muscular contraction. 5. If the motor nerw liber develaps repelilive APs (say, as a result to repetitive slimull) then in response to each AP of the motor nerve, the sareolemma develops an AP, although the muscle itself might have gone into a (complete orincomplele) tetanus [N. B. If a direct stimulation of the muscle (i.e. , not via its nerve), is intended, The muscle has lo be previously curartzed and Then induction shocks have to be applied by placing hand electrodes directly on the surface of the muscle. ELECT ROM VOGRAPHV (EMG) In EMG practice, electrodes are placed on the surface of the skin or needle