VPB 121: Veterinary Physiology - II (2+1)

THERMAL CHANGES DURING MUSCLE CONTRACTION

• Out of total energy liberated by the hydrolysis of ATP in a contracting muscle, only 40-45% can be converted into work energy and the rest is evolved as heat; i.e. the efficiency of muscle contraction is about 45%. It is recorded by using thermopile. Thermopile has plates of antimony and bismuth connected to galvanometer. In a single twitch 0.001° to 0.005° C temperature produced.
• Total heat Produced = Wt. of muscle (gm) × Sp. Heat × Extent of temperature.

Fenn effect

• When a work is performed by the muscle and energy is required. Heat generation by a muscle is directly proportional to its work performance due to increase hydrolysis of ATP. This Of the total energy liberated from ATP, the muscle utilises 40 to 50% energy in performing work and the rest is liberated as heat to maintain body temperature.
• The liberated heat is classified as
• Resting heat: Used for biochemical reactions during resting state
• Initial heat: It is produced both at initiation and during the course of muscle contraction. It is dependant on aerobic change in the muscle due to breakdown of ATP and creatine PO₄ and formation of lactic acid. It consists of
  • Activation heat: produced due to Ca transport associated with initiation of contraction
  • Shortening heat: Liberated by sliding reaction, muscle lifts load and does external work.
  • Maintenance heat: Heat liberated in a muscle that is stimulated but does not lead to physical work (isometric contraction); it is proportional to duration of contraction and tension developed during contraction.
  • Recovery heat: Heat liberated after contraction of muscle fibre. It is due to pumping of Ca⁺⁺ back into the tubules and resynthesis of ATP for next cycle.

Effect of temperature in the muscle

• An increase of temperature shortens the latent and contraction periods whereas relaxation is not much affected.
• A decrease of temperature has the opposite effect causing increased latent and contraction period and prolonged relaxation period.
• When temperature exceeds a few degrees above 40 ° C, irreversible changes take place in the sarcoplasm.
• There is a minimum temperature (near 0⁰c) is required for muscle contraction, below which the muscle fibres fail to respond to stimulation; but the loss of excitation is reversible.