- Fatigue is defined as decrease in performance due to continuous and prolonged activity.
- This could be due to lack of nutrition, accumulation of waste metabolites or depletion of neurotransmitter.
Q.1 What is the site and cause of fatigue in the
nerve-muscle preparation?
Site of fatigue:
- The nerve fibers, the neuromuscular junctions, and the muscle fibers. The fact that the nerve is practically unfatiguable, and that direct stimulation of muscle causes contraction, indicates, by exclusion, that neuromuscular junction is the seat of fatigue in this very artificial preparation which has no blood supply.
Cause of fatigue:
- Depletion of acetylcholine from the motor nerve endings and interference with neuromuscular transmission by substances like pyruvic and lactic acids, and breakdown products of ATP.
Q.2 What is contraction remainder and what is its cause?
- A delay in the relaxation period is an early sign of fatigue. When fatigue sets in, the muscle is unable to relax fully and remains in a state of partial contraction called contraction remainder. Since ATP, by removing Ca2+ ions from the cytoplasm, is responsible for relaxation, a decrease of ATP and accumulation of metabolites appear to be responsible for the inability of all the myosin heads to disengage from the active sites on actin filaments (Compare with rigor mortis).