Discussion

Match the following and select the correct answer from the codes given below :

Site of Fatigue	Proposed Mechanism
(1) Neuromuscular junction	(I) Lack of oxygen and inadequate blood flow
(2) Contractile mechanism	(II) Local distribution caused by contractile fatigue signals
(3) Central nervous system	(III) Decreased release of acetylcholine at nerve ending

Answer: A

The correct match is 1-III, 2-I, 3-II.

At the neuromuscular junction, fatigue is attributed to decreased release of acetylcholine at the nerve ending, so the signal no longer passes to the muscle fibre (1-III).
In the contractile mechanism, fatigue is linked to lack of oxygen and inadequate blood flow, which lead to accumulation of lactic acid and depletion of energy stores (2-I).
In the central nervous system, local disturbance caused by fatigue signals from the contracting muscles reduces the drive to the muscles (3-II).

Codes that put acetylcholine release at the CNS or blood flow at the junction mismatch these sites.

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