Question

18). Explain the events that occur in sequence from when an efferent (motor) neuron releases ACh to the motor end plate of a skeletal muscle cell until calcium ions contact troponin.

19). Describe the differences between muscle atrophy & muscle hypertrophy & give at least two (2) causes for each condition.

20). Describe four (4) causes of skeletal muscle fatigue.

Answer 1

18. When stimulus reach the neuromuscular junction acetylcholine choline vessicles fuse with the presynaptic neurone. This due to the opening of Voltage gated calcium channels. Thus ACH is released to the synaptic cleft. The Ach released gets in contact with the receptors of the motor endplate of the post synaptic membrane. This leads to influx of Na+ and efkux of K+ ions. The calcium is secreted by the sarcoplasmic reticulum via T tubules. The calcium that reaches the sarcolemma binds with the troponin tropomyosin complex which acts as blockage to the myosin binding site of the actin and thus remove the blockage.

19. Atrophy is the decrease in the muscle strength and thus leads to thinning the thinning of muscles. It's due to the loss of muscle mass. Hypertrophy if muscle is the enlargement of the muscle due to the increment in components of the muscle tissue. Atrophy may be caused by lack of exercise and poor nutrition. Hypertrophy may be caused by weight lifting, and increment in testosterone supply in the body.

20. Anemia can be a reason. In Anemia the RBC availability is less. So there is reduction in oxygen supply. So due to lack of oxygen anaerobic mechanism starts and lactic acid accumulate leading to muscle fatigue

Age is another reason. With age there is loss of myoglobin in the muscle. As this protein is lost muscle dont get enough oxygen and leads to fatigue.

Anaerobic infections. Due to this the lactic acid formed cannot be removed and leads to the fatigue situation.

Anxiety. Due to this the nerve fibres sends an increase in impulse leading to more contraction and the oxygen demand increase in the muscle due to the sympathetic stimulation and leads to fatigue.