Question

1. What is responsible for wave summation:

1. Reduced zone of overlap
2. Excess ATP in the sarcoplasm between muscle contractions
3. Excess calcium in the sarcoplasm between muscle contractions
4. Over compressed sarcomeres

2. Which of the following is incorrect:

1. Curare mediates presynaptic blockade
2. The motor end plate contains nicotinic receptors
3. Junctional folds are sarcolemma
4. T tubules contain voltage-gated Na+ channels
5. The SR membrane contains RyR, CSQ, and SERCA

3. Which of the following associations is incorrect

1. Fast-twitch fibers :   Myoglobin
2. Type llx fibers   :   Powerful/quick contractions
3. Red meat    :    Slow twitch fibers
4. “Pay as you twitch” fibers   :   Relatively fatigue resistant

4. Which of the following proteins does Ca2+ bind to once it is released from the SR:

1. G-actin
2. Tropomyosin
3. Nebulin
4. Troponin

5. In the knee jerk reflex, which muscle group is being inhibited

1. Quadriceps
2. Calves
3. Hamstrings
4. Glutes

Answer 1

Ans1. Excess calcium in the sarcoplasm between muscle contractions

If the fibers are stimulated while a previous twitch is still occurring, the second twitch will be stronger. This response is called wave summation, because the excitation-contraction coupling effects of successive motor neuron signaling is summed.At the molecular level, summation occurs because the second stimulus triggers the release of more Ca++ ions, which become available to activate more cross-bridging while the muscle is still contracting from the first stimulus. Summation results in greater contraction of the motor unit.

Ans 2. Because T tubules contain voltage-gated Ca+ channels.

Ans3. A. Fast twitch fibres :myoglobin

Fast-twitch fibers are constituents of white muscles and have less or no myoglobin due to their primary reliance on glycolysis (anaerobic respiration) to fuel muscle contractions.

Ans 4. Troponin

Ca2+ ions that are stored in the SR are released to the cytosol via the activated RyR1, where they bind to troponin C, which then activates a series of contractile proteins and induces skeletal muscle contraction.

Ans 5. Hamstrings

When knee jerk reflex is elicited it inhibits the hamstring motor neurons while the quadriceps are stimulated to contract.