1. Each muscle fiber is a bundle of myofibrils. Each myofibril is a series of sa
ID: 49991 • Letter: 1
Question
1. Each muscle fiber is a bundle of myofibrils. Each myofibril is a series of sarcomeres. Thus, a muscle fiber contracts when each sarcomere within a series contracts simultaneously. Such coincidence is mirrored by each myobril within the muscle fiber. What enables the extent to which molecular motors contract simultaneously within an innervated muscle fiber?
a. the frequency of acetylcholine secretion within the neuromuscular synapse
b. the frequency of Ca2+ oscillations within the muscle fiber
2. A living muscle fiber experiences dynamic frequencies of Ca2+ oscillations. In effect, Ca2+ acts as a second messenger when it disperses throughout the fluid-filled spaces between actin and myosin filaments. What is the source of this second message?
a. extracellular fluid b. sarcoplasmic reticulum
3. Why might a muscle fiber need an ample amount of Na+, K+-ATPase on its surface?
a. as evident by the value of the cell’s membrane potential, muscle fibers are leaky to Na+
b. to counter the effect of numerous action potentials per second
4. Assume that you could “see” nicotinic acetylcholine receptors within the musculature. How would they be arranged spatially?
a. evenly distributed on the cell’s surface like voltage-gated Na+ and K+ channels
b. in dense arrays within the motor end plate
5. Assume that you could “see” neurosecretion from -motor neurons within the musculature of an animal standing still. What would this “look” like?
a. uniform, baseline secretion throughout the musculature
b. enhanced acetylcholine secretion within antigravity muscles, baseline secretion elsewhere
Explanation / Answer
1. Answer is a. the frequency of acetylcholine secretion within the neuromuscular synapse
When nerve impulse arrives at the end plate of motor neuron, it causes the release of acetylcholine into synaptic cleft between the end plate and the folded muscle fiber membrane. This produces EPP( end plate potential) in excess of excitation threshold and generating impulses which travel over the muscle fiber membrane and ultimately deep into the muscle fiber. This activates the contractile process of the muscle fibre.
2. Answer is b. sarcoplasmic reticulum.
Most of the calcium that act on the muscle fibre come from sarcoplasmic reticulum. SR is a place in muscle fibre which stores the calcium ion and release it when there is muscular contraction.
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