Question

1. The loss of which of the following would prevent depolarization traveling into the skeletal muscle fiber?

Transverse tubules

Sarcolemma

Sarcomeres

The sarcoplasmic reticulum

Myosin filaments

Answer 1

Option B: Sarcolemma is the correct answer.

Explanation:

Without any stimulation, the cells present in resting membrane potential. If the signals starts, it creates depolarization known as action potential.

It spreads the impulses to the receiver.

Action potential in muscle fibres:

• It started from the motor nerve, the end point is known as axonal terminal. It reaches the muscle through the neuromuscular junction.
• In the junction, impulses passes from the presynaptic membrane into post synaptic membrane by the release of acetylcholine neurotransmitter.

Muscle cell:

Muscle cell is called as muscle fibre. The muscle cell has all the parts like the other cells. The cytoplasm of muslce cell is known as sarcoplasm.

The plasma membrane is called as sarcolemma.

It has the nucleus, sarcoplasmic reticulum, golgi apparatus & mitochondria.

How action potential enters muscle:

• The post synaptic membrane is the muscle.
• Each muscle cell/ fibre is covered by sarcolemma. In the post synaptic membrane, the action potential is reaches the sarcolemma of the muscle fibre.
• The sarcolemma is opens into the interior of muscle fibre as Transverse - tubules. They spreads the action potential into all parts of muscle.
• Then impulses reaches L - tubules which releases the calcium ions. The released C+ ions reaches the tropomysin C & opens the actin site free.
• So the myosin head attaches to the actin site. This binding action results in muscular contraction.

In the post synaptic membrane, the outer covering of the muscle cell, sarcolemma is responsible for the depolarization of the muscle. Loss of this part may results in the absence of depolarization of muscle.

Option A: T - tubules is wrong. Because from the sarcolemma only the impulses reaches T- tubules. The main function of these tubules is the rapid spread of action potential into the muscle.

Option C: Sarcomere is wrong. Sarcomere is the basic structural & functional unit of muscle cell. The muscle cell has the myofibrils ( filaments). Sarcomere is the basic part of these filaments.

It responsible for the muscle contraction.

But loss of these may affects the contractions but not the depolarization.

Option D: Sarcoplasmic reticulum is wrong. This structure presents inside the cell. T & L tubules embedded here. Its main function is to store the calcium ions. The depolarizarion spreads into L - tubules & releases the calcium. Absence of this part won't stop the depolarization.

Option E: Myosin filaments were the part of sarcomere. It is one of the contractile elements in sarcomere. Takes part in muscle contraction but no action with the depolarization.