Question

Nervous stimulation of muscles a. occurs at a neuromuscular junction. b. results in an impulse that travels down the T system. c. causes calcium to be released from expanded regions of the sarcoplasmic reticulum. d. All of these are correct.

Short answer

Nervous stimulation of muscles occurs at a neuromuscular junction, results in an impulse that travels down the T system, and causes calcium to be released from expanded regions of the sarcoplasmic reticulum. Therefore, the correct answer is (d) All of these are correct.

Step-by-step solution

Understanding the neuromuscular junction

Neuromuscular junction is the point where a motor neuron communicates with a muscle cell by releasing neurotransmitters. The released neurotransmitters then bind to receptors on the muscle cell's membrane, causing electrical signals to be generated in the muscle cell, leading to muscle contraction.

Explaining the T system

The T system (also called the transverse tubule system) is an extensive network of tubules that extend deep into the muscle cell. It serves as a pathway for electrical signals, like the ones generated by nervous stimulation, to travel inside the cell and reach the sarcoplasmic reticulum.

Addressing calcium release

The sarcoplasmic reticulum (SR) is an organelle found within muscle cells and is responsible for the storage and release of calcium ions. Expanded regions of the SR, called the terminal cisternae, release calcium ions into the cytoplasm of the muscle cell when stimulated by electrical signals. The released calcium ions then bind to the protein called troponin, which eventually leads to muscle contraction.

Evaluating the options

Now that we have understood each statement, let's evaluate the exercise options: a. True. Nervous stimulation of muscles occurs at a neuromuscular junction, as explained in Step 1. b. True. The impulse generated by nervous stimulation travels down the T system to reach the sarcoplasmic reticulum, as explained in Step 2. c. True. Calcium is released from expanded regions of the sarcoplasmic reticulum, called terminal cisternae, as explained in Step 3. Since all of the statements are correct, the answer is: d. All of these are correct.