Dr Gawad Physiology Course Online Exam - Excitable – Course Lecture 6

During skeletal muscle relaxation, one of the steps involves the pumping of calcium (Ca) back into the sarcoplasmic reticulum. This process is essential for muscle relaxation as it helps to decrease the concentration of Ca in the cytoplasm. When the muscle is contracted, Ca is released from the sarcoplasmic reticulum, which allows for the binding of Ca to troponin C, leading to muscle contraction. However, during relaxation, the Ca needs to be removed from the cytoplasm to allow the muscle to return to its resting state. The pumping of Ca back into the sarcoplasmic reticulum helps to achieve this and allows for the muscle to relax.

After the spike potential, the muscle excitability is not abolished. In fact, after the spike potential, the muscle excitability is increased. This is due to the release of calcium ions from the sarcoplasmic reticulum, which triggers muscle contraction. Therefore, the statement "After the spike potential, the muscle excitability is abolished" is not true.

During isotonic muscle contraction, most of the energy is transformed into heat. Isotonic contraction refers to a type of muscle contraction where the muscle length changes while maintaining a constant tension. This type of contraction is responsible for movement and work done by the muscles. As the muscle contracts and shortens, it generates heat due to metabolic processes and energy expenditure. Therefore, during isotonic contraction, a significant amount of energy is converted into heat.

The correct answer states that the one-way conduction at the M.E.P. (motor end plate) is due to the location of the chemical mediator, acetylcholine, in the nerve terminals. This means that acetylcholine is released from the nerve terminals and binds to receptors on the motor end plate, triggering muscle contraction. This one-way conduction ensures that the signal travels in only one direction, from the nerve to the muscle, allowing for precise control of muscle movement.

The chronaxie is the minimum duration of an electrical stimulus required to elicit a response in a muscle or nerve. In the case of the reaction of degeneration, which occurs in damaged or denervated muscles, the muscle has a longer chronaxie. This means that it requires a longer duration of electrical stimulus to cause a contraction in the muscle. This is due to the loss of normal muscle innervation and the changes that occur in the muscle fibers as a result.

The transverse tubules (T.T.) do not contain Ca voltage gated channels. These channels are actually located on the sarcoplasmic reticulum, which is a specialized type of smooth endoplasmic reticulum found in muscle cells. The Ca voltage gated channels on the sarcoplasmic reticulum are responsible for releasing Ca ions into the cytoplasm of the muscle cell, which then bind to troponin C and initiate muscle contraction. The transverse tubules, on the other hand, are invaginations of the cell membrane that help to propagate action potentials deep into the muscle cell, allowing for synchronous contraction of the entire muscle fiber.

When a series of stimuli causes summation of contractions, it leads to tetanus. Tetanus is a sustained contraction of a muscle due to a rapid succession of stimuli. In this state, the muscle remains contracted and does not relax. This can occur naturally during certain activities or can be artificially induced in medical procedures. It is different from contracture, which refers to a prolonged muscle contraction due to a lack of relaxation, and tonus, which is the normal level of tension in a muscle at rest. Rigor refers to a stiffening of muscles after death, and spasm is an involuntary and sudden contraction of a muscle.