Dr Gawad Physiology Course Online Exam - Excitable – Nerve Exam

Stimulation with a threshold stimulus leads to a propagated action potential. This means that the stimulus is strong enough to depolarize the membrane of a neuron or muscle cell, causing an electrical impulse to be generated and travel along the length of the cell. This impulse can then be transmitted to other cells or muscle fibers, allowing for communication and coordinated movement.

The main cause of depolarization of a nerve is the influx of sodium ions (Na+). When the nerve cell is at rest, there is a higher concentration of sodium ions outside the cell compared to inside. However, when the nerve is stimulated, sodium channels open, allowing sodium ions to rush into the cell. This influx of positive ions depolarizes the cell, creating an electrical impulse that can be transmitted along the nerve.

The whole skeletal muscle is not applying the all or none rule. The all or none rule states that when a nerve impulse reaches a muscle fiber, the fiber will contract fully or not at all. However, in the case of a whole skeletal muscle, it is composed of multiple muscle fibers that can contract independently. This means that not all fibers within the muscle will contract simultaneously, and therefore the whole skeletal muscle does not follow the all or none rule.

The action potential of a nerve refers to the electrical signal that is generated and propagated along the nerve cell. It is a rapid and brief change in the membrane potential, which allows for the transmission of signals between neurons. The action potential is propagated along the length of the nerve cell, allowing for the communication of information over long distances. Therefore, the correct answer is "propagated."

After hyperpolarization occurs when the membrane potential becomes more negative than the resting potential. This is caused by the delayed closure of voltage-gated potassium channels. These channels open in response to depolarization and allow the outflow of potassium ions, which repolarizes the membrane. However, in the case of after hyperpolarization, these channels remain open for an extended period of time, causing an excessive outflow of potassium ions and leading to a more negative membrane potential.

The nodes of Ranvier are the most excitable areas of a myelinated nerve fiber. These are the small gaps in the myelin sheath where the axon is exposed. They contain a high concentration of voltage-gated sodium channels, which are responsible for the generation of action potentials. The myelin sheath insulates the axon and helps to speed up the conduction of electrical signals, but the nodes of Ranvier are necessary for the regeneration and propagation of the action potential along the nerve fiber.

The statement that the larger the diameter, the longer the duration of the spike is false. In reality, the larger the diameter of the nerve fiber, the shorter the duration of the action potential. This is because larger diameter fibers have lower internal resistance, allowing for faster depolarization and repolarization. Therefore, the duration of the spike is shorter in larger diameter fibers.

The given answer states that local response or local excitatory state is not a propagated potential. This means that it does not spread or propagate to neighboring areas. Local response refers to the changes in membrane potential that occur at a specific location in response to stimuli. Unlike action potentials, which are propagated along the length of the neuron, local responses are confined to the specific area where the stimulus was applied. Therefore, it is correct to say that local response is not a propagated potential.

During the stage of complete depolarization of the action potential, the potential difference between the outer and inner surface is zero. This is because the depolarization process involves the influx of positively charged ions, such as sodium (Na+), into the cell, which neutralizes the negative charge on the inner surface of the cell membrane. As a result, the potential difference across the membrane becomes zero, indicating a state of depolarization.

The correct answer is that the outer membrane is more negative than the inner membrane. This is because the outer membrane of a cell is typically more negatively charged compared to the inner membrane due to the presence of negatively charged molecules and ions on its surface. This difference in charge helps to maintain the electrochemical gradient across the cell membrane, which is essential for various cellular processes such as ion transport and cell signaling.

Unmyelinated nerve fibers conduct impulses in the form of continuous conduction. In continuous conduction, the nerve impulse travels along the entire length of the nerve fiber, without jumping from one node of Ranvier to another as in saltatory conduction. Continuous conduction is slower compared to saltatory conduction, but it does not require the additional energy needed to regenerate the action potential at each node. Therefore, continuous conduction is the correct answer as it accurately describes the conduction in unmyelinated nerve fibers.

The strength-duration curve is a graph that shows the relationship between the strength of an electrical stimulus and the duration required to elicit a response. The correct answer states that minimal time is the fastest response, regardless of the strength of the stimulus. This means that even a very weak stimulus can produce a response if it is applied for a short enough duration. This is because the minimal time required to elicit a response is independent of the strength of the stimulus.

The (Na-K) pump is a transmembrane protein that pumps sodium ions out of the cell and potassium ions into the cell. It does not have a large number of binding sites on its exterior aspect. Instead, it has binding sites on its interior aspect where the ATPase activity takes place. The ATPase activity is responsible for producing a conformational change that allows 2 K+ ions to be pumped inside the cell. The ions are pumped uphill against both the concentration and electrical gradients. The binding of (Na – K) to their respective binding sites activates the inner ATPase.

The first point of repolarization refers to the initial stage of the repolarization process, which occurs after the cell has been depolarized. During depolarization, the cell's membrane potential becomes more positive, and repolarization involves restoring the membrane potential back to its resting state. Therefore, the correct answer is "the first point stimulated (depolarized)" because it accurately describes the initial point in the repolarization process where the cell is stimulated and depolarized.

Hypocalcemia is not a membrane stabilizer because it refers to low levels of calcium in the blood, which can lead to various symptoms and complications but does not directly affect the stability of cell membranes. Procaine, on the other hand, is a local anesthetic that works by stabilizing the cell membranes, preventing the initiation and conduction of nerve impulses. Hypoxia and hypokalemia can also affect cell membrane stability, as they disrupt the balance of ions and oxygen necessary for proper cell function.

After depolarization is a representation of hypopolarized state. Depolarization refers to the change in the electrical potential across a cell membrane, making it less negative. After depolarization, the cell membrane returns to its resting potential, which is more negative than the depolarized state. In a hypopolarized state, the cell membrane is still slightly depolarized, but not as much as during the rapid depolarization stage. Therefore, option b is the correct representation of hypopolarized state.

Chemical and metabolic changes, specifically the breakdown of ATP, occur in the nerve during both the resting membrane potential (RMP) and depolarization. During the RMP, the nerve is at its resting state and ATP is broken down to provide energy for various cellular processes. During depolarization, there is a change in the electrical potential across the nerve cell membrane, and ATP breakdown is necessary to support the influx of ions and the propagation of the nerve impulse. Therefore, both options 1 and 2 are correct.