Dr Gawad Physiology Course Online Exam - Excitable - Lec 1 (Introduction, Resting Membrane Potential, Action Potential)

The main cause of depolarization of a nerve is the influx of sodium ions (Na+). When a nerve is at rest, there is a higher concentration of sodium ions outside the cell compared to inside. However, when a nerve is stimulated, sodium channels open, allowing sodium ions to enter the cell. This influx of positive ions leads to a change in the electrical charge of the cell membrane, causing depolarization and the generation of an action potential.

During repolarization of a nerve, the cell membrane returns to its resting state after depolarization. This is achieved by the out flux of potassium ions (K+) from the cell. As the K+ ions move out of the cell, the positive charge inside the cell decreases, leading to the restoration of the negative resting membrane potential. Therefore, the out flux of K+ is responsible for repolarization in nerve cells.

The ascending limb of nerve action potential is due to the movement of Na+ ions through voltage-gated channels. These channels open in response to a change in the membrane potential, allowing Na+ ions to flow into the cell and depolarize it. This depolarization is responsible for the propagation of the nerve impulse along the axon. Leak channels allow for the passive movement of ions down their concentration gradient, while ligand-gated channels open in response to the binding of a specific molecule. Therefore, neither leak channels nor ligand-gated channels are responsible for the ascending limb of the nerve action potential.

The resting membrane potential (RMP) is due to a combination of factors. Passive movements of ions along the membrane contribute to the establishment of RMP. The selective permeability of the membrane allows certain ions to pass through more easily, influencing the RMP. Active transport of sodium (Na) and potassium (K) ions also plays a role in maintaining RMP. Additionally, the impermeability of the membrane to proteins helps maintain the electrical balance required for RMP. Therefore, all of the given options contribute to the establishment of RMP.

The given statement suggests that all the statements regarding the physiology of the active (Na-K) pump are true. This means that the active (Na-K) pump is a transmembrane protein with a large number of binding sites on its interior aspect. It has inner ATPase activity, which produces a conformational change followed by the pumping of 2 K+ ions inside. The ions migrate uphill against both the concentration and electrical gradients. The binding of (Na-K) to their respective binding sites activates the inner ATPase.

The correct answer is that the outer membrane is more negative than the inner membrane. This is because the outer membrane of a cell typically has a higher concentration of negatively charged ions compared to the inner membrane. This difference in charge creates a polarity across the cell membrane, with the outer membrane being more negative and the inner membrane being more positive. This polarity is important for various cellular processes, including the movement of ions and the generation of electrical signals.

At the stage of complete depolarization of the action potential curve, the potential difference between the outer and inner surface is zero. This means that the electrical charge inside and outside the cell membrane is equal, resulting in no potential difference. This occurs when the cell membrane is fully depolarized and the action potential has reached its peak.

The point of rapid complete depolarization occurs when the potential difference between the outer and inner membranes is zero. This means that there is no electrical charge difference between the two membranes, indicating a state of equilibrium.