Dr Gawad Physiology Course Online Exam - Excitable - Lec 2 (Action Potential, Compound Action Potential, All Or None Rul

1.

The main cause of depolarization of nerve is:
- A.
  
  K outflux
- B.
  
  Na influx
- C.
  
  Cl outflux
- D.
  
  None of the above
Correct Answer
B. Na influx

Explanation
The main cause of depolarization of a nerve is the influx of sodium ions (Na+). When a nerve is stimulated, the membrane becomes permeable to sodium ions, allowing them to enter the cell. This influx of positive ions leads to a change in the electrical charge across the membrane, resulting in depolarization. This depolarization is an essential step in the transmission of nerve impulses.

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2.

At stage of complete depolarization of action potential of the curve
- A.
  
  K out flux is the major change
- B.
  
  Na out flux is the major change
- C.
  
  The potential difference between outer and inner surface is Zero
- D.
  
  Na-K pump is acting with full capacity
Correct Answer
C. The potential difference between outer and inner surface is Zero

Explanation
At the stage of complete depolarization of the action potential, the potential difference between the outer and inner surface is zero. This is because during depolarization, the membrane potential becomes more positive, reaching a peak value. At this point, the electrical charge inside and outside the cell equalizes, resulting in zero potential difference. This is a characteristic feature of the depolarization phase of the action potential.

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3.

Reversal of polarity, which is true:
- A.
  
  Outer membrane is more negative than inner membrane.
- B.
  
  Action potenial is – 50 mv
- C.
  
  Potential magnitude is + 35 mv
- D.
  
  None of the above
Correct Answer
A. Outer membrane is more negative than inner membrane.

Explanation
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 negative charge due to the presence of negatively charged molecules, such as phospholipids and proteins. On the other hand, the inner membrane usually has a positive charge. This difference in charge between the outer and inner membranes creates a polarity, with the outer membrane being more negative.

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4.

Repolarization of nerve coincides with:
- A.
  
  Influx of Na
- B.
  
  Out flux of K
- C.
  
  Out flux of Cl
- D.
  
  Impermeability of the membrane to protein
Correct Answer
B. Out flux of K

Explanation
During repolarization, the cell membrane returns to its resting state after depolarization. This is achieved by the outflux of potassium ions (K+) from the cell. As the potassium channels open, potassium ions move out of the cell, restoring the negative charge inside the cell and bringing it back to its resting membrane potential. Therefore, the outflux of K+ ions is responsible for repolarization of the nerve.

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5.

Ascending limb of nerve action potential is due to Na movement through
- A.
  
  Leak channels
- B.
  
  Ligand gated channels
- C.
  
  Voltage gated channels
- D.
  
  None of the above
Correct Answer
C. Voltage gated channels

Explanation
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 membrane potential, allowing Na+ ions to flow into the cell, resulting in depolarization and the generation of an action potential. Leak channels allow the passive movement of ions across the membrane, but they do not play a significant role in the ascending limb of the nerve action potential. Ligand-gated channels open in response to the binding of specific molecules, but they are not responsible for the ascending limb of the action potential either.

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6.

Which of the following is a representation of hypopolarized state:
- A.
  
  Stage of rapid depolarization
- B.
  
  After depolarization
- C.
  
  After hyperpolarization
- D.
  
  All after potential stages
Correct Answer
B. After depolarization

Explanation
After depolarization refers to the stage that occurs immediately after depolarization, where the membrane potential returns to its resting state. During depolarization, the membrane potential becomes more positive, and after depolarization, it returns to its negative resting state. This is a representation of a hypopolarized state because the membrane potential is lower than its resting potential.

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7.

Which of the following is false regarding compound action potential:
- A.
  
  The largest the diameter the fastest velocity conduction
- B.
  
  Myleinated (medullated) nerves are faster than non myleinated
- C.
  
  The larger the diameter the longer the duration of the spike
- D.
  
  - the larger the diameter the bigger the magnitude of action potential
Correct Answer
C. The larger the diameter the longer the duration of the spike

Explanation
The larger the diameter of a nerve, the faster the velocity of conduction because a larger diameter allows for a greater surface area for ion channels to be present, resulting in faster transmission of the action potential. Myleinated (medullated) nerves are indeed faster than non-myleinated nerves due to the presence of myelin sheath, which acts as an insulator and speeds up conduction. However, the statement that the larger the diameter, the longer the duration of the spike is false. The duration of the spike is not dependent on the diameter of the nerve but rather on other factors such as the properties of the ion channels involved and the refractory period of the nerve.

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8.

Which of the following is not applying all or none rule:
- A.
  
  Single nerve fiber
- B.
  
  Single nerve fiber of mixed nerve
- C.
  
  Whole skeletal muscle
- D.
  
  Cardiac muscle
Correct Answer
C. Whole skeletal muscle

Explanation
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. In the case of a whole skeletal muscle, it is made up of multiple muscle fibers that can contract individually. Therefore, the contraction of the whole skeletal muscle is not dependent on the all or none rule, as not all fibers may contract simultaneously.

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9.

The main cause of after hyperpolarization is
- A.
  
  Delayed Na channel closure
- B.
  
  Massive inward movement of Cl ions
- C.
  
  Delayed voltage K channels closure
- D.
  
  Na-K pump activation
Correct Answer
C. Delayed voltage K channels closure

Explanation
After hyperpolarization refers to a period of hyperpolarization following an action potential, where the membrane potential becomes more negative than the resting potential. This is caused by the delayed closure of voltage-gated potassium (K+) channels. These channels open during the depolarization phase of the action potential, allowing K+ ions to leave the cell and repolarize the membrane. However, they do not immediately close after repolarization, leading to an efflux of K+ ions and further hyperpolarization. Therefore, the delayed closure of voltage-gated K+ channels is the main cause of after hyperpolarization.

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Dr Gawad Physiology Course Online Exam - Excitable - Lec 2 (Action Potential, Compound Action Potential, All Or None Rul

The main cause of depolarization of nerve is:

At stage of complete depolarization of action potential of the curve

Reversal of polarity, which is true:

Repolarization of nerve coincides with:

Ascending limb of nerve action potential is due to Na movement through

Which of the following is a representation of hypopolarized state:

Which of the following is false regarding compound action potential:

Which of the following is not applying all or none rule:

The main cause of after hyperpolarization is