Question

Nerve impulses are initiated by nerve fibres only when the membrane shall become more permeable to:
A. Adrenaline
B. Phosphorus
C. Sodium ions
D. Potassium ions

Answer 1

Hint: The transmission of nerve impulses between nerve cells is governed by polarisation processes like depolarization and repolarization. Any nerve starts off in the resting potential stage, but when an impulse is produced, it depolarizes and an action potential is produced, which is what transmits the impulse.

Complete Step by Step Answer:
Nerve cells have an electrical charge across their membranes when they are at rest, resulting in a positive charge on the outside and a negative charge on the inside of the cell. The cell's internal polarisation processes aid in the transmission of nerve impulses between nerve cells. When the nerve cell reverses these charges and returns them to the resting state, depolarization is considered to have taken place. When exposed to stimuli like heat, chemicals, light, electrical stimulation, etc., neurons react by depolarizing. In order to do this, neurons produce another electrical signal.

Sodium ions rush into the neuron as soon as they receive the signal, changing the membrane potential from negative to positive. By activating sodium and potassium channels, sodium ions are allowed to travel inside the cell, causing the charge to change from negative to positive. There will still be a significant nerve impulse produced even if only a small fraction of the neuron is depolarized.

Hence, the correct option is C. Sodium ions.

Note: Special channels are required for sodium to enter a cell; otherwise, the cell would become toxic as a result of allowing entry of all ions. Therefore, nerve cells use ion gated channels to control ion entry in order to stop this process. Sodium ions open the channel, which is a particular protein enmeshed in the plasma membrane.