Question

If a part of an axonal membrane becomes more permeable to ${\mathrm{Na}}^{+}$ ions, the membrane becomes .

• A. hyperpolarised
• B. depolarised
• C. polarised

Answer 1

The correct option is B depolarised

Charged ions are separated across the plasma membrane. In the normal resting state, the outer side of the nerve fibre carries postive charge. This is called polarised state. This polarisation is due to more ${\mathrm{Na}}^{+}$ions outside the axon membrane. On stimulation, the axon membrane at that spot becomes more permeable to ${\mathrm{Na}}^{+}$ ions which move inwards and causes loss of polarisation (depolarisation). This region of the axon is also known as the excited region. The point of depolarisation becomes a stimulus for the next neighbouring area of the membrane which inturn becomes depolarised. Meanwhile, the previous area becomes reploarised due to active transport of ${\mathrm{Na}}^{+}$ ions to the outside. If there is increased outward flow of ${\mathrm{Na}}^{+}$ compared to the resting stage then the membrane is said to be hyperpolarised.