What is the cause of hyperpolarization?
a. due to excess K+ outfit
b. due to influx of Cl- ions
c. after releasing of GABA
d. all the above

Hint: Hyperpolarization takes place when the cell membrane's potential becomes more negative than the resting potential i.e., -70mV. It is the opposite of Depolarization.

Complete answer:
When at rest, a neuron has a resting potential of -70 mV. This indicates that the interior of the cell is negatively charged as compared to the outside of the cell. When a signal is to be transmitted through neurons, it requires the development of an Action potential (+30 mV). On the other hand, to prevent any stimulus that is already sent up through the axon, from triggering an action potential in a subsequent neuron, Hyperpolarization is required.


To make the membrane potential more negative resulting in hyperpolarization, it will require either of the following ways:
1. The opening of channels leads to the flow of positive charge out of the membrane. Eg.: Opening of channels that let K+ out of the cell.
2. The opening of channels leads to the flow of negative charge into the cell membrane. Eg.: Influx of Cl- into the cell.
3. Release of an Inhibitory neurotransmitter like GABA forms the presynaptic neuronal membrane that makes the resting potential more negative. Such a hyperpolarization is referred to as Inhibitory Postsynaptic Potential (IPSP).
Therefore, hyperpolarization can be caused due to excess K+ outfit, the influx of Cl- ions or after releasing GABA.

The correct option is D. All of the above.

Note: Resting membrane potential of a neuron is about -70mV which means that the inside of the neuron is 70mV less than the outside. The membrane is said to be Depolarized when this resting potential becomes more positive and hyperpolarized when the resting potential becomes more negative.