Question

How does a cell membrane become polarized?

Answer 1

Hint: The structure of the cell that forms a covering around the cell and helps the cell to take up essential nutrients and remove waste from the cell is known as a cell membrane. The polarization of the cell membrane means there is the presence of positively charged ions on one side and negatively charged ions on the other side of the membrane.

Complete answer:
Cell polarity can be seen in different types of cells like epithelial cells, neurons, etc. The difference in ion concentration inside and outside the cell is known as the polarity of the cell. It can enable the cell to carry out a specific function. For example, if we consider a nerve cell called a neuron. Conduction of impulse is based on the charge difference inside and outside the nerve cell.
The cell membrane of a neuron contains thousands of tiny molecules known as channels that allow either sodium or potassium ions to pass through. Generally, the channels of the neurons are closed and the membrane is said to be in a resting state. In this state, the charge of the inside of the cell membrane is more negative than the outside (approximately -70 millivolt). Because of this electrical difference across the cell membrane, the cell membrane of the neuron is polarized. The nerve impulse is initiated when pressure or any sensory inputs disturbs a neuron plasma membrane to point that the threshold reaches -55 millivolt. This causes many sodium channels from that region of the membrane to open which allows positively charged sodium ions to flow inside the cell membrane. In this instance, the inside of the cell becomes more positive compared to the outside on a temporary basis. This is known as the depolarizing state of the cell membrane. As the impulse passes further, the potassium channels begin to open allowing the positively charged potassium ions to flow out which causes the inside of the axon to resume the net negative charge hence known as the repolarized stage of the membrane.

Hence, we can say that when the negative charge is present more inside the cell membrane compared to outside of the cell membrane it is said to be a polarized cell membrane.

Note:
This depolarization and repolarization of the cell membrane of the neuron or specifically the axon are known as an action potential of the neuron. The nerve impulse passed through the neuron cell can be called the action potential of the cell.