Difference Between Polarised and Non Polarised Cells

The key difference between polarised and non polarised cells is that the polarised cells undergo repolarisation to become polarised where the resting membrane potential is restored after each event of depolarisation while non polarised cells undergo depolarisation to become non polarised where the resting membrane potential is lost by the change in the polarisation of the cell membrane.

Repolarization makes cells polarised while depolarization makes cells non polarised. Both depolarization and repolarization are two sequential processes that take place in the cell membrane during the transmission of nerve impulses. Hence, polarised and non polarised cells occur due to the alteration of charge of the inner membrane of the cell during both processes. The inner membrane has a less negative charge during depolarization (non polarised cell). However, this is restored during repolarization (polarised cell).

CONTENTS

1. Overview and Key Difference
2. What are Polarised Cells
3. What are Non Polarised Cells
4. Similarities Between Polarised and Non Polarised Cells
5. Side by Side Comparison – Polarised vs Non Polarised Cells in Tabular Form
6. Summary

What are Polarised Cells?

Polarised cells undergo repolarization to become polarised. Repolarization is a process where, followed by a depolarization event, restoration of the resting membrane potential takes place. During repolarization, closure of membrane sodium channels takes place. Therefore, this creates a less negative charge inside the cell. At the same time, membrane potassium channels open up since more positive ions (Na⁺) are present inside the cell. Hence, potassium ions (K⁺) move out from the cell through the potassium channels, making the cell interior more negative. Therefore, a combination of all these events restores the resting membrane potential and convert the cell into a polarised stage.

Cell polarization does not trigger any mechanical activity in effector organs (e.g. muscles) through signaling. The main function of a polarised cell is to make the cell membrane ready to transmit a nerve impulse through depolarization.

What are Non Polarised Cells?

Depolarization creates non polarised cells. It occurs due to the alteration in the resting membrane potential to a less negative value (more positive value). The normal resting membrane potential of a cell is -70mV. Therefore, the inner membrane (cell interior) of the cell has a more negative charge in comparison to the outside (cell exterior).

Several factors influence the resting membrane potential. These factors are diffusion of potassium ions (K⁺) from the cell continuously, the action of the sodium-potassium pump (pumping 03 Na⁺ ions out and taking 02 K⁺ in) and the presence of more negatively charged ions (proteins and phosphate ions) in the interior of the cell. These factors change during the firing of an action potential (a nerve impulse) by breaking the membrane resting potential.

An action potential causes the pumping of more sodium ions into the cells, reducing the negative charge of the inner membrane. Firing of a nerve impulse occurs when the resting membrane potential decreases from -70mV to -55mV. However, during the transmission of nerve impulses, the cell membrane potential remains at +30mV.

What are the Similarities Between Polarised and Non Polarised Cells?

• Both polarised and non polarised cells occur due to a change in membrane potential of nerve cells during the transmission of nerve impulses.
• Also, the formation of both types of cells is due to opening and closing of ion channels and due to the activity of sodium potassium

What is the Difference Between Polarised and Non Polarised Cells?

Polarised cells undergo repolarization to become polarised while non polarised cells undergo depolarization to become non polarised. So, this is the key difference between polarised and non polarised cells. Moreover, a further difference between polarised and non polarised cells is that the non polarised cells involve an alteration of the resting potential membrane while polarised cells involve a restoration of resting potential membrane.  Furthermore, in polarised cells, inner membrane remains more positive while in non polarised cells, inner membrane remains negative. Therefore, we can consider this also as a difference between polarised and non polarised cells.

Below infographic summarizes the difference between polarised and non polarised cells.

Summary – Polarised vs Non Polarised Cells

The polarised and non polarised cells occur due to reploarization and depolarization, respectively. Both processes take place due to a change of potential in the cell membrane. Non polarised cells involve an alteration of the resting potential membrane while polarised cells involve a restoration of resting potential membrane. They are sequential processes that occur during the transmission of nerve impulses. Both types of cells are essential for the transmission of nerve impulses and for its regulation. Thus, this summarizes the difference between polarised and non polarised cells.

Reference:

1. Nguyen, David H. “Depolarization & Repolarization of the Cell Membrane.” Sciencing.com, Sciencing, 2 Mar. 2019, Available here.
2.“Q & A: Neuron Depolarization, Hyperpolarization, and Action Potentials.” Khan Academy, Khan Academy, Available here.

Image Courtesy:

1. “Ion channel activity before during and after polarization” By Robert Bear and David Rintoul – (CC BY 4.0) via Commons Wikimedia
2. “Action Potential” By Laurentaylorj – Own work (CC BY-SA 3.0) via Commons Wikimedia