The process of depolarization begins with a stimulus. This stimulus can be a simple touch, light, foreign particle, or even electrical stimulus. This stimulus causes a voltage change in the cell. This initial voltage change causes the opening of voltage-gated sodium and calcium channels inside the cell membrane.
The positively charged ions rush through these channels. As a result, the inside of the cell becomes more positive. The membrane potential changes from negative to positive state. The basic principle of depolarization is the same as described under the heading of physiology. However, different cells in the body respond to different stimuli and use different ion channels to undergo the process of depolarization.
All this is in coherence with the function of that cell. We will discuss the process of depolarization in reference to neurons, endothelial cells, and cardiac cells. Neurons can undergo depolarization in response to a number of stimuli such as heat, chemical, light, electrical or physical stimulus.
These stimuli generate a positive potential inside the neurons. When the positive potential becomes greater than the threshold potential, it causes the opening of sodium channels. The sodium ions rush into the neuron and cause the shift in membrane potential from negative to positive.
Depolarization of a small portion of neuron generates a strong nerve impulse. The nerve impulse travels along the entire length of neuron up to the synaptic terminal. Once the nerve impulse reaches the synaptic terminal, it causes release of neurotransmitters. These neurotransmitters diffuse across the synaptic cleft. They act as a chemical stimulus for the post-synaptic neuron. These neurotransmitters, in turn, cause the depolarization of postsynaptic neurons.
Vascular endothelial cells line the inner surface of blood vessels. These cells have structural capability to withstand the cardiovascular forces. They also play an important role in maintaining the functionality of the cardiovascular system.
These cells use the process of depolarization to alter their structural strength. When the endothelial cells are in a depolarized state, they have marked decreased structural strength and rigidity. In depolarized state , endothelial cells also cause a marked decrease in vascular tone of blood vessels.
Depolarization of cardiac myocytes causes contraction of the cells and thus heart contraction occurs. Depolarization first begins in the SA node, which is also called the cardiac pacemaker. SA node has automaticity. The resting membrane potential of SA node is less negative than that of other cardiac cells.
Learn how they provide best-in-class solutions for the entire range of patch-clamp experiments. What is an action potential? Stimulus starts the rapid change in voltage or action potential.
In patch-clamp mode, sufficient current must be administered to the cell in order to raise the voltage above the threshold voltage to start membrane depolarization. Depolarization is caused by a rapid rise in membrane potential opening of sodium channels in the cellular membrane, resulting in a large influx of sodium ions.
Membrane Repolarization results from rapid sodium channel inactivation as well as a large efflux of potassium ions resulting from activated potassium channels. Depolarization is caused when positively charged sodium ions rush into a neuron with the opening of voltage-gated sodium channels.
Repolarization is caused by the closing of sodium ion channels and the opening of potassium ion channels. Hyperpolarization occurs due to an excess of open potassium channels and potassium efflux from the cell.
Key Terms action potential. As additional sodium rushes in, the membrane potential actually reverses its polarity. The repolarization or falling phase is caused by the slow closing of sodium channels and the opening of voltage-gated potassium channels. As a result, the membrane permeability to sodium declines to resting levels. As the sodium ion entry declines, the slow voltage-gated potassium channels open and potassium ions rush out of the cell.
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