Resting membrane potential and action potential pdf

In muscle cells, the generation of an action potential causes the muscle to contract. For the vast majority of solutes, intracellular and extracellular concentrations differ. As a result, there is often a driving force for the movement of solutes across the plasma membrane. The direction of this driving force involves two components: the concentration gradient and the electrical gradient.

Regarding the concentration gradient, a solute will move from an area where it is more concentrated to a separate area with a lower concentration. Regarding the electrical gradient, a charged solute will move from an area with a similar charge towards a separate area with an opposite charge. All solutes are affected by concentration gradients, but only charged solutes are affected by electrical gradients.

In the absence of other forces, a solute that can cross a membrane will do so until it reaches equilibrium. For a non-charged solute, equilibrium will take place when the concentration of that solute becomes equal on both sides of the membrane. In this case, the concentration gradient is the only factor that produces a driving force for the movement of non-charged solutes. However, for charged solutes, both the concentration and electrical gradients must be taken into account, as they both influence the driving force.

A charged solute is said to have achieved electrochemical equilibrium across the membrane when its concentration gradient is exactly equal and opposite that of its electrical gradient. During electrochemical equilibrium for a charged solute, there is usually still a concentration gradient, but an electrical gradient oriented in the opposite direction negates it.

Under these conditions, the electrical gradient for a given charged solute serves as an electrical potential difference across the membrane. The value of this potential difference represents the equilibrium potential for that charged solute. Under physiological conditions, the ions contributing to the resting membrane potential rarely reach electrochemical equilibrium.

One reason for this is that most ions cannot freely cross the cell membrane because it is not permeable to most ions. This factor brings up an important point: the more permeable the plasma membrane is to a given ion, the more that ion will contribute to the membrane potential the overall membrane potential will be closer to the equilibrium potential of that 'dominate' ion. Both the generation and maintenance of the resting membrane potential are of great importance in excitable cells neurons and muscle.

Conditions that alter the resting membrane potential of these cells can have a profound impact on their proper functioning. This results in hyperpolarization of the cells and requires a greater stimulus to achieve action potential.

This leads to a more negative potential in cardiac muscles as a result of the recovery of sodium channel inactivation. Low potassium levels lead to delayed ventricular repolarization, which can contribute to reentrant arrhythmias.

This depolarization inactivates sodium channels, which increases the refractory period and may lead to major arrhythmias, for example. Note: Depolarization refers to the increase in the positivity of membrane potential while hyperpolarization refers to the increase in negativity of membrane potential. These two events commonly occur in excitable cells that have an action potential, whereas most other cells have a constant resting membrane potential that does not change. Most are familiar with the concept of depolarization when referring to an action potential.

For an action potential, an initial graded depolarization of the membrane results in the opening of the voltage-gated sodium channels. As large numbers of positive sodium ions rush into the cell through open channels, the interior of the cell becomes more positively charged, the membrane potential becomes more positive, and depolarization occurs.

However, depolarization does not always result in an action potential. Action potentials occur only when the graded potentials initiated by synaptic activity are of significant strength to cause the membrane voltage to pass a threshold, after which the voltage-gated sodium channels open. This book is distributed under the terms of the Creative Commons Attribution 4.

Turn recording back on. National Center for Biotechnology Information , U. StatPearls [Internet]. Search term. Physiology, Resting Potential Steven M. Author Information Authors Steven M. Affiliations 1 Western University of Health Sciences. Introduction The resting membrane potential is the result of the movement of several different ion species through various ion channels and transporters uniporters, cotransporters, and pumps in the plasma membrane.

There are two important concepts central for the understanding of any membrane potential: The first is that the difference in the concentration gradient of an ion across a semipermeable membrane drives the direction of movement of the ion.

Organ Systems Involved All cells within the body have a characteristic resting membrane potential depending on their cell type. Potential of Membrane If the stimulus is at or above threshold intensity, the action potential is therefore all or none in character. Accommodation; a process that slowly raising currents fail to fire the nerve because the nerve adapts to the applied stimulus. The magnitude of this response drops off rapidly as the distance between the stimulating and recording electrodes is increased.

Conversely, an anodal current produces a hyperpolarizing potential change of similar duration. These potential changes are called electrotonic potentials. Potential of Membrane Local responses; Effect on membrane potential due to an application of subthreshold stimuli but do not produce an action potential. Firing level; A threshold level that makes excitable membrane is triggered to undergo an action potential. Absolute refractory period; the period from the time the firing level is reached until repolarization is about complete.

Relative refractory period; lasting from the repolarization is about complete to the start of after hyper-depolarization. Electrogenesis of the Action Potential Nerve cell membrane is polarized at rest, charges along the outside of the membrane and charges along the inside. Saltatory Conduction Jumping of depolarization from node to node at myelinated nerve axon. Open navigation menu. Close suggestions Search Search. User Settings.

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