Resting Membrane Resting Membrane PotentialPotential

Membrane PotentialsMembrane Potentials

Electrical signals are the basis for processing Electrical signals are the basis for processing information and neuronal responseinformation and neuronal response

The impulses are conducted by presynaptic and The impulses are conducted by presynaptic and postsynaptic neuronspostsynaptic neurons

The The Resting PotentialResting Potential in cells are normally more in cells are normally more negative inside than outside. This varies from -9mV negative inside than outside. This varies from -9mV to -100mV. This is to -100mV. This is just the opposite of osmolarityjust the opposite of osmolarity

Excitable tissues of nerves and muscles cells have Excitable tissues of nerves and muscles cells have higher potentials than other cells (epithelial cells and higher potentials than other cells (epithelial cells and connective tissue cells).connective tissue cells).

Dead cells do not have membrane potentials. Dead cells do not have membrane potentials.

The membrane potential is due to the sodium ions found in the extracellular matrix and the potassium ions found in the intracellular matrix

Figure 6-9

A cell is “polarized” because theinterior (ICF) side of the membrane is relatively more negative than the exterior (ECF).

Widmaier, et al., 2006

Membrane potentials are due to the Membrane potentials are due to the diffusiondiffusion of ions down their concentration of ions down their concentration gradients, the gradients, the electric chargeelectric charge of the ion, of the ion, and any and any membrane pumpsmembrane pumps for that ion. for that ion.

InfluxInflux is the net movement of ions into the is the net movement of ions into the cell from the ECF.cell from the ECF.

EffluxEfflux is the net movement of ions out of is the net movement of ions out of the cell to the ECF.the cell to the ECF.

FluxFlux (the movement of charges) is always (the movement of charges) is always measured in millivolts (mV).measured in millivolts (mV).

Action PotentialsAction Potentials An An action potentialaction potential occurs when there is a reversal of occurs when there is a reversal of

the normal resting potential,goin from negative to the normal resting potential,goin from negative to positive. Also called positive. Also called depolarizationdepolarization..

Depolarization occurs when a stimulus causes the Depolarization occurs when a stimulus causes the voltage-gated Navoltage-gated Na++ channels channels to open, allowing Na to open, allowing Na++ to to rapidly influx down its concentration gradient.rapidly influx down its concentration gradient.

The sudden The sudden in-rush of positive sodium ionsin-rush of positive sodium ions reverses reverses the membrane potential for a few milliseconds.the membrane potential for a few milliseconds.

Then the Then the voltage-gated K+ channelsvoltage-gated K+ channels open, allowing K open, allowing K++ to rapidly efflux due to its concentration gradient. This to rapidly efflux due to its concentration gradient. This brings the membrane back to negative inside and is brings the membrane back to negative inside and is called called repolarizationrepolarization..

Action PotentialsAction Potentials Even though the voltage has returned to Even though the voltage has returned to

negative, the membrane is not at resting negative, the membrane is not at resting potential because it now has too much Napotential because it now has too much Na++ inside and not enough Kinside and not enough K++ ions. ions.

The presence of high NaThe presence of high Na++ inside causes the inside causes the NaNa++/K/K++ pumps to increase by a power of 3. The pumps to increase by a power of 3. The faster pump rate quickly restores the faster pump rate quickly restores the membrane back to its steady-state resting membrane back to its steady-state resting condition. condition.

Sodium channels have 2 gates, a normal voltage (activation) gate (which is closed at rest) and an inactivation gate (which is open at rest). The rapid opening of the voltage gate lets Na+ rush in and depolarizes the cell. This is immediately followed by closing of the inactivation gate which stops the Na+ influx. At the same time the K+ gate opens letting K+ efflux (repolarization).

Figure 6-18

Widmaier, et al., 2006

RefrencesRefrences

Bennett,Tom, PowerPoint slides, 3/23/05Bennett,Tom, PowerPoint slides, 3/23/05 Jack, Pasternak J. Jack, Pasternak J. An Introduction to An Introduction to

Human Molecular GeneticsHuman Molecular Genetics. 2nd ed. New . 2nd ed. New Jersey: Wiley-Liss, 2005. Jersey: Wiley-Liss, 2005.