<< Chapter < Page Chapter >> Page >
The resting membrane potential is a result of different concentrations inside and outside the cell.
Ion Concentration Inside and Outside Neurons
Ion Extracellular concentration (mM) Intracellular concentration (mM) Ratio outside/inside
Na + 145 12 12
K+ 4 155 0.026
Cl 120 4 30
Organic anions (A−) 100
The resting membrane potential of minus seventy volts is maintained by a sodium/potassium transporter that transports sodium ions out of the cell and potassium ions in. Voltage gated sodium and potassium channels are closed. In response to a nerve impulse, some sodium channels open, allowing sodium ions to enter the cell. The membrane starts to depolarize; in other words, the charge across the membrane lessens. If the membrane potential increases to the threshold of excitation, all the sodium channels open. At the peak action potential, potassium channels open and potassium ions leave the cell. The membrane eventually becomes hyperpolarized.
The (a) resting membrane potential is a result of different concentrations of Na + and K + ions inside and outside the cell. A nerve impulse causes Na + to enter the cell, resulting in (b) depolarization. At the peak action potential, K + channels open and the cell becomes (c) hyperpolarized.

Action potential

A neuron can receive input from other neurons and, if this input is strong enough, send the signal to downstream neurons. Transmission of a signal between neurons is generally carried by a chemical called a neurotransmitter. Transmission of a signal within a neuron (from dendrite to axon terminal) is carried by a brief reversal of the resting membrane potential called an action potential    . When neurotransmitter molecules bind to receptors located on a neuron’s dendrites, ion channels open. At excitatory synapses, this opening allows positive ions to enter the neuron and results in depolarization    of the membrane—a decrease in the difference in voltage between the inside and outside of the neuron. A stimulus from a sensory cell or another neuron depolarizes the target neuron to its threshold potential (-55 mV). Na + channels in the axon hillock open, allowing positive ions to enter the cell ( [link] and [link] ). Once the sodium channels open, the neuron completely depolarizes to a membrane potential of about +40 mV. Action potentials are considered an "all-or nothing" event, in that, once the threshold potential is reached, the neuron always completely depolarizes. Once depolarization is complete, the cell must now "reset" its membrane voltage back to the resting potential. To accomplish this, the Na + channels close and cannot be opened. This begins the neuron's refractory period    , in which it cannot produce another action potential because its sodium channels will not open. At the same time, voltage-gated K + channels open, allowing K + to leave the cell. As K + ions leave the cell, the membrane potential once again becomes negative. The diffusion of K + out of the cell actually hyperpolarizes the cell, in that the membrane potential becomes more negative than the cell's normal resting potential. At this point, the sodium channels will return to their resting state, meaning they are ready to open again if the membrane potential again exceeds the threshold potential. Eventually the extra K + ions diffuse out of the cell through the potassium leakage channels, bringing the cell from its hyperpolarized state, back to its resting membrane potential.

Art connection

Graph plots membrane potential in millivolts versus time. The membrane remains at the resting potential of -70 millivolts until a nerve impulse occurs in step 1. Some sodium channels open, and the potential begins to rapidly climb past the threshold of excitation of -55 millivolts, at which point all the sodium channels open. At the peak action potential, the potential begins to rapidly drop as potassium channels open and sodium channels close. As a result, the membrane repolarizes past the resting membrane potential and becomes hyperpolarized. The membrane potential then gradually returns to normal.
The formation of an action potential can be divided into five steps: (1) A stimulus from a sensory cell or another neuron causes the target cell to depolarize toward the threshold potential. (2) If the threshold of excitation is reached, all Na + channels open and the membrane depolarizes. (3) At the peak action potential, K + channels open and K + begins to leave the cell. At the same time, Na + channels close. (4) The membrane becomes hyperpolarized as K + ions continue to leave the cell. The hyperpolarized membrane is in a refractory period and cannot fire. (5) The K + channels close and the Na + /K + transporter restores the resting potential.

Potassium channel blockers, such as amiodarone and procainamide, which are used to treat abnormal electrical activity in the heart, called cardiac dysrhythmia, impede the movement of K + through voltage-gated K + channels. Which part of the action potential would you expect potassium channels to affect?

Questions & Answers

prove starch in a mango leaf
Ruth Reply
prove starch in a leaf
draw and name the plant cell
wat is classification
levels of classification
classification of what
Identify the caste of termites or Honey bees
Mensah Reply
Soldier Winged reproductive Worker King and queen
what is biology
Jackson Reply
biology is a study of living organism
what is the myelin sheath?
description on how an enzyme such as pepsin breaks down a substrate
linister Reply
what is biology
Kanzy Reply
study of life
the study of life..meaning studying all aspects of life in humans,animals and everything inside the global
study of life
is the branch of science which deal with the study of living and non living things
Is the study of living organisms or living things
draw the taxonomic hierarchy of classification
KC Reply
Kingdom Class Order Family Genus Species
explain the following bush burning, deforestation, over grazing
Thomas Reply
what is biodiversity
No idea
Please what are alleles
Deforestation: this is the cutting down of trees without planting new ones
over grazing is the continuously planting of crops in one particular land.
what is afforestation
Bush burning is the removal of the natural vegetation cover, that protects the soil surface through the use of fire. Deforestation is the actor process of establishing a forest especially on land not previously forested.
Over grazing is the practice of grazing toi many livestock for too long a period on a land unable to recover its vegetation.
what is physiology
Joseph Reply
the study of physical things
dealing with those things which you can see by your neck eyes
Further explanation please
the study of things tt interact with time,energy
Is the scientific study of chemistry and physics of the structure of the body
can a lactating mother get pregnant
Elias Reply
what is cell
Deng Reply
the basic building blocks of all living matter...
cell is a basic unit of life
building blocks ie cells not a cell there4 a cell is the basic unit of biotic things
Cell is a basic unit of life
A cell is the basic structural and functional unit of life
what's microscope
Emmanuel Reply
is any instrument that use to wiew or to see the small object that you can't see with our naked eye
is any instrument used to magnifie small object
Is an instrument that produces an enlarged image of an object or specimen that is too small to be seen with our naked eye
what is the function of the spinal cord
Gaone Reply
For responsible of movement and sensation
A cell is the structural and fictional unit of life
Evelyn Reply
what is tidal volume
tidal volume is the volume of each breath measured during inspiration or expiration or averged for the entire respiratory cycle
Give function of the long strands of slippery or jelly like substance in eggs of the amphibians in water ?
the long strands of slippery or jelly like substance him eggs of amphibians in water helps in keeping the eggs moist and protection from predators
sorry not him in
what's is microscope
How do bacteria useful?
how can plant feed other animals
Nana Reply
After the animals has death and decayed then the plant used the nutrients to manufacture there food.
Plants and animals depends on each other. Meaning, plants help animals with greens and fruits or vegetables while animals provides nutrients when dead and decayed. Therefore,as you see the food web and food chain, you'll have more.

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now

Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?