Action Potential Essay free essay sample

RESTING POTENTIAL Resting potential is the membrane potential when a neuron is not conducting any electrical impulse or signal. The resting potential is around -75 mV. During resting potential, the inside of the axon is negative GRADED POTENTIAL ACTION POTENTIAL Action potential is a fleeting reversal of the membrane potential, caused by changes in permeability of the plasma membrane of neuron to potassium and sodium ions causing an electrical impulse to be transmitted along the axon. When a stimulus depolarizes the membrane, a few of the voltage-gated sodium channels that are found in the neuronal plasma membrane open permitting sodium ions to pass through. Since there is much greater concentration of sodium ions outside the axon than inside, they diffuse in through the open sodium channels down their concentration gradient. This result in the relatively high concentrations of positively charged sodium ions inside the axon and makes it less negative inside that it was before. We will write a custom essay sample on Action Potential Essay or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page The continue diffusion of sodium ions into the axon depolarizes the membrane more and brings it closer to the threshold. When the potential across the membrane reach the threshold (about –55 mV), additional voltage-gated sodium channel open. When this happens, there is rapid and intense influx of sodium ions into the axon causing the inside of the axon swiftly continues to build up more positive charges, until the membrane potential reaches a potential of about +40 mV compared with the outside. At this point, the sodium channels are temporary close and are inactivated, so the sodium ions stop diffusing into the axon. At the same time, the voltage-gated potassium channels open. Potassium ions therefore diffuse out of the axon, down their concentration gradient. The outward movement of potassium ions removes positive charge from inside the axon to the outside, thus beginning to return the potential difference to normal. This is called repolarisation or refractory period. Since there are so many potassium ions leave the axon and the potassium channels close too slowly, he potential difference across the membrane briefly becomes even more negative. This is called temporary hyperpolarisation. The potassium channels then close, and the sodium-potassium pump begin to act again, restoring the normal/original distribution of sodium and potassium ions across the membrane, and therefore restoring the resting potential. This process takes time. THE REFRACTORY PERIOD Refractory period i s the period of time during which a neuron is recovering from an action potential, and during which another action potential cannot be generated. At this period, the voltage-gated sodium channels are still firmly closed (or temporary inactivated) and the membrane cannot produce an action potential, regardless of the stimulation. CONDUCTION/PROPAGATION/TRANSMISSION OF ACTION POTENTIAL An action potential at any point along an axon’s plasma membrane triggers the production of an action potential in the membrane on either side of it. During the action potential, sodium ions enter a point on the axon. The temporary depolarization of the membrane where the action potential is causes a ‘local circuit’ to be set between the depolarized region and the resting regions on either side of it. Sodium ions flow sideways inside the axon, away from the positively charged region towards the negatively charged regions on either side. This depolarizes these adjoining regions and so generates During the action potential, sodium ions enter a point on the axon. Temporarily, that location is positively charged in comparison with neighboring/adjacent areas along the axon. The positive ions sideways inside the axon, away from the The positive charges now inside the membrane slightly depolarize the adjacent areas of the membrane, causing the next area to reach its threshold and regenerate the action potential. In this manner, the action potential travels like a wave along the axon. SPEED OF CONDUCTION OF ACTION POTENTIAL An action potential can travel long distances by regenerating itself along the axon At the site where the action potential is generated, usually the axon hillock, an electrical current depolarizes the neighboring region of the axon membrane