Action Potential Essay

What opens first in response to a threshold comment?Voltage Gated (activation gates) Na+ carry open and Na+ diffuses in the cytoplasmWhat characterizes depolarization, 1st phase of fill probable?Membrane changes from a negative harbor to a positive observeWhat characterizes repolarization, 2nd phase of action potential?Once the tissue layer depolarizes to a peak shelter of 30+, it repolarizes to to its negative resting value of -70What event triggers the generation of an action potential?The tissue layer potential must depolarize from the resting electromotive force of -70 mV to a threshold value of -55 mV. ( This is the minimum value required to open enough electric potential-gated Na+ channels so that depolarization is irreversible.)What is the first change to occur in response to a threshold stimulant drug?Voltage-gated Na+ channels change shape, and their activation gates openResting StateAll gated Na+ and K+ channels are closedStep 2Depolarization Na+ Channels OpenDurin g the depolarization phase of the action potential, open Na+ channels allow Na+ ions to diffuse into the cell. This inward nominal head of positive charge makes the membrane potential more positive (less negative). The depolarization phase is a positive feedback cycle where open Na+ channels find depolarization, which in turn causes more voltage-gated Na+ channels to open.Step 3Repolarization Na+ channels are inactivating and K+ Channels OpenStep 4Hyperpolarization Some K+ channels remain open and Na+ channels resetHow many gates/states do voltage gated Na+ channels consent?two gates and three statesClosed Na+at the resting state, no Na+ enters the cell through themOpened Na+opened by depolariztion, allowing Na+ to enter the cellInactivatedchannels automatically blocked by inactivation gates soon after they openHow many gates/states do voltage gated K+ channels have?one gate, two statesClosed K+at the resting state, no K+ leavesOpened K+at depolarization, after delay, allowing K+ to leave wherefore is an action potential self-generating?depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segmentThe Na+ diffusing into the axon during the first phase of the action potential creates a depolarizing current that brings the next segment, or node, of the axon to threshold.Why does regeneration of the action potential occur in one direction, rather than in two directions?The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potentialAt the peak of the depolarization phase of the action potential, the inactivation gates close. Thus, the voltage-gated Na+ channels do absolutely refractory to another depolarizing stimulus.What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?Inactivation gates of voltage-gated Na+ channels close, duration activation gates of voltage-gated K+ channels openClosing of voltage-gate d channels is time dependent. Typically, the inactivation gates of voltage-gated Na+ channels close about a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+ channels open.What marks the end of the depolarization phase?As voltage-gated Na+ channels begin to inactivate, the membrane potential stops becoming more positive This marks the end of the depolarization phase of the action potential. Then, as voltage-gated K+ channels open, K+ ions rush out of the neuron, following their electrochemical gradient. This exit of positively-charged ions causes the interior of the cell to become more negative, repolarizing the membrane.The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________.The opening of voltage-gated K+ channels allows K+ ions to exit the cell, repolarizing the membrane. In other words, the exit of K+ ions makes the membrane potential more n egative. K+ also exits through leakage channels during this phase because leakage channels are always active. However, most of the membrane permeableness to K+ during this phase is due to voltage-gated channels. Voltage-gated K+ channels make the action potential more brief than it would otherwise be if only leakage channels were available to repolarize the membrane.During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.The large number of voltage-gated K+ channels opening during the repolarization phase readily makes the membrane potential more negative as positively-charged K+ ions leave the cell. K+ ions continue to leave through open channels as the membrane potential passes (becomes more negative than) the resting potential. This hyperpolarization phase of the action potential is therefore due to K+ ions diffusing through voltage-gated K+ channels. The membrane potential clay more negative than th e resting potential until voltage-gated K+ channels close. This period of hyperpolarization is important in relieving voltage-gated Na+ channels from inactivation, readying them for another action potential.During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?Voltage-gated K+ channels are opened by depolarization. This means that as the membrane potential repolarizes and then hyperpolarizes, these K+ channels close. With the closing of voltage-gated K+ channels, the membrane potential returns to the resting membrane potential via leakage channel activity. Resetting voltage-gated Na+ channels to the closed (but not inactivated) state prepares them for the next action potential.During the hyperpolarization phase of the action potential, voltage eventually returns to the resting membrane potential. What processes are primarily responsible for this return t o the resting membrane potential?Voltage-gated K+ channels close. K+ and Na+ diffuse through leakage channels.