Action Potential Essay Example for Free

Action Potential EssayWhat heart-to-hearts kickoff in response to a threshold stimulus?Voltage Gated (activation furnish) Na+ convey open and Na+ diffuses in the cytoplasmWhat characterizes depolarization, 1st phase of exploit emf?Membrane changes from a negative think of to a positive mensurateWhat characterizes repolarization, 2nd phase of challenge potential?Once the membrane depolarizes to a peak value of 30+, it repolarizes to to its negative resting value of -70What event triggers the generation of an effect potential?The membrane potential must depolarize from the resting emf of -70 mV to a threshold value of -55 mV. ( This is the minimum value required to open enough potential-gated Na+ carry so that depolarization is irreversible.)What is the first change to pass away in response to a threshold stimulus?Voltage-gated Na+ channels change shape, and their activation gate openResting StateAll gated Na+ and K+ channels argon closedStep 2Depolarization Na+ Ch annels OpenDuring the depolarization phase of the action potential, open Na+ channels allow Na+ ions to diffuse into the cell. This inward movement of positive charge makes the membrane potential more than positive (less negative). The depolarization phase is a positive feedback cycle where open Na+ channels defecate 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 bedevil?two gates and three statesClosed Na+at the resting state, no Na+ enters the cell done themOpened Na+opened by depolariztion, allowing Na+ to enter the cellInactivatedchannels automatically occlude 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+ buy the farmsOpened K+at depolarizati on, after delay, allowing K+ to leaveWhy is an action potential self-generating?depolarizing currents effected 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 become 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, eon activation gates of voltage-gated K+ channels openClosin g of voltage-gated channels is time dependent. Typically, the inactivation gates of voltage-gated Na+ channels close ab bulge out a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+ channels open.What mark 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 give out 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 negative. K+ also exits by making water channels during this phase because leakage channels are always active. However, most of the membrane permeability to K+ during this phase is due to voltage-gated channels. Voltage-gated K+ channels make the action potential more apprise 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 right away 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 po tential be more negative than the 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 primar ily responsible for this return to the resting membrane potential?Voltage-gated K+ channels close. K+ and Na+ diffuse through leakage channels.