Resting Membrane Potential

Transcription

1 Resting Membrane Potential

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5 Recording of Resting and It is recorded by cathode ray oscilloscope action potentials mv + it is negative in polarized (resting, the membrane can be excited) state with the potential difference inside the cell membrane is negative relative to the outside. 5 Dentistry Voltmeter

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7 Terminology Associated with Changes in Membrane Potential F8-7, F8-8 Depolarization- a decrease in the potential difference between the inside and outside of the cell. Hyperpolarization- an increase in the potential difference between the inside and outside of the cell. Repolarization- returning to the RMP from either direction. Overshoot- when the inside of the cell becomes +ve due to the reversal of the membrane potential polarity.

8 Types of Ion Channels

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11 Nernest equation E (mv) = - 61.log (Ci/Co) E = Equilibrium potential for a univalent ion Ci = conc. inside the cell. Co = conc. outside the cell.

12 Membrane Potential: Goldman Equation V m RT F log P K P K [ K [ K ] o ] i P P Na Na [ Na [ Na ] ] o i P P cl cl [ Cl [ Cl ] ] o i P = permeability at rest: P K : P Na : P Cl = 1.0 : 0.04 : 0.45 Net potential movement for all ions known V m :Can predict direction of movement of any ion ~

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14 Graded Potentials F8-9 Graded potentials are depolarizations or hyperpolarizations whose strength is proportional to the strength of the triggering event. Graded potentials lose their strength as they move through the

15 Graded Potentials Above Threshold Voltage Trigger Action Potentials Graded potentials travel through the neuron until they reach the trigger zone. If they depolarize the membrane above threshold voltage (about -55 mv in mammals), an action potential is triggered and it travels down the axon. F8-10

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23 An action potential is: The action potential (AP) A regenerating depolarization of membrane potential that propagates along an excitable membrane. [propagates = conducted without decrement (an active membrane event)] [excitable = capable of generating action potentials] Action potentials: are all-or-none events need to reach threshold have constant amplitude do not summate are initiated by depolarization involve changes in permeability rely on voltage-gated ion channels (mv) ms E Na downstroke E K

24 Recording membrane potential mv Electrotonic potential Localized non propagated Action potential

25 Properties of action potentials Action potentials: +60 are all-or-none events threshold voltage (usually 15 to 20 mv positive to resting potential) mv threshold are initiated by depolarization APs do not summate - information is coded by frequency not amplitude.

26 Threshold and Action Potentials Threshold membrane is depolarized by 15 to 20 mv Established by the total amount of current flowing through the membrane Weak (subthreshold) stimuli are not relayed into action potentials Strong (threshold) stimuli are relayed into action potentials All-or-none phenomenon action potentials either happen completely, or not at all

27 The Action Potential Equilibrium potential of sodium (+60 mv) - 75 mv K Na K K Na Passive increase in positive charge Electrotonic potential Resting potential (-75 mv) Equilibrium potential of potassium (-95 mv)

28 The Action Potential Equilibrium potential of sodium (+60 mv) - 55 mv K Na K K Na threshold Electrotonic potential Opening of voltage-gated sodium channel Resting potential (-75 mv) Equilibrium potential of potassium (-95 mv)

29 The Action Potential Equilibrium potential of sodium (+60 mv) - 40 mv Depolarisation due to sodium influx K Na K K Na Opening of voltage-gated sodium channel Electrotonic potential Resting potential (-75 mv) Equilibrium potential of potassium (-95 mv)

30 The Action Potential voltage-gated sodium channels turn to the inactivation phase Equilibrium potential of sodium (+60 mv) + 50 mv Depolarisation due to sodium influx K Na K K Na Inactivation of voltage-gated sodium channel Electrotonic potential Resting potential (-75 mv) Equilibrium potential of potassium (-95 mv)

31 The Action Potential Equilibrium potential of sodium (+60 mv) + 50 mv Depolarisation due to sodium influx K Na K K Na opening of voltage-gated potassium channel Electrotonic potential Resting potential (-75 mv) Equilibrium potential of potassium (-95 mv)

32 The Action Potential Equilibrium potential of sodium (+60 mv) - 85 mv Repolarization due to potassium influx Depolarisation due to sodium influx K Na K K Na opening of voltage-gated potassium channel Electrotonic potential Resting potential (-75 mv) Equilibrium potential of potassium (-95 mv)

33 The Action Potential Membrane potential approaches the E Na and voltage-gated sodium channels turn to the inactivation phase Equilibrium potential of sodium (+60 mv) - 75 mv repolarization due to potassium influx Depolarisation due to sodium influx K Na K K Na closing of voltage-gated potassium channel Electrotonic potential Hyperpolarising afterpotential Resting potential (-75 mv) Repolarisation due to potassium influx

34 The Action Potential Inactivation of voltage-controlled sodium channel Equilibrium potential of sodium (+60 mv) Opening of voltagecontrolled sodium channel threshold Electrotonic potential Opening of voltagecontrolled potassium channel Resting potential (-75 mv) Hyperpolarization due to more outflux of potassium ions Dentistry 07 34

35 The Action Potential (excitability changes) Absolute refractory period Relative refractory period E Na (+60 mv) Depolarisation (due to sodium influx) Resting potential (-75 mv) Polarized state (resting) Hyperpolarising afterpotential E K (-95 mv) 35

36 threshold The Action Potential

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41 neuron from the inferior olive