Resting membrane potential by DR. IRUM


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  • Charged particles are called ions. Negatively charged ones are ‘anions’, while positive ones are ‘cations’. Proteins are negatively charged particles and they remain inside the cell
  • Ion channel : A specialized protein molecule that permits specific ions to enter or leave the cell. Voltage-dependent ion channel : An ion channel that opens or closes according to the value of the membrane potential. Depolarization: Reduction (toward zero) of the membrane potential of a cell from its normal resting potential. Normal depolarizing events are termed EPSPs – excitatory post-synaptic potentials – and result from opening of Na+ channels. Hyperpolarization: An increase in the membrane potential of a cell, relative to the normal resting potential. Hyperpolarizing events are termed IPSPs – inhibitory post-synaptic potentials – and result from opening of Cl- channels (Cl- higher outside than in, so flow in and make cell more negative). Also can result from opening K+ channels. Action potential : The brief electrical impulse that provides the basis for conduction of information along an axon. Threshold of excitation : The value of the membrane potential that must be reached to produce an action potential. Cable properties : The passive conduction of electrical current, in a decremental fashion, down the length of an axon. Saltatory conduction ; Conduction of action potentials by myelinated axons. The action potential appears to jump from one node of Ranvier to the next. All-or-none law : The principle that once an action potential is triggered in an axon, it is propagated without decrement to the end of the fiber. Rate law : The principle that variations in the intensity of a stimulus or other information being transmitted in an axon are represented by variations in the rate at which that axon fires.
  • Resting membrane potential by DR. IRUM

    1. 2. By Dr Irum Junaid
    2. 3. <ul><ul><li>Cell Body </li></ul></ul><ul><ul><li>Dendrites (input structure) </li></ul></ul><ul><ul><ul><li>receive inputs from other neurons </li></ul></ul></ul><ul><ul><ul><li>perform spatio-temporal integration of inputs </li></ul></ul></ul><ul><ul><ul><li>relay them to the cell body </li></ul></ul></ul><ul><ul><li>axon (output structure) </li></ul></ul><ul><ul><ul><li>a fiber that carries messages (spikes) from the cell to dendrites of other neurons </li></ul></ul></ul>
    3. 4. <ul><li>The cell membranes of all the excitable body cells in the resting condition are, polarized which means that they show an electrical potential difference. </li></ul><ul><li>Membrane potential refers to a separation of charges across the membrane or a difference in the relative number of cations and anions in the ICF and ECF. </li></ul>
    4. 5. <ul><li>Diffusion potential </li></ul><ul><li>Equilibrium potential </li></ul>
    5. 6. Ion Inside Outside Cross PM K+ 140 4 yes NA+ 14 142 no Cl- 5 125 yes H2O 55,000 55,000 yes Anion- 108 0 no
    6. 7. <ul><li>Nernst equilibrium? </li></ul><ul><li>For any univalent ion at body temperature of 37 ° C </li></ul><ul><li>EMF (mV)= ±61log (Conc. inside/Conc. outside) </li></ul><ul><li>Calculate for K + and Na + </li></ul><ul><ul><li>K= -61log(140/4) </li></ul></ul><ul><ul><li>Na= -61log(14/142) </li></ul></ul><ul><ul><li>Sign is –ve shows the polarity inside the cell. </li></ul></ul>
    7. 8. <ul><li>If K o = 5 mM and K i = 140 mM </li></ul><ul><li>E K = -61 log(140/4) </li></ul><ul><li>E K = -61 log(35) </li></ul><ul><li>E K = -94 mV </li></ul>
    8. 9. <ul><li>If Na o = 142 mM and Na i = 14 mM </li></ul><ul><li>E K = -61 log(14/142) </li></ul><ul><li>E K = -61 log(0.1) </li></ul><ul><li>E K = +61 mV </li></ul>
    9. 10. <ul><li>Concept of ‘Selective membrane’ </li></ul><ul><li>How permeable the membrane is to proteins, K+, and Na+ </li></ul><ul><li>Diffusion and electrostatic forces and how they act on K+ and Na+ </li></ul><ul><li>Concept of ‘Dynamic equilibrium’ </li></ul><ul><li>Concept of ‘Membrane potential’ </li></ul><ul><li>ATP Na/K pump and its role in maintaining the membrane potential </li></ul>
    10. 11. <ul><ul><li>Polarity of each ion </li></ul></ul><ul><ul><li>Membrane permeability of the ions </li></ul></ul><ul><ul><li>Concentrations of respective ions on both sides: (i= inside), (o= outside) </li></ul></ul>
    11. 12. OUTSIDE INSIDE K + = Potassium ; Na + = Sodium ; Cl - = Chloride ; Pr - = proteins + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - Closed channel open channel open channel no channel Resting Membrane Potential - 65 mV Na + Na + K + K + Force of Diffusion Electrostatic Force Cl - Force of Diffusion Cl - Electrostatic Force Pr - 3Na/2K pump
    12. 14. <ul><li>Ions are electrically-charged molecules e.g. sodium (Na+), potassium (K+), chloride (Cl-). </li></ul><ul><li>The resting potential exists because ions are concentrated on different sides of the membrane. </li></ul><ul><ul><li>Na + and Cl - outside the cell. </li></ul></ul><ul><ul><li>K + and organic anions inside the cell. </li></ul></ul>inside outside Na + Cl - Na + K + Cl - K + Organic anions (-) Na + Na + Organic anions (-) Organic anions (-)
    13. 17. <ul><li>Electrogenic pump </li></ul><ul><li>Maintains Concentration </li></ul><ul><li>gradient </li></ul><ul><li>Contributes -4mV. </li></ul>
    14. 19. <ul><li>These are rapid transient changes in the membrane potential that spread in the form of a chain reaction rapidly along the nerve fiber membrane . </li></ul>
    15. 20. Action Potentials Can travel up to 100 meters/second Usually 10-20 m/s 0.1sec delay between muscle and sensory neuron action potential
    16. 21. <ul><li>When partial depolarization reaches the activation threshold, voltage-gated sodium ion channels open. </li></ul><ul><li>Sodium ions rush in. </li></ul><ul><li>The membrane potential changes from -70mV to +40mV. </li></ul>Na + Na + Na + - + + -
    17. 22. <ul><li>Sodium ion channels close and become refractory . </li></ul><ul><li>Depolarization triggers opening of voltage-gated potassium ion channels. </li></ul><ul><li>K+ ions rush out of the cell, repolarizing and then hyperpolarizing the membrane. </li></ul>K + K + K + Na + Na + Na + + -
    18. 23. <ul><li>Potassium channels close. </li></ul><ul><li>Repolarization resets sodium ion channels. </li></ul><ul><li>Ions diffuse away from the area. </li></ul><ul><li>Sodium-potassium transporter maintains polarization. </li></ul><ul><li>The membrane is now ready to “fire” again. </li></ul>K + K + K + K + Na + K+ K+ K+ K+ Na+ Na+ Na+ K+ K+ K+ K+ K+ K+ K+ K+ K+
    19. 26. <ul><li>#1 Triggered by depolarization </li></ul><ul><li>a less negative membrane potential that occurs transiently </li></ul>
    20. 27. <ul><li>Threshold depolarization needed to trigger the action potential </li></ul><ul><li>10-20 mV depolarization must occur to trigger action potential </li></ul>
    21. 28. <ul><li>Are all-or- none event </li></ul><ul><li>Amplitude of AP is the same regardless of whether the depolarizing event was weak (+20mV) or strong (+40mV). </li></ul>
    22. 29. <ul><li>Propagates without decrement along axon </li></ul>The shape (amplitude & time) of the action potential does not change as it travels along the axon
    23. 30. <ul><li>At peak of action potential the membrane potential reverses polarity </li></ul><ul><li>Becomes positive inside as predicted by the E na Called OVERSHOOT </li></ul><ul><li>Return to membrane potential to a more negative potential than at rest </li></ul><ul><li>Called UNDERSHOOT </li></ul>
    24. 31. <ul><li>Absolute refractory period follows an action potential. Lasts 1 msec </li></ul><ul><li>During this time another action potential CANNOT be fired even if there is a transient depolarization. </li></ul><ul><li>Limits firing rate to 1000AP/sec </li></ul>
    25. 37. <ul><li>The number of voltage gated sodium channels per square micrometer of the membrane in mylinated neuron is; </li></ul><ul><li>A. cell body 50-75 </li></ul><ul><li>B. initial segment 350-500 </li></ul><ul><li>C. on the surface of the myelin <25 </li></ul><ul><li>D. Node of the ranvier 2000-12000 </li></ul><ul><li>E. axon terminal 20-75 </li></ul><ul><li>Unmylinated neuron: 110 </li></ul>
    26. 38. Copyright © Allyn & Bacon 2004 <ul><ul><li>Membrane Potentials </li></ul></ul><ul><ul><ul><li>1. </li></ul></ul></ul><ul><ul><ul><li>Resting Potential </li></ul></ul></ul><ul><ul><ul><li>(just described) </li></ul></ul></ul>threshold <ul><ul><ul><li>2. Excitatory Post-synaptic potential </li></ul></ul></ul><ul><ul><ul><li>4. </li></ul></ul></ul><ul><ul><ul><li>Inhibitory </li></ul></ul></ul><ul><ul><ul><li>Post-synaptic potential </li></ul></ul></ul><ul><ul><ul><li>3. </li></ul></ul></ul><ul><ul><ul><li>Action </li></ul></ul></ul><ul><ul><ul><li>Potential </li></ul></ul></ul>
    27. 39. <ul><li>Increase internal diameter of axon which decreases the internal resistance to ion flow </li></ul><ul><li>Increase the resistance of the plasma membrane to charge flow by insulating it with myelin. </li></ul>
    28. 44. <ul><ul><li>Sodium: Decreasing the external Na + concentration reduces the size of the action potential but has little effect on the resting membrane potential. The lack of much effect on the resting membrane potential would be predicted, since the permeability of the membrane to Na + at rest is relatively low. </li></ul></ul><ul><ul><li>Potassium: Conversely, increasing the external K + concentration decreases the resting membrane potential. </li></ul></ul><ul><ul><li>Calcium: </li></ul></ul>
    29. 46. <ul><li>It is possible to determine the minimal intensity of stimulating current (threshold intensity) that, acting for a given duration, will just produce an action potential. </li></ul><ul><li>Action potential fails to occur if the stimulus is subthreshold in magnitude,produces graded potentials. </li></ul><ul><li>Suprathreshold stimuli produce action potential during relative refractory period. </li></ul>