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Memb potential.sept 13. 1 st
 

Memb potential.sept 13. 1 st

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MEMBRANE POTENTIAL AND DEVELOPMENT OF AP IN EXCITABLE TISSUE.

MEMBRANE POTENTIAL AND DEVELOPMENT OF AP IN EXCITABLE TISSUE.

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    Memb potential.sept 13. 1 st Memb potential.sept 13. 1 st Presentation Transcript

    • 24 Oct. 2012 Ashok Solanki 1 Action Potentials- the language of excitable tissue How neurons conduct impulses How the muscle contract? How the heart pump?
    • Resting membrane potential created by semi-permeable membrane and ions • Intracellular – Na 50 – K 400 – Cl 52 • Resting membrane potential created by semi- permeable membrane and ions • Intracellular – Na 50 – K 400 – Cl 52 2Ashok Solanki24 Oct. 2012
    • Cell – the functional unit. • 100 trillion cells organize systems of the body. Ashok Solanki 324 Oct. 2012
    • 4Ashok Solanki24 Oct. 2012
    • Ashok Solanki 524 Oct. 2012
    • AP OBEYS ALL OR NONE LAW ALL-OR-NONE RESPONSE A stimulus below the threshold also will not stimulate the neuron once a threshold limit is reached any stronger stimulus will not increase the cell's response 24 Oct. 2012 6Ashok Solanki
    • 24 Oct. 2012 Ashok Solanki 7 What starts an Action Potential?? • STIMULATION (chemical, electrical, mechanical) opens Na+ channels – low intensity stimulation opens few channels, – local, graded potential – resting potential restored without action potential
    • 8Ashok Solanki24 Oct. 2012
    • THE NEURON MEMBRANE AT REST • Neuron maintains a resting membrane potential of about -70 millivolts across the cell membrane • Sodium(Na+) and potassium(K+) are the main ions involved • Na+ and K+ cannot pass through the lipid bilayer membrane • move through the membrane by using 24 Oct. 2012 9Ashok Solanki
    • ACTION POTENTIAL • What is it? • Excitable tissue. • All or none law of A.P. • Change in RMP. • Role of ions? • Propagation of. • Propreties of A.P. 10Ashok Solanki24 Oct. 2012
    • Distribution of important ions in ECF & ICF Na+ K+ Cl- INSIDE 14 mEq / L 120 mEq / L 8 mEq / L OUTSIDE 142 mEq / L 4.5 mEq / L 107 mEq / L 24 Oct. 2012 11Ashok Solanki
    • Ashok Solanki 1224 Oct. 2012
    • 24 Oct. 2012 13Ashok Solanki
    • 24 Oct. 2012 Ashok Solanki 14 Action Potential • ALL-OR-NONE phenomenon • All Action Potentials are the same intensity. – stronger sensations result from more impulses, not stronger impulses. – more impulses from same neuron – more impulses from many neurons
    • Na+ / K+ PUMP Membrane proteins actively transport sodium out of the cell potassium in Three Na+ are pumped out for every two K+ pumped in result is the cell has more Na+ on the outside and more K+ on the inside 24 Oct. 2012 15Ashok Solanki
    • 16Ashok Solanki24 Oct. 2012
    • 17Ashok Solanki24 Oct. 2012
    • 24 Oct. 2012 Ashok Solanki 18 How neurons conduct impulses: • Membrane potential (as seen in muscle cells) • K+ diffuses out of neurons faster than Na+ diffuses in, • Na-K pump moves 3Na+ back out for 2K+ back in • Cl-, phosphate, protein anions balance cations • “Resting potential” = - 70 mV
    • 24 Oct. 2012 19Ashok Solanki
    • 24 Oct. 2012 Ashok Solanki 20 How neurons conduct impulses: • Action potential – describes events at one point of nerve fiber – 1: stimulus to threshold potential – 2: Na+ channels open, Na+ diffuses in • Polarity briefly reversed, to +30 mV – 3: Na+ channels close
    • 24 Oct. 2012 21Ashok Solanki
    • The Lipid Barrier of the Cell Membrane, and Cell Membrane Transport Proteins • Active Transport" of Substances Through Membranes • Primary Active Transport and Secondary Active Transport • Co-Transport of Glucose and Amino Acids Along with Sodium Ions • Sodium Counter-Transport of Calcium and Hydrogen Ions • Na+-K+ pump performs a continual surveillance role in maintaining normal cell volume. • A Positive-Feedback Cycle Opens the Sodium Channels • Threshold for Initiation of the Action Potential • A major function of the voltage-gated calcium ion channels is to contribute to the depolarizing phase on the action potential in some cells 22Ashok Solanki24 Oct. 2012
    • Ashok Solanki 2324 Oct. 2012
    • 24 Oct. 2012 Ashok Solanki 24 What starts an Action Potential?? • STIMULATION opens Na+ channels – higher magnitude stimulation opens more channels, local potential exceeds threshold at trigger zone, – Na+ floods in depolarization
    • Ashok Solanki 2524 Oct. 2012
    • STIMULATED NEURON Nerve cells are unique in their ability to carry a signal using membrane potential changes Stimulation of a neuron opens some of the membrane proteins (a.k.a. Na+gates) allows Na+ to pass freely into the cells free flow of Na+ into the cell causes a reversal of membrane polarity polarity reversal is called the action potential 24 Oct. 2012 26Ashok Solanki
    • Resting Potential • At rest, the inside of the cell is at -70 microvolts • With inputs from dendrites inside becomes more positive • If resting potential rises above threshold, an action potential starts to travel from cell body down the axon • Figure shows resting axon being approached by an AP 24 Oct. 2012 27Ashok Solanki
    • How Neurons Communicate • Action Potential is the electrical process that neurons use to communicate with each other • Action Potentials are based on movements of ions (charged particles) between the outside and inside of the axon • Action Potential is an All or Nothing Process (like a gun firing) 24 Oct. 2012 28Ashok Solanki
    • 24 Oct. 2012 Ashok Solanki 29 Conduction of an Action Potential • Propagation of A.P. along neuron membrane • Na+ diffuses, attracted to negative charges in front of impulse • A.P. at "A"
    • 24 Oct. 2012 Ashok Solanki 30 What Keeps Impulse Going the Same Way ? • Limits to stimulation of neuron/membrane • Absolute Refractory Period • Relative Refractory Period
    • Ashok Solanki 31 35. Regarding the ionic basis of action potential in cardiac muscle cells, which one of the following is incorrect? A. Phase 0: Na influx B. Phase 1: K influx C. Phase 2: Ca influx D. Phase 3: K efflux 24 Oct. 2012
    • GOLDMAN–HODGKIN–KATZ EQUATION • V = 60mV log10 PNaNao • + + PKKo • + + PClCli • − • _________ ________ • PNaNai • + + PKKi • + + PClClo Ashok Solanki 3224 Oct. 2012
    • 24 Oct. 2012 Ashok Solanki 33 How neurons conduct impulses: – 3: K+ channels open, K+ diffuses out, Potential returns to zero – 4: All channels closed, Na-K pump moves Na+ back out & K+ back in – Hyperpolarization – Resting potential restored
    • 24 Oct. 2012 Ashok Solanki 34 How neurons conduct impulses: • Action potential – describes events at one point of nerve fiber – 1: stimulus to threshold potential – 2: Na+ channels open, Na+ diffuses in • Polarity briefly reversed, to +30 mV – 3: Na+ channels close
    • Two Ionic Equilibria and Resting Membrane Potentials • The resting membrane potential plays a central role in the excitability of nerve and muscle • An action potential is a rapid change in the membrane potential followed by a return to the resting membrane potential 35Ashok Solanki24 Oct. 2012
    • Generation and Conduction of Action Potentials • An action potential is propagated with the same shape and size along the whole length of a nerve or muscle cell • The action potential is the basis of the signal- carrying ability of nerve cells • In muscle cells, an action potential allows the entire length of these long cells to contract almost simultaneously. • Voltage-dependent ion channel proteins in the plasma membrane are responsible for action potentials. 36Ashok Solanki24 Oct. 2012
    • Ashok Solanki 3724 Oct. 2012
    • Ashok Solanki 3824 Oct. 2012
    • Ashok Solanki 3924 Oct. 2012
    • Voltage dependent ion channels • Extracellular Na activation gate with intracellular inactivation gate and slow K activation gait • Conformational changes due to membrane potential changes influence ion permeability 40Ashok Solanki24 Oct. 2012
    • 41Ashok Solanki24 Oct. 2012
    • Nomenclature • Polarized membrane: Intracellular potential is negative relative to extracellular space • Depolarization = less polarization of the membrane -80mV -> +20mV • Hyperpolarization = more polarization of membrane -80mV -> -100mV 42Ashok Solanki24 Oct. 2012
    • Cell membrane • Necessary for life as we know it • Border role for cell – Separates intracellular from extracellular milleau • Allows ion and protein concentration gradients to exist – Creates electric charge gradients 43Ashok Solanki24 Oct. 2012
    • LECTURE SUMMARY Ashok Solanki 4424 Oct. 2012