nerve nernst potential pptx great use in study

nerve nernst potential pptx great use in study

• 1.
  Membrane Potentials
• 3.
  Lecture Objectives At theend of lecture students should be able to: Nerve and its classification • Recognize the various ion channels. • Recognize and describe forces acting on ions. • Discuss diffusion potential. • Discuss Nernst potential. • Apply Nernst s equation to calculate membrane potential. • Apply Goldman-Hodgkin-Katzequation to calculate membrane potentials. • Explain the origin of resting membrane potential.
• 8.
  Neuron structure
• 11.
  Structural classification of neuron
• 12.
  Types of neuron
• 17.
  Classification of nervefiber • On the bases of structure Mylinated Unmylinated On the bases of function: Sensory (Afferent) Motor (Efferent )
• 20.
  Membrane potential
• 21.
  Basic Physics ofMembrane Potentials • Diffusion potential is the potential difference generated across a membrane because of a concentration difference of an ion. • It can be generated only if the membranes is permeable to the ion.
• 24.
  Ion concentration Na andchloride are usually present at higher concentrations outside the cell.
• 25.
  Negativity of cells •In neuron K and organic anions (such as those found in proteins and amino acids) are present at higher concentrations inside the cell than outside creating intracellular more negative
• 31.
  Electro chemical forces
• 32.
  Driving Forces • Chemicalgradient : arises from the concentration difference between the two compartments Diffusion of force causes of movement potassium ion from inside to out side through leaky channels due chemical gradient . • Electrical gradient develop Electrical forces pulls potassium ion inside the cell Two forces become balanced and prevent further diffusion of ions called equilibrium potential or nernst potential
• 33.
  Cont: • Chemical gradient,which arises from the concentration difference between the two compartments; and • Electrical gradient, which initially does not exist, but is established as soon as K+ begins to move from compartment inside to outside , and gets larger and larger as more and more K+ ions diffuse down their concentration gradient from compartment i to o. then move from outside to inside due to electrical gradient • Therefore, it can be seen that the larger the chemical gradient (i.e., concentration gradient) across the membrane, the larger the resulting electrical gradient will be in order to balance the diffusion of the ion from the compartment with high concentration to the compartment with low concentration.
• 35.
  Nernst potential • Whenthe Electrical gradient ,which tends to keep K+ inside equal , the concentration gradient (which tend to push K+ outside)→ there will be no net K+ movement across the membrane. • Similarly Na is move inside the cell due to concentration gradient carrying positive charge inside cell and progresively decreasing the negativity inside the cell • When the electrical force (which tends to push Na out side the cell) become equal to concentration gradient (which tend to push Na inside the cell) → there will be no net Na+ movement across the membrane
• 36.
  Nernst potential • alsocalled equilibrium potential or Electrochemical potential • The potential which prevent the further diffusion of ions in spite of existing concentration difference of ions is called Nernst potential. • electrical gradient will completely balance the chemical gradient and there is no net movement of ions between the two compartments
• 38.
  Nernst equation used tocalculate Nernst potential of individual ions • EMF millivolts = + 61 log Concentration inside Concentration outside
• 39.
  The Nernst Potential ForK + EMF = -61 log 140/4 = - 61 log 35 = - 61* 1.54 = - 94 mv
• 40.
  Nernst Potential (equilibriumpotential) • The value of the equilibrium potential for any ion depends upon the concentration gradient for that ion across the membrane. • If the concentrations on the two sides were equal, the force of the concentration gradient would be zero, and the equilibrium potential would also be zero. • The larger the concentration gradient, the larger is the equilibrium potential. The equilibrium potential for any ion can be calculated using the so called Nernst equation.
• 41.
  Diffusion Potential ofthe Membrane permeable to Several Ions When a membrane is permeable to several different ions, the diffusion potential that develops depends on three factors: • the polarity of the electrical charge of each ion • the permeability of the membrane (P) to each ion, • the concentrations (C) of the respective ions on the inside (i) and outside (o) of the membrane.
• 42.
  Goldman equation • Theinfluence of multiple ions is best determined using the Goldman Equation,
• 43.
  The Goldman-Hodgkin-Katz equation • TheGoldman-Hodgkin-Katz equation, gives the calculated membrane potential on the inside of the membrane when two univalent positive ions, sodium (Na+) and potassium (K+), and one univalent negative ion, chloride (Cl–), are involved.
• 44.
  Goldman equation • Goldmanequation gives a potential • inside the membrane of –86 millivolts, which is near the potassium potential (- 94)
• 45.
  Resting membrane potential
• 46.
  The Resting Potential •Difference in electrical charges across the membrane during the resting stage of cell is called resting membrane potential. • The resting potential (when the cell is not firing) is a 70 to 90 mV difference between the inside and the outside. inside outside Resting potential of neuron = -70mV + - + - + - + - + -
• 47.
  Ions and theResting Potential • Ions are electrically-charged molecules e.g. sodium (Na+), potassium (K+), chloride (Cl-). • The resting potential exists because ions are concentrated on different sides of the membrane. – Na+ and Cl- outside the cell. – K+ and organic anions inside the cell. inside outside Na+ Cl- Na+ K+ Cl- K+ Organic anions (-) Na+ Na+ Organic anions (-) Organic anions (-)
• 48.
  Negativity of cell
• 50.
  RMP • Resting membranepotential is the difference in the electrical potential between the interior and exterior of cell when the cell is at rest. • There is a separation of charges • Membrane is polarized at resting stage
• 51.
  Factors Affecting RMP •3 factors – Polarity of each ion – Membrane permeability of the ions – Concentrations of respective ions on both sides: (i= inside), (o= outside)
• 52.
  Ion Intracellular ExtracellularNormal Plasma Value K+ 150 5 3.5-5.0 Na+ 12 140 135-145 Cl- 10 105 100-108 Organic Anions 65 0 T3-5 • Difference in ion concentration between compartments gives rise to the resting membrane potential (RMP). Membrane permeability to these ions also influences the RMP. • Transient changes from the RMP produce electrical signals which transmit information in nerve cells. Changes in the Membrane Potential Produce Electric Signals in Nerve Cells
• 53.
  Resting Potential In aresting neuron (one that is not conducting an impulse), there is a difference in electrical charges on the outside and inside of the plasma membrane. The outside has a positive charge and the inside has a negative charge.
• 54.
  • Considerable energyis expended by cells to move Na+ and K+ • inside of the cell is more negative due to presences of negative charge proteins and phosphate ions inside the cell that cannot cross the membrane.
• 55.
  Origin of theNormal Resting Membrane Potential • Contribution of the Potassium Diffusion Potential • Contribution of Sodium Diffusion Through the Nerve Membrane • Contribution of the Na+-K+ Pump.
• 56.
  Contribution of thePotassium Diffusion Potential • if potassium ions were the only factor causing the resting potential, the resting potential inside the fiber would be equal to –94 millivolts
• 58.
  Contribution of SodiumDiffusion Through the Nerve Membrane • The ratio of sodium ions from inside to outside the membrane is 0.1, and this gives a calculated Nernst potential for the inside of the membrane of +61 millivolts.
• 59.
  Contribution of passivediffusion The sodium-potassium pump creates a concentration and electrical gradient for Na+ and K+, which means that K+ tends to diffuse (‘leak’) out of the cell and Na+ tends to diffuse in. BUT, the membrane is much more permeable to K+, so K+ diffuses out along its concentration gradient much more slowly.
• 61.
  role of pumpsodium-potassium pump • sodium-potassium pump maintain a electrochemical gradient which is necessary for the establishment of resting membrane potential. • Na- k pump (active transport) is not involve in action potential . • it help in generation of restoring of RMP .
• 62.
  origin RMP • Inresting potential Contribution by passive transport is -86mv ( calculated by Goldman equation) • Contribution by sodium-potassium pump is - 4mv • RMP is -90 mv • In resting membrane potential the main contribution is of potassium ions
• 64.
  Resting membrane potential(RMP) • diffusion through Potassium sodium (K+-Na+) “leak” channel needs concentration gradient • Potassium is 100 time permeable than Na through channel • In resting membrane potential the main contribution is of potassium ions •
• 66.
  RESULTS IN: a netpositive charge outside & a net negative charge inside. Such a membrane is POLARISED
• 67.
  Explanation • one cansee that if the membrane is highly permeable to potassium but only slightly permeable to sodium. • it is logical that the diffusion of potassium contributes far more to the membrane potential than does the diffusion of sodium. • In the normal nerve fiber, the permeability of the membrane to potassium is about 100 times as great as its permeability to sodium. • Using this value in the Goldman equation gives a potential inside the membrane of –86 millivolts, which is near the potassium potential
• 68.
  Factors Affecting RMP •3 factors – Polarity of each ion – Membrane permeability of the ions – Concentrations of respective ions on both sides: (i= inside), (o= outside)
• 70.
  Key points • Aresting (non-signaling) neuron has a voltage across its membrane called the resting membrane potential, or simply the resting potential. • The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion. • In a resting neuron, there are concentration gradients across the membrane for Na and K • Ions move down their gradients via channels, leading to a separation of charge that creates the resting potential. • The membrane is much more permeable to k than Na,so resting potential is close to the equilibrium potential of K, the potential that would be generated by K, if it were the only ion in the system).
• 72.
  Action Potential
• 73.
  Action potential Rapid transientchanges in electrical potential across a plasma membrane of excitatory cell (as of a neuron or muscle fiber) that spread rapidly along the nerve/muscle fiber membrane . it occurs when a cell has been activated by a stimulus
• 74.
  Action potentials: Rapiddepolarization • When partial depolarization reaches the activation threshold, voltage-gated sodium ion channels open. • Sodium ions rush in. • The membrane potential changes from -70mV to +40mV. Na+ Na+ Na+ - + + -
• 76.
  threshold • Threshold potential:Minimum potential required to generate action potential (-55 t0 - 65 Mv) • the threshold for activation of a fiber depends not only on stimulus strength, but also on the duration of the stimulus • Thus when the stimulus is stronger, a larger number of fibres reach threshold.
• 77.
  When enough sodium ionsenter the cell to depolarise the membrane to a critical level (threshold level) an action potential arises which generates an impulse. In order for the neuron to generate an action potential the membrane potential must reach the threshold of excitation.
• 78.
  • http://highered.mheducation.com/sites/0072 495855/student_view0/chapter14/animation_ _the_nerve_impulse.html • http://highered.mheducation.com/sites/0072 943696/student_view0/chapter8/animation__ the_nerve_impulse.html
• 81.
  Events during an action potential
• 82.
  Figure 4-7
• 83.
  Na channel
• 85.
  • QUESTION: Giventhat the Na+ equilibrium potential is +60 mV and the membrane potential moves from its resting level to 0 mV, in what direction will Na+ now move through any open Na+ channels? • QUESTION: If the K+ equilibrium potential is -90 mV and the membrane potential is -70 mV, in what direction will K+ move through open K+ channels?
• 87.
  Restoring of theResting Potential Na+/K+ pumps gradually restores the concentration gradients disrupted by action potentials. • 3 Sodium ions are pumped into the ECF • 2 Potassium ions are pumped into the ICF
• 89.
  • Na- potassiumpump bring the membrane towards resting membrane potential • Sodium- potassium pump have no role in generation of action potential
• 90.
  Channel responsible foraction potential (Summary )
• 91.
  The action potential 1.RMP: • Resting membrane potential is the difference in the electrical potential between the interior and exterior of cell when the cell is at rest. -70 to -90 Mv in neurons 2. THRESHOLD potential :minimum potential required to generate action potential (-55 t0 - 65 Mv)
• 92.
  3.DEPOLARIZATION : • Influxof Na ion through voltage gated Na channels causes the inside of the membrane to become increasingly more + ve:
• 93.
  4. Spike potential( over shoot potential ) This is the peak of the action potential, that membrane is about +35 to +40 mV. As the voltage becomes positive, the sodium channels close, or inactivate, and the voltage- gated potassium channels open.
• 94.
  5. REPOLARIZATION: • K+ions diffuse out of the cell down the electrochemical diffusion gradient, through voltage gated K+channels so making the inside of the cell more negative again:
• 95.
  6. HYPERPOLARIZATION: • K+channels close slowly , greater amount of potassium moves out and membrane potential becomes even more negative than the resting potential for a brief period; this is called hyperpolarization
• 96.
  • Recovery (potassiumchannels close ) Na+/K+ pumps gradually restores RMP and reestablish the concentration gradients of Na+ and K+ ions disrupted by action potentials. • 3 Sodium ions are pumped into the ECF • 2 Potassium ions are pumped into the ICF
• 97.
  Properties of theaction potential • It is propagative • Have Refractory period • Impulse always transmit away from stimulus(orthrodromic conduction) • Unidirectional because of refractory period • same size and shape • within specific time • All-or-None Principle
• 98.
  Properties of actionpotential • Have same size and shape for specific cells, irrespective of the intensity of the stimulus • specific time : Exists within a specific time frame 1 to 5 msec.- (i.e time duration of the action potential is always the same for a specific tissue • has fixed amplitude
• 99.
  The Action PotentialTypes
• 100.
  Refractory period When anaction potential is being produced, a second stimulus will not generate a second action potential • Duration :about 1 ms • the ion channels remain closed and cannot be made to reopen so no further depolarisation is possible