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ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
ACTION POTENTIAL - IONIC BASIS AND RECORDING
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ACTION POTENTIAL - IONIC BASIS AND RECORDING

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  • Andrew Huxley (right)
  • Absolute Refractory period – infatiguabilityAccommodation
  • Sushi chefs who are trained to remove the ovaries safely are licensed by the government to prepare puffer fish. Despite these precautions, each year several people die from eating improperly prepared puffer fish.
  • Transcript

    • 1. 1 IONIC BASIS AND RECORDING OF ACTION POTENTIAL Dr.Anu Priya.J. 12/11/2013
    • 2. 2          Introduction History Resting membrane potential Graded potential Action potential Ionic basis Types Recording Applied aspects 12/11/2013
    • 3. Introduction 3 • Nerve and muscle are excitable tissues • Can undergo rapid changes in their membrane potentials • Change their resting potentials into electrical signals that aid in cellular communication • These signaling events are mediated by ion channels 12/11/2013
    • 4. History 4  Since the 18th century, when Galvani introduced the concept of "animal electricity", electric potentials have been observed and recorded in different nerves and muscles. 12/11/2013
    • 5. 5  Illustration of Italian physician Luigi Galvani's experiments, in which he applied electricity to frogs legs; from his book De Viribus Electricitatis in Motu Musculari (1792). 12/11/2013
    • 6. History 6   1963- A. L. Hodgkin and A. F. Huxley - Nobel prize in Physiology or Medicine- study of sodium and potassium channels – voltage clamp method Sir John Carew Eccles-shared-work on synapse 12/11/2013
    • 7. History 7   The patch clamp technique - Erwin Neher and Bert Sakmann - Nobel Prize in Physiology or Medicine in 1991 Record the currents of single ion channels for the first time, proving their involvement in fundamental cell processes such as action potential conduction. 12/11/2013
    • 8. History 8  Sir A. F. Huxley passed away on 30 May 2012 – age 94 years 12/11/2013
    • 9. Resting Membrane Potential 9    It is the potential difference existing across the cell membrane at rest Interior of the cell is negatively charged in relation to the exterior State of polarisation 12/11/2013
    • 10. Resting Membrane Potential 10 RMP is maintained by: 1. Natural concentration gradient 2. Selective permeability of cell membrane 3. Impermeable anions 4. Sodium-potassium ATPase pump 12/11/2013
    • 11. Resting Membrane Potential 11        Neurons have a selectively permeable membrane During resting conditions membrane is:  permeable to potassium (K+) (channels are open)  impermeable to sodium (Na+) (channels are closed) Diffusion force pushes K+ out (concentration gradient) This creates a positively charged extra-cellular space. Electrostatic force pushes K+ in Thus, there is a ‘dynamic equilibrium’ with zero net movement of ions. The resting membrane potential is negative 12/11/2013
    • 12. Graded potential 12 Subthreshold stimuli cause sensory receptors to depolarize and produce a voltage called a generator potential(Receptor Potential)  Does not obey all or none law  Graded response  it is not propagated  Summation  No refractory period  Duration(5-10 ms) 12/11/2013
    • 13. Graded potential & Action potential 13 12/11/2013
    • 14. Action potential 14      An action potential is a rapid change in the membrane potential in response to a threshold stimulus followed by a return to the resting membrane potential. The size and shape of action potentials differ considerably from one excitable tissue to another. An action potential is propagated with the same shape and size along the whole length of a cell. The action potential is the basis of the signal-carrying ability of nerve cells. Voltage-dependent ion channel proteins in the plasma membrane are responsible for action potentials. 12/11/2013
    • 15. 15 12/11/2013
    • 16. 16 12/11/2013
    • 17. Hodgkin cycle 17 12/11/2013
    • 18. Graded potential & Action potential 18 12/11/2013
    • 19. 19 12/11/2013
    • 20. 20 12/11/2013
    • 21. 21 12/11/2013
    • 22. 22 Role of other ions  Impermeable Anions  Calcium ions 12/11/2013
    • 23. Properties 23  Voltage inactivation  Refractory period  All or none law  Propagative  depolarization and repolarization  No summation 12/11/2013
    • 24. Recording of action potential 24   Mammalian axons less than 20 μm diameter Squid-giant cells-largest axon in neck regionabout 1 mm diameter 12/11/2013
    • 25. Recording of action potential 25  a) b) Requirements of instrument used : It should be capable of responding extremely rapidly The potential changes which are in millivolts has to be amplified before being recorded 12/11/2013
    • 26. Recording of action potential 26  1. 2. 3. The instruments used are: Microelectrodes Electronic amplifiers Cathode ray oscilloscope (CRO) 12/11/2013
    • 27. Microelectrodes 27  Micropipette – tip size less than 1 mm diameter  Filled with strong electrolyte solution- KCl  Resistance – 1 billion Ω  The tip of the micropipette is passed through the cell membrane of the nerve fibre  Indifferent electrode – in extracellular fluid  Connected to cathode ray oscilloscope through amplifier 12/11/2013
    • 28. Electronic amplifier 28  magnify the potential changes of the tissue to be recorded on the oscilloscope screen 12/11/2013
    • 29. Cathode ray oscilloscope 29 Rapid and instantaneous recording of electrical events of living tissues  Parts i. Glass tube ii. Cathode iii. Fluorescent screen iv. Two sets ( horizontal and vertical ) electrically charged plates  12/11/2013
    • 30. Cathode ray oscilloscope 30 12/11/2013
    • 31. Recording of action potential 31   Patch clamp method Voltage clamp method 12/11/2013
    • 32. Patch clamp method 32 12/11/2013
    • 33. Voltage clamp method 33 12/11/2013
    • 34. Types 34    Monophasic Biphasic Compound 12/11/2013
    • 35. Biphasic action potential 35 12/11/2013
    • 36. Biphasic action potential 36 12/11/2013
    • 37. Compound action potential 37     Peripheral nerves in mammals are made up of many axons bound together in a fibrous envelope called the epineurium. Potential changes recorded extracellularly from such nerves therefore represent an algebraic summation of the all-or-none action potentials of many axons. The thresholds of the individual axons in the nerve and their distance from the stimulating electrodes vary. With subthreshold stimuli, none of the axons are stimulated and no response occurs. 12/11/2013
    • 38. 38     When the stimuli are of threshold intensity, axons with low thresholds fire and a small potential change is observed. As the intensity of the stimulating current is increased, the axons with higher thresholds are also discharged. The electrical response increases proportionately until the stimulus is strong enough to excite all of the axons in the nerve. The stimulus that produces excitation of all the axons is the maximal stimulus, and application of greater, supramaximal stimuli produces no further increase in the size of the observed potential. 12/11/2013
    • 39. Compound action potential 39 12/11/2013
    • 40. Applied aspects 40 Hereditary spherocytosis (HS)  Plasma membrane of red cells three times more permeable to Na+  The level of Na+,K+-ATPase elevated.  When HS red blood cells have sufficient glucose to maintain normal ATP levels, they extrude Na+ as rapidly as it diffuses into the cell cytosol. Hence the red blood cell volume is maintained. 12/11/2013
    • 41. Applied aspects 41     When HS erythrocytes are delayed in the venous sinuses of the spleen, where glucose and ATP are present at low levels, the intracellular ATP concentration falls. Therefore, Na+ cannot be pumped out by the Na+,K+-ATPase as rapidly as it enters. The red blood cells swell - osmotic effect of elevated intracellular Na+ concentration. Spleen targets these swollen erythrocytes for destruction - anemia. 12/11/2013
    • 42. Applied aspects 42   Tetrodotoxin (TTX)- a potent poison - specifically blocks the Na+ channel- binds to the extracellular side of the sodium channel. Tetraethylammonium (TEA+), another poison, blocks the K+ channel when it is applied to the interior of the nerve fiber.  12/11/2013
    • 43. Applied aspects 43  The ovaries of certain species of puffer fish, also known as blowfish, contain TTX. Raw puffer fish - Japan. 12/11/2013
    • 44. Applied aspects 44  Saxitoxin is another blocker of Na+ channels that is produced by reddish-colored dinoflagellates that are responsible for so-called red tides. 12/11/2013
    • 45. Applied aspects 45  Shellfish eat the dinoflagellates and concentrate saxitoxin in their tissues.  A person who eats these shellfish may experience lifethreatening paralysis within 30 minutes after the meal 12/11/2013
    • 46. Applied aspects 46     In an inherited disorder, called primary hyperkalemic paralysis, patients have episodes of painful spontaneous muscle contractions, followed by periods of paralysis of the affected muscles. Elevated levels of K+ in the plasma and extracellular fluid. Some patients with this disorder have mutations of voltagegated Na+ channels that result in a decreased rate of voltage inactivation. This results in longer-lasting action potentials in skeletal muscle cells and increased K+ efflux during each action potential. This can raise the extracellular levels of K+. 12/11/2013
    • 47. Applied aspects 47     The elevation of extracellular K+ causes depolarization of skeletal muscle cells. Initially, the depolarization brings muscle cells closer to threshold, so that spontaneous action potentials and contractions are more likely. As depolarization of the cells becomes more marked, the cells accommodate because of the voltage-inactivated Na+ channels. Consequently, the cells become unable to fire action potentials and are unable to contract in response to action potentials in their motor axons. 12/11/2013
    • 48. Applied aspects 48   Low potentials recorded in neuropathy and spinal cord compression INJURY POTENTIAL The difference in electrical potential between the injured and uninjured parts of a nerve or muscle – also called demarcation potential 12/11/2013
    • 49. Applied aspects 49 TETANY  Hypocalcemia – sodium channels activated by very little increase of membrane potential from resting state 12/11/2013
    • 50. 50 12/11/2013
    • 51. References 51  Guyton and Hall Textbook of Medical Physiology 12th edition  Ganong's Review of Medical Physiology 23rd edition  Berne & Levy Physiology 6th edition  Boron and Boulpaep Medical physiology 2nd edition  Basics of Medical physiology by Dr.Venkatesh.D 3rd edition  Textbook Of Medical Physiology by Indu Khurana 1st edition  Internet references 12/11/2013

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