7147633 membrane-physiology

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7147633 membrane-physiology

  1. 1. MEMBRANEMEMBRANE PHYSIOLOGYPHYSIOLOGY Anita Ocampo-So, MD, FPSP, DPBA, MHA Professor
  2. 2. Nervous SystemNervous System A complex array of specialized structures which serve to: • Receive • Store • Transmit information • Consist of the CNS and the PNS • Neuron- basic unit of the NS – 1 trillion neurons
  3. 3. NeuronsNeurons • Made up of dendrites • Soma • Axon- axon terminal • Has different organelles but no centromere • Classification according to 1. structure 2. Form 3. covering – Schwann cells
  4. 4. NeuronsNeurons
  5. 5. NeuronsNeurons • structures aside from organelles 1. astrocytes 2. microglia 3. oligodendroglia – apoptosis
  6. 6. NeuronsNeurons • Bell-Magendie Law • Afferent – sensory • Efferent – motor • Afferent  200,000 interneuron  10 efferent
  7. 7. NeuronsNeurons
  8. 8. Classification of NerveClassification of Nerve FibersFibers Class Conduction Velocity (m/sec) Size ( μm) Functions A α 70-120 12-20 Proprioception Somatic motor β 30-70 5-12 Touch pressure γ 15-30 3-6 Motor to muscle spindle δ 12-30 2-5 Pain,touch, cold temp B 3-5 <3 Preganglionic, Autonomic C 0.5-2 0.4-1.2 pain, temperature, mechanoreception
  9. 9. Classification of NerveClassification of Nerve FibersFibers
  10. 10. Coverings of NerveCoverings of Nerve FibersFibers 1. endoneurium 2. perineurium 3. epineurium
  11. 11. Coverings of NerveCoverings of Nerve FibersFibers
  12. 12. Properties of NerveProperties of Nerve FibersFibers 1. Excitability 2. Conductivity
  13. 13. Myelinated FibersMyelinated Fibers • Schwann cells • Nodes of Ranvier • Saltatory Conduction –Advantages • faster conduction • saves energy • less loss of ions
  14. 14. Myelinated FibersMyelinated Fibers
  15. 15. Resting MembraneResting Membrane PotentialPotential • Cells under resting conditions have an electrical potential difference across their plasma membrane. This potential is the Resting Membrane Potential (RMP) • The cytoplasm is electrically (-) relative to the ECF • The RMP plays a vital role in the excitability of nerve and muscle cells and in other cellular responses
  16. 16. Genesis of the RMPGenesis of the RMP 1.Distribution of ions • movement of ions depend on: a. Concentration b. Electrical potential difference • if forces are equal = no movement – Nernst equation – Nernst equilibrium EMF (mo) = (-)61log conc 1/conc 0 = (+)61
  17. 17. Genesis of the RMPGenesis of the RMP – Gibbs-Donnan equilibrium – Goldman-Hodgkin-Katz 2. Selective Permeability of the Membrane 3. Na+ - K+ pump • RMP – skeletal muscle (-)90mV – nerve (-) 70 mV
  18. 18. Action PotentialAction Potential
  19. 19. Action PotentialAction Potential • All-or-Nothing Principle • Strength – duration curve –Rheobase –Utilization time –Chronaxie
  20. 20. Refractory PeriodsRefractory Periods • Absolute Refractory Period • Relative Refractory Period –nerve fibers are not susceptible to fatigue • Accommodation
  21. 21. Refractory PeriodsRefractory Periods Local Excitatory States • subthreshold stimulus • inadequate duration of applications According to their location • receptor potential • synaptic potential • pacemaker potential • end-plate potential In general, moves the RMP closer to the threshold potential
  22. 22. Synapse and SynapticSynapse and Synaptic TransmissionTransmission Synapse • an anatomically specialized junction between two neurons • important in the transport of nerve signals from one neuron (presynaptic) to the next neuron (postsynaptic) – 100 quadrillon synapses in the CNS – 2 types a. Electrical b. Chemical
  23. 23. Presynaptic andPresynaptic and Postsynaptic NeuronPostsynaptic Neuron Presynaptic neuron • has lots of mitochondria • has NTs inside vesicles • usual forms are ; round, dense, flat and sphenoid • intertwining – cerebellum • basket and climbing – midbrain Postsynaptic neuron • contains the receptor proteins
  24. 24. Presynaptic andPresynaptic and Postsynaptic NeuronPostsynaptic Neuron Presynaptic Postsynaptic
  25. 25. Presynaptic andPresynaptic and Postsynaptic TransmissionPostsynaptic Transmission 1. axo-axonic 2. axo-dendritic 3. axo-somatic
  26. 26. Characteristics ofCharacteristics of SynapsesSynapses 1.convergence 2.divergence 3.facilitation 4.post-tetanic potentiation 5.fatigue 6.after discharge
  27. 27. Characteristics ofCharacteristics of SynapsesSynapses 7. subliminal fringe 8. occlusion 9. reverberation 10.inhibition 11.summation – temporal – spatial
  28. 28. Synaptic ResponsesSynaptic Responses 1. excitatory postsynaptic potential – can be graded response which will bring the RMP closer to the TP 2. inhibitory postsynaptic potential – makes the membrane hyperpolarized
  29. 29. Classes ofClasses of NeurotransmittersNeurotransmitters 1. Acetylcholine 2. Biogenic amines – catecholamines, serotonin, histamine 3. Amino acids – glutamate, GABA 4. Neuropeptides – endogenous opioids 5. Miscellaneous – nitric acid, adenosine
  30. 30. Factors Affecting SynapticFactors Affecting Synaptic EffectivenessEffectiveness 1. Presynaptic factors 2. Postsynaptic factors 3. General factors
  31. 31. ModulatorsModulators Chemical messengers that elicit complex responses that cannot be described as either IPSPs or EPSPs
  32. 32. Factors Affecting SynapticFactors Affecting Synaptic TransmissionTransmission 1. acid-base states a. alkalosis b. acidosis 2. oxygen and CO2 concentrations • Drugs – those that excite – those that inhibit
  33. 33. Neuromuscular JunctionNeuromuscular Junction and N-M Transmissionand N-M Transmission
  34. 34. NeurotransmitterNeurotransmitter ReceptorsReceptors • metabotropic receptors • ionophore
  35. 35. Acetylcholine SynthesisAcetylcholine Synthesis and Metabolismand Metabolism • Acetyl choline cholinesterase acetate + choline
  36. 36. Events during N-MEvents during N-M TransmissionTransmission Action potential in Presynaptic Motor axon terminal Increase in Ca++ ion permeability and influx of Ca++ into the Axon Terminal Release of Ach from the Synaptic Vesicles into the Synaptic Cleft Diffusion of Ach to Postjunctional membrane
  37. 37. Events during N-MEvents during N-M TransmissionTransmission Combination of Ach with specific receptors on postjunctional membrane Increase in permeability of postjunctional membrane to Na++ and K+ causes EPP Depolarization of areas of Muscle membrane adjacent to end plate and initiation of AP
  38. 38. Factors affecting NMFactors affecting NM TransmissionTransmission 1. Ions 2. Drugs – curare, antibiotics 3. Acid – base conditions 4. Temperature
  39. 39. Clinical ApplicationsClinical Applications • Hemicholiniums • Curare • Myasthenia Gravis • Denervation supersensitivity • Eaton-Lambert Myasthenia Syndrome
  40. 40. Thank YouThank You andand Good DayGood Day

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