Membrane Physiology
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Transcript of Membrane Physiology
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MEMBRANE MEMBRANE PHYSIOLOGYPHYSIOLOGY
Anita Ocampo-So, MD, FPSP, DPBA, MHA
Professor
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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
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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
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NeuronsNeurons
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NeuronsNeurons
• structures aside from organelles1. astrocytes
2. microglia
3. oligodendroglia – apoptosis
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NeuronsNeurons
• Bell-Magendie Law
• Afferent – sensory
• Efferent – motor
• Afferent 200,000 interneuron 10 efferent
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NeuronsNeurons
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Classification of Nerve Classification 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
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Classification of Nerve Classification of Nerve FibersFibers
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Coverings of Nerve Coverings of Nerve FibersFibers
1. endoneurium
2. perineurium
3. epineurium
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Coverings of Nerve Coverings of Nerve FibersFibers
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Properties of Nerve Properties of Nerve FibersFibers
1. Excitability
2. Conductivity
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Myelinated FibersMyelinated Fibers
• Schwann cells• Nodes of Ranvier• Saltatory Conduction
–Advantages• faster conduction• saves energy• less loss of ions
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Myelinated FibersMyelinated Fibers
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Resting Membrane Resting 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
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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
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Genesis of the RMPGenesis of the RMP
– Gibbs-Donnan equilibrium– Goldman-Hodgkin-Katz
2. Selective Permeability of the Membrane3. Na+ - K+ pump
• RMP– skeletal muscle (-)90mV– nerve (-) 70 mV
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Action Potential Action Potential
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Action PotentialAction Potential
• All-or-Nothing Principle
• Strength – duration curve–Rheobase
–Utilization time
–Chronaxie
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Refractory PeriodsRefractory Periods
• Absolute Refractory Period
• Relative Refractory Period–nerve fibers are not
susceptible to fatigue
• Accommodation
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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
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Synapse and Synaptic Synapse 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
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Presynaptic and Presynaptic 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
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Presynaptic and Presynaptic and Postsynaptic NeuronPostsynaptic Neuron
Presynaptic
Postsynaptic
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Presynaptic and Presynaptic and Postsynaptic Postsynaptic TransmissionTransmission
1. axo-axonic
2. axo-dendritic
3. axo-somatic
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Characteristics of Characteristics of SynapsesSynapses
1.convergence2.divergence3.facilitation4.post-tetanic potentiation5.fatigue6.after discharge
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Characteristics of Characteristics of SynapsesSynapses
7. subliminal fringe8. occlusion9. reverberation10.inhibition11.summation
– temporal– spatial
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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
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Classes of Classes of NeurotransmittersNeurotransmitters
1. Acetylcholine
2. Biogenic amines – catecholamines, serotonin, histamine
3. Amino acids – glutamate, GABA
4. Neuropeptides – endogenous opioids
5. Miscellaneous – nitric acid, adenosine
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Factors Affecting Factors Affecting Synaptic EffectivenessSynaptic Effectiveness
1. Presynaptic factors
2. Postsynaptic factors
3. General factors
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ModulatorsModulators
Chemical messengers that elicit complex responses that cannot be described as either IPSPs or EPSPs
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Factors Affecting Factors Affecting Synaptic TransmissionSynaptic Transmission
1. acid-base statesa. alkalosisb. acidosis
2. oxygen and CO2 concentrations
• Drugs– those that excite– those that inhibit
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Neuromuscular Junction Neuromuscular Junction and N-M Transmissionand N-M Transmission
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Neurotransmitter Neurotransmitter ReceptorsReceptors
• metabotropic receptors
• ionophore
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Acetylcholine Synthesis Acetylcholine Synthesis and Metabolismand Metabolism
• Acetyl choline cholinesterase acetate + choline
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Events during N-M Events 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
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Events during N-M Events 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
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Factors affecting NM Factors affecting NM TransmissionTransmission
1. Ions
2. Drugs – curare, antibiotics
3. Acid – base conditions
4. Temperature
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Clinical ApplicationsClinical Applications
• Hemicholiniums
• Curare
• Myasthenia Gravis
• Denervation supersensitivity
• Eaton-Lambert Myasthenia Syndrome
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Thank YouThank Youand and
Good DayGood Day