7147633 membrane-physiology
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Transcript of 7147633 membrane-physiology
MEMBRANE MEMBRANE PHYSIOLOGYPHYSIOLOGY
Anita Ocampo-So, MD, FPSP, DPBA, MHA
Professor
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
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
NeuronsNeurons
NeuronsNeurons
• structures aside from organelles1. astrocytes
2. microglia
3. oligodendroglia – apoptosis
NeuronsNeurons
• Bell-Magendie Law
• Afferent – sensory
• Efferent – motor
• Afferent 200,000 interneuron 10 efferent
NeuronsNeurons
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
Classification of Nerve Classification of Nerve FibersFibers
Coverings of Nerve Coverings of Nerve FibersFibers
1. endoneurium
2. perineurium
3. epineurium
Coverings of Nerve Coverings of Nerve FibersFibers
Properties of Nerve Properties of Nerve FibersFibers
1. Excitability
2. Conductivity
Myelinated FibersMyelinated Fibers
• Schwann cells• Nodes of Ranvier• Saltatory Conduction
–Advantages• faster conduction• saves energy• less loss of ions
Myelinated FibersMyelinated Fibers
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
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
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
Action Potential Action Potential
Action PotentialAction Potential
• All-or-Nothing Principle
• Strength – duration curve–Rheobase
–Utilization time
–Chronaxie
Refractory PeriodsRefractory Periods
• Absolute Refractory Period
• Relative Refractory Period–nerve fibers are not
susceptible to fatigue
• Accommodation
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
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
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
Presynaptic and Presynaptic and Postsynaptic NeuronPostsynaptic Neuron
Presynaptic
Postsynaptic
Presynaptic and Presynaptic and Postsynaptic Postsynaptic TransmissionTransmission
1. axo-axonic
2. axo-dendritic
3. axo-somatic
Characteristics of Characteristics of SynapsesSynapses
1.convergence2.divergence3.facilitation4.post-tetanic potentiation5.fatigue6.after discharge
Characteristics of Characteristics of SynapsesSynapses
7. subliminal fringe8. occlusion9. reverberation10.inhibition11.summation
– temporal– spatial
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
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
Factors Affecting Factors Affecting Synaptic EffectivenessSynaptic Effectiveness
1. Presynaptic factors
2. Postsynaptic factors
3. General factors
ModulatorsModulators
Chemical messengers that elicit complex responses that cannot be described as either IPSPs or EPSPs
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
Neuromuscular Junction Neuromuscular Junction and N-M Transmissionand N-M Transmission
Neurotransmitter Neurotransmitter ReceptorsReceptors
• metabotropic receptors
• ionophore
Acetylcholine Synthesis Acetylcholine Synthesis and Metabolismand Metabolism
• Acetyl choline cholinesterase acetate + choline
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
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
Factors affecting NM Factors affecting NM TransmissionTransmission
1. Ions
2. Drugs – curare, antibiotics
3. Acid – base conditions
4. Temperature
Clinical ApplicationsClinical Applications
• Hemicholiniums
• Curare
• Myasthenia Gravis
• Denervation supersensitivity
• Eaton-Lambert Myasthenia Syndrome
Thank YouThank Youand and
Good DayGood Day