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