Biofisika Neuron 2006-A

BIOFISIKA NEURONBIOFISIKA NEURON(Biophysics of Neuron)(Biophysics of Neuron)

H Aqsa SjuhadaH Aqsa SjuhadaBuilding DR-GBuilding DR-G

Dept of Physiology, Airlangga UniversityDept of Physiology, Airlangga UniversityTel. (031) 71200 999Tel. (031) 71200 999

E-mail. draqsas@yahoo.caE-mail. draqsas@yahoo.ca

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BODY LIQUIDBODY LIQUID Total : 60%Total : 60% Intracellular: 40%Intracellular: 40% Extracell: 20% (kecuali cair Extracell: 20% (kecuali cair

serebrospinal, cairan sendi, cairan serebrospinal, cairan sendi, cairan saliva)saliva)

- cairan interstitial 15%- cairan interstitial 15%- cairan plasma 5%- cairan plasma 5%- cairan sel darah- cairan sel darah- cairan intra vaskuler- cairan intra vaskuler

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TRANSPORT BAHANTRANSPORT BAHAN

ACTIVE TRANSPORTACTIVE TRANSPORT1. primary1. primary2. secondary 2. secondary

- bulk transport- bulk transport- exocytosis- exocytosis- endocytosis- endocytosis

- phagocytosis- phagocytosis- pinocytosis- pinocytosis

PASSIVE TRANSPORTPASSIVE TRANSPORT- osmosis- osmosis- diffusion- diffusion- filtration- filtration-solvent dragsolvent drag

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ACTIVE ACTIVE TRANSPORTTRANSPORT

PASSIVE PASSIVE TRANSPORTTRANSPORT

CELLULAR CELLULAR ENERGYENERGY

requiredrequired not required, not required, only kinetic only kinetic energyenergy

PROCESSPROCESS physiology - physiology - biologybiology

physicsphysics

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DIFFUSIONDIFFUSION

Particle movementParticle movement Simple diffusion : Simple diffusion : O2, CO2, alcoholO2, CO2, alcohol Facilitated diffusion : Facilitated diffusion : glucose, amine acidglucose, amine acid

OSMOSISOSMOSIS Liquid movementLiquid movement Hypotonic -Hypotonic - Hypertonic Hypertonic

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MACAMMACAM GERAKAN GERAKAN DARIDARI

ARAH ARAH GERAKAGERAKANN

PLASMA PLASMA MEMBRAMEMBRANN

CARRIER CARRIER SYSTEMSYSTEM

ENERGY ENERGY CELLULACELLULARR

OsmosOsmosisis

SolventSolvent C↓→C↑ C↓→C↑ SPSP TidakTidak TidakTidak

DiffusiDiffusi SolutSolut C↑→C↓ C↑→C↓ +/-+/- TidakTidak TidakTidak

Active Active TranspTransp

SolutSolut C↓→C↑ C↓→C↑ SPSP AdaAda AdaAda

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SEL EKSITABELSEL EKSITABEL

Sel yg mampu menimbulkan / Sel yg mampu menimbulkan / menjalankan impuls elektrokimia menjalankan impuls elektrokimia sepanjang membran plasmanya.sepanjang membran plasmanya.

→ → Sel saraf, sel otot, sel kelenjarSel saraf, sel otot, sel kelenjar

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MEMBRAN PLASMAMEMBRAN PLASMASTRUKTUR DAN KOMPOSISI MEMBRAN PLASMASTRUKTUR DAN KOMPOSISI MEMBRAN PLASMA Lemak → dynamic mozaic design / lipid bilayer 42%Lemak → dynamic mozaic design / lipid bilayer 42% Protein 55%Protein 55% Karbohidrat 3%Karbohidrat 3%

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SIFATSIFAT - Elastis tipis, ketebalan 6-10nmElastis tipis, ketebalan 6-10nmFUNGSIFUNGSI- Physical isolationPhysical isolation- Regulation of exchange with the Regulation of exchange with the

environment --- nutrition, ionenvironment --- nutrition, ion- Sensitivity --- receptor functionSensitivity --- receptor function- Structural supportStructural supportJENISJENIS- ImpermeableImpermeable- Semi permeableSemi permeable- Selective permeableSelective permeable

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PROTEINPROTEIN

Sebagian besar glicoproteinSebagian besar glicoprotein

Protein integral / protein perifer, fungsinya:Protein integral / protein perifer, fungsinya: membatasi pergerakan membran plasmamembatasi pergerakan membran plasma sebagai channelsebagai channel carrier systemcarrier system enzymeenzyme receptorreceptor

Karbohidrat; berada di luar berikatan dg Karbohidrat; berada di luar berikatan dg glicoprotein maupun lipid bilayer, fungsi: glicoprotein maupun lipid bilayer, fungsi: sebagai indikator sel.sebagai indikator sel.

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NEURONEURONN

= Sel saraf= Sel saraf

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DentritesDentrites Cell BodyCell Body AxonAxon TerminalTerminal

A Typical Neuron OverviewA Typical Neuron Overview

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Diverse Neuron Forms and FunctionsDiverse Neuron Forms and Functions

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Basic ConceptsBasic Concepts

VoltVolt

A charge difference between two A charge difference between two points in spacepoints in space

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Basic ConceptsBasic Concepts

Ions – charged particlesIons – charged particles

Anions – Negatively charged Anions – Negatively charged particlesparticles

Cations – Positively charged Cations – Positively charged particlesparticles

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Basic ConceptsBasic ConceptsForces that determine ionic Forces that determine ionic

movementmovement Electrostatic forcesElectrostatic forces

Opposite charges attract, Identical charges Opposite charges attract, Identical charges repelrepel

Concentration forcesConcentration forces Diffusion – movement of ions through Diffusion – movement of ions through

semipermeable membranesemipermeable membrane Osmosis – movement of water from region of Osmosis – movement of water from region of

high concentration to lowhigh concentration to low Hydrostatic ForcesHydrostatic Forces

Gravity forces upon osmosisGravity forces upon osmosisThe combination of these forces leads to The combination of these forces leads to

dynamic equilibrium in the cellular dynamic equilibrium in the cellular environmentenvironment

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Besar RMP –70 mV Besar RMP –70 mV Artinya ?Artinya ? Potensial elektriks di dalam membran sel Potensial elektriks di dalam membran sel

lebih negatif dibandingkan di luar lebih negatif dibandingkan di luar membran sel sebesar 70mVmembran sel sebesar 70mV

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POTENSIAL MEMBRANPOTENSIAL MEMBRAN Perbedaan muatan listrik di luar dan Perbedaan muatan listrik di luar dan

di dalam membran seldi dalam membran selRMPRMP =Resting Membran Potential=Resting Membran Potential =Potensial Membran Istirahat=Potensial Membran Istirahat Berbedaan muatan listrik di luar dan Berbedaan muatan listrik di luar dan

di dalam membran sel dalam keadaan di dalam membran sel dalam keadaan tidak ada aktivitas elektris.tidak ada aktivitas elektris.

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RANGSANGANRANGSANGAN

AdekuatAdekuat Tidak adekuatTidak adekuat

Mencapai thresholdMencapai threshold Tidak mencapai Tidak mencapai thresholdthreshold

POTENSIAL AKSIPOTENSIAL AKSI LOCAL LOCAL POTENTIALPOTENTIAL

Dirambatkan ke segala arahDirambatkan ke segala arah Tidak Tidak dirambatkandirambatkan

Hukum ALL OR NONEHukum ALL OR NONE SumasiSumasi

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Action Potential SequenceAction Potential Sequence

Involves the action of voltage-gated channelsInvolves the action of voltage-gated channels Exchanges of ions in and out of the cellExchanges of ions in and out of the cell

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Action Potential Stages: Action Potential Stages: OverviewOverview

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ANIMASI ACTION POTENTIALANIMASI ACTION POTENTIAL

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Action Action Potential Potential

SequenceSequence

Saluran Na+ terbuka, terjadilah Saluran Na+ terbuka, terjadilah fast natrium influx, depolarisasi.fast natrium influx, depolarisasi.

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Action Action Potential Potential

SequenceSequence

Pada keadaan +40 mV, saluran Na+ menutup, tetapi Pada keadaan +40 mV, saluran Na+ menutup, tetapi saluran K+ sekarang terbuka, menyebabkan pengeluaran saluran K+ sekarang terbuka, menyebabkan pengeluaran ion K+ (gradien konsentrasi), menyebabkan penurunan ion K+ (gradien konsentrasi), menyebabkan penurunan gradien elektris.gradien elektris.

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Action Action Potential Potential

SequenceSequence

Saluran K+ menutup, Saluran K+ menutup, terjadilah akumulasi ion K+ di terjadilah akumulasi ion K+ di ekstrasel. Hal ini ekstrasel. Hal ini menyebabkan depolarisasi, menyebabkan depolarisasi, sedemikian rupa sehingga sedemikian rupa sehingga terjadi undershoot pada akhir terjadi undershoot pada akhir action potentialaction potential

Equilibrium membran potential dikembalikan

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Action Action Potential Potential

SequenceSequence

Na+-K+ pump (pompa Na+-K+) berfungsi Na+-K+ pump (pompa Na+-K+) berfungsi mengembalikan keadaan serupa, yaitu RMP.mengembalikan keadaan serupa, yaitu RMP.

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Membrane & Channel Changes Membrane & Channel Changes during an Action Potentialduring an Action Potential

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Refractory PeriodRefractory Period

Two typesTwo types AbsoluteAbsolute

When Na+ channels close, at peak When Na+ channels close, at peak of AP, they do not reopen for a timeof AP, they do not reopen for a time

RelativeRelative Membrane hyperpolarizedMembrane hyperpolarized Some Na+ channels still refractorySome Na+ channels still refractory

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Propagation of the Action Propagation of the Action PotentialPotential

Action Potential spreads down Action Potential spreads down the axon in a chain reaction the axon in a chain reaction

Unidirectional Unidirectional it does not spread into the cell body it does not spread into the cell body

and dendrite due to absence of and dendrite due to absence of voltage-gated channels therevoltage-gated channels there

Refraction prevents spread back Refraction prevents spread back across axonacross axon

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Propagation of the Action Propagation of the Action PotentialPotential

Speed of propagation varies with Speed of propagation varies with the axon diameterthe axon diameter

Faster with larger axonsFaster with larger axons In large axons of mammalsIn large axons of mammals

5m/second 25m/second 2m axonsm axons 20m/second in 2020m/second in 20m axonsm axons

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Propagation of the Action Propagation of the Action PotentialPotential

Speed of propagation also Speed of propagation also assisted by the myelin sheathassisted by the myelin sheath Provides resistance to APProvides resistance to AP

Regular gaps in the myelin Regular gaps in the myelin sheath (1mm intervals)sheath (1mm intervals) ““Nodes of Ranvier”Nodes of Ranvier” Increase conduction speed up to 15 Increase conduction speed up to 15

timestimes

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