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Biofisika Neuron 2006-A

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BIOFISIKA NEURON(Biophysics of Neuron)H Aqsa SjuhadaBuilding DR-G Dept of Physiology, Airlangga University Tel. (031) 71200 999 E-mail. [email protected]

BODY LIQUID Total : 60% Intracellular: 40% Extracell: 20% (kecuali cair serebrospinal, cairan sendi, cairan saliva) - cairan interstitial 15% - cairan plasma 5% - cairan sel darah - cairan intra vaskulerBiofisika Neuron 2

TRANSPORT BAHANPASSIVE TRANSPORT - osmosis - diffusion - filtration -solvent drag ACTIVE TRANSPORT 1. primary 2. secondary - bulk transport - exocytosis - endocytosis - phagocytosis - pinocytosis

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CELLULAR ENERGY PROCESS

ACTIVE TRANSPORT required

PASSIVE TRANSPORT not required, only kinetic energyphysics

physiology biology

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DIFFUSION

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

OSMOSIS

Liquid movement Hypotonic - Hypertonic5

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MACAM

GERAKAN DARI

ARAH GERAKAN

PLASMA CARRIER MEMBRAN SYSTEM

ENERGY CELLULAR

Osmosis Solvent Diffusi Active Transp Solut Solut

CC CC CC

SP +/SP

Tidak Tidak Ada

Tidak Tidak Ada

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SEL

EKSITABEL

Sel yg mampu menimbulkan / menjalankan impuls elektrokimia sepanjang membran plasmanya. Sel saraf, sel otot, sel kelenjar

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

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SIFAT - Elastis tipis, ketebalan 6-10nm FUNGSI - Physical isolation - Regulation of exchange with the environment --nutrition, ion - Sensitivity --- receptor function - Structural support JENIS - Impermeable - Semi permeable - Selective permeableBiofisika Neuron 13

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PROTEINSebagian besar glicoprotein Protein integral / protein perifer, fungsinya: membatasi pergerakan membran plasma sebagai channel carrier system enzyme receptor Karbohidrat; berada di luar berikatan dg glicoprotein maupun lipid bilayer, fungsi: sebagai indikator sel.Biofisika Neuron 15

NEURON= Sel saraf

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A Typical Neuron Overview

Dentrites Cell Body Axon Terminal

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Diverse Neuron Forms and Functions

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Basic Concepts

Volt

A charge difference between two points in space

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Basic Concepts

Ions charged particles Anions Negatively charged particles Cations Positively charged particles

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Basic Concepts Forces that determine ionic movement

Electrostatic forces

Opposite charges attract, Identical charges repel Diffusion movement of ions through semipermeable membrane Osmosis movement of water from region of high concentration to low Gravity forces upon osmosis

Concentration forces

Hydrostatic Forces

The combination of these forces leads to dynamic equilibrium in the cellular environmentBiofisika Neuron 22

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Besar RMP 70 mV Artinya ? Potensial elektriks di dalam membran sel lebih negatif dibandingkan di luar membran sel sebesar 70mV

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POTENSIAL MEMBRAN Perbedaan muatan listrik di luar dan di dalam membran sel RMP =Resting Membran Potential =Potensial Membran Istirahat Berbedaan muatan listrik di luar dan di dalam membran sel dalam keadaan tidak ada aktivitas elektris.Biofisika Neuron 26

RANGSANGANAdekuat Mencapai threshold Tidak adekuat Tidak mencapai threshold

POTENSIAL AKSIDirambatkan ke segala arah Hukum ALL OR NONE

LOCAL POTENTIALTidak dirambatkan Sumasi

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Action Potential Sequence

Involves the action of voltage-gated channels Exchanges of ions in and out of the cell28

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Action Potential Stages: Overview

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ANIMASI ACTION POTENTIAL

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Action PotentialSequence

Saluran Na+ terbuka, terjadilah fast natrium influx, depolarisasi.31

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Action PotentialSequence

Pada keadaan +40 mV, saluran Na+ menutup, tetapi saluran K+ sekarang terbuka, menyebabkan pengeluaran ion K+ (gradien konsentrasi), menyebabkan penurunan gradien elektris.32

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

Equilibrium membran potential dikembalikanBiofisika Neuron 33

Action PotentialSequence

Na+-K+ pump (pompa Na+-K+) berfungsi mengembalikan keadaan serupa, yaitu RMP.34

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Membrane & Channel Changes during an Action Potential

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Refractory Period

Two types Absolute

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

RelativeMembrane hyperpolarized Some Na+ channels still refractory

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Propagation of the Action Potential

Action Potential spreads down the axon in a chain reaction Unidirectionalit does not spread into the cell body and dendrite due to absence of voltage-gated channels there Refraction prevents spread back across axon

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Propagation of the Action Potential

Speed of propagation varies with the axon diameter Faster with larger axons In large axons of mammals5m/second 2um axons 20m/second in 20um axons

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Propagation of the Action Potential

Speed of propagation also assisted by the myelin sheath

Provides resistance to AP

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

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