BIOFISIKA NEURON(Biophysics of Neuron)

Aqsa SjuhadaDept of Physiology / Oral Biology, Airlangga University@aqsas

http://aqsas.blogspot.com

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BODY LIQUID

Total : 60%

Intracellular: 40%

Extracell: 20% (kecuali cair serebrospinal, cairansendi, cairan saliva)

- cairan interstitial 15%

- cairan plasma 5%

- cairan sel darah

- cairan intra vaskuler

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TRANSPORT BAHAN

ACTIVE TRANSPORT

1. primary

2. secondary

- bulk transport

- exocytosis

- endocytosis

- phagocytosis

- pinocytosis

PASSIVE TRANSPORT

- osmosis

- diffusion

- filtration

-solvent drag

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ACTIVE

TRANSPORT

PASSIVE

TRANSPORT

CELLULAR

ENERGY

required not required, only

kinetic energy

PROCESS physiology -

biology

physics

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DIFFUSION

Particle movement

Simple diffusion : O2, CO2, alcohol

Facilitated diffusion : glucose, amine acid

OSMOSIS Liquid movement

Hypotonic - Hypertonic

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DIFFUSION

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OSMOSIS

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MACAM GERAKAN

DARI

ARAH

GERAKAN

PLASMA

MEMBRAN

CARRIER

SYSTEM

ENERGY

CELLULAR

Osmosis Solvent CC SP Tidak Tidak

Diffusi Solut CC +/- Tidak Tidak

Active

Transp

Solut CC SP Ada 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 PLASMA

STRUKTUR 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 permeable

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PROTEIN

Sebagian 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.

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NEURON

= Sel saraf

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Dentrites

Cell Body

Axon

Terminal

A Typical Neuron Overview

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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

Concentration forces

Diffusion movement of ions through semipermeable membrane

Osmosis movement of water from region of high concentration to low

Hydrostatic Forces

Gravity forces upon osmosis

The combination of these forces leads to dynamic equilibrium in the cellular environment

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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.

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Apa penyebab Resting Membrane

Potential mempunyai beda

potensial -70 mV ?

Adanya perbedaan distribusi ion di luar dan

di dalam membran sel, terutama ion K+

dan Na+

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Perbedaan distribusi ion di luar dan di dalam

membran

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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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RANGSANGAN

Adekuat Tidak adekuat

Mencapai threshold Tidak mencapai

threshold

POTENSIAL AKSI LOCAL POTENTIAL

Dirambatkan ke segala arah Tidak dirambatkan

Hukum ALL OR NONE Sumasi

Rangsangan menyebabkan

Natrium+ influx

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Action Potential Sequence

Involves the action of voltage-gated channels

Exchanges of ions in and out of the cell

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Action Potential Stages: Overview

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ANIMASI ACTION POTENTIAL

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Action Potential

Sequence

Saluran Na+ terbuka, terjadilah fast natrium

influx, depolarisasi.

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Action Potential

Sequence

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

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Action Potential

Sequence

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

Equilibrium

membran

potential

dikembalikan

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Action Potential

Sequence

Na+-K+ pump (pompa Na+-K+) berfungsi

mengembalikan keadaan serupa, yaitu RMP.

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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

Relative

Membrane 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

Unidirectional

it 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 mammals

5m/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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Terima Kasih

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