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BIOFISIKA NEURON(Biophysics of Neuron)

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

s eyeem.com/asa

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BODY LIQUIDTotal : 60% Intracellular: 40% Extracell: 20% (kecuali cair

serebrospinal, cairan sendi, cairansaliva)

- 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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ACTIVETRANSPORT

PASSIVETRANSPORT

CELLULARENERGY

required not required,only kineticenergy

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 GERAKANDARI

ARAHGERAKAN

PLASMAMEMBRAN

CARRIERSYSTEM

ENERGYCELLULAR

Osmosis

Solvent CC SP Tidak Tidak

Diffusi Solut CC +/- Tidak Tidak

ActiveTransp

Solut CC SP Ada Ada

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SEL EKSITABELSel yg mampu menimbulkan /

menjalankan impuls elektrokimiasepanjang 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 dgglicoprotein 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 twopoints in space

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Basic Concepts

Ions charged particles

Anions Negatively chargedparticles

Cations Positively chargedparticles

B i C t

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Basic ConceptsForces that determine ionic

movement Electrostatic forces

Opposite charges attract, Identical chargesrepel

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 todynamic 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 didalam membran sel dalam keadaantidak ada aktivitas elektris.

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Apa penyebab Resting MembranePotential mempunyai beda potensial-70 mV ?

Adanya perbedaan distribusi ion di luar dan didalam membran sel, terutama ion K+ dan Na+

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Perbedaan distribusi ion di luar dandi dalam membran

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

lebih negatif dibandingkan di luarmembran sel sebesar 70mV

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RANGSANGAN

Adekuat Tidak adekuat

Mencapai threshold Tidak mencapaithreshold

POTENSIAL AKSI LOCAL POTENTIAL

Dirambatkan ke segala arahTidak dirambatkan

Hukum ALL OR NONE Sumasi

angsangan

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angsanganmenyebabkan 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

Action Potential Stages:

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Action Potential Stages:Overview

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ANIMASI ACTION POTENTIAL

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ActionPotential

Sequence

Saluran Na+ terbuka, terjadilah fast

natrium influx, depolarisasi.

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ActionPotential

Sequence

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

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ActionPotential

Sequence

Saluran K+ menutup, terjadilah

akumulasi ion K+ di ekstrasel. Hal inimenyebabkan depolarisasi,sedemikian rupa sehingga terjadiundershoot pada akhir action potential

Equilibrium

membran

potential

dikembalikan

i

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ActionPotential

Sequence

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

keadaan serupa, yaitu RMP.

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Membrane & Channel Changes

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Membrane & Channel Changesduring an Action Potential

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Refractory Period

Two types Absolute

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

Relative Membrane hyperpolarized

Some Na+ channels still refractory

P i f h A i

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Propagation of the ActionPotential

Action Potential spreads downthe axon in a chain reaction

Unidirectional it does not spread into the cell body

and dendrite due to absence ofvoltage-gated channels there

Refraction prevents spread backacross axon

P ti f th A ti

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Propagation of the ActionPotential

Speed of propagation varies withthe axon diameter

Faster with larger axons In large axons of mammals

5m/second 2m axons 20m/second in 20m axons

P ti f th A ti

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Propagation of the ActionPotential

Speed of propagation alsoassisted by the myelin sheath Provides resistance to AP

Regular gaps in the myelinsheath (1mm intervals) Nodes of Ranvier

Increase conduction speed up to 15times

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T i K ih

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Terima Kasihwww.flickr.com/humanis