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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