BIOFISIKA NEURON BIOFISIKA NEURON (Biophysics of Neuron (Biophysics of Neuron ) ) Aqsa Sjuhada Aqsa Sjuhada Dept of Physiology / Oral Biology, Dept of Physiology / Oral Biology, Airlangga University Airlangga University @aqsa @aqsa s s eyeem.com/ eyeem.com/ aqsa aqsa
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BIOFISIKA NEURONBIOFISIKA NEURON(Biophysics of Neuron(Biophysics of Neuron))
Aqsa SjuhadaAqsa SjuhadaDept of Physiology / Oral Biology, Airlangga UniversityDept of Physiology / Oral Biology, Airlangga University@aqsa@aqsa
ss eyeem.com/eyeem.com/aqsaaqsa
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BODY LIQUIDBODY LIQUID Total : 60%Total : 60% Intracellular: 40%Intracellular: 40% Extracell: 20% (kecuali cair Extracell: 20% (kecuali cair
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
SIFATSIFAT - Elastis tipis, ketebalan 6-10nmElastis tipis, ketebalan 6-10nmFUNGSIFUNGSI- Physical isolationPhysical isolation- Regulation of exchange with the Regulation of exchange with the
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
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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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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Apa penyebab Resting Membrane Apa penyebab Resting Membrane Potential mempunyai beda Potential mempunyai beda potensial -70 mV ?potensial -70 mV ?
Adanya perbedaan distribusi ion di luar Adanya perbedaan distribusi ion di luar dan di dalam membran sel, terutama ion dan di dalam membran sel, terutama ion K+ dan Na+K+ dan Na+
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Perbedaan distribusi ion di luar dan Perbedaan distribusi ion di luar dan di dalam membran di dalam membran
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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
Biofisika Neuron 30eyeem.com/eyeem.com/
aqsaaqsa
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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
Rangsangan Rangsangan menyebabkan Natrium+ menyebabkan Natrium+
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
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