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BIOFISIKA NEURON(Biophysics of Neuron)
Aqsa SjuhadaDept of Physiology / Oral Biology, Airlangga
[email protected]
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
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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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