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Dasar Fisik Sel Saraf

Oct 08, 2015

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fisiologi hewan
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  • DASAR FISIK FUNGSI SARAFGambar sel sarafMekanisme transmisi signal dalam sebuah neuron

  • peranan gradien ion dan ion channel sebagai penyebab terjadinya perubahan potensial membran selPerubahan aliran ion sekitar membran selama membran tereksitasiterjadinya gradding potensial dan potensial aksipropagasi potensial aksi sepanjang akson

  • *Neurophysiology - Part OneNeuronal Structure, Function & OrganizationNeuron are highly specialized cells to receive, process and transmit information with high fidelity & without loss of signal strength over distanceBasic structure soma (cell body) & thin fibers emanating from soma (nerve processes) = 2 types:Multiple dendrites & a single axonDendrites (many branches = the more branches, the more input from many other neurons) receive information & axon conducts signal from soma (tend to be longer) ending in axon terminals to other neurons, glands or muscles myelin sheath

    Neurophysiology - Part One

  • *Neurophysiology - Part OneSignal TransmissionMotor-neuron as an Exampleplasma membrane of dendrites & soma receive signal from (innervation) terminals of other neuronsSpike-initiating zone (specific region of membrane) integrates signal = thus determines if neuron will generate its own signal (action potential or AP)In AP = the voltage across membrane rapidly rises & falls = spike/nerve impulseAxon carries AP from point of origin to axon terminals & to skeletal muscle fibersSome spike-initiating zones = axon hillocks near soma

    Neurophysiology - Part One

  • *Neurophysiology - Part OnePhysiological BehaviorDepends on passive electrical properties e.g. capacitance & resistance (like other electrical conductors discussed later) & active electrical properties = allow conduction without decrement (no loss of signal strength)Active properties depend on presence of voltage-gated ion channels in plasma membrane (specific proteins) allowing ions to move across membrane in regulated fashion ion channels localized to special regions having specialized signaling functions e.g. axon membrane is specialized for conduction of APs by having fast-acting, voltage-gated ion channels selectively allowing Na+ & K+ to cross membrane

    Neurophysiology - Part One

  • *Neurophysiology - Part OneMembrane ExcitationStable voltage (electric potential difference) exists across plasma membrane of all animal cells however, only membranes of electrically excitable cells (neurons/muscle fibers) can respond to changes in transmembrane potential differences by generating APsMembrane potential (difference across the membrane) measured in volts

    Neurophysiology - Part One

  • *Neurophysiology - Part OneMore TerminologyHyperpolarization increase in potential difference across plasma membrane when current pulse causes positive charge to exit i.e. interior of cell becomes more negative - cell membrane responds passivelyDepolarization decrease in potential difference across plasma membrane if current pulse causes addition of positive charge to interior of cell =some voltage-gated channels selectively perm to Na+ to open & if sufficiently depolarized, AP is triggered) - Threshold potential the value of the membrane potential where an AP is triggered 50% of time

    Neurophysiology - Part One

  • *Neurophysiology - Part OneRole/Types of Ion Channelsion selectivity (electrochemical gradient; specific to certain ions e.g. Na+, K+)voltage-gated (produce APs & open when plasma membrane depolarizes)leak (maintain resting potential where passive change occurs during hyperpolarization mostly K+)ligand-gated (bind to messenger molecules e.g. neurotransmitters)

    Neurophysiology - Part One

    *Capacitance = ability to store electrical charge