Graduate Seminar, NJIT June 14, 2012 Analytical & Computational Neuroscience: Lecture 2 Action Potentials and Chemical Synapses Math 430 * Math 635 * Fall.

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Presentation transcript:

Graduate Seminar, NJIT June 14, 2012 Analytical & Computational Neuroscience: Lecture 2 Action Potentials and Chemical Synapses Math 430 * Math 635 * Fall 2015 * Victor Matveev

Graduate Seminar, NJIT June 14, 2012 Neuron is charged: V in  V out ≈  70mV Outside: high Na +, low K + Inside: low Na +, high K + Neurons and synapses Human brain: ~10 11 neurons ~10 15 synapses Node of Ranvier

Graduate Seminar, NJIT June 14, 2012 Synapses are connections between two neurons Structure of neuron in more detail Neuron is charged: V in  V out ≈  70mV Outside: high Na +, low K + Inside: low Na +, high K + Human brain: ~10 11 neurons ~10 15 synapses

Graduate Seminar, NJIT June 14, 2012 Myelin Sheath and Nodes of Ranvier Schwann cells (peripheral NS) similar to Oligodendrocytes (CNS) Myelinated axonal segments: Electric potential propagates passively and fast Nodes of Ranvier Action potential initiated at first node of Ranvier, and is amplified at other nodes by voltage-dependent ion channels

Graduate Seminar, NJIT June 14, 2012 g Na gKgK gLgL V Na VKVK VLVL CmCm VmVm Action potential (spike) Excitable cells: neurons, endocrine cells, muscle cells Low K + Moderate Ca 2+ High Na + Equivalent RC circuit V m (t ) V rest =-75 mV Applied current g Ca g Na gKgK (A) V m increases (B) Na + channels open (C) K + channel open AP time course VmVm High K + Very low Ca 2+ Low Na + Cell Blood Molec Cell Biol (2000) 4 th Ed. Lodish, Berk, Zipursky et al Units: mM

Graduate Seminar, NJIT June 14, 2012 g Na gKgK gLgL V Na VKVK VLVL CmCm VmVm Equivalent RC circuit V m (t ) V rest =-75 mV Applied current g Ca g Na gKgK (A) V m increases (B) Na + channels open (C) K + channel open (D) Na + channels close (E) K + channels close AP time course A B C D E Action potential (spike) Excitable cells: neurons, endocrine cells, muscle cells VmVm High K + Very low Ca 2+ Low Na + Low K + Moderate Ca 2+ High Na + Cell Blood Molec Cell Biol (2000) 4 th Ed. Lodish, Berk, Zipursky et al Units: mM

Graduate Seminar, NJIT June 14, 2012 Chemical Synaptic Transmission Neurotransmitter-filled vesicles Presynaptic cell (axon) Ca 2+ ions ~40nm Postsynaptic cell (neuron or muscle) Neurotransmitters: glutamate, GABA, acetylcholine, serotonin, dopamine…

Graduate Seminar, NJIT June 14, 2012 Chemical Synaptic Transmission Action potential (depolarizing pulse) Ca 2+ ions Ca 2+ channels open Neurotransmitter-filled vesicles Presynaptic cell (axon) Postsynaptic cell (neuron or muscle) Neurotransmitters: glutamate, GABA, acetylcholine, serotonin, dopamine… ~40nm

Graduate Seminar, NJIT June 14, 2012 Chemical Synaptic Transmission Ca 2+ channels open Several Ca 2+ ions bound to release site Presynaptic cell (axon) Action potential (depolarizing pulse) Postsynaptic cell (neuron or muscle) ~40nm

Graduate Seminar, NJIT June 14, 2012 Chemical Synaptic Transmission Exocytosis (fusion) Neurotransmitter receptors/channels Neurotransmitter diffuses into synaptic cleft Presynaptic cell (axon) Postsynaptic cell (neuron or muscle) ~40nm Vesicle fusion initiated by SNARE protein complex interacting with Ca 2+ -sensor synaptotagmin

Graduate Seminar, NJIT June 14, 2012 Chemical Synaptic Transmission Neurotranmitter binds to postsynaptic receptors Neurotransmitter receptors/channels Presynaptic cell (axon) Postsynaptic cell (neuron or muscle) ~40nm

Graduate Seminar, NJIT June 14, 2012 Chemical Synaptic Transmission Postsynaptic ion channels open Neurotransmitter receptors/channels Presynaptic cell (axon) Postsynaptic cell (neuron or muscle) ~40nm

Graduate Seminar, NJIT June 14, 2012 Chemical Synaptic Transmission Postsynaptic ion channels open Influx of Na + & Ca 2+ (excitation) K + efflux, Cl - influx (inhibition) Presynaptic cell (axon) Postsynaptic cell (neuron or muscle) ~40nm Total transmission delay ~ 200 μs

Graduate Seminar, NJIT June 14, 2012 Synapses and Neurotransmitters (NT) In mammalian brain: roughly 10 4 synapses per neuron: total A given neuron secretes a single NT (single type on NT load), e.g.: Dopaminergic neuron: synapses release dopamine Cholinergic neuron: synapses release acetylcholine …Etc. A given neuron may be activated by many NTs Afferents (inputs): multiple NTs Efferent (output): single NT (…well, for the most part)

Graduate Seminar, NJIT June 14, 2012 Synapses and Neurotransmitters (NTs) Gap junctions: direct “pore”; no NT needed! Chemical: ○ Ionotropic (fast): receptors activate ion channels ○ Metabotropic (slow): receptors activate second messengers Depending on NT, chemical synapses may be ○ Excitatory - Examples (ionotropic): glutamatergic, cholinergic - Postsynaptic channels permeable to Na + and Ca ++ ○ Inhibitory - Examples (ionotropic): GABAergic - Postsynaptic channels permeable to K + and Cl - Note: chemical synapses allow inhibitory interaction between neurons!

Graduate Seminar, NJIT June 14, 2012 “Excitable” Cells Neurons are not the only cells that change V m Endocrine cells Hormone similar to neurotransmitter Muscle Cells Ca 2+ important for AP and muscle contraction