cogs 107b - winter 2010 - lecture 1 - introduction & review of brain electrical potentials
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COGS 107B - Winter 2010 - Lecture 1 - Introduction & review of brain electrical potentialsTRANSCRIPT
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the knee-jerk reflex – a neuro “system”
Cogs 107b – Systems Neuroscience
www.dnitz.com
lec01052010 – brain potentials, levels of analysis
principles: ‘the neuron doctrine’ & ‘the law of dynamic polarization’
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systems neuroscience = structure dynamics
structure:
(micro) synapses neurons nuclei regions (macro)
dynamics:
synaptic & action potentials (micro) field potentials / EEG fMRI (macro)
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neurons come in variety of shapes and sizes
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Cajal’s ‘neuron doctrine’: the neuron as the basic structural and functional unit of the brain
Cajal’s ‘law of dynamic polarization’: neural / electrical transmission proceeds in one direction -
dendrite / soma axon axon terminal
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membrane potential: the voltage difference between the intracellular space of a neuron and the surrounding extracellular space (includes resting, synaptic, and action potentials)
synaptic potentials: excitatory and inhibitory inputs from one neuron (at its axon terminal) onto another (at its dendrite or soma)
action potentials: all-or-none electrical events in a neuron which reflect the spatial and temporal integration of synaptic potentials and the intrinsic excitability of the neuron
equilibrium potentials: the membrane potential at which the net flux of ions across the membrane is 0 given the overall concentrations of that ion on either side of the membrane
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recording membrane potentials
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electrical potentials reflect the dynamics of ion concentrations at the membrane surfaces
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properties of ion channels:
*ion selectivity – e.g., Na+, Ca++, K+, Cl-
*gating – e.g., by voltage, ligand
*kinetics – e.g., open-time
*state – e.g., activated, inactivated, deinactivated, persistent
*distribution – e.g., in dendrites, at axon hillock
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The Nernst Equation
-used to determine the equilibrium potential
-relates ion concentration gradients to electrical charge gradients (i.e., defines
how they balance each other out)
Eion=RT/zF*ln([ion]o/[ion]i)
(R=gas constant T=temp. z=valence (+1,-1) F=Faraday’s constant)
E=membrane potential at which net ion flux is 0 (equilibrium) given specific intracellular
and extracellular concentrations of ions.
equilibrium potentials
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action potentials
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action potentials: reflect dynamics of Na+ and K+ ion movements across the membrane
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action potential conduction speed is a function of axon length and myelination (or lack thereof)
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synaptic potentials
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neurotransmitters: mediating information exchange between neurons through generation of synaptic potentials
three basic types of neurotransmitter:
1. excitatory (glutamate, ACh)
2. inhibitory (GABA, glycine)
3. neuromodulatory (NE, 5-HT, DA, HA, Ach)
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synaptic integration
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synaptic integration: temporal vs. spatial
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