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22 Cards in this Set
- Front
- Back
What are the three most important types of channels?
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voltage gated (channels are either open or closed)
ligand gated second messenger gated channels (binding site is on the inside) |
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Voltage Gating
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charged amino acids within the structure of the channel move in response to a change in voltage
-causes a change in the conformation that opens the gate of the channel |
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inactivate
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opening of channel exposes site on cytoplasmic side of protein that acts as a binding site for the part of the channel itself, which bind to an blocks (inactivates) the channel
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How do we know how channels work?
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patch clamp recording
pipette is pushed up against cell and pressure is applied glass fuses with membrane of cell, making possible the recording of the currents of single channels |
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stochastic
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opening is stochastic: not every channel opens at exactly the same time, and once channel opens, it stays open for a random interval and then inactivates (closes)
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What is the most important thing that channels do?
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produce action potentials (spikes)
first one recorded by hodgkin and huxley from giant axon of squid = 1 ms |
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Action Potential
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resting potential = -60 mV
up to 50 mV = depolarizing repolarization - below resting membrane potential sudden, brief reversal of polarity of the membrane potential membrane potential at any given time depends on how many and which channels are open |
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What causes depolarization?
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glutamate binding to receptors
produced by synaptic input next: Na+ enters the cell, depolarizes cell more, more Na+ channels open -causes a rapid spike = depolarizatoin to +50 mV. amount of Na in cell is actually very small, but enough charge has entered cell to create an action potential |
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All or none action potentials
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depolarization opens Na channels, which lets in positive ions which depolarize the membrane and open more channels
-this is why AP's are always of the same amplitude as soon as enough NA channels open, membrane is de-polarized enough to trigger response Vm then depolarizes to Nernst potential for NA (+50mV) |
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Refractory Period
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limits rate at which action potential can be produced
after inactivation gate closes during AP, remains closed for a few milliseconds even though the mem pot goes back to resting. membrane is resistant to initiation of a further action potential length of refractory period sets the max rate at which a neuron can fire repeating AP's |
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Saltatory Conduction
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how an action potential propagates by jumping down axon from node of ranvier to node, because of myelinated schwann cells
the node is packed with voltage gated ion channels. myelin = no ion channels voltage spreads efficiently from node to node myelinated action potentials can go up to 100 meters per second |
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Ca 2+ is more concentrated inside or outside of the cell?
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outside
Ca ATPase pumps CA out of the cell |
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What breaks down Ach after it is released from the presynaptic cell?
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achetylcholinesterase
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why is it that when Ach binds, the channel opens?
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thought to be because the amino acids twist around the channel pore, change conformation
kinks of amino acids are no longer orientated in a way that closes the channel, leaves space for things to pass through |
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what is the most common neurotransmitter in the brain?
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glutamate
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Ach and Glutamate open channels that allow____
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cations like Na
this produces a depolarization |
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Glycine and GABA activate receptors whose channels allow ______
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anions like Cl- (chlorIDE)
activation of these receptors produces a hyperpolarization -action potential will never reach threshold that is why these are INHIBITORS! |
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Excitatory Ligand-Gated Channels
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permeable to cations (Na+ K+)
produce depolarizations (excitatory postsynaptic potentials or EPSP's) ex. receptors for ach, glutamate, serotonin |
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Inhibitory Ligand-Gated Channels
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permeable to anion (Cl- chlorIDE)
produce hyperpolarizations (inhibitory postsynaptic potentials of IPSP's) ex. receptors for glycine, GABA |
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summation and the generation of an action potential occurs where?
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at the axon hillock which is unmyelinated and has many voltage gated Na+ channels
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spatial summation
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adds up simultaneous influences of synapses at different sites on the postsynaptic cell
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temporal summation
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adds up postsynaptic potentials generated at the sam site in a rapid sequence
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