Term
All bioelectrical signals are...... |
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Definition
-changes in the underlying resting membrane potential (VM)
- • Action potentials (including EEG, EMG, ECG), synaptic potentials, receptor potentials, field potentials, , nerve conduction velocity
• “Typical” VM: ~ -70 mV (neurons), ~90 mV (muscles)
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Term
Ion channels are transport proteins
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Definition
-• Ion channels facilitate diffusion of ionic species, multiple cations
(+H2O)
• Must consider concentration (chemical) and charge (electrical)
gradients = electrochemical gradient
• No binding, so very fast (max 108/s)
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Term
Typical plasma membrane is highly permeable |
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Definition
-to K+
• High density of “passive” channels allows K+ influx or efflux , (direction depends on electrochemical gradient and VM)
-Membrane is “freely” permeable: PK = 1
-Little resistance (R) to K+ flux
• Passive “Leak” flux refers to all sources of resting fluxes, but is mostly K+
• Ionic flux is a type of “conductance” (G)
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Term
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Definition
• Open or close due to physical stimulus, depolarization of VM,
presence/absence of a chemical ligand
-Key role in generating bioelectrical signals
• Typically contribute little to VM, but can help maintain it
. Passive ion channels are largely responsible for the resting membrane potential, but gated channels can help to maintain it
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Term
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Definition
-(Eion) also called “Nernst potential"
-•maximum potential due to diffusion of a single ionic
species or of several ions through a single type of ion channel
• If negative z or negative log (ratio is a fraction), Eion will be negative
Also called “reversal” potential
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Term
“Typical” mammalian Eion values
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Definition
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• EK = -90 mV, because [K+]inside : [K+]outside = 40 (not 10)
• ENa = +60 mV; ECl = -75 mV; ECa = +120 mV; Ecation = 0 mV
• Actual Eion will slightly differ due to presence of other types of ionic transport (e.g., Cl-) and co transporters that use ionic gradients (e.g., Na+)
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Term
The VM is “stored” by......
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Definition
-the membrane capacitance (CM)
-• Membrane is a capacitor (CM): insulator (lipid bilayer) separating charges (anions and cations) inside and outside
• Membrane resistance (RM): density of open channels permeable to ions that are out of equilibrium (i.e., VM ¹ Eion)
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Term
Extracellular K+ concentration is clinically important
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Definition
• Increasing [K+]out depolarizes:
VM seeks more positive EK
-Results in “hyperexcitability “
• Low [K+]out hyperpolarizes
-Results in “hypoexcitability”,
cause cause paralysis
• Small increases in [Na+]out
have little effect
-Pump can handle leakage
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Term
The Goldman-Hodgkin-Katz equation |
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Definition
-describes VM due to multiple ionic permeabilities
• Note inclusion of P values, absence of z values, and reversed Cl- ratio
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Term
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Definition
-prevents VM from running down due to Na+ leakage
-• Pumps 3 Na+ out + 2 K+ in per ATP hydrolysis
• Pump is electrogenic: it adds ~-3 mV to VM
• Maintains osmotic balance
-More solute extrusion than uptake, H2O follows solutes ... )
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Term
Resting VM is a steady-state, not equilibrium, potential
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Definition
-• Energy (ATP hydrolysis) is required to:
-Transport Na+ against its electrical + chemical gradients
-Transport K+ against its chemical gradient
-Pump is needed to maintain the steady state
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