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15 Cards in this Set
- Front
- Back
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types of neuronal electrical signals
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receptor potentials:
- activation of sensory neurons by external stimuli (light, sound, heat) synaptic potentials: - communication between neurons at synaptic contacts - occurs during activation of synapses - transmission of information from one neuron to another action potentials: - electrical signal that travels along long axons - long-range transmission of information within NS to target organs |
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cellular membranes have a membrane potential
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plasma membranes of excitable cells have membrane potential
- electrical voltage difference across membrane - due to differences in sodium and potassium ion concentration in and out of cell - potassium: higher inside cell; sodium: higher outside cell inside of cell: higher concentration of negative phosphate ions and proteins |
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some basic electrical concepts
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voltage (V)
- potential to do work - can be positive or negative - volts (mV) current (I) - flow of positively or negatively charged ions - results from movement of charge from one side of membrane to another - amps (micro or nano) resistance (R) - something that impedes flow of ions - ohms - opposite of resistance: conductance (g) (how rapidly ions flow) - Ohms law: V=IR or I=V/R = Vg |
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polarized
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difference in net charge on either side of membrane
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hyperpolarized
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more negatively charged (downward deflection of the voltage trace)
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depolarized
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more positively charged (upward deflection of the voltage trace)
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membrane permeability
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neuronal membranes are composed of a phospholipid bilayer
essentially impermeable to: - polar molecules (charged and large uncharged) - ions - slightly permeable to water itself - permeable to gases and small uncharged polar molecules thus, most molecules need a pathway across the membrane |
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the membrane potential
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electrical gradient across plasma membrane: -60 to -80 mV
inside negative relative to outside simplified model: - cytosolic and extracellular solutions are separated by impermeable membrane - voltmeter used; no potential difference is observed because there is no difference across membrane (in ionic balance) |
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electrochemical equilibrium
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concentration gradient: entropically favorable
as you lose positive ions, the inside becomes more negative and wants positive ions to come back into the membrane electrical gradient: as positive ions move down a concentration gradient, they move AGAINST electric gradient (energetically unfavorable) |
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equilibrium potentials
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potassium: -90 mV
sodium: +60 mV rest: -60 mV |
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what establishes the membrane potential?
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what happens if the membrane is now mostly permeable to K+?
- by inclusion of K+ channels in membrane "leak channels": constant flow of K+ outside the cell - K+ ions will move "down" concentration gradient and leave Cl- ions behind. This creates a net charge difference - eventually an equilibrium is reached between the concentration gradient and the electrical gradient (no net movement will occur) (electrochemical equilibrium) |
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electrochemical equilibrium
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E = 58/z mV x log (ion out/ion in)
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membrane potential influences ion flux
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concentration gradient:
- entropically favorable to have equal concentrations of ions on each side of membrane electrical gradient: - potential across membrane will ATTRACT positive charge and REPEL negative charge |
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resting potential is determined by K+ permeability
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resting potential is set by non-gated K+ channels (leak/open channels)
- these channels are always open - different from K+ channels that play role in action potential (voltage gated) |
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Na+ has little effect on resting membrane potential
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sodium has very little effect on because there is little to no permeability at rest
HOWEVER, it DOES affect the action potential |
