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50 Cards in this Set

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resting membrane potential
constant voltage generated across membrane when cell is at rest

-40 to -90 mV
receptor potential
result of sensory neuron activated by external stimulus
synaptic potential
result of activation of synapses

allows info to be transmitted from one neuron to another
hyperpolarization
current makes membrane potential more negative

passive electrical response: doesn't require any unique property
current-dependent
membrane potential changes in proportion to magnitude of injected current (hyperpolarization - negative current)
depolarization
current delivered makes the membrane potential more positive than the resting potential
action potential
transmembrane potential goes from negative to positive

occurs when membrane potential becomes depolarized beyond (more positive than) the threshold potential

active response generated by the neuron

all or none: does not depend on magnitude of injected current
threshold potential
beyond this level of membrane potential, an action potential occurs
how is an electrical potential generated?
by different ion concentrations inside and outside of the cell

ions flow down concentration gradient and take their electrical charge with them as they go
electrochemical equilibrium
force of chemical concentration gradients balances electrical force generated by charges on ions
to which ions is the membrane most permeable when at rest?
K+ and Cl-
equilibrium potential
electric potential across the membrane at electrochemical equilibrium

predicted by the Nernst eqn
Nernst eqn
used to predict equilibrium potential (membrane potential when the cell is at electrochemical equilibrium)

Eion = (60/z)log([conc. ion outside cell]/[conc. ion inside cell])
what is inside cell in large amounts?
K+
anions
what is inside cell in small amounts?
Na+
Cl-
HCO3-
what is outside cell in large amounts?
Na+
Cl-
HCO3-
what is outside cell in small amounts?
K+
anions
K+
inside cell in large amounts
outside cell in small amounts

2nd ion to move in action potential

blocked by TEA
Cl-
inside cell in small amounts
outside cell in large amounts
anions
inside cell in large amounts
outside cell in small amounts
Na+
inside cell in small amounts
outside cell in large amounts

1st ion to move in action potential

blocked by TTX
HCO3-
inside cell in small amounts
outside cell in large amounts
Ca++
inside cell in very small amounts
outside cell in relatively large (but still small) amounts
current
flow of positive ions

positive current (K+) flows out of cell at rest, making it more negative
Ek
-90 mV
Ena
+65 mV
Ecl
-60 mV
Eca
+120
resistance
opposition to ion flow
conductance
ease of ion flow = 1/resistance = g

gNa
gK
etc.
goldman "cord" eqn
weighted average of ion permeabilities to determine equilibrium potential for all ions across a membrane

takes into account to which ion the membrane is most permeable / which ion has greatest conductance
which ion moves in 1st part of action potential?
Na+
which ion moves in 2nd part of action potential?
K+
TTX
blocks Na+
TEA
blocks K+
what happens during an action potential?
membrane of a resting cell is most permeable to K+

during an action potential, membrane is transiently predominantly permeable to Na+

Na+ flows into cell down its concentration gradient, hyperpolarizing membrane potential

positive feedback loop is an action potential

secondary transient increase in K+ permeability repolarizes the neuronal membrane
what is the primary source of the resting membrane potential?
permeability to K+
time constant
time required for membrane potential to reach 67% of its final value

time constant = resistance*capacitance
length constant
distance over which membrane potential decays to 37% of its initial value
what happens to voltage as it travels further from source?
signal is debased and degraded (gets smaller and slower)
voltage-dependent ionic current
ionic permeability of membranes is voltage-sensitive
early influx of Na+
produces transient inward current (positive charge flows in but eventually inactivates)
delayed efflux of K+
produces sustained outward current (positive charge flows out)
differential sensitivity of Na+ and K+ to TTX and TEA
Na+ and K+ flow through independent permeability pathways (selectively permeable ion channels)
what does depolarization of the membrane cause?
causes Na+ conductance to increase (activate) over time, then decrease (inactivate)
time-dependent
Na+ and K+ conductances are both time dependent

Na+ conductance is rapidly activated, then inactivated

K+ conductance has a delayed activation
voltage-dependent
Na+ and K+ conductance increase progressively with progressive neuronal depolarization
myelination
increases velocity of conduction

insulates axon, improving passive flow of electrical current

prevents current from leaking across the membrane
where and how does action potential occur?
by saltatory conduction at the nodes of Ranvier, where there is a gap in the myelination
nodes of Ranvier
gaps in axon myelin

action potential is generated here b/c this is the only place that has voltage-gated Na+ channels