action potentials Flashcards
Concentration of ions differs on opposite sides of the membrane.
T/F
T
Resting membrane potentials (RPM) are Positive (inside relative to the outside).
T/F
F. they are NEGATIVE
graded potentials
Non-Excitable cells respond to stimulation with a proportional change in membrane potential
Hyperpolarize VS
Depolarize
Hyperpolarize: create a more negative membrane potential
Depolarize: create a more positive membrane potential
Ohm’s Law:
Ohm’s Law: V= I x R or I = V x g
Voltage (V) –
Current (I) – the rate of flow of electrical charge between two points
Resistance (R) – hindrance to charge flow
Conductance (g) – allowance to charge flow (1/R)
Insulator VS Conductor
Insulator – substance with high electrical resistance
Conductor – substance with low electrical resistance
Electrical vs chemical gradient
Electrical gradient: A difference in electrical charge across a membrane
Ions flow along their electrical gradient toward an area of opposite charge.
Chemical gradient: A difference in ion concentration across a membrane
Ions flow along their chemical gradient from an area of high concentration to an area of low concentration.
what is nernst equation ?
used to calculate equilibrium potential E=(RT/zF)ln(Xout/Xin) R- gas constant T-temp in K z-valence F-faraday's constant Xout- concentraton outside cell
Typical Ion Concentrations for Mammalian Neurons
K+: IN: 145 OUT:5
Na+: IN:5-15 OUT:145
Cl- IN:4-30 OUT:110
Ca2+: IN .0001 OUT 1-2
Equilibrium Potential for Important Ions in a Neuron
K+: -80 TO -90 mV
Cl-: -60 to -70
Na=: 55 to 60
Ca2+: 100 to 130
Leakage/Passive channels
Leakage/Passive channels – Always open, allow passive diffusion of specific ions
Chemically/ligand gated channels
Chemically/ligand gated channels – open with binding of a specific neurotransmitter
Mechanically gated channels
Mechanically gated channels – open and close in response to physical deformation of receptors
Voltage-gated channels
Voltage-gated channels – open and close in response to changes in membrane potential
What determines duration of a graded potential
Duration is directly proportional to the duration of the triggering event
graded potentials Initiated by
Initiated by ion flow through gated channels
or
activation of voltage gated channels
when can graded potential produce an action potential
Graded Potentials That Reach Threshold Can Induce Action Potentials
spatial vs temporal summation
multiple excitatory neurons at once
temporal
excitatory neurons come back to back
creating AP
normakalemia
When serum K+ is in normal range (normokalemia):
a stimulus that depolarizes the cell by ≥15mV elicits an action potential.
hyperkalemia
When serum K+ is high (hyperkalemia):
The Vm is depolarized
Vm is closer to threshold
a previously subthreshold stimulus now elicits an action potential.
hypokalemia
When serum K+ is low (hypokalemia):
The Vm is hyperpolarized.
Vm is farther from threshold.
a previously suprathreshold stimulus now fails to elicit an action potential.
Hyperpolarizing involving Cl- flow is an example of graded potential T/F
True
types of gated ion channels involved in AP vs Gated
AP:Voltage gated
gated : mechanically, chemically, or voltage gated
where do graded potentials occur
dendrites and cell body
where do AP occur
trigger zone through axon
Contiguous Conduction
Depolarization spreads from one area to adjacent areas.
Occurs in unmyelinated fibers.
Action Potentials Vary by Cell Type
cardiac?
skeletal muscle?
motor neuron ?
200 msec
5 msec
2msec
Goldman’s equations is a measure of
resting Membrane potential depending on distribution and permeability of Na+, K+ and Cl- ions.
