Test 1: Review/Membrane and Synaptic Physiology Flashcards
Where does info transfer in neuron?
synapse
What leads to complex neural control system?
convergence and divergence
what does Intracellular recording electrode measure?
measure membrane electrical potential
What is the ground?
extracellular space
What is the electric potential?
Between electrode and ground
What is resting potential?
Potential at equilibrium
If equal on both sides, then zero. But if stuff has to cross, it will change
What is the transmembrane potential?
A function of cell’s ability to maintain concentration gradients of different ion species across cell’s membrane.
A rest membrane potential primarily determined by
K+ ions, tend to flow OUT along concentration gradient
As K+ flow out
other cations in. Electrical gradient
Equilibrium potential is a
linear function of the log of the concentration ratio
Nerst Equation: getting equilibrium with 1 ion only
E(ion) = Transmembrane voltage at equilbirum
RT/zF ln (ion out)/(ion in)
Cations on top.
2 chamber: where do ions flow?
For K+
if greater than -58, go left
if lower than -58, go right
Why is the resting membrane potential not the equilibrium potential for K+?
Because determined by multiple ions
E (Na+)
E (K+)
E (Cl-)
E (Ca2+)
E(Na+)= +56mV
E (K+)= -102mV
E (Cl-)= -76mV
E (Ca2+)= +125mV
Goldman Equation
Em = RT/F ln (p(ion) + p(ion)/p(ion) + p(ion)
Cations have “out” on top
PK: PNA: PCL is 1: 0.04: 0.045
Membrane potential function of relative permeabilities
Na/K+ pump
main gradients ATPase convert ATP to ADP and phosphate restores ion concentration gradients maintains resting potential electrogenic - 3Na+ out, 2K+ in 20-40% energy consumption
Hyperkalemia
high K+ depolarized excitable membrane
cardiac muscle become hyperexcitable, fibrillation- uncontrolled contraction.
Hypoxia/stroke: ATP runs down, cell can’t maintain differential gradient, depolarized, increased excitotoxicity.
The time required to reach __% o final voltage is membrane time constant tau
63%
resistance * capacitance
why are membranes SLOW to depolarize?
capacitance properties
Time constant is time when voltage response rise to
1-(1/e) or 63% of Vinfinity (steady state membrane charge)
You need a (longer/short) tau to fire AP.
Longer
What is ^?
Length constant
Depends on membrane resistance
Calculate ^
SQRT(membrane resistance) /
SQRT(intra r + extra r)
best passive current: lower intra/extra r and higher membrane resistance
Increase strength of depolarization: does this make bigger AP?
no, more AP but not bigger
Passive responses
below thershold
active response/conductance
above threshold
negative current
hyperpolarization
Rising phase
rapid depolarization
overshoot
positive to 0 mV
Falling phase
repolarization
undershoot
hyperpolarization following the spike
Voltage Clamp Technique
studies AP
clamp amplifier injects current to axon through 2nd electrode
By measuring the current injected, determine amp. and time of ionic current across membrane `
What happens in squid axon if you replace Na+ with choline?
only outward current now
Does K+ activate faster or slower than Na+?
Slower
Block Na+
TTX
Block K+
TEA
Steps of AP
- activate Na+ = Na+ ions into cell, depolarize, activates K+ channels
- Inactive Na+
- Hyperpolarize K+
- Na+ inactive portion removed
Patch clamp allows for
individual or small numbers of ion channels
Cell-attached recording
response of channels/channels pipette has covered
Whole-cell recording
more suction, membrane disrupted
electrode interior continuous with cell interior
Inside-out recording
intact membrane, suction away from cell
Outside-out recording
pull back some membrane, and have it reform such that cytoplasmic side frees electrode.
Na+ conductance
rapid onset (activation) rapid offset (inactivation)
K+ conductance
slow onset/offset
after hyperpolarization (undershoot)
Refractory period: absolute refractory period
Na+ channel inactivation
relative refractory period
afterhyperpolarization
higher threshold
