Neuronal electrophysiology Flashcards
Length (space) constant definition
Distance over which a subthreshold depolarization will spread and influence the next segment of membrane
The longer the space constant …
The faster the conduction
Equation for length constant
Square root of (membrane resistance over internal resistance)
All-or-none response
A stimulus will either elicit an action potential or fail to do so
Length of Na+ channel upstroke
0.5 ms
Upstroke of action potential chart
Caused by increase in Na+ channel conductance
Causes repolarization of membrane
Delayed increase in K+ channel conductance along with the decrease in Na+ channel conductance
Deactivation of K+ channel conductance
Caused by repolarization of the membrane potential
Where on the scale of Em does action potential take place?
Between E(na) and E(k)
Resting channel (w/r/t m and h)
M activation gate closed, H inactivation gate open
Activated channel (w/r/t m and h)
Both m and h open to allow Na+ influx
Inactivated channel (w/r/t m and h)
m gate open, h gate closed
Regenerative depolarization
“Positive feedback mechanism” that allows for more influx of sodium when some gates have already opened
When do Na+ channels close?
Rapidly at depolarization
What is the main difference between Na+ and K+ channels?
K+ channels are never deactivated during depolarization, and will only shut off once it has reached repolarization
Absolute vs. relative refractory period
Absolute: another AP cannot be elicited no matter what Relative: it can make a new AP, it just takes extra stimulation than normal
What happens to the resting membrane potential with hyperkalemia?
Becomes more positive
As a result of hyperkalemia, what happens to Na+ channels?
They become less available (they inactivate) and conduction slows
Signs and symptoms of hyperkalemia
Slow mentation, muscle weakness
How Ca2+ affects Na+
Modulates channel activity by altering membrane surface charge
Effect on Na+ channels during hypercalcemia
Extra Ca2+ raises threshold for Na+ channel activation and decreases membrane excitability
Effect on Na+ channels during hypocalcemia
Lowers threshold for Na+ channel activation and increases membrane excitability
Hyperventilation and Ca2+
Decreases free plasma calcium to increase neuronal membrane excitability
Hypoventilation and Ca2+
Increases free plasma calcium to decrease neuronal membrane excitability
Myelinated axons are ___x less in diameter than unmyelinated axons
100
Myelin sheath increases ___, therefore also increasing ___
membrane resistance, length constant
Internodal distance
1-2 mm
Commonalities between MS and diabetic neuropathies
Both destroy myelination and severely slow neuronal conduction
Post-synaptic potentials
Local, graded responses propagated passively
Excitatory neurotransmitters
ACh, glutamate
Inhibitory neurotransmitters
GABA, glycine
EPSP ion influx
Cations (Na in, K out)
IPSP ion influx
Anions (Cl- in)
EPSP membrane potential change
Positive; toward E(Na,K)
IPSP membrane potential change
Negative; toward E(Cl)
Temporal summation
Different locations stimulated at the same time
Spacial summation
Same area affected in a short timespan
