N110 MIDTERM 1 EXAM QUESTIONS AND ANSWERS
WITH COMPLETE SOLUTIONS GRADED A++
Axon vs. electrical wire
1. Axon membrane insulates like plastic coating around a wire
2. Axoplasm conducts electricity like copper wire
How is an axon different from an electric wire?
1. Axoplasm is not a perfect conductor because it has electrical resistance.
2. The axon membrane is not a perfect insulator.
3. The axon membrane acts like a capacitor.
Diffusion Potential
A voltage generated by passive diffusion of ions down a concentration gradient.
Nernst Equation
For a monovalent ion at RT: E= 58 mV*log([K+]right/[K+]left)
For a divalent ion at RT: E= 29 mV*log([Ca 2+]right/[Ca 2+]left)
Goldman Equation
*Where RT/F=58 and ln = log
K+ concentration gradient
Resting membrane potential is set by...
, Concentration of Na+ out
The peak height of the action potential depends on...
Characteristics of an action potential
1) Threshold level of depolarization required to trigger an action potential.
2) Action potentials are all-or-none events.
3) Action potentials propagate without decrement at a finite speed.
4) Action potentials have a refractory period.
Refractory Period
It prevents action potentials from going backwards & it sets a limit to the maximum
frequency of action potentials a nerve cell can transmit.
Equilibrium potentials for K+ and Na+.
K+ = -80 mV
Na+ = +60 mV
--> Note: very little Na+ is required to change the membrane capacitance to +60 mV
during an AP.
Membrane potential and current
- Hyperpolarizing a squid axon from -60 mV to -130 mV causes tiny current due to
leakage through the membrane.
Voltage-activated currents in response to depolarizing from -65 mV to 0 mV.
WITH COMPLETE SOLUTIONS GRADED A++
Axon vs. electrical wire
1. Axon membrane insulates like plastic coating around a wire
2. Axoplasm conducts electricity like copper wire
How is an axon different from an electric wire?
1. Axoplasm is not a perfect conductor because it has electrical resistance.
2. The axon membrane is not a perfect insulator.
3. The axon membrane acts like a capacitor.
Diffusion Potential
A voltage generated by passive diffusion of ions down a concentration gradient.
Nernst Equation
For a monovalent ion at RT: E= 58 mV*log([K+]right/[K+]left)
For a divalent ion at RT: E= 29 mV*log([Ca 2+]right/[Ca 2+]left)
Goldman Equation
*Where RT/F=58 and ln = log
K+ concentration gradient
Resting membrane potential is set by...
, Concentration of Na+ out
The peak height of the action potential depends on...
Characteristics of an action potential
1) Threshold level of depolarization required to trigger an action potential.
2) Action potentials are all-or-none events.
3) Action potentials propagate without decrement at a finite speed.
4) Action potentials have a refractory period.
Refractory Period
It prevents action potentials from going backwards & it sets a limit to the maximum
frequency of action potentials a nerve cell can transmit.
Equilibrium potentials for K+ and Na+.
K+ = -80 mV
Na+ = +60 mV
--> Note: very little Na+ is required to change the membrane capacitance to +60 mV
during an AP.
Membrane potential and current
- Hyperpolarizing a squid axon from -60 mV to -130 mV causes tiny current due to
leakage through the membrane.
Voltage-activated currents in response to depolarizing from -65 mV to 0 mV.
