ACTION POTENTIAL EXAM QUESTIONS AND ANSWERS
, What does it mean when the plasma membrane of the neuron is polarized? - Answer - When there is a
separation of charge across the membrane. Specifically, a polarized neuron is one where the inside is
more negative and the outside is more positive. This is the state when the neuron is at rest.
What gives rise to the gradient across the membrane? - Answer - The chemical and voltage gradients of
potassium and sodium. Potassium wants to move from inside to outside. Sodium wants to move from
outside to inside.
What is meant by the membrane potential? - Answer - Measure of the voltage across the plasma
membrane
Why is the neuron considered to be a biological battery? - Answer - The voltage difference across
membrane allows the neuron to perform work.
What is meant by the testing potential? - Answer - This is when the neuron is not firing. Both K+ and N+
voltage hated channels are closed, but K+ is able to diffuse down it's concentration gradient through
passive ungated leak channels out of the neuron. N+ also diffuses into the neuron, but the Na+/K+ pump
pushes the Na+ out. So the resting potential is maintained by 2 primary forces. a) K+ diffusing out
through ungated leak channels b)Na+/K+ pump pushing Na+ out
What is the value in mV of a neuron at rest? Explain why this is the value. - Answer - Around -70 mV
because the inside is more negative than the outside due to potassium diffusing out and Na+ being
actively pumped out.
Generally in a neuron, describe the K+ concentration gradient across the membrane. - Answer -
Potassium is about 10 times more concentrated on the inside and wants to move out.
What is meant by the equilibrium potential for K+? - Answer - When the diffusion of potassium moving
out is balanced by the voltage gradient pushing K+ back in. K+ has an equilibrium potential of -90 mV.
Explain the role of the sodium/potassium for K+? - Answer - When the diffusion of potassium moving
out is balanced by the voltage gradient pushing K+ back in. K+ has an equilibrium potential of -90 mV
What are the two main factors that contribute to the resting potential? - Answer - Potassium gradient
and the sodium/potassium pump
What are 2 types of stimuli that can cause a nerve impulse? - Answer - Electrical and chemical
What does it mean when the neuron is depolarized? - Answer - Na+ voltage hated channels open and
Na+ gushes in. This causes the inside to become more positive, which decreases the polarization.
What does it mean when the neuron is hyperpolarized? - Answer - When a stimulus causes the inside of
the neuron becomes even more negative than at rest. Hyperpolarization results from any stimulus that
increases outflow of positive ions or the inflow of negative ions. Hyperpolarization is due to gated K+
channels now opening, which are closed at rest. Hyperpolarization causes the neuron to become closer
to the equilibrium potential of potassium which is -90 mV
, What does it mean when the plasma membrane of the neuron is polarized? - Answer - When there is a
separation of charge across the membrane. Specifically, a polarized neuron is one where the inside is
more negative and the outside is more positive. This is the state when the neuron is at rest.
What gives rise to the gradient across the membrane? - Answer - The chemical and voltage gradients of
potassium and sodium. Potassium wants to move from inside to outside. Sodium wants to move from
outside to inside.
What is meant by the membrane potential? - Answer - Measure of the voltage across the plasma
membrane
Why is the neuron considered to be a biological battery? - Answer - The voltage difference across
membrane allows the neuron to perform work.
What is meant by the testing potential? - Answer - This is when the neuron is not firing. Both K+ and N+
voltage hated channels are closed, but K+ is able to diffuse down it's concentration gradient through
passive ungated leak channels out of the neuron. N+ also diffuses into the neuron, but the Na+/K+ pump
pushes the Na+ out. So the resting potential is maintained by 2 primary forces. a) K+ diffusing out
through ungated leak channels b)Na+/K+ pump pushing Na+ out
What is the value in mV of a neuron at rest? Explain why this is the value. - Answer - Around -70 mV
because the inside is more negative than the outside due to potassium diffusing out and Na+ being
actively pumped out.
Generally in a neuron, describe the K+ concentration gradient across the membrane. - Answer -
Potassium is about 10 times more concentrated on the inside and wants to move out.
What is meant by the equilibrium potential for K+? - Answer - When the diffusion of potassium moving
out is balanced by the voltage gradient pushing K+ back in. K+ has an equilibrium potential of -90 mV.
Explain the role of the sodium/potassium for K+? - Answer - When the diffusion of potassium moving
out is balanced by the voltage gradient pushing K+ back in. K+ has an equilibrium potential of -90 mV
What are the two main factors that contribute to the resting potential? - Answer - Potassium gradient
and the sodium/potassium pump
What are 2 types of stimuli that can cause a nerve impulse? - Answer - Electrical and chemical
What does it mean when the neuron is depolarized? - Answer - Na+ voltage hated channels open and
Na+ gushes in. This causes the inside to become more positive, which decreases the polarization.
What does it mean when the neuron is hyperpolarized? - Answer - When a stimulus causes the inside of
the neuron becomes even more negative than at rest. Hyperpolarization results from any stimulus that
increases outflow of positive ions or the inflow of negative ions. Hyperpolarization is due to gated K+
channels now opening, which are closed at rest. Hyperpolarization causes the neuron to become closer
to the equilibrium potential of potassium which is -90 mV
