PSB 3002 Exam 2 Review Questions with
answers
Define (a) membrane potential (b) resting potential and (c) action potential. -
CORRECT ANSWERS ✔✔a.) membrane potential - the difference in charge
across the membrane (hyperpolarized: inside more negative than outside;
depolarized: inside more positive)
b.) resting potential: charge of the neuron when at rest; -70 mV
c.) main electrical event of an axon, triggered by a threshold of excitation; rapid
depolarization followed by hyperpolarization
What two forces determine the distribution of ions across the cell membrane? -
CORRECT ANSWERS ✔✔1.) *diffusion:* molecules move from an area of
higher concentration to an area of lower concentration (DOWN the
concentration gradient); molecules become evenly distributed over time
2.) *electrostatic pressure:* opposite charges attract, like charges repel
Describe the concentration gradients across the cell membrane for (a)
potassium (b) chloride and (c) sodium. How are these gradients maintained
while the cell is at rest? - CORRECT ANSWERS ✔✔a.) *potassium (K+):*
highly concentrated on the inside (diffuses OUT, electrostatic pressure pushes
in); little net movement
,b.) *chloride (Ci-):* more concentrated outside than inside (diffuses INTO the
cell, electrostatic pressure pushes them out); no net movement
c.) *sodium (Na+):* more concentrated on the outside; diffusion AND
electrostatic pressure pushes sodium in; relatively impermeable to membrane
except when facilitated by a sodium-potassium pump
What is the function of the sodium-potassium pump? - CORRECT ANSWERS
✔✔located within the membrane uses high levels of energy to pump 3 sodium
out of the cell and 2 potassium into the cell; helps keep sodium levels low
inside the neuron
(a) Describe the ionic movements (and their relative timing) that occur during
an action potential. (b) What triggers an action potential? - CORRECT
ANSWERS ✔✔*a.)*
1.) resting potential of neurons is -70mV. When it becomes more positive to
reach the threshold of excitation (about -55 mV), voltage-dependent sodium
ion channels open.
2.) Na+ enters the cell, making the membrane potential even more positive
3.) once the membrane potential reaches around +40mV, Na+ channels close
and become refractory (can't open again until it goes back to resting potential)
, 4.) when Na+ channels become refractory, K+ (potassium) channels open and
allow potassium to leave the cell, making the membrane potential more
negative
5.) K+ continues leaving the cell, making the inside more negative and
eventually causing membrane potential to return to normal levels (-70mV).
5.) once at normal levels, Na+ channels reset, and Na+ & K+ pumps help
reestablish membrane potential
*b.)*
an action potential is triggered when reaching the threshold of excitation (-55
mV), which is triggered when neurotransmitters diffuse across the cleft to the
postsynaptic cell. once in the postsynaptic cell, it attaches to receptors, which
opens ion channels + depolarizes the postsynaptic cell.
How do the ions pass through the cell membrane? - CORRECT ANSWERS
✔✔ions are hydrophilic, so they cannot easily cross the hydrophobic part of
the membrane (tails). they must be facilitated through the membrane with the
help of transmembrane proteins which are like pores that allow ions to pass
through (such as ion channels).
What is the all-or-none law? - CORRECT ANSWERS ✔✔an action potential
either occurs, or does not occur; once initiated, is always transmitted down the
axon at the same size
answers
Define (a) membrane potential (b) resting potential and (c) action potential. -
CORRECT ANSWERS ✔✔a.) membrane potential - the difference in charge
across the membrane (hyperpolarized: inside more negative than outside;
depolarized: inside more positive)
b.) resting potential: charge of the neuron when at rest; -70 mV
c.) main electrical event of an axon, triggered by a threshold of excitation; rapid
depolarization followed by hyperpolarization
What two forces determine the distribution of ions across the cell membrane? -
CORRECT ANSWERS ✔✔1.) *diffusion:* molecules move from an area of
higher concentration to an area of lower concentration (DOWN the
concentration gradient); molecules become evenly distributed over time
2.) *electrostatic pressure:* opposite charges attract, like charges repel
Describe the concentration gradients across the cell membrane for (a)
potassium (b) chloride and (c) sodium. How are these gradients maintained
while the cell is at rest? - CORRECT ANSWERS ✔✔a.) *potassium (K+):*
highly concentrated on the inside (diffuses OUT, electrostatic pressure pushes
in); little net movement
,b.) *chloride (Ci-):* more concentrated outside than inside (diffuses INTO the
cell, electrostatic pressure pushes them out); no net movement
c.) *sodium (Na+):* more concentrated on the outside; diffusion AND
electrostatic pressure pushes sodium in; relatively impermeable to membrane
except when facilitated by a sodium-potassium pump
What is the function of the sodium-potassium pump? - CORRECT ANSWERS
✔✔located within the membrane uses high levels of energy to pump 3 sodium
out of the cell and 2 potassium into the cell; helps keep sodium levels low
inside the neuron
(a) Describe the ionic movements (and their relative timing) that occur during
an action potential. (b) What triggers an action potential? - CORRECT
ANSWERS ✔✔*a.)*
1.) resting potential of neurons is -70mV. When it becomes more positive to
reach the threshold of excitation (about -55 mV), voltage-dependent sodium
ion channels open.
2.) Na+ enters the cell, making the membrane potential even more positive
3.) once the membrane potential reaches around +40mV, Na+ channels close
and become refractory (can't open again until it goes back to resting potential)
, 4.) when Na+ channels become refractory, K+ (potassium) channels open and
allow potassium to leave the cell, making the membrane potential more
negative
5.) K+ continues leaving the cell, making the inside more negative and
eventually causing membrane potential to return to normal levels (-70mV).
5.) once at normal levels, Na+ channels reset, and Na+ & K+ pumps help
reestablish membrane potential
*b.)*
an action potential is triggered when reaching the threshold of excitation (-55
mV), which is triggered when neurotransmitters diffuse across the cleft to the
postsynaptic cell. once in the postsynaptic cell, it attaches to receptors, which
opens ion channels + depolarizes the postsynaptic cell.
How do the ions pass through the cell membrane? - CORRECT ANSWERS
✔✔ions are hydrophilic, so they cannot easily cross the hydrophobic part of
the membrane (tails). they must be facilitated through the membrane with the
help of transmembrane proteins which are like pores that allow ions to pass
through (such as ion channels).
What is the all-or-none law? - CORRECT ANSWERS ✔✔an action potential
either occurs, or does not occur; once initiated, is always transmitted down the
axon at the same size
