PSB 3002 Exam 2 Review Questions UPDATED ACTUAL Questions And
Correct Answers
C
Terms in this set (46)
Define (a) membrane potential (b) resting potential and a.) membrane potential - the difference in charge across the membrane
(c) action potential. (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 1.) diffusion: molecules move from an area of higher concentration to an area of
the cell membrane? 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 a.) potassium (K+): highly concentrated on the inside (diffuses OUT, electrostatic
membrane for (a) potassium (b) chloride and (c) sodium. pressure pushes in); little net movement
How are these gradients maintained while the cell is at
rest? 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? 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 a.)
timing) that occur during an action potential. (b) What
triggers an action potential? 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? 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? an action potential either occurs, or does not occur; once initiated, is always
transmitted down the axon at the same size
Explain how the presence of myelin on an axon speeds called saltatory conduction; myelin sheaths create gaps (called nodes of ranvier).
up conduction velocity. What is this form of conduction instead of having ion channels along the whole axon, ion channels are ONLY at
called? those nodes. that means that ion channels do not need to wait for the adjacent
ion channel to open and create an action potential in order to trigger the opening
of the next. instead, the conduction remains depolarized to the threshold while
traveling under myelin sheath (decremental conduction). once it reaches the node
of ranvier then, it can trigger the opening of ion channels + an action potential at
that node, rather than along the length of the whole axon
Describe the events that take place at the axon terminal 1.) vesicles containing NT dock against the presynaptic membrane (proteins on the
from the time an action potential arrives to the time vesicle bind with proteins on the membrane)
neurotransmitter is released into the synapse.
2.) action potential comes along terminal buttons; if depolarized to a certain
point, calcium channels will open, and calcium will enter the cell.
3.) calcium binds with docking proteins on the presynaptic membrane, bringing
about the fusion of the vesicles to the membrane to release NT.
Correct Answers
C
Terms in this set (46)
Define (a) membrane potential (b) resting potential and a.) membrane potential - the difference in charge across the membrane
(c) action potential. (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 1.) diffusion: molecules move from an area of higher concentration to an area of
the cell membrane? 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 a.) potassium (K+): highly concentrated on the inside (diffuses OUT, electrostatic
membrane for (a) potassium (b) chloride and (c) sodium. pressure pushes in); little net movement
How are these gradients maintained while the cell is at
rest? 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? 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 a.)
timing) that occur during an action potential. (b) What
triggers an action potential? 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? 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? an action potential either occurs, or does not occur; once initiated, is always
transmitted down the axon at the same size
Explain how the presence of myelin on an axon speeds called saltatory conduction; myelin sheaths create gaps (called nodes of ranvier).
up conduction velocity. What is this form of conduction instead of having ion channels along the whole axon, ion channels are ONLY at
called? those nodes. that means that ion channels do not need to wait for the adjacent
ion channel to open and create an action potential in order to trigger the opening
of the next. instead, the conduction remains depolarized to the threshold while
traveling under myelin sheath (decremental conduction). once it reaches the node
of ranvier then, it can trigger the opening of ion channels + an action potential at
that node, rather than along the length of the whole axon
Describe the events that take place at the axon terminal 1.) vesicles containing NT dock against the presynaptic membrane (proteins on the
from the time an action potential arrives to the time vesicle bind with proteins on the membrane)
neurotransmitter is released into the synapse.
2.) action potential comes along terminal buttons; if depolarized to a certain
point, calcium channels will open, and calcium will enter the cell.
3.) calcium binds with docking proteins on the presynaptic membrane, bringing
about the fusion of the vesicles to the membrane to release NT.
