PGY 451 EXAM 1 QUESTIONS WITH VERIFIED SOLUTIONS LATEST UPDATE 2026
What does the nernst equation measure? - Answers The electrochemical difference of an ion across a
membrane
Ex = (61.5 mV)/Zx log ([Xo]/[Xi])
Describe chemical and electrical potential.. - Answers The chemical difference has to do with the
intercellular and extracellular concentrations of the ion. The ion will want to move from high to low.
The electrical difference has to do with the charge of the ion. The inside of the cell is negatively
charged and the outside of the cell is positively charged. The ion will want to move toward the side
opposite its own charge.
Describe the chemical and electrical potentials of glucose.. - Answers It chemical gradient flows from
outside to inside.
It has no electrical potential because glucose has no charge.
Describe the chemical and electrical potentials of sodium.. - Answers Sodiums concentration on the
outside is 12X higher than the inside, therefore its chemical gradient moves from outside to inside.
Sodium has a positive charge and therefore its electrical gradient flows from outside to inside.
Describe the chemical and electrical potentials of potassium.. - Answers Potassiums concentration on
the inside it 30X higher then on the outside, therefore its chemical gradient flows from the inside to
the outside.
Potassium has a positive charge and therefore its electrical gradient flows from outside to inside.
Describe the chemical and electrical potentials of chloride ion.. - Answers Chlorides concentration on
the outside is 3X higher than on the inside, therefore its chemical gradient flows from the outside to
the inside.
Chloride has a negative charge and therefore its electrical gradient flows from the inside to outside.
What is the nernst equilibrium potential of an ion? - Answers The Vm at which there is no net
movement of the ion
What are the nernst equilibriums of Na+, K+, Cl-? - Answers Na+ ~+65, K+ ~-90, Cl- ~-33
What is hypokalemia? - Answers A decrease in EK+ which hyperpolarizes the membrane making it
more difficult for a heart cell to produce an action potential resulting in cardiac arrhythmia and arrest.
Caused by diuretics.
What is hyperkalemia? - Answers An increase in EK+ which depolarizes the membrane and makes it
easier for a heart cell to generate action potentials resulting in cardiac arrythmia and arrest. Caused
by kidney failure.
How is lethal injection done? - Answers A rapid infusion of a high concentration of KCl resulting in
hyperkalemia.
What is resting membrane potential (RMP)? - Answers A Vm where there is no net movement of all
ions across the membrane. It is a weighted sum EK+ (80%), ENa+(15%), ECl-(5%) based on
contributions of a conductance in the total conductance.
Is -70 mV for a neuron, -10 mV for RBC, and -90 mV for skeletal and cardiac muscle
Chord Conductance Equation - Answers -Sums up Nernst Potential for all important ions
- and adjust for relative permeability for each ion
What does RMP depend on? - Answers -Concentration of ions inside and outside the cell
-Relative permeability of the cell membrane to the different ions
-It is primarily determined by K+ because the membrane is most permeable to it
What is the driving force of an ion? - Answers It is the reason each ion moves. It is the difference
between the Vm and their E (nernst equilibrium potential). The farther the Vm is from their E the
greater its driving force.
What is depolarization? - Answers increase in Vm from RMP (closer to ENa+)
What is hyperoplarization? - Answers Decrease in Vm from RMP (closer to EK+)
What is repolarization? - Answers Return back to RMP after being depolarized
The Vm can fluctuate between what two limits? - Answers EK+<Vm<ENa+
What percentage of K+ ions must diffuse out of the cell to establish RMP? - Answers 0.002%
What is the Na+, K+ ATPase responsible for - Answers the uneven ion concentrations of Na+ and K+
pumps 3 Na+ out for every 2 K+ in --> net negative charge inside cell
What do voltage gated ion channels respond to? - Answers Changes in Vm
, What to ligand gated ion channels respond to? - Answers Whether or not a ligand (neurotransmitter)
is present
Describe the Na+ and K+ ion channels.. - Answers They are voltage-gated ion channels. the alpha
subunits are responsible for the passive flow of ions. the beta subunits are responsible for assembly
delivery and regulation. 4 alpha domains/units with 6 transmembrane regions each. the fourth
transmembrane region in each domain is the voltage sensor. The pore region is between
transmembrane five and six (the ions pass through the pore).
Na+: pseudotetramer. K+: tetramer
What is a subthreshold stimulation? - Answers Is a subthreshold (below threshold) depolarization
that is graded (increases with increasing stimulus strength), non-regenerative potential that is
conducted with decrement (decays in amplitude over time and distance)
What is a threshold? - Answers It is a membrane potential that must be reached before an AP can be
generated. It is usually 15-20 mV higher/more positive than the RMP. (In neurons its about -55mV)
Describe the positive feedback loop of Na+ activation.. - Answers Once the threshold is reached a
positive feedback loop develops starting with a massive increase in gNa+ due to the increase in Vm
from being above the threshold that leads to the rapid Na+ entry that is followed by more
depolarization of the membrane which in turn will activate even more Na+ channels.
What causes the rapid upstroke and the rapid downstroke of AP? - Answers The rapid upstroke is
produced by Na+ activation and the downstroke is produces by Na+ inactivation and the increase in
gK+ due to potassiums large driving force
What is the inactivation loop of the voltage gated Na+ channel? - Answers The inactivation point is
the loop between the 6th transmem of the 3rd unit and 1st transmem of the 4th unit (it acts as the
gate swings close to inactive the channel).
-is what causes closing of Na+ channels to initiate downstroke
Describe the chemical and electrical potentials of K+ and Na+ at the peak of AP.. - Answers Na+:
electrical and chemical potentials are opposite each other (chemical pushes in while electrical pushes
out-due to reverse of mem pot)
K+: both electrical and chemical potentials drive K+ out of the cell (Chemical push out and electrical
push out). K+ also has a very large driving force at peak
Describe the absolute refractory period of an AP.. - Answers Parallels the time course for Na+
activation and inactivation, it lasts about 1 msec in an axon, and no AP can be produced non matter
how strong the stimulus is
Occurs when Na+ channels are closed so no AP can be generated
Describe the relative refractory period of an AP.. - Answers Parallels the time course for changes in
gK+, it lasts about 3-4 msec in an axon, and a second AP can be generated if there is a suprathreshold
stimulus
Occurs when K+ is leaving cell so hyperpolarized but Na+ channels open so AP can be generated
What do Na+ channel blockers do? - Answers They stop the generation of AP's by preventing Na+
entry into the cell. (if you block communication (AP's) between neurons you also block sensation).
Used as local anesthetic (lidocaine, tetracaine) and for dental procedures (novocaine)
Describe local anesthetics.. - Answers Derived from cocaine but lack the addictive properties. They
block the Na+ channel from the outside of the membrane and prevent Na+ entry during
depolarizations above threshold. Thus they block the generation of AP's in sensory neurons that send
pain signals to the brain. However they can block the generation of AP's in all neurons (both sensory
and motor) which high dosages. They act on unmyelinated axons (typically sensory) first and with high
enough dosages will also act on myelinated (typically motor).
What is tetrodoxin? - Answers TTX, poison from the Japanese puffer fish that is eaten raw or cooked
What is saxitoxin? - Answers STX, poison from the marine bacteria (dinoflagellate= red tide) that are
eaten by shellfish, the toxin is resistant to cooking so you become ill if you eat contaminated shellfish.
What is the mechanism, symptoms, and treatments for poisons? - Answers They bock Na+ channels
from outside to prevent the generation of AP's in neurons and skeletal muscle cells. The Na+ channel
in the heart have a one amino acid sequence change in the pore region that prevents these toxins
from blocking AP's in this organ.
Symptoms: tingling of lips and tongue, nausea, vomiting, muscle cramps, muscle weakness and
paralysis.
Treatment: Gastric lavage and emetics if detected early enough, mechanical ventilation until the body
metabolizes the toxin.
What does the nernst equation measure? - Answers The electrochemical difference of an ion across a
membrane
Ex = (61.5 mV)/Zx log ([Xo]/[Xi])
Describe chemical and electrical potential.. - Answers The chemical difference has to do with the
intercellular and extracellular concentrations of the ion. The ion will want to move from high to low.
The electrical difference has to do with the charge of the ion. The inside of the cell is negatively
charged and the outside of the cell is positively charged. The ion will want to move toward the side
opposite its own charge.
Describe the chemical and electrical potentials of glucose.. - Answers It chemical gradient flows from
outside to inside.
It has no electrical potential because glucose has no charge.
Describe the chemical and electrical potentials of sodium.. - Answers Sodiums concentration on the
outside is 12X higher than the inside, therefore its chemical gradient moves from outside to inside.
Sodium has a positive charge and therefore its electrical gradient flows from outside to inside.
Describe the chemical and electrical potentials of potassium.. - Answers Potassiums concentration on
the inside it 30X higher then on the outside, therefore its chemical gradient flows from the inside to
the outside.
Potassium has a positive charge and therefore its electrical gradient flows from outside to inside.
Describe the chemical and electrical potentials of chloride ion.. - Answers Chlorides concentration on
the outside is 3X higher than on the inside, therefore its chemical gradient flows from the outside to
the inside.
Chloride has a negative charge and therefore its electrical gradient flows from the inside to outside.
What is the nernst equilibrium potential of an ion? - Answers The Vm at which there is no net
movement of the ion
What are the nernst equilibriums of Na+, K+, Cl-? - Answers Na+ ~+65, K+ ~-90, Cl- ~-33
What is hypokalemia? - Answers A decrease in EK+ which hyperpolarizes the membrane making it
more difficult for a heart cell to produce an action potential resulting in cardiac arrhythmia and arrest.
Caused by diuretics.
What is hyperkalemia? - Answers An increase in EK+ which depolarizes the membrane and makes it
easier for a heart cell to generate action potentials resulting in cardiac arrythmia and arrest. Caused
by kidney failure.
How is lethal injection done? - Answers A rapid infusion of a high concentration of KCl resulting in
hyperkalemia.
What is resting membrane potential (RMP)? - Answers A Vm where there is no net movement of all
ions across the membrane. It is a weighted sum EK+ (80%), ENa+(15%), ECl-(5%) based on
contributions of a conductance in the total conductance.
Is -70 mV for a neuron, -10 mV for RBC, and -90 mV for skeletal and cardiac muscle
Chord Conductance Equation - Answers -Sums up Nernst Potential for all important ions
- and adjust for relative permeability for each ion
What does RMP depend on? - Answers -Concentration of ions inside and outside the cell
-Relative permeability of the cell membrane to the different ions
-It is primarily determined by K+ because the membrane is most permeable to it
What is the driving force of an ion? - Answers It is the reason each ion moves. It is the difference
between the Vm and their E (nernst equilibrium potential). The farther the Vm is from their E the
greater its driving force.
What is depolarization? - Answers increase in Vm from RMP (closer to ENa+)
What is hyperoplarization? - Answers Decrease in Vm from RMP (closer to EK+)
What is repolarization? - Answers Return back to RMP after being depolarized
The Vm can fluctuate between what two limits? - Answers EK+<Vm<ENa+
What percentage of K+ ions must diffuse out of the cell to establish RMP? - Answers 0.002%
What is the Na+, K+ ATPase responsible for - Answers the uneven ion concentrations of Na+ and K+
pumps 3 Na+ out for every 2 K+ in --> net negative charge inside cell
What do voltage gated ion channels respond to? - Answers Changes in Vm
, What to ligand gated ion channels respond to? - Answers Whether or not a ligand (neurotransmitter)
is present
Describe the Na+ and K+ ion channels.. - Answers They are voltage-gated ion channels. the alpha
subunits are responsible for the passive flow of ions. the beta subunits are responsible for assembly
delivery and regulation. 4 alpha domains/units with 6 transmembrane regions each. the fourth
transmembrane region in each domain is the voltage sensor. The pore region is between
transmembrane five and six (the ions pass through the pore).
Na+: pseudotetramer. K+: tetramer
What is a subthreshold stimulation? - Answers Is a subthreshold (below threshold) depolarization
that is graded (increases with increasing stimulus strength), non-regenerative potential that is
conducted with decrement (decays in amplitude over time and distance)
What is a threshold? - Answers It is a membrane potential that must be reached before an AP can be
generated. It is usually 15-20 mV higher/more positive than the RMP. (In neurons its about -55mV)
Describe the positive feedback loop of Na+ activation.. - Answers Once the threshold is reached a
positive feedback loop develops starting with a massive increase in gNa+ due to the increase in Vm
from being above the threshold that leads to the rapid Na+ entry that is followed by more
depolarization of the membrane which in turn will activate even more Na+ channels.
What causes the rapid upstroke and the rapid downstroke of AP? - Answers The rapid upstroke is
produced by Na+ activation and the downstroke is produces by Na+ inactivation and the increase in
gK+ due to potassiums large driving force
What is the inactivation loop of the voltage gated Na+ channel? - Answers The inactivation point is
the loop between the 6th transmem of the 3rd unit and 1st transmem of the 4th unit (it acts as the
gate swings close to inactive the channel).
-is what causes closing of Na+ channels to initiate downstroke
Describe the chemical and electrical potentials of K+ and Na+ at the peak of AP.. - Answers Na+:
electrical and chemical potentials are opposite each other (chemical pushes in while electrical pushes
out-due to reverse of mem pot)
K+: both electrical and chemical potentials drive K+ out of the cell (Chemical push out and electrical
push out). K+ also has a very large driving force at peak
Describe the absolute refractory period of an AP.. - Answers Parallels the time course for Na+
activation and inactivation, it lasts about 1 msec in an axon, and no AP can be produced non matter
how strong the stimulus is
Occurs when Na+ channels are closed so no AP can be generated
Describe the relative refractory period of an AP.. - Answers Parallels the time course for changes in
gK+, it lasts about 3-4 msec in an axon, and a second AP can be generated if there is a suprathreshold
stimulus
Occurs when K+ is leaving cell so hyperpolarized but Na+ channels open so AP can be generated
What do Na+ channel blockers do? - Answers They stop the generation of AP's by preventing Na+
entry into the cell. (if you block communication (AP's) between neurons you also block sensation).
Used as local anesthetic (lidocaine, tetracaine) and for dental procedures (novocaine)
Describe local anesthetics.. - Answers Derived from cocaine but lack the addictive properties. They
block the Na+ channel from the outside of the membrane and prevent Na+ entry during
depolarizations above threshold. Thus they block the generation of AP's in sensory neurons that send
pain signals to the brain. However they can block the generation of AP's in all neurons (both sensory
and motor) which high dosages. They act on unmyelinated axons (typically sensory) first and with high
enough dosages will also act on myelinated (typically motor).
What is tetrodoxin? - Answers TTX, poison from the Japanese puffer fish that is eaten raw or cooked
What is saxitoxin? - Answers STX, poison from the marine bacteria (dinoflagellate= red tide) that are
eaten by shellfish, the toxin is resistant to cooking so you become ill if you eat contaminated shellfish.
What is the mechanism, symptoms, and treatments for poisons? - Answers They bock Na+ channels
from outside to prevent the generation of AP's in neurons and skeletal muscle cells. The Na+ channel
in the heart have a one amino acid sequence change in the pore region that prevents these toxins
from blocking AP's in this organ.
Symptoms: tingling of lips and tongue, nausea, vomiting, muscle cramps, muscle weakness and
paralysis.
Treatment: Gastric lavage and emetics if detected early enough, mechanical ventilation until the body
metabolizes the toxin.
