8/11/25, 4:59 PM Actual exam for NBME Physiology 2025 update | comprehensive questions and verified answers (complete solutions) GRADE A+!! …
Actual exam for NBME Physiology 2025 update |
comprehensive questions and verified answers (complete
solutions) GRADE A+!
Reflection coefficient A number between zero and 1 that describes the ease
with which a solute permeates a membrane?
Rf= 1 means the solute is
IMPERMEABLE (100%
reflection)
Rf= 0 means the solute is
COMPLETELY PERMEABLE
Rf= 1 reflection coefficient of serum albumin? (a large solute)
Rf=0 Reflection coefficient of urea? (a small solute)
Small Cations A small ion channel lined with negatively charged groups will be
selective for?
*will exclude large molecules
and anions
Equilibrium potential Refers to the potential difference that would exactly
balance (oppose) the tendency for diffusion down a
*At electrochemical concentration gradient?
equilibrium, the chemical
and electrical driving forces
that act on an ion are equal
and opposite*, and no more
net diffusion of the ion
occurs.
g… 1/50
,8/11/25, 4:59 PM Actual exam for NBME Physiology 2025 update | comprehensive questions and verified answers (complete solutions) GRADE A+!! …
Approximate equilibrium potentials in
E Na=
nerve and muscle? E Na= ?
+65 mV E
E
Ca= +120
Ca=
mV E K=
?E
-85 mV
K=
E Cl= -85 mV
?
E Cl= ?
Depolarization (cell interior _ ___ makes the membrane potential less negative
becomes less negative)
_ __ makes the membrane potential more negative
Repolarization (cell interior
becomes more negative
Inward current Refers to the flow of positive charge into the cell?
**depolarizes the cell (current)
outward current Refers to the flow of positive charge out of the cell?
**hyperpolarizes the cell (current)
NO: Action potentials are all Are action potentials different sizes dependent on different
or nothing magnitudes of stimuli?
Threshold The membrane potential at which an action potential is
inevitable?
-70 mV Normal resting membrane potential?
**A result of the high resting
conductance to K+ which
drives the membrane
potential toward the K+
equilibrium potential (-85
mV)
g… 2/50
,8/11/25, 4:59 PM Actual exam for NBME Physiology 2025 update | comprehensive questions and verified answers (complete solutions) GRADE A+!! …
1. Inward current What causes the upstroke of the action potential?
depolarizes the
membrane potential
to threshold
2. Depolarization causes
opening of Na channels
3. Rapid depolarization
occurs due to the increased
conductance of Na (inward
Na Current)
**brief period where
membrane potential is
positive
Repolarization is caused by an What causes repolarization of the action potential?
OUTWARD
K+ current
Tetrodotoxin (TTX) Two drugs that block voltage gated Na channels, abolishing
action potentials?
Lidocaine
Tetraethylammonium (TEA) Drug that blocks voltage gated K+ channels?
Absolute refractory period Period where another action potential cannot be elicited?
(explanation:
Na+ channels remain closed
until repolarization occurs)
Relative refractory period period that begins at the end of the absolute
refractory period and ends when the membrane
**action potential can be potential returns to resting levels?
elicited during this period,
but only if a larger than
usual inward current is
provided.
1. INCREASED fiber size: What two things increase conduction velocity in nerves?
increased
diameter= decreased internal
resistance= increased
conduction velocity
g… 3/50
, 8/11/25, 4:59 PM Actual exam for NBME Physiology 2025 update | comprehensive questions and verified answers (complete solutions) GRADE A+!! …
2. myelination: allows
for saltitiory
conduction at nodes
of Ranvier.
1. Action potential in How do action potentials allow for neuromuscular/
presynaptic cell synaptic transmission (using NTs)?
depolarizes the
presynaptic terminal
2. Ca++ enters the
presynaptic terminal
causing release of NT into
the synaptic cleft
3. NT diffuses and combines
w/ receptors on the post-
synaptic membrane
Hyperpolarize Inhibitory NTs __ the postsynaptic membrane
Depolarize Excitatory NTs _ the postsynaptic membrane
Acetylcholine (ACh) NT released from the presynaptic terminal at the neuromuscular
junction?
**Postsynaptic membrane
contains a nicotinic receptor
(Na/K ligand-gated
channel)
Acetyl-CoA and choline Acetylcholine is generated from _________ and _.
Choline acetyltransferase Enzyme that catalyzes this reaction?
**ACh is stored in synaptic
vesicles for later release
Ca++ _ __ Uptake causes release of Ach into the synaptic cleft?
**Synaptic vesicles fuse with
plasma
membrane and empty their
g… 4/50
Actual exam for NBME Physiology 2025 update |
comprehensive questions and verified answers (complete
solutions) GRADE A+!
Reflection coefficient A number between zero and 1 that describes the ease
with which a solute permeates a membrane?
Rf= 1 means the solute is
IMPERMEABLE (100%
reflection)
Rf= 0 means the solute is
COMPLETELY PERMEABLE
Rf= 1 reflection coefficient of serum albumin? (a large solute)
Rf=0 Reflection coefficient of urea? (a small solute)
Small Cations A small ion channel lined with negatively charged groups will be
selective for?
*will exclude large molecules
and anions
Equilibrium potential Refers to the potential difference that would exactly
balance (oppose) the tendency for diffusion down a
*At electrochemical concentration gradient?
equilibrium, the chemical
and electrical driving forces
that act on an ion are equal
and opposite*, and no more
net diffusion of the ion
occurs.
g… 1/50
,8/11/25, 4:59 PM Actual exam for NBME Physiology 2025 update | comprehensive questions and verified answers (complete solutions) GRADE A+!! …
Approximate equilibrium potentials in
E Na=
nerve and muscle? E Na= ?
+65 mV E
E
Ca= +120
Ca=
mV E K=
?E
-85 mV
K=
E Cl= -85 mV
?
E Cl= ?
Depolarization (cell interior _ ___ makes the membrane potential less negative
becomes less negative)
_ __ makes the membrane potential more negative
Repolarization (cell interior
becomes more negative
Inward current Refers to the flow of positive charge into the cell?
**depolarizes the cell (current)
outward current Refers to the flow of positive charge out of the cell?
**hyperpolarizes the cell (current)
NO: Action potentials are all Are action potentials different sizes dependent on different
or nothing magnitudes of stimuli?
Threshold The membrane potential at which an action potential is
inevitable?
-70 mV Normal resting membrane potential?
**A result of the high resting
conductance to K+ which
drives the membrane
potential toward the K+
equilibrium potential (-85
mV)
g… 2/50
,8/11/25, 4:59 PM Actual exam for NBME Physiology 2025 update | comprehensive questions and verified answers (complete solutions) GRADE A+!! …
1. Inward current What causes the upstroke of the action potential?
depolarizes the
membrane potential
to threshold
2. Depolarization causes
opening of Na channels
3. Rapid depolarization
occurs due to the increased
conductance of Na (inward
Na Current)
**brief period where
membrane potential is
positive
Repolarization is caused by an What causes repolarization of the action potential?
OUTWARD
K+ current
Tetrodotoxin (TTX) Two drugs that block voltage gated Na channels, abolishing
action potentials?
Lidocaine
Tetraethylammonium (TEA) Drug that blocks voltage gated K+ channels?
Absolute refractory period Period where another action potential cannot be elicited?
(explanation:
Na+ channels remain closed
until repolarization occurs)
Relative refractory period period that begins at the end of the absolute
refractory period and ends when the membrane
**action potential can be potential returns to resting levels?
elicited during this period,
but only if a larger than
usual inward current is
provided.
1. INCREASED fiber size: What two things increase conduction velocity in nerves?
increased
diameter= decreased internal
resistance= increased
conduction velocity
g… 3/50
, 8/11/25, 4:59 PM Actual exam for NBME Physiology 2025 update | comprehensive questions and verified answers (complete solutions) GRADE A+!! …
2. myelination: allows
for saltitiory
conduction at nodes
of Ranvier.
1. Action potential in How do action potentials allow for neuromuscular/
presynaptic cell synaptic transmission (using NTs)?
depolarizes the
presynaptic terminal
2. Ca++ enters the
presynaptic terminal
causing release of NT into
the synaptic cleft
3. NT diffuses and combines
w/ receptors on the post-
synaptic membrane
Hyperpolarize Inhibitory NTs __ the postsynaptic membrane
Depolarize Excitatory NTs _ the postsynaptic membrane
Acetylcholine (ACh) NT released from the presynaptic terminal at the neuromuscular
junction?
**Postsynaptic membrane
contains a nicotinic receptor
(Na/K ligand-gated
channel)
Acetyl-CoA and choline Acetylcholine is generated from _________ and _.
Choline acetyltransferase Enzyme that catalyzes this reaction?
**ACh is stored in synaptic
vesicles for later release
Ca++ _ __ Uptake causes release of Ach into the synaptic cleft?
**Synaptic vesicles fuse with
plasma
membrane and empty their
g… 4/50
