SOLUTION FOR PRINCIPLES OF NEUROBIOLOGY
What is current? - CORRECT ANSWER✅✅✅Current is the movement of charge (or ions).
Quantitatively, it is the RATE at which charge moves (change in charge/change in time). In the
physical systems, a current is the NET MOVEMENT of ions across the cell membrane. By
convention, current represents the movement of POSITIVE CHARGE
What are the conditions for getting charge to flow across a membrane? - CORRECT
ANSWER✅✅✅1. IONS
2. CHANNELS
3. DRIVING FORCE (electrical or chemical gradient)
What are five important properties of ion channels? - CORRECT ANSWER✅✅✅1.
SELECTIVITY
2. GATED: have an open and closed state regulated by voltage, ligand binding, or mechanical
changes
3. MEMBRANE-SPANNING: many trans-membrane domains
4. ALLOW RAPID ION MOVEMENT
5. MODULATED: many channel's function can be modified by auxiliary subunits, G proteins,
neuromodulators, etc.
Who are Hodgkin and Huxley? - CORRECT ANSWER✅✅✅They discovered the basic
cellular mechanism of action potentials (AP) in their study of squid giant axons. Posited it as the
differential opening and closing of ION CHANNELS. They used a VOLTAGE CLAMP and
measured the currents, and via this predicted the existence of ion channels that open and close
with voltage, and are selective for different types of ions
Who are Neher and Sakmann and what laboratory method did they discover? - CORRECT
ANSWER✅✅✅PATCH-CLAMP TECHNIQUE. The pipette tip is placed against the
membrane of a cell, and SUCTION is applied to create a tight seal. It is used to study the
properties of a small patch of membrane. In the patch-clamp, you can control the CURRENT or
the VOLTAGE of the cell you are recording from. Use hollow glass capillary tube, which can be
filled with any solution. The resulting electrial current can be measured with an ultrasensitive
electronic amplifier
,What is the cell-attached patch clamp recording method? - CORRECT
ANSWER✅✅✅Pipette forms tight seal with membrane. All the ions that flow when a single
ion channel opens must flow into the pipette; the resulting electrical current, though small, can
be measured with an ultra-sensitive electronic amplifier connected to the pipette. Record of
current flowing through single ion channel reveals when the channel is in an open v. closed state.
What is the difference between microscopic currents and macroscopic currents? - CORRECT
ANSWER✅✅✅The currents flowing through a SINGLE CHANNEL are called microscopic
currents to distinguish them from macroscopic currents flowing through a large number of
channels distributed over a much more extensive region of surface membrane. Macroscopic
currents are WHOLE-CELL CURRENTS and are composed of single channel currents.
What is the whole-cell recording method of the patch-clamp technique? - CORRECT
ANSWER✅✅✅If the membrane patch within the pipette is disrupted by briefly applying
STRONG SUCTION, the interior of the pipette becomes continuous with the cell cytoplasm; this
arrangement allows the measurements of electrical potentials and currents from the ENTIRE
CELL
What is the INSIDE-OUT recording method of the patch-clamp technique? - CORRECT
ANSWER✅✅✅Retracting a pipette that is in the cell-attached configuration causes a small
vesicle of membrane to remain attached to the pipette, with its (former) intracellular surface
exposed. This INSIDE-OUT patch recording configuration allows the measurement of single-
channel currents with the ADDED benefit of making it possible to change the medium to which
the intracellular surface of the membrane is exposed.
What is the outside-out recording method of the patch-clamp technique? - CORRECT
ANSWER✅✅✅After the whole cell configuration is formed, the electrode is slowly
withdrawn from the cell and patches of membrane rip from the cell and anneal together; this
means the fluid in the pipette will be simulating the intracellular fluid. Allows researches to
examine properties of a channel when it is exposed to different extracellular fluids, and how the
channel will react in the presence of an extracellular neurotransmitter or other drug (extracellular
signals)
What is a CURRENT CLAMP? - CORRECT ANSWER✅✅✅Control the CURRENT
injected, and measure the VOLTAGE. In current clamp mode, the membrane potential is free to
,vary, and the amplifier records whatever voltage the cell generates on its own from the current
stimulation.
What is a VOLTAGE CLAMP? - CORRECT ANSWER✅✅✅Control the VOLTAGE,
measure the CURRENT. This makes it possible to measure how much ionic current crosses a
cell's membrane at any given voltage.
How does the voltage clamp work? - CORRECT ANSWER✅✅✅In order to keep the
voltage at a given value, the circuit will continually inject current through an amplifier to
maintain the desired voltage in the cell. The current injected by the amplifier is EQUAL TO but
OPPOSITE in sign to the current that is flowing through the cell; indirectly allows you to
determine how much current is flowing through the channel. An amplifier compares the
command potential (voltage set point) with the measured membrane potential. When there is a
difference in these two values, current is injected until V command - V mem = 0.
What would the voltage clamp read if you DEPOLARIZED a cell with a regular non-voltage
gated potassium channel under the condition that [Kin]=[Kout]? Hyperpolarized? - CORRECT
ANSWER✅✅✅A depolarizing voltage to the cell will cause current to flow OUT (drawn as
UP) of the cell. Since LIKE CHARGES repel one another, more + charges will push K out of the
cell so the charges will equilibrate across the membrane. When a HYPERPOLARIZING (-)
charge is given to the cell, K ions will flow IN (down) to the cell across the membrane
What would happen if TWICE the voltage were injected? What would be affected and what
would remain the same? - CORRECT ANSWER✅✅✅The AMPLITUDE of the current will
reflect the increase in voltage. Would NOT affect how LONG or how OFTEN the channel itself
is open.
How can the current/voltage relationship be graphically represented? - CORRECT
ANSWER✅✅✅Can be plotted on an I/V plot where V (membrane potential) is on the X-
axis, and I (current) is on the Y-axis.
What happens in a voltage camp as K leaks IN or OUT of a cell? How do the intracellular and
extracellular concentrations of potassium vary? - CORRECT ANSWER✅✅✅As K leaks in
or out, a voltage gradient is created which the voltage clamp will either INJECT or
WITHDRAW current in order to maintain the desired voltage. Changes in the concentration of K
are SO SMALL that its safe to assume that the concentration of K does not change. It is possible
, to produce BIG CHANGES in voltage across the cell membrane with only SLIGHT CHANGES
in K concentrations inside and outside the cell
How is the I/V plot made? - CORRECT ANSWER✅✅✅Apply several voltages to the cell
and measure the resulting current amplitudes (pA). These are your data points (mV, pA), and
when they are plotted they will demonstrate a LINEAR or EXPONENTIAL relationship
What does it mean when there is a LINEAR relationship in the I/V plot? - CORRECT
ANSWER✅✅✅Linear relationships follow Ohm's Law (V=IR), and are referred to as
Ohmic.
What is Ohm's Law? How can it be rewritten? - CORRECT ANSWER✅✅✅Ohm's Law is
V=IR, which can be rewritten as i=gV, where i is a single channel's current and g is the single
channel conductance. In this equation, V does NOT correspond to the actual membrane potential,
rather it is the DRIVING FORCE, or the difference between the MEMBRANE POTENTIAL
and the EQUILIBRIUM POTENTIAL. Therefore i=(Vm-Eion)g.
What does the magnitude of the CURRENT depend upon according to Ohm's Law? -
CORRECT ANSWER✅✅✅The magnitude of the current depends upon
1. ion concentration gradient
2. membrane potential
3. Conductance
What is the SLOPE of the I/V curve? - CORRECT ANSWER✅✅✅CONDUCTANCE. The
higher the conductance the more steep the slope. the MORE IONS in solution, the higher the g,
and the steeper the slope
What is CONDUCTANCE (g)? - CORRECT ANSWER✅✅✅Conductance is a measure of
how many IONS the channel can pass, which is influenced by how EASILY the channel can
pass ions (PERMEABILITY), and how many IONS are available to pass (total number of
available ions); it can be thought of as how GOOD a channel is at letting current through.
Conductance is the INVERSE of resistance (g=1/R).
What is current? - CORRECT ANSWER✅✅✅Current is the movement of charge (or ions).
Quantitatively, it is the RATE at which charge moves (change in charge/change in time). In the
physical systems, a current is the NET MOVEMENT of ions across the cell membrane. By
convention, current represents the movement of POSITIVE CHARGE
What are the conditions for getting charge to flow across a membrane? - CORRECT
ANSWER✅✅✅1. IONS
2. CHANNELS
3. DRIVING FORCE (electrical or chemical gradient)
What are five important properties of ion channels? - CORRECT ANSWER✅✅✅1.
SELECTIVITY
2. GATED: have an open and closed state regulated by voltage, ligand binding, or mechanical
changes
3. MEMBRANE-SPANNING: many trans-membrane domains
4. ALLOW RAPID ION MOVEMENT
5. MODULATED: many channel's function can be modified by auxiliary subunits, G proteins,
neuromodulators, etc.
Who are Hodgkin and Huxley? - CORRECT ANSWER✅✅✅They discovered the basic
cellular mechanism of action potentials (AP) in their study of squid giant axons. Posited it as the
differential opening and closing of ION CHANNELS. They used a VOLTAGE CLAMP and
measured the currents, and via this predicted the existence of ion channels that open and close
with voltage, and are selective for different types of ions
Who are Neher and Sakmann and what laboratory method did they discover? - CORRECT
ANSWER✅✅✅PATCH-CLAMP TECHNIQUE. The pipette tip is placed against the
membrane of a cell, and SUCTION is applied to create a tight seal. It is used to study the
properties of a small patch of membrane. In the patch-clamp, you can control the CURRENT or
the VOLTAGE of the cell you are recording from. Use hollow glass capillary tube, which can be
filled with any solution. The resulting electrial current can be measured with an ultrasensitive
electronic amplifier
,What is the cell-attached patch clamp recording method? - CORRECT
ANSWER✅✅✅Pipette forms tight seal with membrane. All the ions that flow when a single
ion channel opens must flow into the pipette; the resulting electrical current, though small, can
be measured with an ultra-sensitive electronic amplifier connected to the pipette. Record of
current flowing through single ion channel reveals when the channel is in an open v. closed state.
What is the difference between microscopic currents and macroscopic currents? - CORRECT
ANSWER✅✅✅The currents flowing through a SINGLE CHANNEL are called microscopic
currents to distinguish them from macroscopic currents flowing through a large number of
channels distributed over a much more extensive region of surface membrane. Macroscopic
currents are WHOLE-CELL CURRENTS and are composed of single channel currents.
What is the whole-cell recording method of the patch-clamp technique? - CORRECT
ANSWER✅✅✅If the membrane patch within the pipette is disrupted by briefly applying
STRONG SUCTION, the interior of the pipette becomes continuous with the cell cytoplasm; this
arrangement allows the measurements of electrical potentials and currents from the ENTIRE
CELL
What is the INSIDE-OUT recording method of the patch-clamp technique? - CORRECT
ANSWER✅✅✅Retracting a pipette that is in the cell-attached configuration causes a small
vesicle of membrane to remain attached to the pipette, with its (former) intracellular surface
exposed. This INSIDE-OUT patch recording configuration allows the measurement of single-
channel currents with the ADDED benefit of making it possible to change the medium to which
the intracellular surface of the membrane is exposed.
What is the outside-out recording method of the patch-clamp technique? - CORRECT
ANSWER✅✅✅After the whole cell configuration is formed, the electrode is slowly
withdrawn from the cell and patches of membrane rip from the cell and anneal together; this
means the fluid in the pipette will be simulating the intracellular fluid. Allows researches to
examine properties of a channel when it is exposed to different extracellular fluids, and how the
channel will react in the presence of an extracellular neurotransmitter or other drug (extracellular
signals)
What is a CURRENT CLAMP? - CORRECT ANSWER✅✅✅Control the CURRENT
injected, and measure the VOLTAGE. In current clamp mode, the membrane potential is free to
,vary, and the amplifier records whatever voltage the cell generates on its own from the current
stimulation.
What is a VOLTAGE CLAMP? - CORRECT ANSWER✅✅✅Control the VOLTAGE,
measure the CURRENT. This makes it possible to measure how much ionic current crosses a
cell's membrane at any given voltage.
How does the voltage clamp work? - CORRECT ANSWER✅✅✅In order to keep the
voltage at a given value, the circuit will continually inject current through an amplifier to
maintain the desired voltage in the cell. The current injected by the amplifier is EQUAL TO but
OPPOSITE in sign to the current that is flowing through the cell; indirectly allows you to
determine how much current is flowing through the channel. An amplifier compares the
command potential (voltage set point) with the measured membrane potential. When there is a
difference in these two values, current is injected until V command - V mem = 0.
What would the voltage clamp read if you DEPOLARIZED a cell with a regular non-voltage
gated potassium channel under the condition that [Kin]=[Kout]? Hyperpolarized? - CORRECT
ANSWER✅✅✅A depolarizing voltage to the cell will cause current to flow OUT (drawn as
UP) of the cell. Since LIKE CHARGES repel one another, more + charges will push K out of the
cell so the charges will equilibrate across the membrane. When a HYPERPOLARIZING (-)
charge is given to the cell, K ions will flow IN (down) to the cell across the membrane
What would happen if TWICE the voltage were injected? What would be affected and what
would remain the same? - CORRECT ANSWER✅✅✅The AMPLITUDE of the current will
reflect the increase in voltage. Would NOT affect how LONG or how OFTEN the channel itself
is open.
How can the current/voltage relationship be graphically represented? - CORRECT
ANSWER✅✅✅Can be plotted on an I/V plot where V (membrane potential) is on the X-
axis, and I (current) is on the Y-axis.
What happens in a voltage camp as K leaks IN or OUT of a cell? How do the intracellular and
extracellular concentrations of potassium vary? - CORRECT ANSWER✅✅✅As K leaks in
or out, a voltage gradient is created which the voltage clamp will either INJECT or
WITHDRAW current in order to maintain the desired voltage. Changes in the concentration of K
are SO SMALL that its safe to assume that the concentration of K does not change. It is possible
, to produce BIG CHANGES in voltage across the cell membrane with only SLIGHT CHANGES
in K concentrations inside and outside the cell
How is the I/V plot made? - CORRECT ANSWER✅✅✅Apply several voltages to the cell
and measure the resulting current amplitudes (pA). These are your data points (mV, pA), and
when they are plotted they will demonstrate a LINEAR or EXPONENTIAL relationship
What does it mean when there is a LINEAR relationship in the I/V plot? - CORRECT
ANSWER✅✅✅Linear relationships follow Ohm's Law (V=IR), and are referred to as
Ohmic.
What is Ohm's Law? How can it be rewritten? - CORRECT ANSWER✅✅✅Ohm's Law is
V=IR, which can be rewritten as i=gV, where i is a single channel's current and g is the single
channel conductance. In this equation, V does NOT correspond to the actual membrane potential,
rather it is the DRIVING FORCE, or the difference between the MEMBRANE POTENTIAL
and the EQUILIBRIUM POTENTIAL. Therefore i=(Vm-Eion)g.
What does the magnitude of the CURRENT depend upon according to Ohm's Law? -
CORRECT ANSWER✅✅✅The magnitude of the current depends upon
1. ion concentration gradient
2. membrane potential
3. Conductance
What is the SLOPE of the I/V curve? - CORRECT ANSWER✅✅✅CONDUCTANCE. The
higher the conductance the more steep the slope. the MORE IONS in solution, the higher the g,
and the steeper the slope
What is CONDUCTANCE (g)? - CORRECT ANSWER✅✅✅Conductance is a measure of
how many IONS the channel can pass, which is influenced by how EASILY the channel can
pass ions (PERMEABILITY), and how many IONS are available to pass (total number of
available ions); it can be thought of as how GOOD a channel is at letting current through.
Conductance is the INVERSE of resistance (g=1/R).
