Ion channels and action potential Flashcards
Always open and allow ___ to passively diffuse down concentration gradient (out of cell)
K+ Leak channels
Always open and allow ___ nto passively diffuse down concentration gradient (into cell )
Na+ leak channels
open when threshold is reached and allows Na+ influx
Voltage Gated Na+ Channels
Open around peak of action potential and allow K+ efflux
delayed recitifier voltage gated K+ Channel
RMP (-70 mV)
K+ makes a bigger contribution to establishing the RMP than Na+
Depolarization
amount of Na+ entering cell is greater than the amount of K+ leaving cell through K+ leak channel, so nerve interior becomes increasingly positive and depolarizes
threshold
voltage the membrane potential must increase to in order for an action potential to occur
Peak
Membrane potential of nerve peaks near Nernst potential of Na+. Voltage gated Na+ channels close
and Delayed Rectifier Voltage Gated K+ Channel opens. Na+ stops flowing into cell and K+ starts
flowing out of cell through leak channels and Delayed Rectifier V-Gated K+ channel. Cell interior stops
becoming increasingly positive and instead starts to become negative as K+ leaves cell
Repolarization
Only channel open is Voltage Gated Delayed Rectifier K+ channels, so cell interior is
getting increasingly negative as amount of K+ flowing out > amount of Na+ flowing in
Undershoot
Delayed Rectifier K+ channels are slow to open and close, so membrane potential dips
slightly below RMP as K+ continues to flow out of cell as gate on Delayed Rectifier K+ channel slowly
closes (Results in hyperpolarization)
voltage clamping
technique that enables you to hold the membrane voltage of an excitable cell at a fixed voltage while you measure the current passing through the cell membrane
current =
Conductance * Voltage
if there is an inward and outward current, ions must be moving in and out of the ___
neuron
how do we know which parts of the current curves are due to the movement of Na+ or K+
TTX- toxin by puffer fish block Na+ channels
TEA : selectively blocks potassium channels
above the y axis corresponds to ____ ions leaving the cell
positive
Na+ channels open __ and open ___
first and quickly
K+ channels open ___ and ___
after and slowly
hold voltage constant and measure change in current
Voltage clamp
hold current constant and measure change in voltage
current clamp
same principle as voltage clamp but measures the current in a single channel at fixed voltage
patch clamp
depolarization
Depolarization, in biology, refers to a sudden change within a cell, during which the
cell undergoes a dramatic electrical change. Most cells, especially those that compose
the tissues of highly organized animals, typically maintain an internal environment
that is negatively charged compared to the cell’s surrounding environment. This difference in charge is called the cell’s membrane potential. In the process of depolarization,
the negative internal charge of the cell becomes positive for a very brief time. This shift
from a negative to a positive internal cellular environment allows for the transmission
of electrical impulses both within a cell and, in certain instances, between cells. This
communicative function of depolarization is essential to the function of many cells,
communication between cells, and the overall function of an organism.
open and close fast (slope is greater )
Voltage gated Na+ Channels
Time dependent because it has an inactivation gate
Voltage gated Na+ Channels
(Certain amount of time (and voltage) has to pass
before it will reopen after depolarizing - inactivation
period)
Voltage gated Na+ Channels
3 conformations: Open, closed-inactivated, and closed
Voltage gated Na+ Channels
Responsible for depolarization
Voltage gated Na+ Channels
Responsible for absolute refractory period
Voltage gated Na+ Channels
Allows for passage of Na+ into cell
Voltage gated Na+ Channels
Open and close slow (Why we call them “Delayed
Rectifier”)
Voltage Gated K+ Channels
Time independent (no inactivation period) because it does not have an inactivation gate
Voltage Gated K+ Channels
2 confirmations open, closed
Voltage Gated K+ Channels
responsible for repolarization
Voltage Gated K+ Channels
responsible for relative refractory period
Voltage Gated K+ Channels
allows for passage of K+ out of cell
Voltage Gated K+ Channels
___ channels can be target for local anesthetics lidocaine or drugs cocaine
Na
absolute refractory period
time period where another action potential cannot occur no matter how strong of a stimulus is applied
Na+ channels being in their close inactivated state
absolute refractory period
relative refractory period
another action potential can occur but the stimulus must be stronger than normal because the cell is hyperpolarized
“persistant activation” of the delayed recitifier V gated K+ channels
relative refractory period
factors that can affect threshold
number of K+ leak channels
local circuit
current that is produced during an action potential which triggers depolarization to spread to a nearby membrane
Refractory periods (Closed-inactivated state of V-Gated Na+ channels) prevent
backwards propagation of an action potential.
true
local potential
change in membrane potential due to an applied stimulus. The change in potential is
dependent on how strong the stimulus is
High Ca2+ levels results in decreased ____ because
excess calcium binds to the ____ This
causes the Na+ channels to have decreased excitability because the
positive charges seem to alter the ability of the channel to sense the
changes in voltage, which means a stronger ____ will be
needed for these Na+ channels to open to generate an action
potential
excitability
voltage sensor of Na+ channels. depolarization
Low Ca2+ levels results in _____ because the
voltage sensors are ___ shielded and perceive stimuli to be greater
than they actually are. Thus, a ____ than normal depolarization
will open the V-Gated Na+ channels and generate an action
potential
hyperexcitability
less shielded
a weaker
Nodes of Ranvier
points along an axon with no myelination. There
are also a lot of Na+ and K+ channels concentrated there, with a higher
density of Na+ channels than K+ channels. The high density of Na+
channels is what enables saltatory conduction (action potentials
bypassing a myelinated section of neuron and jumping from node to
node). K+ channels are more highly concentrated in the paranodal
axolemma (next to the node).
axon
long fiber-like structures responsible for sending signals in the
form of action potentials to adjacent cells
myelination
What influences conduction velocity in different neurons?
Two inherent properties of the neurons: (1) the space constant and (2) the time constant
space constant
distance an action potential can travel before it reaches 37% of its inital strength
What biologically increases the space constant (and thus increases conduction velocity)?
(1) Properties of phospholipids, number of leak channels, and presence of myelin→Increase
membrane resistance
(2) More layers of myelin → Increases axon diameter which decreases internal resistance
Time Constant is
is the amount of time required to charge and discharge the membrane. It is
calculated with the equation
Myelination increases the membrane resistance and decreases membrane
capacitance. It may look like the two changes cancel each other out since we are multiplying
them by each other, but the decrease in membrane capacitance outweighs the increase in
membrane resistance. So, myelination overall decreases the time constant, thereby increasing
conduction velocity.
T
1) INCREASING THE SPACE CONSTANT INCREASES
CONDUCTION VELOCITY
THE TIME CONSTANT INCREASES CONDUCTION VELOCITY
(2) DECREASING
myelin increases conduction velocity in 3 ways
increases membrane resistance (Rm)
Decreases internal resistance
decreases membrane capacitance
diseases of nervous system that involve pathologic loss of myelin
mulitple scelrosis and guillain barre syndrome
