Chapter 4: The Action Potential Flashcards
Is caused by the opening of voltage-gated sodium channels? These ion channels are activated once the cell’s membrane potential reaches threshold and open immediately. The electrochemical gradients drive sodium into the cell causing the depolarization.
Rising Phase
The peak of the action potential where the membrane potential is positive. During depolarization, the inside of the cell becomes more and more electropositive, until the potential gets closer the electrochemical equilibrium for sodium of +61 mV
Overshoot
Caused by the inactivation of the voltage-gated sodium channels and the opening of the voltage-gated potassium channels.
Falling Shoot
The voltage-gated potassium channels stay open a little longer than needed to bring the membrane back to its resting potential; the membrane potential briefly dips lower (more negative) than its resting potential.
Undershoot
an inhibitory mechanism that limits neuronal activity by promoting firing frequency adaptation and termination of the AP burst
After-Hyperpolarization
the value of the membrane potential which, if reached, leads to the all-or-nothing initiation of an action potential.
Threshold
a period of time when the neuron is not able to send additional action potentials. It is caused by the voltage gated sodium channels shutting and not opening for a short period of time.
Na+ channels are inactivated until
membrane goes negative enough to de-
inactivate channels
Absolute Refractory Period
the interval of time during which a second action potential can be initiated, but initiation will require a greater stimulus than before. These periods are caused by the inactivation gate of the Na+ channel. Membrane stays
hyperpolarized until K+ channels close.
Relative Refractory Period
A technique in neuroscience in which genes for light-sensitive proteins are introduced into specific types of brain cells in order to monitor and control their activity precisely using light signals.
Optogenetics
Will iteratively measure the membrane potential, and then change the membrane potential (voltage) to a desired value by adding the necessary current. This “clamps” the cell membrane at a desired constant voltage, allowing the clamp to record what currents are delivered.
* If we know the components of the ionic current (K+
and Na+), we can isolate them individually
* Indicates how membrane potential influences ionic
current flow across the membrane
Voltage Clamp
The basic ion channels for neuronal excitability; much more selective for
Na+ (12x)
Voltage sensor s4:
opens in response to change in Vm. A stimulus that causes sufficient depolarization promptly causes these channels to open, allowing a small amount of Na+ to enter the cell down its electrochemical gradient.
Voltage-Gated Sodium Channel
Allowed the measurement
of currents through single ion channels;
Allowed in-depth study of ion (e.g., voltage-gated) channels.
1. Open without delay when a critical level of
Vm depolarization is reached
2. Stay open for ~1ms then close (inactivate)
3. Cannot be opened again until membrane
repolarizes near RMP (de-inactivate)
Patch Clamp
Interferes with the transmission of signals from nerves to muscles by blocking sodium channels.
Tetrodotoxin (TTX)
Are transmembrane channels responsible for returning the depolarized cell to a resting state after each nerve impulse. They are, therefore, important in modulating neuronal excitability in the CNS and peripheral nervous system; Depolarization also opens these channels, allowing K+ efflux, which, together with rapid Na+ channel inactivation, quickly repolarizes the membrane during the falling phase of the action potential.
Voltage-gated Potassium
Channel
corresponds to the site where action potentials are initiated; axon hillock
Spike-initiation zone
Conveys information over distances without a loss of signal; regenerative; AKA nerve impulse/spikes
Action Potential
describes how nerve cells either fire at full strength or do not; ALWAYS THE SAME SIZE!
All-or-nothing response
reflects the magnitude
of the depolarizing
current
Firing frequency
Used voltage clamp to measure
sodium and potassium currents at
different membrane voltages; Constructed a mathematical
model of action potential
Hodgkin and Huxley
pharmacological research agent that blocks selective potassium channels; The molecule is thought to physically enter the pore and block the channel. In excitable cells, the primary result of this effect is a prolongation of action potential duration.
Tetraethylammonium
(TEA)
How are voltage gated sodium and potassium channels opened?
Activated (opened) by
depolarization above threshold
(g Na and g K)
How are voltage gated sodium channels closed?
Inactivated (closed) when the
membrane sits at a positive
potential (g Na)
How are voltage gated sodium channels deactivated?
de-inactivated when membrane
potential returns to RMP
Rising phase is the activation of __________ conductance (early inward current)
sodium
Falling phase is the activation of __________ conductance (delayed outward current)
potassium
Fast activation in response
to depolarization
* Equilibrium potential:
~+55mV
* Inactivation
Voltage gated sodium channels
- Slow activation in
response to depolarization - Delayed rectifier
- serves to reset
membrane potential - Equilibrium potential: -80mV
- No inactivation
- “Slow to open, slow to
close”
Voltage gated potassium channels
Membrane depolarization rapidly activates a ____________ feedback cycle fueled by the voltage dependent activation of Na + conductance
positive
comes second; the slower activation of a _____________ feedback loop as depolarization activates a K + conductance
negative
What does it means by an action potential is regenerative?
An action potential is a depolarization of a neural cell membrane caused by some stimulus. The structure of an action potential roughly is a stimulus that triggers a depolarization, followed by repolarization back to baseline cell membrane resting potential. The characteristics of an action potential include that they are regenerative, “all or nothing,” self-limiting, unidirectional, and refractory.
Increases membrane resistance; a very efficient insulator that allows almost no current to pass (will not leak out)
Myelin sheath
Describes the way an electrical impulse skips from node to node down the full length of an axon, speeding the arrival of the impulse at the nerve terminal in comparison with the slower continuous progression of depolarization spreading down an unmyelinated axon.
Saltatory Conduction
In myelinated axons, regeneration
of action potential occurs only at the __________________.
Nodes of Ranvier
diseases that develop because of defects in ion channels caused by either genetic or acquired factors; Mutations in genes encoding ion channels, which impair channel function, are the most common cause.
Channelopathy
