Chapter 4: The Action Potential

Question 1

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.

Answer 1

Rising Phase

Question 2

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

Answer 2

Overshoot

Question 3

Caused by the inactivation of the voltage-gated sodium channels and the opening of the voltage-gated potassium channels.

Answer 3

Falling Shoot

Question 4

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.

Answer 4

Undershoot

Question 5

an inhibitory mechanism that limits neuronal activity by promoting firing frequency adaptation and termination of the AP burst

Answer 5

After-Hyperpolarization

Question 6

the value of the membrane potential which, if reached, leads to the all-or-nothing initiation of an action potential.

Answer 6

Threshold

Question 7

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

Answer 7

Absolute Refractory Period

Question 8

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.

Answer 8

Relative Refractory Period

Question 9

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.

Answer 9

Optogenetics

Question 10

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

Answer 10

Voltage Clamp

Question 11

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.

Answer 11

Voltage-Gated Sodium Channel

Question 12

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)

Answer 12

Patch Clamp

Question 13

Interferes with the transmission of signals from nerves to muscles by blocking sodium channels.

Answer 13

Tetrodotoxin (TTX)

Question 14

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.

Answer 14

Voltage-gated Potassium
Channel

Question 15

corresponds to the site where action potentials are initiated; axon hillock

Answer 15

Spike-initiation zone

Question 16

Conveys information over distances without a loss of signal; regenerative; AKA nerve impulse/spikes

Answer 16

Action Potential

Question 17

describes how nerve cells either fire at full strength or do not; ALWAYS THE SAME SIZE!

Answer 17

All-or-nothing response

Question 18

reflects the magnitude
of the depolarizing
current

Answer 18

Firing frequency

Question 19

Used voltage clamp to measure
sodium and potassium currents at
different membrane voltages; Constructed a mathematical
model of action potential

Answer 19

Hodgkin and Huxley

Question 20

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.

Answer 20

Tetraethylammonium
(TEA)

Question 21

How are voltage gated sodium and potassium channels opened?

Answer 21

Activated (opened) by
depolarization above threshold
(g Na and g K)

Question 22

How are voltage gated sodium channels closed?

Answer 22

Inactivated (closed) when the
membrane sits at a positive
potential (g Na)

Question 23

How are voltage gated sodium channels deactivated?

Answer 23

de-inactivated when membrane
potential returns to RMP

Question 24

Rising phase is the activation of __________ conductance (early inward current)

Answer 24

sodium

Question 25

Falling phase is the activation of __________ conductance (delayed outward current)

Answer 25

potassium

Question 26

Fast activation in response
to depolarization
* Equilibrium potential:
~+55mV
* Inactivation

Answer 26

Voltage gated sodium channels

Question 27

• Slow activation in
  response to depolarization
• Delayed rectifier
• serves to reset
  membrane potential
• Equilibrium potential: -80mV
• No inactivation
• “Slow to open, slow to
  close”

Answer 27

Voltage gated potassium channels

Question 28

Membrane depolarization rapidly activates a ____________ feedback cycle fueled by the voltage dependent activation of Na + conductance

Answer 28

positive

Question 29

comes second; the slower activation of a _____________ feedback loop as depolarization activates a K + conductance

Answer 29

negative

Question 30

What does it means by an action potential is regenerative?

Answer 30

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.

Question 31

Increases membrane resistance; a very efficient insulator that allows almost no current to pass (will not leak out)

Answer 31

Myelin sheath

Question 32

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.

Answer 32

Saltatory Conduction

Question 33

In myelinated axons, regeneration
of action potential occurs only at the __________________.

Answer 33

Nodes of Ranvier

Question 34

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.

Answer 34

Channelopathy