Section 43.2.2 (Exam 4) APs Flashcards
Neurons Generate and Transmit Electric Signals
What are action potentials (APs)?
sudden, large, temporary (transient) changes in membrane potential, generated by the action of voltage-gated Na+ channels
Are the voltage-gated channels open or closed at resting potential?
closed
What causes the voltage-gated Na+ channels to open?
Slight depolarization
The slight depolarization is called a graded potential. How does it spread, and where does it spread to from the soma?
The graded potential spreads via local current flow to the axon hillock.
What is special about the axon hillock?
A high concentration of voltage-gated Na+ channels.
What would happen if the voltage-gated Na+ channels were opened?
Depolarization, since positively charged Na+ ions would enter the neuron and make the resting potential go from a -70 mV closer to 0 mV
What is the threshold for an action potential?
5 to 10 mV greater than resting potential (closer to 0, since negative)
What occurs when the membrane potential threshold is reached?
A large number of Na+ channels suddenly open, depolarization occurs, and an action potential is generated
When does the axon return to resting potential? How do the Na+ ions return to the outside of the neuron after the sudden influx?
As voltage-gated Na+ channels close and voltage-gated K+ channels open the resting potential is restored
The sodium-potassium pump sends 3 Na+ out of the cell and 2 K+ into the cell
Describe the two gates of voltage-gated Na+ channels.
Activation gate—closed at rest but opens quickly at threshold
Inactivation gate—open at rest and closes at threshold; reopens 1–2 milliseconds later than the activation gate closes
What contributes to the refractory period of neurons?
Voltage-gated Na+ channel inactivation gates being closed for 1-2 milliseconds after the activation gate closes
Voltage-gated K+ channels remain open for a little too long, causing hyperpolarization
The neuron is unable to trigger an action potential until it returns to resting potential
What are the two features of APs that allow them to travel over long distances with no loss of signal?
It is an all-or-none event—positive feedback to voltage-gated Na+ channels ensures the maximum action potential.
An action potential is self-regenerating it spreads to adjacent membrane regions. It can’t reverse direction because of the refractory period of channels behind it.
What are the two factors that affect the speed of an action potential in different axons?
The larger the diameter of an axon leads to faster conduction
If an axon is myelinated then the action potential will travel faster
What are Nodes of Ranvier?
regularly spaced gaps in the myelin along an axon
nodes are the only places in myelinated axons with voltage-gated ion channels
Define saltatory conduction.
A form of propagation where action potentials appear to jump from node to node
