Mastering Homework Questions And Notes: Action Potential

Axon hillock. this region (first part of the axon) receives local signals (graded potentials) from the soma and dendrites and has a high concentration of voltage-gated Na+ channels.

Voltage gated sodium channels. when the voltage-gated Na+ channels open, Na+ rushes into the cell causing depolarization.

the opening of voltage-gated K+ channels. as the voltage-gated K+ channels open, K+ rushes out of the cell, causing the membrane potential to become more negative on the inside, thus repolarizing the cell.

slow closing of voltage-gated K+ channels. the slow closing of the voltage-gated K+ channels means that more K+ is leaving the cell, making it more negative inside.

100 mV. the membrane goes from -70 mV to +30 mV. Thus, during the action potential, the inside of the cell becomes more positive than the outside of the cell.

Voltage-gated Na+ channels.

The membrane potential changes from a negative value to a positive value.

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

Voltage-gated Na+ channels change shape, and their activation gates open.

Continuous conduction. An action potential is conducted continuously along an unmyelinated axon from its initial segment to the axon terminals. The term continuous refers to the fact that the action potential is regenerated when voltage-gated Na+‎ channels open in every consecutive segment of the axon, not at nodes of Ranvier.

Myelinated axons with the largest diameter

depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment. The Na+‎ diffusing into the axon during the first phase of the action potential creates a depolarizing current that brings the next segment, or node, of the axon to threshold.

The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential.

myelinated; move from one node of Ranvier to another. Saltatory propagation is much faster than continuous propagation. The speed of propagation along an axon varies in two ways: 1) myelin sheaths limit the movement of ions across the axon membrane, thereby requiring the action potentials to "leap" from node to node during propagation, thus traveling at a greater speed; and 2) the diameter of the axon directly relates to the speed of propagation (i.e., the larger the diameter of the axon, the faster the speed of propagation).