Lecture 15/ Neuro I

1 2 3 4 5 6 7

depending on the membrane potential.

b. Transporters
i. Na⁺/K⁺pump
ii. K+ channels
iii. Voltage-gated K+ channels
iv. Voltage-gated Na+ channels

It's important to note that although a particular K+ or Na+ channel is either open or closed, a neuron has several classes that open at different membrane potentials. If a few K+ or Na+ channels open, the resting potential goes down or up transiently, and then the Na+/K+ pump reestablishes the resting state.

But if the membrane potential goes up to reach a threshold, more Na + channels open. This creates a positive feedbacksituation and results in a rapid depolarization (from -60 meV to +50 meV) known as an action potential. Just as rapidly, the cell repolarizes; the whole thing only lasts 1-2 milliseconds.

The time course of the action potential is determined by the characteristics of the voltage-gated Na+ and K+ channels.

response
to depolarization opens
closes

opens

Channel
Na+ (activation)
(inactivation)

K+

Resting state closed
open

closed

speed fast
slow

slow

The Na+ channel behaves as if it has two gates, both of which must be open to allow Na+ to flow.

2. The basics of the action potential48.7
a. Resting state
i. K+ gate closed
ii. Na+ activation gate closed
- neither ion can cross

The K+ gate are closed and one of the Na+ gates, preventing both ions from crossing.


depending on the membrane potential. b. Transporters i. Na⁺/K⁺pump ii. K+ channels iii. Voltage-gated K+ channels iv. Voltage-gated Na+ channels It's important to note that although a particular K+ or Na+ channel is either open or closed, a neuron has several classes that open at different membrane potentials. If a few K+ or Na+ channels open, the resting potential goes down or up transiently, and then the Na+/K+ pump reestablishes the resting state. But if the membrane potential goes up to reach a threshold, more Na + channels open. This creates a positive feedbacksituation and results in a rapid depolarization (from -60 meV to +50 meV) known as an action potential. Just as rapidly, the cell repolarizes; the whole thing only lasts 1-2 milliseconds. The time course of the action potential is determined by the characteristics of the voltage-gated Na+ and K+ channels.
		response to depolarization opens closes opens
Channel Na+ (activation) (inactivation) K+	Resting state closed open closed	response to depolarization opens closes opens	speed fast slow slow
The Na+ channel behaves as if it has two gates, both of which must be open to allow Na+ to flow. 2. The basics of the action potential48.7 a. Resting state i. K+ gate closed ii. Na+ activation gate closed - neither ion can cross The K+ gate are closed and one of the Na+ gates, preventing both ions from crossing.