Lecture 15/ Neuro I

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b. Depolarization
i. Na+ activation gate opens rapidly
- Na+ flows into cell

When the cell reaches the threshold, all of the gates start to respond. The Na+ activation gate is the fastest, so for a short while the Na+ channel is open, allowing Na+ to pour into the cell.

c. Repolarization
i. K+ channel opens
ii. Na+ inactivation gate closes
- K+ flows out of the cell

Both of the K+ gate and the Na+ inactivation gate actually respond to the initial depolarization, but because they are much slower than the Na+ activation gate, there is a delay. The Na+ channel closes and K+ flows out of the cell. Initially, K+ is flowing down both a concentration gradient and a charge gradient.

d. Undershoot
The K+ gate is slow to openin response to depolarization, and it is also slow to closewhen the membrane potential becomes negative. This causes the membrane potential to briefly become more negative than the resting state.

e. Refractory period
Before the neuron can respondagain the membrane potential, ion concentrations and Na+ inactivation gate all have to returnto the resting state.

3. Properties of the action potential
a. threshold
b. positive feedback
c. rapid
d. transient
e. all-or-nothing

Once the cell reaches the threshold, the depolarizationis determined by the number of Na+ channels; it becomes independentof the strength of the stimulus.


			b. Depolarization i. Na+ activation gate opens rapidly - Na+ flows into cell
		When the cell reaches the threshold, all of the gates start to respond. The Na+ activation gate is the fastest, so for a short while the Na+ channel is open, allowing Na+ to pour into the cell.
			c. Repolarization i. K+ channel opens ii. Na+ inactivation gate closes - K+ flows out of the cell
		Both of the K+ gate and the Na+ inactivation gate actually respond to the initial depolarization, but because they are much slower than the Na+ activation gate, there is a delay. The Na+ channel closes and K+ flows out of the cell. Initially, K+ is flowing down both a concentration gradient and a charge gradient. d. Undershoot The K+ gate is slow to openin response to depolarization, and it is also slow to closewhen the membrane potential becomes negative. This causes the membrane potential to briefly become more negative than the resting state. e. Refractory period Before the neuron can respondagain the membrane potential, ion concentrations and Na+ inactivation gate all have to returnto the resting state. 3. Properties of the action potential a. threshold b. positive feedback c. rapid d. transient e. all-or-nothing Once the cell reaches the threshold, the depolarizationis determined by the number of Na+ channels; it becomes independentof the strength of the stimulus.