SME
Human Anatomy & Physiology · Problem type
Phases of an action potential
Use this to record a neuron’s membrane potential every 0.5 ms and name the phases of its action potential.
Record and look
0 mV
−55
−70
−70
−60
−55
+10
+30
0
−50
−75
−80
−75
−70
0 ms
0.5 ms
1 ms
1.5 ms
2 ms
2.5 ms
3 ms
3.5 ms
4 ms
4.5 ms
5 ms
Threshold, −55 mV
Resting, −70 mV
0 ms
0.5 ms
1 ms
1.5 ms
2 ms
2.5 ms
3 ms
3.5 ms
4 ms
4.5 ms
5 ms
Membrane potential (mV)
−70
−60
−55
+10
+30
0
−50
−75
−80
−75
−70
Depolarization: past −55 mV, Na⁺ rushes in and the potential climbs to +30 mV at 2 ms.
Repolarization: K⁺ flows out and it falls back toward rest.
Undershoot: it dips to −80 mV, below rest, before settling back.
Tap a bar at the height you want.
Assumptions
•
At rest the membrane sits near −70 mV; at the threshold, about −55 mV, voltage-gated Na⁺ channels open.
•
Near the peak the Na⁺ channels inactivate and slower voltage-gated K⁺ channels open, so K⁺ flows out.
•
The K⁺ channels close slowly, so the membrane dips below rest before settling back.
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