Today I Learned... for Monday, September 17

Today I learned:

- What squamous, cuboidal, and columnar cells look like. I can identify simple and pseudostratified columnar, and stratified squamous fairly reliably, but the rest need some practice.

- About action potentials in neurons. If the graded potential* is still at -55mV or higher by the time it reaches the axon hillock** then it will trigger an action potential, which involves the opening of voltage-gated Na-channels, allowing Na+ to enter the cell down its electrochemical gradient, causing the membrane potential (Vm) to spike as high as +30mV. This triggers the closing of the Na-channels. At some point during all this the voltage-gated K-channels open, allowing K+ to leave the cell along its electrochemical gradient. The K-channels stay open after the Na-channels close, causing the Vm to drop until it's below its resting potential, at which point all the voltage-gated K-channels close again, leaving onoly a few K-leak channels open to let a bit of K+ in until the Vm is back to its resting point (~70mV) and the cell is at rest again. Two things I'm not entirely clear on:

  1. When do the K-channels open and what triggers it?
  2. At the end of the process the voltage across the membrane (Vm) is restored to its rest state, but the chemical gradient is not. There is too much Na+ and not enough K+. Maybe that's what the K/Na pump is for? But since the K/Na pump exports 3 Na+ for every 2 K+ it imports, using that to restore the concentrations would change the voltage, wouldn't it? It's all very confusing.

- If you're a Psychology prof then you're a Real Scientist(TM) and are entitled to cast aspersions on any scientific theory you want, like for example the big bang, whether you understand it or not.

*Not entirely clear what that is.
**Why hillock? Why not?