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:
- When do the K-channels open and what triggers it?
- 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?
