fundamentals of neuroscience....

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One of the things I totally love about this Massive Open Online Class way of learning is how easy it is to pause the video and answer my own questions.  I can't always find the answer to my questions, but often, I can.............................  This ability to stop, right when I have a question, and find an answer to my question (and maybe learn a few other things I wasn't even looking for!) seriously enriches my experience.

Here's an excerpt from my notes for Fundamentals of Neuroscience.....  The first sentence is a direct quote from the instructor.  Everything green is me -- questions, comments.......

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So we see that there's nothing intrinsically 'directional' about axons that causes propagation in just one direction. 

 

Ok, then, why do action potentials move from one end of an axon to the other?  Why aren’t they sort of waving back and forth and canceling each other out?  Is this because the refractory period stops that waving back and forth?

Wikipedia:  Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and endocrine cells, as well as in some plant cells. In neurons, they play a central role in cell-to-cell communication. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas, they provoke release of insulin.

Wikipedia:  As an action potential travels down the axon, there is a change in polarity across the membrane. The Na+ and K+ voltage-gated ion channels open and close as the membrane reaches the threshold potential, in response to a signal from another neuron. At the beginning of the action potential, the Na+ channels open and Na+ moves into the axon, causing depolarization. Repolarization occurs when the K+ channels open and K+ moves out of the axon. This creates a change in polarity between the outside of the cell and the inside. The impulse travels down the axon in one direction only, to the axon terminal where it signals other neurons.

Wikipedia:  After an action potential has occurred, there is a transient negative shift, called the hyperpolarization or refractory period, due to additional potassium currents. This is the mechanism that prevents an action potential from traveling back the way it just came.  HAH!!!!!!!!

ps – Wikipedia:  In animal cells, there are two primary types of action potentials. One type is generated by voltage-gated sodium channels, the other by voltage-gated calcium channels. Sodium-based action potentials usually last for under one millisecond, whereas calcium-based action potentials may last for 100 milliseconds or longer. In some types of neurons, slow calcium spikes provide the driving force for a long burst of rapidly emitted sodium spikes. In cardiac muscle cells, on the other hand, an initial fast sodium spike provides a "primer" to provoke the rapid onset of a calcium spike, which then produces muscle contraction.   

Of COURSE "only one sort of action potential" would be way too simple/easy/uncomplicated…………..

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End of excerpt.


I just love learning about all of this stuff.............  I am continually astonished at how complex it all is........

And at how old so much of it is.  Many of the mechanisms that influence or control how things work in our cells are as old as "water molecules have a negative end and a positive end, and the positive end of a water molecule is attracted to the negative end of some other molecule, and vice versa".........................

Really, really old, this electromagnetic stuff.  Four billion years?  More I bet.  Since before the beginning of time?



And Mama Nature has woven the most basic fabric of our beings from this ancient -- older than ancient -- sort of truth........



Awesome.

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