I have been reading up on the historical understanding of nerve function and how this understanding has developed over the centuries. What surprised me more than anything is how recent (relatively ) the understanding of nerve function is. So is it any wonder that progress in research is playing catch up to some degree?
For many centuries, it was believed that the nerves functioned via 'animal spirits', which accessed the brain and travelled through the veins to allow movement.
The ancient theory of ‘animal spirits’ (pneuma psychikon in Greek; spiritus animalis in Latin) was first proposed by Alexandrian physicians in the third century BCE. Animal spirits were thought to be weightless, invisible entities that flowed through the hollow nerves to mediate the functioning of the body. The animal spirits theory was related to the notion of the four humours (blood, phlegm, and yellow and black bile), and was popularised by the Roman physician Galen (c. 129 -216) in the second century AD. Because of Galen, animal spirits dominated thinking about the nervous system for 1,500 years; they were exorcised very recently – it was only during the latter part of the 18th century that investigators began to decipher the electrochemical language of the nervous system Source
I am so surprised to see that this theory was never challenged to the point of changing the general opinion on this.
But now we know better!
( Now we know that we can thank these guys for those awful Nerve Tests with the needles! )
HerIn the early 1950s, Alan Hodgkin and Andrew Huxley carried out a series of 5 experiments which would determine how the electrical impulse (or action potential) was generated. By poking newly-developed, very fine microelectrodes directly into the giant axon of the squid, Hodgkin and Huxley measured the changes in membrane voltage that occurred during the action potential.
They thus established precisely the mechanism of the action potential: it was generated by the movements of ions across the nerve cell membrane, in both directions. Like Loewi and Dale before them, Hodgkin and Huxley would share a Nobel prize for their work. Source
I took a second-semester psychology class in community college,...oh,...about 10 years ago. Part of the curriculum ("why", I don't know) was three-weeks worth of learning how nerves were constructed, worked, were damaged, and tried to repair themselves. Actually, I would have preferred that the whole semester be about "nerves", not psychology,...but such was the curriculum. Anyway, the below paragraph from Wikipedia pretty much sums up what I learned in those three weeks. I'm posting it here because, in the weeks and months immediately after my accident, everything I had ever learned about "nerves" became elevated in importance to me. I was facing the limited possibility of nerve regeneration at a very personal level.
"Regeneration of peripheral nerve fibers It has also been discovered through research that if the axons of a neuron were damaged, as long as the cell body of the neuron is not damaged, the axons would regenerate and remake the synaptic connections with neurons with the help of guidepost cells. This is also referred to as neuroregeneration.
The nerve begins the process by destroying the nerve distal to the site of injury allowing Schwann cells, basal lamina, and the neurilemma near the injury to begin producing a regeneration tube. Nerve growth factors are produced causing many nerve sprouts to bud. When one of the growth processes finds the regeneration tube, it begins to grow rapidly towards its original destination guided the entire time by the regeneration tube. Nerve regeneration is very slow and can take up to several months to complete. While this process does repair some nerves, there will still be some functional deficit as the repairs are not perfect."