Noting the people talking about dental implants and dentist agony, do nerve inputs travel at the speed of copper wires, or are there safeguards/high impedence areas in between various parts? Are our brains more sensitive to nerve inputs closer to the brain, or it’s all the same?
No.
Sensory nerve impulses travel relatively slowly. Pain sensation is conducted particularly slowly: one to two meters per second.
This is a relatively easy question to look up.
The fastest conducting primary sensory nerve fibers, Type Ia and Ib involved in proprioception (perception of body movement and position), propagate signals at a speed on close order of 100 meters/second. Others are significantly less. Peripheral motor and sensor fibers have propagation speeds on close order of 50 meters/second.
Stranger
I have read that the Blue Whale, the largest animal ever to live on this planet, is at the upper size of what is possible because of nerve impulse travel times. The tail is so far from the head that it reaches the limits of coordinated movement (you think it, it happens).
That surprises me, because pain is a sort of stimulus that you want to be able to react to especially quickly. Though I suppose that pain signals might not have to travel as far: A lot of that is handled at levels short of the brain.
The explanation I saw is that nociception “wiring” is unmyelinated (lacks a myelin sheath on the transfer axons), so conduction speed is slower. Not sure why they are structured that way.
Another group of sensory nerve fibers do conduct quite fast and their sensation can be perceived as immediate pain for shallow injuries such as burns, which has value in reflex responses like withdrawing from contact with an injuriously hot surface. But more chronic pain is apparently conducted slowly.
Type IV (Erlanger-Gasser classification C) fibers are unmyelinated, but Type I/II/III (E-G Type A) fibers are myelinated. There is an extensive discussion of this in Principles of Neural Science, Kandel, Schwartz, et al (Chapter 24 “The Perception of Pain”) that I’m not going to reproduce here but essentially the functional differences have to do with metabolic demand, specifically that continuous stimulation overwhelms Type A fibers (i.e. intense pain diminishes after the initial impulse) but Type C fibers provide continuous stimulation.
Pain is processed in the brain—there is no ‘local response’ to pain stimuli in mammals—but pathways can be developed in the medial nuclear group with in the thalamus which moderate the perception and response to ‘trained’ noxious conditions, i.e. why an injection hurts the first time you get one but you can become conditioned to receiving injections regularly without any sensation that is perceived as more than irritation.
Stranger