Shooting the gap: Info has to cross synapses
Here’s an old war story. Two men appeared out of the trees on the far side and started waving at me and hollering, “Medic!”
I reached behind me, grabbed the aid bag and clambered out of the top hatch of the armored personnel carrier evacuation vehicle. I put my hand down on the flat top of the vehicle and vaulted off to go render assistance.
In my haste, I put my hand down on top of the radiator grill of the armored personnel carrier, still hot from the motor running all morning. My hand, being smarter than I, pulled itself off of the grill halfway through my vault, which ended with me sprawling awkwardly across the ground.
I pulled my hand up to my face with the other hand already clutching it and thought, very clearly, to myself, as I observed the crisscross white lines of the burn, “Boy, is that going to hurt.”
My body acted, too, and I was conscious of impending pain, before I actually felt the pain. How can that be?
Information is transferred within the body as tiny electrical impulses along cells called neurons. These impulses travel at about 225 mph on peripheral nerves.
But there is more than one neuron between my hand and the highest level of consciousness in the cerebrum. In fact, there may be as many as 12 or 15 neurons. The information must be transferred from one neuron to the next at certain points. These points where one nerve ends, and the next begins, are called synapses.
Synapses are areas between cells, where the two cell membranes are separated by miniscule distances and do not actually touch.
The electrical current is not strong enough to jump the gap as a spark, so instead it causes the release of certain chemicals, called neurotransmitters, which diffuse across the gap. When these touch the membrane on the other side, they start the electrical current on the next neuron again.
Obviously, diffusing chemicals are significantly slower than an electrical current and so information crosses these synapses much more slowly than it flows along the neuron.
This slower transmission time is called synaptic delay. That means that the information about an event that happens to you always arrives at your consciousness just a little later than the event itself occurred. This delay, in milliseconds, is so small that it is mostly insignificant.
At every synapse there is more than one neuron to which the neurotransmitter is sent. This enables the body to send critical information in many directions at once and this enables you to react more quickly, and in coordination, to imminent threats.
Computer scientists call this parallel processing. This also means that frequently your body can make a decision at the synapse and create a bodily reaction to the stimulus before the message even reaches the conscious level of the brain.
In my case, a synapse, probably at the spinal cord, sent messages in several directions at once. One message continued on its way to the highest levels of consciousness, the cerebrum. But the synapse also stimulated another neuron that sent a message back out to the muscles of my arm saying to “Get your hand off that hot radiator, stupid!”
My muscles responded appropriately, although the message to my brain was still passing through several more slow synapses along its pathway.
This, of course, pretty much destroyed my previously described heroic vault.
By the time I completed my ignominious fall, some other synapses had alerted my other hand to clutch the injured one.
My eyes, having fewer synapses to go through, had registered that I had odd burn blisters on my hand. The information to my pain centers was still in progress somewhere when my consciousness evaluated the situation and decided that pain was coming soon. My consciousness was absolutely right.
Gary McCallister is professor of biology at Mesa State College and CEO of Flaming Moth Productions.