Faster Than a Speeding Brain
Electricity travels through a copper wire at 96 percent the speed of light. No such luck when it comes to neural strands. Our body’s neurons come in several different varieties and capacities, but none lets current flow even 1 percent as swiftly as in an electric can opener. Yet we apparently don’t need such light-speed cognition to accomplish everyday mental brilliancies like bagging the garbage. Our actual maximum operating rate of just 390 feet per second, or less than a millionth of light speed, is fast enough to do the job.
This is obvious with a quick experiment. Close your eyes and rapidly flail a hand — over your head, to the sides, anything. You’re always aware of exactly where it’s located, every moment, no matter how quickly you alter its position. Your in-the-moment cognizance of your hand’s location proves that neural signals must reach your brain extremely quickly. In fact, those impulses travel faster than 250 mph.
That’s the nerve transmission speed for essential stuff. But what qualifies as “essential?” Fortunately, you don’t have to personally prioritize the relative importance of all the sensory, muscular, pressure, pain and other inputs. It was taken care of, designed and hardwired before you even left the womb. A friend’s carelessly exuberant hand gesture is about to poke your eye? You instantly blink and evade. You’re eating and would prefer not to stab yourself with the fork? The positional signals from your fingers and lips are in-the-moment. On an overnight camping trip, stepping out of the tent barefoot, you tread on a suspicious object that feels an awful lot like a snake? You yank your leg up in an eyeblink. All these reflexes were neurally commanded at 250 mph.
But now stub your toe. Or just remember when you did. It took several seconds to feel any pain. That’s because pain signals travel along separate cables at a low-priority speed of just 3 mph. There’s no rush to deliver bad news.
Meanwhile, thinking signals occur at an in-between speed. They slither and branch through the cerebral cortex at 70 mph.
All these fast, slow and intermediate electrical impulses and synaptic connections happen continuously, with their pace peaking in the morning. We get a break only when the lights go out: The brain operates at a much-reduced level when we’re asleep.
The nervous system’s activity, which peaks between ages 22 and 27 and starts to diminish thereafter, is of course the control system for a myriad other internal motions. The well-known ones are our breaths and heartbeats.
The heart beats 2.5 billion times in a lifetime. The 5 quarts of blood an adult male continually pumps (4 quarts for women) flow at an average speed of 3 to 4 mph — walking speed. That’s fast enough so that a drug injected into an arm reaches the brain in only a few seconds. But this blood speed is just an average. It starts out by rushing through the aorta at an impressive 15 inches a second, then slows to different rates in various parts of the body.
Normally, liquids like water speed up when forced to flow through a narrower pipe. Kids like to squeeze a hose to make the water jump farther, to douse their friends. But the opposite happens in the narrow capillaries. Here is where blood flow is slowest.
It’s all part of the oxygen-exchange plan. The reason goes beyond the fact that capillaries are farthest from the heart. Rather, there are so many of them that their cross-sectional area is greater than what’s found in veins and arteries. The blood volume is essentially spread out there.
Lymph fluid moves through its own system of channels, at the low speed of a quarter-inch a minute. But air is much livelier. Men and women normally inhale and exhale about a pint of air — half a quart — 12 or 15 times a minute. This adds up to an air intake just shy of 2 gallons a minute. To make this happen, the lungs and diaphragm move in and out an inch a second.