15: Nervous System

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Medical science in the 20th century has seen a succession of hunters. The bacteriologists, called “microbe hunters”...occupied the spotlight in the first two decades. They were replaced in the next two by the vitamin hunters. Then the enzyme hunters filled the scene in the 1940s and 1950s, and for the past two decades the gene hunters have been in fashion.... Should the neurobiologists succeed in developing effective new molecular techniques, these hunters—we might call them “head hunters”—may dominate the last part of our century.

From For the Love of Enzymes, 1989, by Nobel laureate Arthur Kornberg

Imagine a worldwide network of 8 billion computers—one for every person in the world. It doesn’t come even close to the communication system of the human nervous system.

Our brain has about 85 billion neurons (nerve cells), with each neuron having up to about 1,000 extensions to network within the brain and communicate with cells throughout the body. When we accidentally touch a hot iron, nerve impulses pass the message. We immediately feel the pain, pull our hand back, and say Ouch!—or something less civil.

Think of the hand-eye coordination needed to hit a baseball closing in at 100 miles an hour. Imagine the fine orchestration of transmissions between neurons that occurs when we feel and respond to the sensations of sitting in the sun while sipping a cold drink and listening to music.

For all its complexity, there are just two basic kinds of cells in the nervous system: neurons (meaning nerves in Greek), which transmit nerve impulses, and glial cells, which play a supporting role. We might think of neurons as royalty, and glial cells as their devoted servants. There are about 50 to 100 times as many glial cells as neurons.

Glial cells appear packed between neurons, and were first thought of as the glue that held neurons together (glial means glue in Greek). But glial cells are quite complex, and a wide variety of them nurture and protect the neurons. Glial cells retain the ability to divide (grow). Most brain tumors occur in glial cells (e.g., glioblastoma).