What part of the brain that send signals?

*** Your Wonderful Neurons

A NEURON is a nerve cell with all its processes. Your nervous system contains many types of neurons, which total about 500 billion. Some are sense receptors that send information from different parts of the body to your brain. Neurons in the higher region of your brain function like a video recorder. They can permanently store information that comes from your eyes and ears. Years later you can “play back” these sights and sounds, along with thoughts and other sensations that no man-made machine can record.

Human memory is still a mystery. It has something to do with the way neurons connect. “The average brain cell,” explains Karl Sabbagh in his book The Living Body, “links up with about 60,000 others; indeed some cells have links with up to a quarter of a million others. . . . The human brain could hold at least 1000 times as much information in the pathways connecting its nerve cells as is contained in the largest encyclopedia—say 20 or 30 big volumes.”

But how does one neuron pass information to another? Creatures with a simple nervous system have many nerve cells that are joined together. In such a case, an electrical impulse crosses the bridge from one neuron to the next. The crossing is called an electrical synapse. It is fast and simple.

Strange as it may seem, most neurons in the human body pass messages via a chemical synapse. This slower, more complex method can be illustrated by a train that reaches a river without a bridge and has to be ferried across. When an electrical impulse reaches a chemical synapse, it has to stop because a gap separates the two neurons. Here the signal is “ferried” across by the transfer of chemicals. Why this complex electro-chemical method of passing nerve impulses?

Scientists see many advantages in the chemical synapse. It ensures that messages pass one way. Also, it is described as plastic because its function or structure can easily change. Here signals can be modified. Through use, some chemical synapses get stronger while others disappear because of disuse. “Learning and memory could not develop in a nervous system that had only electrical synapses,” states Richard Thompson in his book The Brain.

Science writer Smith explains in his book The Mind: “Neurons do not just fire and not fire . . . they must be capable of passing on much more subtle information than yes or no. They are not just hammers hitting the next nail, either more frequently or less so. They are, to complete this analogy, a carpenter’s kit, with screwdrivers, pliers, pincers, mallets—and hammers. . . . Each neural impulse is transformed along the way, and nowhere else than at the synapses.”

The chemical synapse has a further advantage. It takes less space than an electrical synapse, which explains why the human brain has so many synapses. The journal Science gives a figure of 100,000,000,000,000—equivalent to the number of stars in hundreds of Milky Way galaxies. “We are what we are,” adds neuroscientist Thompson, “because our brains are basically chemical machines rather than electrical ones.”