Your Brain—A Marvel of Intricacy

“The human brain presents the ultimate riddle: how can a mass of tissue with the consistency of raw egg be responsible for your ‘mind,’ your thoughts, your personality, your memories and feelings, and even your actual consciousness?”—Professor Susan A. Greenfield, The Human Mind Explained.

YOUR brain regulates how your body operates. It enables you to learn new concepts, even new languages, and it stores and recalls the memories of your lifetime. Yet, neurobiologist James Bower admits: “We really don’t know what kind of machine the brain is.” Neuroscientist Richard F. Thompson agrees: “There is far more to be learned than we know now.” So great is the interest in unraveling the brain’s mysteries that the U.S. Congress declared the ’90’s to be the Decade of the Brain.

A Glimpse Inside Your Head

The gnarled lobes of the cerebral cortex, or the brain’s outer layer, present the most striking feature. (See the diagram on page 4 and the box on page 8.) This convoluted layer of pinkish-gray matter, which is about one eighth inch thick, houses some 75 percent of the brain’s 10 billion to 100 billion neurons (nerve cells). But some scientists say that even this vast quantity cannot account for the brain’s complexity.

Many neurons have a long taillike structure called an axon. The other fibers that spread out from the neuron are tiny dendrites, which resemble branches and twigs on a budding tree. These provide a typical neuron with thousands of links to other neurons. The neurons never actually touch each other. Across the intervening gap, called the synapse, tiny amounts of chemicals flow, adding a new dimension to the complexity of the whole structure.

“The number of possible different combinations of synaptic connections” in your brain is “larger than the total number of atomic particles that make up the known universe,” estimates one expert.

Although the neuron-filled cortex is perhaps the best-known part of the brain, what about the regions that lie beneath the cortex? For example, your corpus callosum provides the vital link between the left and right cerebral hemispheres. Nearby are your thalamus (from the Greek for inner chamber), through which passes most of the information your brain receives; the associated hypothalamus (Greek for below inner chamber), which helps regulate your blood pressure and body temperature; and a small extension called the pituitary gland. This master gland controls your endocrine system by secreting chemicals called hormones, which influence what is produced by all the other glands of the body. Then you have the pons, which processes information about the movements you make, and the medulla, which controls your breathing, circulation, heartbeat, and digestion. They do all of this without your even realizing that they are there!

With such diversity of parts, how does the brain work? And how can you make the best use of your brain? The following two articles offer some possible answers.

[Box on page 4]

Why We Don’t Need a Bigger Head

“If the human brain’s cerebral cortex was smooth rather than wrinkled, the brain would have to be about the same size as a basketball, instead of about the size of two clenched fists held side by side.”—Professor Susan A. Greenfield

[Diagram on page 4, 5]

(For fully formatted text, see publication)

SOME COMPONENTS OF THE BRAIN

Illustrated at actual size

Cerebral cortex

The relatively thin outer layer of each cerebral hemisphere

Cerebrum

The large rounded structure of the brain. It occupies most of the cranium

Visual cortex

Cerebellum

Literally “little brain.” A structure found at the rear base of the whole brain

Pons

Medulla

INNER CORE

Corpus callosum

A bundle of nerve fibers linking the cerebral hemispheres

Thalamus

Hypothalamus

Controls certain autonomic bodily functions

Pituitary gland

[Credit Line]

Based on The Human Mind Explained, by Professor Susan A. Greenfield, 1996