“Our active memories hold several billion times more information than a large contemporary research computer.”​—Science writer Morton Hunt⁠^e

6. How do nerve signals flow from neuron to neuron?

⁶ The key brain cells​—the neurons—​do not actually touch one another. They are separated by synapses, tiny spaces less than one millionth of an inch across. These gaps are bridged by chemicals called neurotransmitters, 30 of which are known, but the brain may possess many more. These chemical signals are received at one end of the neuron by a maze of tiny filaments called dendrites. The signals are then transmitted at the other end of the neuron by a nerve fiber called an axon. In the neurons the signals are electrical, but across the gaps they are chemical. Thus the transmission of nerve signals is electrochemical in nature. Each impulse is of the same strength, but the intensity of the signal depends upon the frequency of the impulses, which may be as high as one thousand a second.

7. What feature of the brain has the Bible commented on, and what have scientists learned that agrees with this?

⁷ It is not certain just what physiological changes take place in the brain when we learn. But experimental evidence suggests that as we learn, especially in early life, better connections are formed, and more of the chemicals bridging the gaps between neurons are released. Continued use strengthens the connections, and thus learning is reinforced. “Pathways that are often activated together are strengthened in some way,” reports Scientific American.⁠³ Interesting on this point is the Bible’s comment that deeper matters are more easily understood by mature people “who through use have their perceptive powers trained.” (Hebrews 5:14) Research has revealed that unused mental powers fade away. Thus the brain, like a muscle, is strengthened by use and weakened by disuse.

8. What is one of the great unresolved issues concerning the brain?

⁸ The vast numbers of microscopic nerve fibers making these connections within the brain are often referred to as its “wiring.” They are precisely placed within a maze of staggering complexity. But how they are placed in the exact spots called for by the “wiring diagrams” is a mystery. “Undoubtedly the most important unresolved issue in the development of the brain,” one scientist said, “is the question of how neurons make specific patterns of connections. . . . Most of the connections seem to be precisely established at an early stage of development.”⁠⁴ Another researcher adds that these specifically mapped-out areas of the brain “are common throughout the nervous system, and how this precise wiring is laid down remains one of the great unsolved problems.”⁠⁵

9. How many connections do scientists estimate exist within the brain, and what does one authority say as to its capacity?

⁹ The number of these connections is astronomical! Each neuron may have thousands of connections with other neurons. Not only are there connections between neurons, but there are also microcircuits that are set up directly between the dendrites themselves. “These ‘microcircuits,’” says one neurologist, “add a totally new dimension to our already mind-boggling conception of how the brain works.”⁠⁶ Some researchers believe that the “billions upon billions of nerve cells in the human brain make perhaps as many as a quadrillion connections.”⁠⁷ With what capacity? Carl Sagan states that the brain could hold information that “would fill some twenty million volumes, as many as in the world’s largest libraries.”⁠⁸

10. (a) In what ways does man’s cerebral cortex differ from that of animals, and with what advantages to man? (b) What did one researcher say about this?

¹⁰ It is the cerebral cortex of the brain that sets man far apart from any animal. It is less than a quarter of an inch thick, and it forms a fissured mold snug against the skull. If laid out, the cortex would measure about two and a half square feet, with some ten thousand miles of connecting fibers per cubic inch. The human cortex not only is far bigger than that of any animal, but it also has a much larger uncommitted area. That is to say, it is not committed to handling the physical functions of the body but is free for the higher mental processes that separate people from animals. “We are not just smarter apes,” one researcher said. Our minds “make us qualitatively different from all other forms of life.”⁠⁹