Brain Functions and Malfunctions
Chapter 10
Consider the brain - the organ you have made extensive use of this semester
(some of you may feel that "overused" is more apt!). Weighing
in at about 2.8 pounds, it is what allows you to see this screen, interpret
what you are reading right now as a written language, make sense (hopefully!)
of the concepts about which you are reading, and to type in written responses
to questions asked during this course. It also will (again, hopefully!)
allow you in later years to remember this course, although how much information
you "learned" from the course you will be able to remember is
quite variable.
While scientists are quite knowledgable about the basic construction
of the brain, its general regions and major functions, many of the processes
whereby the brain performs its functions are still a mystery. How and why
we dream, how things are stored in and retrieved from memory, and how "rational
thought" is possible, are just a few of the many questions scientists
are actively investigating in brain research.
Sadly, as magnificent a design as the brain is, it is by no means perfect.
Defects, diseases and disorders can be present or develop over time, and
these various conditions are also objects of intense study.
The last chapter you'll be reviewing in this course focuses on these
and other aspects of brain structure, function and malfunction. The chapter
begins first with a review of basic brain structure and function (pages
284 to 288), followed by an examination of the basic cell type that makes
up the brain, the NEURON (see the general diagram below and on page 289).
You may be surprised to learn that the entire nervous system (including
the brain) is actually an electrical system, although it produces at best
a very weak electric field. The electricity is generated by the difference
in electrical charges on substances called ions, which are chemical elements
that have either too many or too few electrons. The most important ions
in nerves are sodium, chloride, (the same two that form table salt), and
calcium. Pages 289 to 292 cover how changes in the number of these ions
inside and outside neurons lead to the generation and movement of an electrical
charge along each neuron.
Neurons never directly touch each other. Instead there is a minute gap
between each called a SYNAPSE. When it reaches the end of one neuron, the
nervous impulse crosses this gap by means of a chemical substance known
as a NEUROTRANSMITTER. There are a variety of neurotransmitters with different
functions, and information about them and how they operate can be found
on pages 292 to 296.
Degeneration of neural tissue in the brain and/or malfunctions in neurotransmitter
production or function can lead to a variety of brain related diseases or
disorders. Among them we have Parkinson's, Huntington's and Alzheimer's
diseases. These diseases are found among many groupswithin the human population,
and each has been diagnosed in at least one famous personality in the last
50 years or so [Parkinson's - actors David Niven and Michael J. Fox; Huntington's
- folk singer Woody Guthrie; Alzheimer's - former president Ronald Reagan].
Depression, a major disorder in many people which can be severe enough to
lead to suicide, is caused by insufficent neurotransmitters. These and other
brain dysfunctions are described on pages 297 to 300.
You are well aware that there are periods during each 24 hour day when
you are tired and others when you are wide awake. If you are not suffering
from a disorder like insomnia, you also know that these periods of wakefulness
and restfulness occur at pretty regular intervals. This rhythmic pattern,
termed a CIRCADIAN RHYTHM (also known as a "biorhythm), is one of many
that work like a preprogrammed clock within the body. Various internal (ENDOGENOUS)
and external (EXOGENOUS) factors can set and in some cases, reset these
clocks. Sleep and wakefulness patterns and circadian rhythms are discussed
on pages 300 to 304.
One of the things that you (and I) hope you are doing during this semester
is LEARNING facts about and concepts of the many issues that have been addressed.
The processes of learning and storing learned information in MEMORY are
complex, and, as mentioned, not completely understood at the neurobiological
level. The last pages of Chapter 10 (pages 304 to 306) present some of the
known information about the concepts of learning and memory.
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