1.1) Introduction to biopsychology – The biological approach to behaviour
A physiological explanation relates a behavior to the activity of the brain and other organs. It
deals with the machinery of the body—for example, the chemical reactions that enable hormones to
influence brain activity and the routes by which brain activity controls muscle contractions
An ontogenetic explanation describes how a structure or behavior develops, including the
influences of genes, nutrition, experiences, and their interactions. For example, the ability to inhibit
impulses develops gradually from infancy through the teenage years, reflecting gradual maturation
of the frontal parts of the brain.
An evolutionary explanation reconstructs the evolutionary history of a structure or behavior. For
example, frightened people get “goose bumps”—erections of the hairs, especially on their arms and
shoulders. Goose bumps are useless to humans because our shoulder and arm hairs are so short. In
most other mammals, however, hair erection makes a frightened animal look larger and more
intimidating (Figure 1.3). An evolutionary explanation of human goose bumps is that the behavior
evolved in our remote ancestors and we inherited the mechanism.
A functional explanation describes why a structure or behavior evolved as it did. Within a small,
isolated population, a gene can spread by accident through a process called genetic drift. For
example, a dominant male with many off - spring spreads all his genes, including neutral and
harmful ones. However, a gene that is prevalent in a large population presumably provided some
advantage—at least in the past, though not necessarily today. A functional explanation identifies
that advantage. For example, many species have an appearance that matches their background
(Figure 1.4). A functional explanation is that camouflaged appearance makes the animal
inconspicuous to predators. Some species use their behavior as part of the camouflage.
Dualism: the belief that mind and body are different kinds of substance that exist independently.
monism, the belief that the universe consists of only one kind of substance. Various forms of
monism are possible, grouped into the following categories:
■ materialism: the view that everything that exists is material, or physical. According to one
version of this view (“eliminative materialism”), mental events don’t exist at all, and any folk
psychology based on minds and mental activity is fundamentally mistaken. However, most of us
find it difficult to believe that our minds are figments of our imagination! A more plausible version
is that we will eventually find a way to explain all psychological experiences in purely physical
■ mentalism: the view that only the mind really exists and that the physical world could not exist
unless some mind were aware of it. It is not easy to test this idea— go ahead and try!—but few
philosophers or scientists take it seriously.
■ identity position: the view that mental processes and certain kinds of brain processes are the
same thing, described in different terms. In other words, the universe has only one kind of
substance, which includes both material and mental aspects. By analogy, one could describe the
Mona Lisa as an extraordinary painting, or one could list the exact color and brightness of each point on the painting. Although the two descriptions appear entirely different, they refer to the
same object. According to the identity position, every mental experience is a brain activity, even
though descriptions of thoughts sound so different from descriptions of brain activities.
Indeed, because we cannot observe consciousness, none of us knows for sure that other people,
much less other species, are conscious. According to the position known as solipsism (SOL-ip-sizm,
based on the Latin words solus and ipse, meaning “alone” and “self ”), I alone exist, or I alone am
conscious. Other people are either like robots or like the characters in a dream. (Solipsists don’t
form organizations because each is convinced that all other solipsists are wrong!) Although few
people take solipsism seriously, it is hard to imagine evidence to refute it. The difficulty of knowing
whether other people (or animals) have conscious experiences is known as the problem of other
David Chalmers (1995) distinguished between what he calls the easy problems and the hard
problem of consciousness. The easy problems pertain to such questions as the difference between
wakefulness and sleep and the mechanisms that enable us to focus our attention. These issues are
difficult scientifically but not philosophically. In contrast, the hard problem concerns why and how
any kind of brain activity is associated with consciousness.
2.1) Nerve Cells and Nerve Impulses – The cells of the nervous system
Neurons receive information and transmit it to other cells.
The surface of a cell is its membrane (or plasma membrane), a structure that separates the inside
of the cell from the outside environment. It is composed of two layers of fat molecules that are free
to flow around one another. Most chemicals cannot cross the membrane, but specific protein
channels in the membrane permit a controlled flow of water, oxygen, sodium, potassium, calcium,
chloride, and other important chemicals. Except for mammalian red blood cells, all animal cells
have a nucleus, the structure that contains the chromosomes. A mitochondrion (pl.:
mitochondria) is the structure that performs metabolic activities, providing the energy that the cell
requires for all other activities. Mitochondria require fuel and oxygen to function. Ribosomes are
the sites at which the cell synthesizes new protein molecules. Proteins provide building materials
for the cell and facilitate various chemical reactions. Some ribosomes float freely within the cell.
Others are attached to the endoplasmic reticulum, a network of thin tubes that transport newly
synthesized proteins to other locations.
The axon is the information sender of the neuron, conveying an impulse toward other neurons or
an organ or muscle. Many vertebrate axons are covered with an insulating material called a myelin
sheath with interruptions known as nodes of Ranvier (RAHN-vee-ay). Invertebrate axons do not
have myelin sheaths. An axon has many branches, each of which swells at its tip, forming a
presynaptic terminal, also known as an end bulb or bouton (French for “button”). This is the point
from which the axon releases chemicals that cross through the junction between one neuron and
the next. Other terms associated with neurons are afferent, efferent, and intrinsic. An afferent axon
brings information into a structure; an efferent axon carries information away from a structure.
Every sensory neuron is an afferent to the rest of the nervous system, and every motor neuron is an
efferent from the nervous system. Within the nervous system, a given neuron is an efferent from
one structure and an afferent to another. (You can remember that efferent starts with e as in exit;
afferent starts with a as in admission.) For example, an axon that is efferent from the thalamus may
be afferent to the cerebral cortex (Figure 2.8). If a cell’s dendrites and axon are entirely contained within a single structure, the cell is an interneuron or intrinsic neuron of that structure. For
example, an intrinsic neuron of the thalamus has its axon and all its dendrites within the thalamus.
Glia (or neuroglia), the other major components of the nervous system, do not transmit information
over long distances as neurons do, although they do exchange chemicals with adjacent neurons.
Oligodendrocytes produce myelin sheaths that insulate certain vertebrate axons in the central
nervous system; Schwann cells have a similar function in the periphery. The oligodendrocyte is
shown here forming a segment of myelin sheath for two axons; in fact, each oligodendrocyte forms
such segments for 30 to 50 axons. Astrocytes pass chemicals back and forth between neurons and
blood and among neighboring neurons. Microglia proliferate in areas of brain damage and remove
toxic materials. Radial glia (not shown here) guide the migration of neurons during embryological
development. Glia have other functions as well.
Why we need a blood-brain barrier?
To minimize the risk of irreparable brain damage, the body builds a wall along the sides of the
brain’s blood vessels. This wall keeps out most viruses, bacteria, and harmful chemicals, but also
The brain has several mechanisms to allow certain chemicals to cross through the endothelial cells.
First, small uncharged molecules, including oxygen and carbon dioxide, cross freely. Water crosses
through special protein channels in the wall of the endothelial cells. Second, molecules that dissolve
in the fats of the membrane also cross passively. Examples include vitamins A and D.
For certain other essential chemicals, the brain uses active transport, a protein-mediated process
that expends energy to pump chemicals from the blood into the brain. Chemicals that are actively
transported into the brain include glucose (the brain’s main fuel), amino acids (the building blocks
of proteins), purines, choline, a few vitamins, iron, and certain hormones. The blood-brain barrier is
essential to health. In people with Alzheimer’s disease or similar conditions, the endothelial cells
lining the brain’s blood vessels shrink, and harmful chemicals enter the brain.
The Nourishment of Vertebrate Neurons
Most cells use a variety of carbohydrates and fats for nutrition, but vertebrate neurons depend
almost entirely on glucose, a simple sugar. (Cancer cells and the testis cells that make sperm also
rely overwhelmingly on glucose.) The metabolic pathway that uses glucose requires oxygen;
consequently, the neurons consume an enormous amount of oxygen compared with cells of other
organs (Wong-Riley, 1989).
Why do neurons depend so heavily on glucose?
Although neurons have the enzymes necessary to metabolize fats and several sugars, glucose is
practically the only nutrient that crosses the blood-brain barrier in adults. The exceptions to this
rule are ketones (a kind of fat), but ketones are seldom available in large amounts, and large
amounts of ketones cause medical complications. Although neurons require glucose, glucose
shortage is rarely a problem. The liver makes glucose from many kinds of carbohydrates and amino
acids, as well as from glycerol, a breakdown product from fats. An inability to use glucose can be a
problem, however. Many chronic alcoholics have a diet deficient in vitamin B1, thiamine, a
chemical that is necessary for the use of glucose. Prolonged thiamine deficiency can lead to death of neurons and a condition called Korsakoff ’s syndrome, marked by severe memory impairments
2.2) Nerve Cells and Nerve Impulses –The Nerve Impulse
The membrane of a neuron maintains an electrical gradient, a difference in electrical charge
between the inside and outside of the cell. All parts of a neuron are covered by a membrane about 8
nanometers (nm) thick (just less than 0.00001 mm), composed of two layers (an inner layer and an
outer layer) of phospholipid molecules (containing chains of fatty acids and a phosphate group).
Embedded among the phospholipids are cylindrical protein molecules. The structure of the
membrane provides it with a good combination of flexibility and firmness and retards the flow of
chemicals between the inside and the outside of the cell. In the absence of any outside disturbance,
the membrane maintains an electrical polarization, meaning a difference in electrical charge
between two locations. The neuron inside the membrane has a slightly negative electrical potential
with respect to the outside, primarily because of negatively charged proteins inside the cell. This
difference in voltage in a resting neuron is called the resting potential. The resting potential is
mainly the result of negatively charged proteins inside the cell.
If charged ions could flow freely across the membrane, the membrane would depolarize at once.
However, the membrane is selectively permeable; that is, some chemicals can pass through it
more freely than others can. Most large or electrically charged ions and molecules cannot cross the
membrane at all. Oxygen, carbon dioxide, urea, and water cross freely through channels that are
always open. A few biologically important ions, such as sodium, potassium, calcium, and chloride,
cross through membrane channels (or gates) that are sometimes open and sometimes closed.
The sodium-potassium pump, a protein complex, repeatedly transports three sodium ions out of
the cell while drawing two potassium ions into it. The sodium-potassium pump is an active
transport requiring energy. Various poisons stop it, as does an interruption of blood flow. As a
result of the sodium-potassium pump, sodium ions are more than 10 times more concentrated
outside the membrane than inside, and potassium ions are similarly more concentrated inside than
outside. The sodium-potassium pump is effective only because of the selective permeability of the
membrane, which prevents the sodium ions that were pumped out of the neuron from leaking right
back in again. As it is, the sodium ions that are pumped out stay out. However, some of the
potassium ions pumped into the neuron do leak out, carrying a positive charge with them. That
leakage increases the electrical gradient across the membrane, as shown in Figure 2.15.
When the neuron is at rest, two forces act on sodium, both tending to push it into the cell. First,
consider the electrical gradient. Sodium is positively charged and the inside of the cell is