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Wilfrid Laurier University
Bruce Mc Kay

Biopsychology 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 terms. ■ 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 minds. 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 most nutrients. 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 (Chapter 13). 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 ne
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