Biological Bases: The Brain and Nervous System
Part V: Content Review for the AP Psychology Exam
INTRODUCTION TO BIOLOGY AND BEHAVIOR
Physiological psychology is the study of behavior as influenced by biology. It draws its techniques and research methods from biology and medicine to examine psychological phenomena.
Many different techniques are used to examine the interrelationship between the brain and behavior. Imaging techniques allow researchers to map the structure and/or activity of the brain and correlate this data with behavior. An EEG (electroencephalogram) measures subtle changes in brain electrical activity through electrodes placed on the head. This data can be filtered mathematically to yield evoked potentials, which allow psychologists to get an electrical picture of brain activity during various cognitive states or tasks.
Computerized axial tomography scans, better known as CAT scans, generate cross-sectional images of the brain using a series of X-ray pictures taken from different angles. MRI (magnetic resonance imaging) uses extremely powerful electromagnets and radio waves to get 3-D structural information from the brain. These techniques capture only “snapshots” of the brain. They do not allow observation of the brain in action over time. Functional MRI (fMRI) and PET scans (positron emission tomography) do allow scientists to view the brain as it is working. Functional MRI provides such viewing by rapid sequencing of MRI images. PET scans provide images via diffusion of radioactive glucose in the brain. Glucose is the primary “fuel” of brain cells; the more glucose being used in a given brain area, the more that area is in active use. This procedure allows psychologists to observe what brain areas are at work during various tasks and psychological events.
FUNCTIONAL ORGANIZATION OF THE NERVOUS SYSTEM
The nervous system can be divided into two distinct subsystems: the central nervous system (CNS)—comprising the brain and the spinal cord—and the peripheral nervous system (PNS)—comprising all other nerves in the body.
The brain is located in the skull and is the central processing center for thoughts, motivations, and emotions. The brain, as well as the rest of the nervous system, is made up of neurons, or nerve cells. The neurons form a network that extends to the spinal cord, which is encased in the protective bones of the spine, or the vertebrae. Both the brain and the spinal cord are bathed in a protective liquid called cerebrospinal fluid. In the spinal cord, the neurons are bundled into strands of interconnected neurons known as nerves. The nerves of the spine are responsible for conveying information to and from the brain and the PNS. Nerves sending information to the brain are sensory (or afferent) neurons; those conveying information from the brain are motor (or efferent) neurons. Although most movements are controlled by the brain, a certain small subset of movements are controlled by direct transmission from afferent to efferent cells at the level of the spinal cord. These responses, known as reflexes, are quick and involuntary responses to environmental stimuli. The path of a reflex arc goes from sensory neurons to motor neurons.
A memory tip for afferent and efferent is that afferent connections are arriving to the brain and efferent are exiting the brain.
The PNS comprises all of the nerve cells in the body with the exception of those in the CNS (the brain and spinal cord). The PNS can be subdivided into the somatic nervous system and the autonomic nervous system. The somatic nervous system is responsible for voluntary movement of large skeletal muscles. The autonomic nervous system controls the nonskeletal or smooth muscles, such as those of the heart and digestive tract. These muscles are typically not under voluntary control. (Think autonomic = automatic.) The autonomic nervous system can be further divided into the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system is associated with processes that burn energy. This is the system responsible for the heightened state of physiological arousal known as the fight-or-flight reaction—an increase in heart rate and respiration, accompanied by a decrease in digestion and salivation. The parasympathetic nervous system is the complementary system responsible for conserving energy. When the sympathetic system is aroused in a fight, for example, digestion ceases, blood transfers to skeletal muscle, and heart rate increases. When the fight ends, however, the parasympathetic system becomes active, sending blood to the stomach for digestion, slowing the heart rate, and conserving energy. This returns the body to homeostasis.
The sympathetic system is sympathetic to you while you deal with a problem. The parasympathetic system helps you come down afterwards, like a parachute.
The brain is divided into three distinct regions that have evolved over time. These are the hindbrain, midbrain, and the forebrain (limbic system and cerebral cortex).
· The oldest part of the brain to develop in evolutionary terms
· Composed of the cerebellum, medulla oblongata, reticular activating system (RAS), and pons
· Cerebellum—controls muscle tone and balance
· Medulla oblongata—controls involuntary actions, such as breathing, digestion, heart rate, and swallowing (basic life functions)
· Reticular activating system (RAS)—controls arousal (wakefulness and alertness). This is also known as reticular formation.
· Pons—Latin for “bridge,” the pons is a way station, passing neural information from one brain region to another. The pons is also implicated in REM sleep.
· Major components of the midbrain are tectum and tegmentum
· These two act as the brain’s roof (tectum) and floor (tegmentum).
· The tectum and tegmentum govern visual and auditory reflexes, such as orienting to a sight or sound.
Q: What parts of the brain are housed in the forebrain?
Answer on this page.
· Contains the limbic system, or emotional center of the brain
· Composed of the thalamus, hippocampus, amygdala, and hypothalamus
· Thalamus—relays sensory information; receives and directs sensory information from visual and auditory systems
· Hippocampus—involved in processing and integrating memories. Damage to the hippocampus does not eliminate existing memories, because memories are stored in the neocortex, but rather it prevents the formation of new memories. This condition is known as anterograde amnesia.
· Amygdala—implicated in the expression of anger and frustration
· Hypothalamus—controls the temperature and water balance of the body; controls hunger and sex drives; orchestrates the activation of the sympathetic nervous system and the endocrine system; and it can be divided into the lateral hypothalamus and ventromedial hypothalamus, the combination of which regulates eating behaviors and body weight. The lateral hypothalamus is the “on switch” for eating, while the ventromedial hypothalamus is the “off switch.” A lesion to the ventromedial part would cause obesity and even death from overeating, while a lesion to the lateral part would lead to a decreased hunger drive and even self-starvation.
Ventromedial lesion ⇒ Give me Very much food!
Lateral lesion ⇒ Give me Less food!.
· Also contains the cerebral cortex, or the wrinkled outer layer of the brain
· The cortex is involved in higher cognitive functions such as thinking, planning, language use, and fine motor control.
· This area receives sensory input (sensory cortex) and sends out motor information (motor cortex).
· The cortex covers two symmetrical-looking sides of the brain known as the left and right cerebral hemispheres. These hemispheres are joined together by a band of connective nerve fibers called the corpus callosum.
· The left hemisphere is typically specialized for language processing, as first noticed by Paul Broca, who observed that brain damage to the left hemisphere in stroke patients resulted in expressive aphasia, or loss of the ability to speak. This area of the brain is known as Broca’s area. Another researcher, Carl Wernicke, discovered an area in the left temporal lobe that, when damaged in stroke patients, resulted in receptive aphasia, or the inability to comprehend speech. This is called Wernicke’s Area.
· Others have noted that the right hemisphere processes certain kinds of visual and spatial information. Roger Sperry demonstrated that the two hemispheres of the brain can operate independently of each other. He did this by performing experiments on split-brain patients who had their corpus callosums severed to control their epileptic seizures. Split brain patients can describe objects without deficit if presented in the right visual field (processed on the left, more verbal side of the brain), but they have great difficulty drawing the image; whereas, if the image is presented in the left visual field (and processed in the more visual right side of the brain), the person can draw or choose the object but cannot explain it verbally. This is called contralateral processing.
· Much of the cerebral cortex is composed of association areas, which are responsible for associating information in the sensory and motor cortices (this is the plural of cortex!). Damage to these association areas can lead to a variety of dysfunctions, including apraxia, the inability to organize movement; agnosia, a difficulty processing sensory input; alexia, the inability to read; and agraphia, the inability to write.
· The cortex can be divided into four distinct lobes: the frontal, the parietal, the temporal, and the occipital.
o The frontal lobe is responsible for higher-level thought and reasoning. That includes working memory, paying attention, solving problems, making plans, forming judgments, and performing movements.
o The parietal lobe handles somatosensory information and is the home of the primary somatosensory cortex. This area receives information about temperature, pressure, texture, and pain.
o The temporal lobe handles auditory input and is critical for processing speech and appreciating music.
o Finally, the occipital lobe processes visual input. This information crosses the optic chiasm.
Much of our discussion has involved the idea of information or stimulation being passed along nerves. Nerves are bundles of neurons, the basic unit of the nervous system. Neurons are cells with a clearly defined, nucleated cell body, or soma. Branching out from the soma are dendrites, which receive input from other neurons through receptors on their surface. The axon is a long, tubelike structure that responds to input from the dendrites and soma. The axon transmits a neural message down its length and then passes its information on to other cells. Some neurons have a fatty coating known as a myelin sheath surrounding the axon. Myelin serves as insulation for the electrical impulses carried down the axon and also speeds up the rate at which electrical information travels down the axon. The better insulated the myelin sheath, the faster and more efficient the sending of action potentials. The myelin looks like beads on a string; the small gaps between the “beads” are known as the nodes of Ranvier. These nodes help speed up neural transmission. The axons end in terminal buttons, knobs on the branched end of the axon. The terminal buttons come very close to the cell body and dendrites of other neurons, but they do not touch. The gap between them is known as a synapse. The terminal buttons release neurotransmitters, chemical messengers, across the synapse, where they bind with receptors on subsequent dendrites.
A: The forebrain is home to the hippocampus, amygdala, and hypothalamus.
Neuronal communication occurs both within and between cells. Communication within cells is electrochemical. An electric potential across the plasma membrane of approximately —70 millivolts (mV), known as the resting membrane potential, exists, in which the interior of the cell is negatively charged with respect to the exterior of the cell. Two primary membrane proteins are required to establish the resting membrane potential: the Na+/K+ ATPase and the potassium leak channels. The Na+/K+ ATPase pumps three sodium ions out of the cell and two potassium ions into the cell. The result is a sodium gradient with high sodium concentration outside of the cell and a potassium gradient with high potassium concentration inside the cell. Leak channels are channels that are open all the time and that simply allow ions to “leak” across the membrane according to their gradient. Potassium leak channels allow potassium, but no other ions, to flow down its gradient out of the cell. The combined loss of many positive ions through Na+/K+ ATPases and the potassium leak channels leaves the interior of the cell with a net negative charge, approximately 70 mV more negative than the exterior of the cell; this difference is the resting membrane potential. Note that there are very few sodium leak channels in the membrane (the ratio of K+ leak channels to Na+ leak channels is about 100:1), so the cell membrane is virtually impermeable to sodium.
The resting membrane potential establishes a negative charge along the interior of axons (along with the rest of the neuronal interior). Thus, the cells can be described as polarized: negative on the inside and positive on the outside. An action potential, also referred to as a nerve impulse, is a disturbance in this membrane potential.
It can be thought of as a wave of depolarization of the plasma membrane that travels along an axon. Depolarization is a change in the membrane potential from the resting membrane potential to a less negative, or even positive, potential. The change in membrane potential during passage of an action potential is caused by movement of ions into and out of the neuron through ion channels, leading to the eventual release of the neurotransmitter. After depolarization, repolarization returns the membrane potential to normal.
Action potentials are “all or none,” meaning that they are either generated or not, with nothing in between. They are always of a fixed strength, never weaker or stronger. After a neuron fires, it passes through an absolute refractory phase, during which no amount of stimulation can cause the neuron to fire again. The absolute refractory phase is followed by the relative refractory phase, in which the neuron needs much more stimulation than usual to fire again.
Communication between cells happens via neurotransmitters, which bind to receptors on the dendrites of the adjacent neurons. Excitatory neurotransmitters serve to excite the cell or cause the neuron to fire. Inhibitory neurotransmitters inhibit (or stop) cell firing. After a neurotransmitter is released and has conducted the impulse to the next cell or cells, it is either broken down by enzymes or is absorbed back into the cell that released it in a process called reuptake. A helpful metaphor for the process of cell communication is thinking of neurotransmitters as keys that open the locks on the postsynaptic cell.
The following are a few key neurotransmitters:
· Acetylcholine, which affects memory function, as well as muscle contraction, particularly in the heart
· Serotonin, which is related to arousal, sleep, pain sensitivity, and mood and hunger regulation
· Dopamine, which is associated with movement, attention, and reward; dopamine imbalances may play a role in Parkinson’s disease and in schizophrenia
· GABA, or gamma-Aminobutyric acid, which is an inhibitory neurotransmitter
· Glutamate, which is an excitatory neurotransmitter and the all-purpose counterpart to GABA
· Norepinephrine, which affects levels of alertness; a lack of norepinephrine is implicated in depression
· Endorphins, which are the body’s natural painkillers
The endocrine system provides another way by which various parts of our bodies relay information to one another. This system works through groups of cells known as glands, which release substances called hormones. Hormones affect cell growth and proliferation. The primary gland is the pituitary gland, which is also known as the master gland. The pituitary releases hormones that in turn control hormonal release by many other glands. Hormones are different from neurotransmitters in many ways. Neurotransmitters are released locally, while hormones are not. Hormones coordinate a wide range of responses, while neurotransmitters trigger highly localized and specific reactions. Hormones are present in the bloodstream, while neurotransmitters work in the synapse. Hormones also affect the body for long periods of time compared with neurotransmitters. The pituitary is located just under the part of the brain that controls it—the hypothalamus. Stressful situations cause the pituitary to release adrenocorticotropic hormone (ACTH), which stimulates the adrenal glands, resulting in fight-or-flight reactions. The adrenal glands secrete epinephrine (adrenaline) and norepinephrine (noradrenaline). The thyroid gland, located at the front of the neck, produces thyroxine, which is important for regulating cellular metabolism.
HEREDITY AND ENVIRONMENT: BEHAVIORAL GENETICS
Behavioral genetics is the application of the principles of evolutionary theory to the study of behavior. Traits are distinctive characteristics or behavior patterns that are determined by genetics. Genes are the basic biological elements responsible for carrying information about traits between successive generations. A dominant trait is more likely to be expressed in offspring than is a recessive trait. A genotype is the genetic makeup of a cell or of an organism. The genotype is distinct from the expressed features, or phenotype, of the cell or organism. Whenever a dominant gene is paired with a recessive gene, the dominant one typically will be shown in the phenotype, the observable result. The phenotype tends to show the recessive trait only when two recessive genes are paired together. Genes reside on rod-shaped chromosomes. Humans have 46 chromosomes, with one set of 23 inherited from each parent, so that half of our genetic makeup comes from each parent.
Nature vs. Nurture
As mentioned earlier, the behavioral-genetics approach examines the ways in which we are different from one another. The term heritability is used here to discuss the degree of variance among individuals that can be attributed to genetic variations. Many physical and psychological characteristics are inherited. However, genes do not determine everything about us. Environmentality is the degree to which a trait’s expression is caused by the environment in which an organism lives. Psychology has long been concerned with the relative influences of genetics and environment. This controversy is known as the nature versus nurture debate. Today, the common view is that nature and nurture work together; our psychological makeup is largely the result of the interaction of these two forces.
Some disorders are the result of genetic abnormalities. Down syndrome occurs when there are three copies of the 21st chromosome, which generally causes some degree of intellectual disability. Huntington’s chorea is a genetic disorder that results in muscle impairment that does not typically occur until after age 40. It is caused by the degeneration of the structure of the brain known as the basal ganglia, and it is fatal. Because of the late onset of the disease, it is frequently passed down to the next generation before its symptoms are manifested. New genetic mapping techniques are revealing other relationships between specific genes and disorders, and scientists are trying to address ways to correct genetic flaws and provide genetic counseling.
It is important to note that the brain can reorganize itself by forming or severing neural connections throughout one’s life. This important ability, called neuroplasticity, allows the brain to compensate for injury or disease, in order to continue responding adaptably to the environment. Michael Gazzaniga has not only done pioneering research in this area, focusing on split-brain patients, he has also published works in cognitive neuroscience for the general reader.
CAT scans (Computerized axial tomography scans)
MRI (magnetic resonance imaging)
Functional MRI (fMRI)
PET scans (positron emission tomography)
Functional Organization of the Nervous System
central nervous system (CNS)
peripheral nervous system (PNS)
somatic nervous system
autonomic nervous system
sympathetic nervous system
parasympathetic nervous system
reticular activating system (RAS)
left and right cerebral hemispheres
Broca’s area and expressive aphasia
Wernicke’s Area and receptive aphasia
nodes of Ranvier
resting membrane potential
adrenocorticotropic hormone (ACTH)
Heredity and Environment: Behavioral Genetics
nature versus nurture debate
Chapter 7 Drill
See Chapter 19 for answers and explanations.
1.Damage to Broca’s area in the left cerebral hemisphere on the brain would likely result in which of the following?
(A)A repetition of the speech of others
(B)A loss of the ability to speak
(C)A loss of the ability to visually integrate information
(D)A loss of the ability to comprehend speech
(E)An inability to solve verbal problems
2.In the neuron, the main function of the dendrites is to
(A)release neurotransmitters to signal subsequent neurons
(B)preserve the speed and integrity of the neural signal as it propagates down the axon
(C)perform the metabolic reactions necessary to nourish and maintain the nerve cell
(D)receive input from other neurons
(E)connect the cell body to the axon
3.Veronica is having trouble balancing as she walks, and her muscles seem to have lost strength and tone. A neuroanatomist looking into her condition would most likely suspect a problem with Veronica’s
(B)right cerebral hemisphere
4.Which of the following neurotransmitters is generally associated with the inhibition of continued neural signaling?
5.A phenotype is best defined as
(A)an observable trait or behavior that results from a particular genetic combination
(B)the underlying genetic composition of a species
(C)a biological unit within which genetic information is encoded
(D)a recessive genetic combination that remains physically unexpressed
(E)the genetic combination given by a parent to his or her offspring
6.John is constantly overeating and can’t seem to control his appetite, no matter how hard he tries. It is possible that John may have damage in which of the following brain structures?
7.A demyelinating disorder, such as multiple sclerosis, would cause all of the following symptoms EXCEPT
(A)a reduction of white matter in the central nervous system
(B)an increased rate of neuronal conduction
(C)a slower propagation of signals along the axon
(D)a deficiency of sensation
(E)a decreased neuronal insulation
8.Which area of the brain is responsible for coordinating complex motor functions?
(C)Reticular activating system
9.All of the following brain areas are associated with the experience of emotion EXCEPT the
10.The correct order of a nerve impulse is
(A)resting potential, depolarization, hyperpolarization, repolarization, resting potential
(B)resting potential, depolarization, repolarization, resting potential, hyperpolarization
(C)resting potential, depolarization, repolarization, hyperpolarization, resting potential
(D)depolarization, resting potential, repolarization, hyperpolarization, resting potential
(E)depolarization, resting potential, repolarization, resting potential, hyperpolarization
Respond to the following questions:
· Which topics in this chapter do you hope to see on the multiple-choice section or essay?
· Which topics in this chapter do you hope not to see on the multiple-choice section or essay?
· Regarding any psychologists mentioned, can you pair the psychologists with their contributions to the field? Did they contribute significant experiments, theories, or both?
· Regarding any theories mentioned, can you distinguish between differing theories well enough to recognize them on the multiple-choice section? Can you distinguish them well enough to write a fluent essay on them?
· Regarding any figures given, if you were given a labeled figure from within this chapter, would you be able to give the significance of each part of the figure?
· Can you define the key terms at the end of the chapter?
· Which parts of the chapter will you review?
· Will you seek further help, outside of this book (such as a teacher, Princeton Review tutor, or AP Students), on any of the content in this chapter—and, if so, on what content?