6 Biological Bases of Behavior
STEP 4 Review the Knowledge You Need to Score High
Neuropsychologists—those who explore the relationships between brain/nervous systems and behavior. Neuropsychologists are also called biological psychologists or biopsychologists, behavioral geneticists, physiological psychologists, and behavioral neuroscientists.
Studying patients with brain damage linked loss of structure with loss of function.
Lesions—precise destruction of brain tissue, enables more systematic study of the loss of function resulting from surgical removal (also called ablation), cutting of neural connections, or destruction by chemical applications.
CT scans and MRIs show structure.
• Computerized axial tomography (CAT or CT)—creates a computerized image using X-rays passed through the brain to show structure and/or the extent of a lesion.
• Magnetic resonance imaging (MRI)—creates more detailed computerized images using a magnetic field and pulses of radio waves that cause emission of signals that depend upon the density of tissue.
EEGs, PET scans, and fMRIs show function.
• EEG (electroencephalogram)—an amplified tracing of brain activity produced when electrodes positioned over the scalp transmit signals about the brain’s electrical activity (“brain waves”) to an electroencephalograph machine.
• Evoked potentials—EEGs resulting from a response to a specific stimulus presented to the subject.
• Positron emission tomography (PET)—shows brain activity when radioactively tagged glucose rushes to active neurons and emits positrons.
• Functional MRI (fMRI)—shows brain activity at higher resolution than the PET scan when changes in oxygen concentration near active neurons alter magnetic qualities.
Central nervous system (CNS)—brain and spinal cord.
Peripheral nervous system (PNS)—portion of the nervous system outside the brain and spinal cord; includes all of the sensory and motor neurons, and subdivisions called the autonomic and somatic nervous systems.
Autonomic nervous system (ANS)—subdivision of PNS that includes motor nerves that innervate smooth (involuntary) and heart muscle. Its sympathetic nervous system prepares the body for “fight or flight”; the parasympathetic nervous system causes bodily changes for maintenance or rest.
• Sympathetic nervous system—subdivision of PNS and ANS whose stimulation results in responses that help your body deal with stressful events.
• Parasympathetic nervous system—subdivision of PNS and ANS whose stimulation calms your body following sympathetic stimulation by restoring normal body processes.
Somatic nervous system—subdivision of PNS that includes motor nerves that stimulate skeletal (voluntary) muscles.
Spinal cord—portion of the central nervous system below the level of the medulla.
Brain—portion of the central nervous system above the spinal cord.
According to the evolutionary model, the brain consists of three sections: reptilian brain (medulla, pons, cerebellum); old mammalian brain (limbic system, hypothalamus, thalamus); and the new mammalian brain (cerebral cortex).
According to the developmental model, it consists of three slightly different sections: the hindbrain (medulla, pons, cerebellum), the midbrain (small region with parts involved in eye reflexes and movements), and the forebrain (including the limbic system, hypothalamus, thalamus, cerebral cortex).
Convolutions—folding-in and out of the cerebral cortex that increases surface area of the brain.
Contralaterality—control of one side of your body by the other side of your brain.
The parts of the brain with the functions associated with each are the following:
• Medulla oblongata—regulates heart rhythm, blood flow, breathing rate, digestion, vomiting.
• Pons—includes portion of reticular activating system or reticular formation critical for arousal and wakefulness; sends information to and from medulla, cerebellum, and cerebral cortex.
• Cerebellum—controls posture, equilibrium, and movement.
• Basal ganglia—regulates initiation of movements, balance, eye movements, and posture, and functions in processing of implicit memories.
• Thalamus—relays visual, auditory, taste, and somatosensory information to/from appropriate areas of cerebral cortex.
• Hypothalamus—controls feeding behavior, drinking behavior, body temperature, sexual behavior, threshold for rage behavior, activation of the sympathetic and parasympathetic systems, and secretion of hormones of the pituitary.
• Amygdala—influences emotions such as aggression, fear, and self-protective behaviors.
• Hippocampus—enables formation of new long-term memories.
• Cerebral cortex—center for higher-order processes such as thinking, planning, judgment; receives and processes sensory information and directs movement.
• Association areas—areas of the cerebral cortex that do not have specific sensory or motor functions but are involved in higher mental functions such as thinking, planning, and communicating.
Geographically, the cerebral cortex can be divided into eight lobes, four on the left side and four on the right side:
• Occipital lobes—primary area for processing visual information.
• Parietal lobes—front strip is somatosensory cortex that processes sensory information including touch, temperature, and pain from body parts; association areas perceive objects.
• Frontal lobes—interpret and control emotional behaviors, make decisions, carry out plans; motor cortex strip just in front of somatosensory cortex initiates movements and integrates activities of skeletal muscles; produces speech (Broca’s area).
• Temporal lobes—primary area for hearing, understanding language (Wernicke’s area), understanding music/tonality, processing smell.
Aphasia—impairment of the ability to understand or use language.
Glial cells—supportive cells of the nervous system that guide the growth of developing neurons, help provide nutrition for and get rid of wastes of neurons, and form an insulating sheath around neurons that speeds conduction.
Neuron—the basic unit of structure and function of your nervous system. Neurons perform three major functions: receive information, process it, and transmit it to the rest of your body. Terms relating to the structure and function of the neuron include the following:
• Cell body—also called the cyton or soma; the part of the neuron that contains cytoplasm and the nucleus, which directs synthesis of such substances as neurotransmitters.
• Dendrites—branching tubular processes of a neuron that have receptor sites for receiving information.
• Axon—a long, single conducting fiber extending from the cell body of a neuron that transmits an action potential and that branches and ends in tips called terminal buttons (a.k.a. axon terminals, or synaptic knobs), which secrete neurotransmitters.
• Myelin sheath—a fatty covering of the axon made by glial cells, which speeds up conduction of the action potential.
• Terminal buttons (a.k.a. axon terminals, end bulbs, or synaptic knobs)—tips at the end of axons that secrete neurotransmitters when stimulated by the action potential.
Neurotransmitters—chemical messengers released by the terminal buttons of the presynaptic neuron into the synapse. Different neurotransmitters have different chemical structures and perform different tasks:
• Acetylcholine (ACh)—a neurotransmitter that causes contraction of skeletal muscles, helps regulate heart muscles, is involved in memory, and also transmits messages between the brain and spinal cord. A lack of ACh is associated with Alzheimer’s disease.
• Dopamine—a neurotransmitter that stimulates the hypothalamus to synthesize hormones and affects alertness, attention, and movement. A lack of dopamine is associated with Parkinson’s disease; too much is associated with schizophrenia.
• Glutamate—a neurotransmitter that stimulates cells throughout the brain, but especially in the hypothalamus, and is associated with memory formation and information processing.
• Serotonin—a neurotransmitter associated with arousal, sleep, appetite, moods, and emotions. A lack of serotonin is associated with depression.
• Endorphin—a neurotransmitter similar to the opiate morphine that relieves pain and may induce feelings of pleasure.
• Gamma-aminobutyric acid (GABA)—a neurotransmitter that inhibits firing of postsynaptic neurons. Huntington’s disease and seizures are associated with malfunctioning GABA systems.
Action potential—also called an impulse, the “firing” of a neuron; a net flow of sodium ions into the cell that causes a rapid change in potential across the membrane when stimulation reaches threshold.
All-or-none principle—the law that the neuron either generates an action potential when the stimulation reaches threshold or doesn’t fire when stimulation is below threshold. The strength of the action potential is constant whenever it occurs.
Nodes of Ranvier—spaces between segments of myelin on the axons of neurons.
Saltatory conduction—rapid conduction of impulses when the axon is myelinated since depolarizations jump from node (of Ranvier) to node.
Synapse—region of communication between the transmitting presynaptic neuron and receiving postsynaptic neuron, muscle, or gland, consisting of the presynaptic terminal buttons, a tiny space, and receptor sites typically on the postsynaptic dendrites.
Excitatory neurotransmitter—chemical secreted at terminal button that causes the neuron on the other side of the synapse to generate an action potential (to fire).
Inhibitory neurotransmitter—chemical secreted at terminal button that reduces or prevents neural impulses in the postsynaptic dendrites.
Reflex—the simplest form of behavior.
Reflex arc—the path over which the reflex travels, which typically includes the following:
• Sensory receptor—cell typically in sense organs that initiates action potentials, which then travel along sensory/afferent neurons to the CNS.
• Afferent neuron—also called sensory neuron; nerve cell in your PNS that transmits impulses from receptors to the brain or spinal cord.
• Interneuron—nerve cell in the CNS that transmits impulses between sensory and motor neurons. Neural impulses travel one way along the neuron from dendrites to axons to terminal buttons, and among neurons from the receptor to the effector.
• Efferent neuron—also called motor neuron; nerve cell in your PNS that transmits impulses from sensory or interneurons to muscle cells that contract or gland cells that secrete.
• Effector—muscle cell that contracts or gland cell that secretes.
Endocrine system—ductless glands that typically secrete hormones directly into the blood, which help regulate body and behavioral processes. Components of the endocrine system include the following:
• Hormone—chemical messenger that travels through the blood to a receptor site on a target organ.
• Pineal gland—endocrine gland in brain that produces melatonin that helps regulate circadian rhythms and is associated with seasonal affective disorder.
• Hypothalamus—portion of brain part that acts as endocrine gland and produces hormones that stimulate (releasing factors) or inhibit secretion of hormones by the pituitary.
• Pituitary gland (sometimes called “master gland”)—endocrine gland in brain that produces stimulating hormones, which promote secretion by other glands including TSH (thyroid-stimulating hormone); ACTH (adrenocorticotropic hormone), which stimulates the adrenal glands; FSH (follicle stimulating hormone), which stimulates egg or sperm production; ADH (antidiuretic hormone) to help retain water in your body; and HGH (human growth hormone).
• Thyroid gland—endocrine gland in neck that produces thyroxine, which stimulates and maintains metabolic activities.
• Parathyroids—endocrine glands in neck that produce parathyroid hormone, which helps maintain calcium ion level in blood necessary for normal functioning of neurons.
• Adrenal glands—endocrine glands atop kidneys. Adrenal cortex—the outer layer—produces steroid hormones such as cortisol, which is a stress hormone. Adrenal medulla—the core—secretes adrenaline (epinephrine) and noradrenaline (norepinephrine), which prepare the body for “fight or flight” like the sympathetic nervous system.
• Pancreas—gland near stomach that secretes the hormones insulin and glucagon, which regulate blood sugar that fuels all behavioral processes. Imbalances result in diabetes and hypoglycemia.
• Ovaries and testes—gonads in females and males, respectively, that produce hormones necessary for reproduction and development of secondary sex characteristics.
Evolutionary psychologists—study how Charles Darwin’s theory of natural selection favored behaviors that contributed to survival and spread of our ancestors’ genes; evolutionary psychologists look at universal behaviors shared by all people.
Behavioral geneticists—study the role played by our genes and our environment in mental ability, emotional stability, temperament, personality, interests, etc.; they look at the causes of our individual differences.
Studies of twins help separate the contributions of heredity from environment.
• Identical twins—also called monozygotic twins; two individuals who share all the same genes/heredity because they develop from the same zygote.
• Fraternal twins—also called dizygotic twins; siblings that share about half of the same genes because they develop from two different zygotes.
Heritability—the proportion of variation among individuals in a population that is due to genetic causes.
When twins grow up in the same environment, the extent to which behaviors of monozygotic twins are behaviorally more similar than dizygotic twins reveals the contribution of heredity to behavior.
If monozygotic twins are separated at birth and raised in different environments (adoption studies), behavioral differences may reveal the contribution of environment to behavior; similarities reveal the contribution of heredity.
In adoption studies, if the children resemble their biological parents, but not their adoptive families, with respect to a given trait, researchers infer a genetic component for that trait.
Gene—each DNA segment of a chromosome that determines a trait.
Chromosome—structure in the nucleus of cells that contains genes determined by DNA sequences.
Human cells contain 23 pairs of chromosomes, 23 of which come from the sperm of the father and 23 of which come from the egg of the mother at fertilization. If the father contributes a Y sex chromosome, the baby is male; otherwise, the baby is female.
Errors during fertilization can result in the wrong number of chromosomes in cells of a baby. These can result in:
• Turner syndrome—females with only one X sex chromosome who are short, often sterile, and have difficulty calculating.
• Klinefelter’s syndrome—males with XXY sex chromosomes.
• Down syndrome—usually with three copies of chromosome 21 in their cells, individuals typically have intellectual disability and have a round head, flat nasal bridge, protruding tongue, small round ears, a fold in the eyelid, and poor muscle tone and coordination.
Genotype—the genetic makeup of an individual.
Phenotype—the expression of the genes.
Homozygous—the condition when both genes for a trait are the same.
Heterozygous—also called hybrid; the condition when the genes for a trait are different.
Dominant gene—the gene expressed when the genes for a trait are different.
Recessive gene—the gene that is hidden or not expressed when the genes for a trait are different.
Tay-Sachs syndrome—recessive trait that produces progressive loss of nervous function and death in a baby.
Albinism—recessive trait that produces lack of pigment and involves quivering eyes and inability to perceive depth with both eyes.
Phenylketonuria (PKU)—recessive trait that results in severe, irreversible brain damage unless the baby is fed a special diet low in phenylalanine.
Huntington’s disease—dominant gene defect that involves degeneration of the nervous system, characterized by tremors, jerky motions, blindness, and death.
Sex-linked traits—recessive genes located on the X chromosome with no corresponding gene on the Y chromosome, which result in expression of recessive trait, more frequently in males.
Color blindness—sex-linked trait with which individual cannot see certain colors, most often red and green.
Consciousness—our awareness of the outside world and of ourselves, including our own mental processes, thoughts, feelings, and perceptions. EEGs show alpha and beta waves.
Levels of consciousness:
• Normally conscious, what you pay attention to is what you process into perceptions, thoughts, and experiences. Attention is a state of focused awareness.
• Preconscious—level of consciousness that is outside of awareness but contains feelings and memories that can easily be brought to conscious awareness.
• Unconscious (subconscious)—level of consciousness that includes often unacceptable feelings, wishes, and thoughts not directly available to conscious awareness.
• Nonconscious—the level of consciousness devoted to processes completely inaccessible to conscious awareness.
• Dual processing—processing information on conscious and unconscious levels at the same time.
Hypothalamus controls your biological clock, regulating changes in blood pressure, body temperature, pulse, blood sugar levels, hormonal levels, activity levels, sleep, and wakefulness over 24 hours in normal environment (25 hours in a place without normal night—day).
Circadian rhythms—daily patterns of changes.
Reticular formation (reticular activating system)—neural network in brainstem (medulla and pons) and midbrain essential to the regulation of sleep, wakefulness, arousal, and attention.
States of consciousness include (normal waking) consciousness, daydreaming, sleep, hypnosis, meditation, and drug-induced states.
Sleep is a complex combination of states of consciousness, each with its own level of consciousness, awareness, responsiveness, and physiological arousal.
• NREM-1 sleep—quick sleep stage with gradual loss of responsiveness to outside, drifting thoughts, and images (the hypnagogic state). EEGs show theta waves.
• NREM-2 sleep—about 50 percent of sleep time. EEGs show high-frequency sleep spindles and K-complexes.
• NREM-3 sleep—Used to be split into 2 separate stages (stages 3 and 4). The beginning of deep sleep, characterized by more delta waves and a lack of muscle activity. Slowed heart rate and respiration, lowered temperature and lowered blood flow to the brain. Growth hormone is secreted.
• REM sleep (Rapid Eye Movement sleep)—sleep stage when eyes dart about. About 80 percent dreaming, 5 to 6 times each night (about 20 percent of sleep time). Called paradoxical sleep because EEGs are similar to stage 1 and wakefulness, but we are in deep sleep with skeletal muscles paralyzed.
• NREM (Non-REM sleep)—sleep stages 1 through 3 without rapid eye movement.
During sleep we synthesize proteins and consolidate memories from the preceding day.
Sleep disorders include insomnia, the inability to fall asleep and/or stay asleep; narcolepsy, sudden and uncontrollable lapse into sleep (usually REM); and sleep apnea, temporary cessations of breathing that awaken the sufferer repeatedly during the night. Sleep disruptions include night terrors, characterized by bloodcurdling screams and intense fear in children during the deepest part of NREM-3 sleep; and sleepwalking (somnambulism), usually in children during the deepest part of NREM-3 sleep.
Three theories of what dreams mean:
1. To (Freudian) psychoanalysts, dreams are a safety valve for unconscious desires.
Manifest content—according to Freud, the remembered story line of a dream.
Latent content—according to Freud, the underlying meaning of a dream.
2. Activation-synthesis theory—during REM sleep the brainstem stimulates the forebrain with random neural activity, which we interpret as a dream.
3. Cognitive information processing theory—dreams are the interplay of brain waves and psychological functioning of interpretive parts of the mind.
Daydreaming—state with focus on inner, private realities, which can generate creative ideas.
Hypnosis—state with deep relaxation and heightened suggestibility. The hidden observer provides evidence for dissociation of consciousness.
Meditation—set of techniques used to focus concentration away from thoughts and feelings in order to create calmness, tranquility, and inner peace.
Psychoactive drug—a chemical that can pass through the blood-brain barrier to alter perception, thinking, behavior, and mood.
Four categories of psychoactive drugs:
1. Depressants—reduce activity of CNS and induce sleep.
2. Narcotics—depress the CNS, relieve pain, and induce feelings of euphoria.
3. Stimulants—activate motivational centers; reduce activity in inhibitory centers of the CNS.
4. Hallucinogens—distort perceptions and evoke sensory images in the absence of sensory input.
Psychological dependence—person has intense desire to achieve the drugged state in spite of adverse effects.
Physiological dependence (addiction)—blood chemistry changes from taking a drug necessitate taking the drug again to prevent withdrawal symptoms.
Withdrawal symptoms—typically intense craving for drug and effects opposite to those the drug usually induces.