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Chapter Summary
1.The evolutionary perspective stresses the role that physiological structures and behaviors play in the organism’s survival and adaptation to the environment. The principle of natural selection states that the strongest or most fit organisms survive because they make the best adaptation to the environment.
2.We use the processes of sensing, processing, and responding to interact in the environment. The nervous system, which is divided into the central nervous system (CNS—brain and spinal cord) and the peripheral nervous system (PNS—all parts of the nervous system outside the CNS), coordinates these three activities.
3.The PNS is composed of the somatic division and the autonomic division. The somatic division consists of afferent (sensory) nerves that run from the receptors to the brain and efferent (motor) nerves that run to the muscles. The autonomic division consists of the sympathetic division, which mobilizes the body’s resources, and the parasympathetic division, which returns the body to a normal state.
4.The spinal cord is composed of sensory (afferent or ascending) and motor (efferent or descending) nerves and small interneurons that may connect the sensory and motor neurons.
5.The brain is divided into the hindbrain (which handles survival functions and motor control), the midbrain (where the reticular formation is located), and the forebrain (which consists of two hemispheres joined by the corpus callosum).
6.The cerebral cortex covers the forebrain and is divided into four areas or lobes: frontal, parietal, temporal, and occipital. A group of subcortical structures involved in such activities as emotion, memory, eating, drinking, and sexual behavior are located beneath the cortex.
7.Early studies of brain functioning involved stimulating or removing portions of the cortex. The stereotaxic instrument allowed examination of the subcortical structures without damaging the cortex.
8.The electroencephalograph (EEG) provides an investigator with a chart of a person’s brain waves. Images of the structures of the brain can be produced by computerized techniques such as the PET (positron emission tomography) scan, the CT or CAT (computerized axial tomography) scan, and the MRI (magnetic resonance imaging) process.
9.The cells that make up the nervous system, neurons, are composed of dendrites, a cell body (soma), an axon, and terminal buttons.
10.Dendrites receive signals from adjacent neurons; axons transmit signals.
The tips of the axon, or terminal buttons, contain chemicals, known as neurotransmitters, that enable the signal from one neuron to be relayed to other neurons across the synaptic cleft, a small gap that separates neurons. Neuromodulators, which have more widespread and indirect effects, also influence transmission between cells.
11.Agonists are drugs that promote the action of a neurotransmitter, and antagonists are drugs that block or oppose the action of a neurotransmitter.
12.The neurotransmitter must be removed from the synaptic cleft before another signal can be transmitted. Removal is accomplished either by destroying the neurotransmitter or by taking it back into the terminal buttons (reuptake) and repackaging it into synaptic vesicles to be used again.
13.Ions (electrically charged particles) are found on the inside and outside of the semipermeable cell membrane of the neuron. When a neuron is in a resting state, more negative ions are on the inside of the cell (measured at -70 mV) than on the outside.
14.Neurotransmitters stimulate the cell membrane to allow ions to enter the neuron. Depending on the location and type of neurotransmitter, its effect is either to depolarize (the neuron positive ions move inside the neuron; the result is excitation) or to hyperpolarize it (additional negative ions move inside; the result is inhibition).
15.If depolarization of the dendrite and soma reaches the threshold level (-65 to -60 mV), the axon quickly reverses its electrical charge (to about +40 mV), and the signal is transmitted to the next neuron.
16.The split-brain operation involves severing the corpus callosum to help reduce epileptic seizures. The study of split-brain patients provides information about the functions of the two hemispheres of the brain. The left hemisphere is responsible primarily for language abilities and the production of speech, as well as rational and logical thought, whereas the right hemisphere is better suited to dealing with spatial relationships and the perception of more holistic concepts.
17.Studying the human brain yields information about aphasias (language deficits) and apraxias (nonverbal deficits).
18.Neuropsychologists study the relationships between the brain and behavior and frequently coordinate and direct treatment programs for brain-injured patients.
19.A major system that affects behavior is the endocrine system, which produces and secretes chemicals (hormones) that regulate body functions. Among the major endocrine glands are the pituitary gland, the thyroid gland, the pancreas, the gonads, and the adrenal glands.
20.The glucostatic theory of hunger stresses the level of usable blood sugar.
Low blood sugar levels signal hunger; high blood sugar levels signal that the organism is full or satiated. This theory accounts for short-term fluctuations in hunger.
21.The lipostatic theory stresses the importance of the level of stored fat in the body. This theory accounts for long-term fluctuations in hunger, which are thought to vary around a setpoint or normal level.
22.The ventromedial (VMH) and lateral (LH) areas of the hypothalamus are major components of a circuit that processes hunger signals. The VMH is involved in the cessation of eating; the LH is involved in the initiation of eating.
23.Volemic thirst is produced when extracellular fluids are depleted; osmotic thirst is produced when intracellular fluids are depleted.
24.Sex is classified as a biological motive, but it differs from other biological motives in important ways. Sexual behavior is influenced by external factors, brain mechanisms, and hormones.
25.Pheromones are chemicals that elicit a response in a member of the same species.
26.The display of sexual behavior in lower organisms is closely tied to the level of sex hormones (estrogens in females, androgens in males). Brain control of sexual behavior is complex and involves the hypothalamus and, quite likely, the limbic system.