Introduction (Psychology and Mental Health)
About two weeks after conception, a fluid-filled cavity called the neural tube begins to form on the back of the human embryo. This neural tube will sink under the surface of the skin, and the two major structures of the central nervous system (CNS) will begin to differentiate. The top part of the tube will enlarge and become the brain; the bottom part will become the spinal cord. The cavity will persist through development and become the fluid-filled central canal of the spinal cord and the four ventricles of the brain. The ventricles and the central canal contain cerebrospinal fluid, a clear plasmalike fluid that supports and cushions the brain and also provides nutritive and eliminative functions for the CNS. At birth, the average human brain weighs approximately 12 ounces (350 grams), a quarter of the size of the average adult brain, which is about 3 pounds (1,200 to 1,400 grams). Development of the brain in the first year is rapid, with the brain doubling in weight in the first six months.
The development of different brain areas depends on intrinsic and extrinsic factors. Internally, chemicals called neurotrophins promote the survival of neurons (the basic cells of the nervous system that are specialized to communicate electrochemically with one another) and help determine where and when neurons will form connections and become diverse neurological structures. Externally, diverse experiences enhance the survival of...
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The Hindbrain (Psychology and Mental Health)
As the spinal cord enters the skull, it enlarges into the bottommost structure of the brain, the medulla (or medulla oblongata). The medulla controls many of the most basic physiological functions for survival, particularly breathing and the beating of the heart. Reflexes such as vomiting, coughing, sneezing, and salivating are also controlled by the medulla. The medulla is sensitive to opiate and amphetamine drugs, and overdoses of these drugs can impair its normal functioning. Severe impairment can lead to a fatal shutdown of the respiratory and cardiovascular systems.
Just above the medulla lie the pons, parts of the reticular formation, the raphe system, and the locus coeruleus. All these structures play a role in arousal and sleep. The pons plays a major role in initiating rapid eye movement (REM) sleep. REM sleep is characterized by repeated horizontal eye movements, increased brain activity, and frequent dreaming. The reticular system (sometimes called the reticular activating system, or RAS) stretches from the pons through the midbrain to projections into the cerebral cortex. Activation of the reticular system, by sensory stimulation or thinking, causes increases in arousal and alertness in diverse areas of the brain. For the brain to pay attention to something, there must be activation from the reticular formation. The raphe system, like the reticular system, can increase the brain’s readiness to respond to stimuli....
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The Midbrain (Psychology and Mental Health)
The superior and posterior part of the midbrain is called the tectum. There are two enlargements on both sides of the tectum known as the colliculi. The superior colliculus controls visual reflexes such as tracking the flight of a ball, while the inferior colliculus controls auditory reflexes such as turning toward the sound of a buzzing insect. Above and between the colliculi lies the pineal gland, which contains melatonin, a hormone that greatly influences the sleep-wake cycle. Melatonin levels are high when it is dark and low when it is light. High levels of melatonin induce sleepiness, which is one reason that people sleep better when it is darker. Another structure near the colliculi is the periaqueductal gray (PAG) area of the ventricular system. Stimulation of the PAG helps to block the sensation of pain.
Beneath the tectum is the tegmentum, which includes some structures involved in movement. Red nucleus activity is high during twisting movements, especially of the hands and fingers. The substantia nigra smooths out movements and is influential in maintaining good posture. The characteristic limb trembling and posture difficulties of Parkinson’s disease are attributable to neuronal damage in the substantia nigra.
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The Forebrain (Psychology and Mental Health)
Right above the midbrain, in the center of the brain, lies the thalamus, which is the center of sensory processing. All incoming sensory information except for the sense of smell goes to the thalamus first before it is sent on to the cerebral cortex and other areas of the brain. Anterior to and slightly below the thalamus is the hypothalamus. Hypothalamic activity is involved in numerous motivated behaviors such as eating, drinking, sexual activity, temperature regulation, and aggression. It does so largely through its regulation of the pituitary gland, which is attached beneath the hypothalamus. The pituitary gland controls the release of hormones that circulate in the endocrine system.Subcortical Structures
Numerous structures lie beneath the cerebral cortex in pairs, one in each hemisphere. Many of these structures are highly interconnected with one another and are therefore seen to be part of a system. Furthermore, most of the subcortical structures can be categorized as belonging to one of two major systems. Surrounding the thalamus is one system called the basal ganglia, which is most prominently involved in movements and muscle tone. The basal ganglia deteriorate in Parkinson’s and Huntington’s diseases, both disorders of motor activity. The three major structures of the basal ganglia are the caudate nucleus and putamen, which form the striatum, and the globus pallidus. The activities of the basal ganglia extend...
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Summary (Psychology and Mental Health)
It has been estimated that the adult human brain contains one hundred billion neurons forming more than thirteen trillion connections with one another. These connections are constantly changing, depending on how much learning is occurring and on the health of the brain. In this dynamic system of different neurological areas concerned with diverse functions, the question arises of how a sense of wholeness and stability emerges. In other words, where is the “me” in the mind? While some areas of the brain, such as the frontal lobe, appear more closely linked with such intimate aspects of identity as planning and making choices, it is likely that no single structure or particular function can be equated with the self. It may take the activity of the whole brain to give a sense of wholeness to life. Moreover, the self is not to be found anyplace in the brain itself. Instead, it is what the brain does—its patterns of activity—that defines the self.
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Sources for Further Study (Psychology and Mental Health)
Goldberg, Stephen. Clinical Neuroanatomy Made Ridiculously Simple. 3d ed. Miami, Fla.: MedMaster, 2007. One of a series of books intended to help students in the medical professions by presenting an abbreviated version of various medical subjects. The use of mnemonic devices, humor, and case studies makes the book accessible to a college-educated audience.
Hendleman, Walter J. Atlas of Functional Neuroanatomy. 2d ed. Boca Raton, Fla.: CRC Press, 2006. Hendleman presents a visual tour of the brain through drawings, photographs, and computer-generated illustrations. Three-dimensional images of the brain can be observed by using the accompanying CD-ROM.
Kalat, James W. Biological Psychology. 10th ed. Belmont, Calif.: Wadsworth/Cengage Learning, 2009. A top-selling book in the area of physiological psychology. While intended for college students, this engaging, easy-to-read text is accessible to general audiences. Contains excellent overviews of brain anatomy and functioning.
Ornstein, Robert. The Right Mind: Making Sense of the Hemispheres. Fort Washington, Pa.: Harvest Books, 1998. The man who helped popularize the left-brain/right-brain dichotomy in The Psychology of Consciousness (1972) reexamines the functioning of the two hemispheres in this book. The result is an easy-to-read, entertaining view of hemispheric lateralization that dispels many myths about...
(The entire section is 252 words.)