The Central Nervous System PDF

Okay, here's the conversion of the provided text into a structured Markdown format. I've focused on accuracy, clarity, and organization, while also summarizing where appropriate to avoid overly verbose descriptions. ### Figure 8.18 Some brain areas involved in emotion **(a)** The orbitofrontal are...

Okay, here's the conversion of the provided text into a structured Markdown format. I've focused on accuracy, clarity, and organization, while also summarizing where appropriate to avoid overly verbose descriptions. ### Figure 8.18 Some brain areas involved in emotion **(a)** The orbitofrontal area of the prefrontal cortex is shown in yellow, and the cingulate gyrus of the limbic system is shown in blue-green (anterior portion) and green (posterior portion). **(b)** The insula of the cortex is shown in purple, the anterior cingulate gyrus of the limbic system in blue-green, and the amygdala in red. 7 inches long and $1\frac{1}{4}$ inches thick - was driven through his left eye and brain and emerged through the top of his skull. After a few minutes of convulsions, Gage got up, rode a horse three-quarters of a mile into town, and walked up a long flight of stairs to see a doctor. He recovered well, with no noticeable sensory or motor deficits. His associates, however, noted striking personality changes. Before the accident, Gage was a responsible, capable, and financially prudent man. Afterward, he appeared to have lost his social inhibitions; for example, he engaged in gross profanity, which he did not do before his accident. He was impulsive, tossed about by seemingly blind whims. He was eventually fired from his job, and his old friends remarked that he was "no longer Gage." **CHECKPOINT** 3a. Describe the locations of the sensory and motor areas of the cerebral cortex and explain how these areas are organized. 3b. Describe the locations and functions of the basal nuclei. Of what structures are the basal nuclei composed? 4a. Identify the structures of the limbic system and explain the functional significance of this system. 4b. Explain the difference in function of the right and left cerebral hemispheres. 5. Describe the functions of the brain areas involved in speech and language comprehension. 6. Describe the brain areas implicated in memory, and their possible functions. ### 8.3 DIENCEPHALON The diencephalon is the part of the forebrain that contains the epithalamus, thalamus, hypothalamus, and part of the pituitary gland. The hypothalamus performs numerous vital functions, most of which relate directly or indirectly to the regulation of visceral activities by way of other brain regions and the autonomic nervous system. #### LEARNING OUTCOME After studying this section, you should be able to: 7. Describe the locations and functions of the thalamus and hypothalamus. The diencephalon, together with the telencephalon (cerebrum) previously discussed, constitutes the forebrain and is almost completely surrounded by the cerebral hemispheres. The third ventricle is a narrow midline cavity within the diencephalon. ### Thalamus and Epithalamus The thalamus composes about four-fifths of the diencephalon and forms most of the walls of the third ventricle (fig. 8.19). It consists of paired masses of gray matter, each positioned immediately below the lateral ventricle of its respective cerebral hemisphere. The thalamus acts primarily as a relay center through which all sensory information (except smell) passes. ### Limbic System and Emotion The parts of the brain that appear to be of paramount importance in the neural basis of emotional states are the hypothalamus (in the diencephalon) and the limbic system. The limbic system consists of a group of forebrain nuclei and fiber tracts that form a ring around the brain stem (limbus = ring). Among the components of the limbic system are the cingulate gyrus (part of the cerebral cortex), the amygdaloid nucleus (or amygdala), the hippocampus, and the septal nuclei (figs. 8.15 and 8.18). The cingulate gyrus is a thick area of cortex that surrounds the corpus callosum and is involved in emotions (particularly negative emotions associated with pain and fear) and motivation. Studies demonstrate that the anterior insula is activated together with the anterior cingulate cortex during emotional experiences. The limbic system was once called the **rhinencephalon**, or "smell brain," because it is involved in the central processing of olfactory information. This may be its primary function in lower vertebrates whose limbic system may constitute the entire forebrain. It is now known, however, that the limbic system in humans is a center for basic emotional drives. The limbic system was derived early in the course of vertebrate evolution, and its tissue is phylogenetically older than the cerebral cortex. There are thus few synaptic connections between the cerebral cortex and the structures of the limbic system, which perhaps helps explain why we have so little conscious control over our emotions. There is a closed circuit of information flow between the limbic system and the thalamus and hypothalamus (fig. 8.15) called the *Papez circuit*. (The thalamus and hypothalamus are part of the diencephalon, described in a later section.) In the Papez circuit, a fiber tract, the fornix, connects the hippocampus to the mammillary bodies of the hypothalamus, which, in turn, project to the anterior nuclei of the thalamus. The thalamic nuclei, in turn, send fibers to the cingulate gyrus, which then completes the circuit by sending fibers to the hippocampus. Through these interconnections, the limbic system and the hypothalamus appear to cooperate in the neural basis of emotional states. Studies of the functions of these regions include electrical stimulation of specific locations, destruction of tissue (producing lesions) in particular sites, and surgical removal, or ablation, of specific structures. These studies suggest that the hypothalamus and limbic system are involved in the following feelings and behaviors: 1. **Aggression.** Stimulation of certain areas of the amygdala produces rage and aggression, and stimulation of particular areas of the hypothalamus can produce similar effects. 2. **Fear.** Fear can be produced by electrical stimulation of the amygdala and hypothalamus, and surgical removal of the limbic system can result in an absence of fear. Monkeys are normally terrified of snakes, for example, but they will handle snakes without fear if their limbic system is removed. Humans with damage to their amygdala have demonstrated an impaired ability to recognize facial expressions of fear and anger. These and other studies suggest that the amygdala is needed for fear conditioning. 3. **Feeding.** The hypothalamus contains both a feeding center and a satiety center. Electrical stimulation of the former causes overeating, and stimulation of the latter will stop feeding behavior in experimental animals. 4. **Sex.** The hypothalamus and limbic system are involved in the regulation of the sexual drive and sexual behavior, as shown by stimulation and ablation studies in experimental animals. The cerebral cortex, however, is also critically important for the sex drive in lower animals, and the role of the cerebrum is even more important for the sex drive in humans. 5. **Goal-directed behavior (reward and punishment system).** Electrodes placed in particular sites between the **Figure 8.15 The limbic system.** The left temporal lobe has been removed in this figure to show the structures of the limbic system (green). The limbic system consists of particular nuclei (aggregations of neuron cell bodies) and axon tracts of the cerebrum that cooperate in the generation of emotions. The hypothalamus, though part of the diencephalon rather than the cerebrum (telencephalon), participates with the limbic system in emotions. Below is a list of the components shown in the diagram: - Cingulate gyrus - Septal nucleus - Preoptic nucleus - Olfactory bulb - Olfactory tract - Corpus callosum - Thalamus - Fornix - Mammillary body - Amygdala - Hippocampus - Cortex of right hemisphere - Hypothalamus *** Detect light passing through their skulls. In mammals, however, the daily cycles of light and darkness influence the SCN by way of tracts from the retina (the neural layer of the eyes) to the hypothalamus (see chapter 11, fig. 11.33). These retinohypothalamic tracts are activated not by the photoreceptors involved in vision (the rods and cones), but rather by a population of retinal ganglion cells that contain their own light-sensitive pigment, melanopsin. These photosensitive ganglion cells in the retina act, via the retinohypothalamic tracts, to entrain the circadian clocks of the SCN to daily cycles of light and darkness. They are also responsible for the pupillary reflex constriction in response to light (chapter 10; see fig. 10.28). Scientists have discovered circadian clock genes in neurons of the SCN and other areas of the brain, as well as in the cells of the heart, liver, kidneys, skeletal muscles, adipose tissue, and other organs. The clock genes are transcribed into mRNA, which are then translated into protein like other genes. However, there appears to be complex networks of *negative feedback loops* that suppress clock gene transcription after a delay, resulting in circadian oscillations of gene activity. Although the "peripheral clocks" (the clocks outside of the SCN) have daily cycles of activity, they would not be synchronized with other peripheral clocks or with the environmental light/dark cycle without the influence of the suprachiasmatic nuclei. The SCN receive photic (*light*) information from the retinohypothalamic tracts and have neural outputs to other nuclei of the hypothalamus, as well as to the thalamus, arcuate nucleus, amygdala, and other brain regions. By means of these neural outputs, the SCN influence circadian rhythms of body temperature, feeding, locomotor activity (movements), the autonomic nervous system, and the secretions of endocrine glands. Through autonomic nerves, the SCN can regulate circadian rhythms in the liver and other visceral organs. By indirectly influencing the secretions of the anterior pituitary, the SCN entrains the adrenal glands to produce circadian rhythms in the secretion of cortisol. The secretion of melatonin from the pineal gland is highest at night because of regulation by the SCN via sympathetic nerves (see fig. 11.33). Melatonin is a major regulator of circadian rhythms, as discussed in chapter 11, section 11.6. For example, the presence of melatonin receptors in the pancreatic islets suggests that melatonin may influence the secretion of insulin, which likewise follows a circadian rhythm. Also, melatonin's ability to promote relaxation of vascular smooth muscles may contribute to the circadian rhythms of blood pressure. **CHECKPOINT** 7a. List the functions of the hypothalamus and indicate the other brain regions that cooperate with the hypothalamus in the performance of these functions. 7b. Explain the structural and functional relationships between the hypothalamus and the pituitary gland. *** **Figure 8.20 A diagram of some of the nuclei within the hypothalamus.** The hypothalamic nuclei, composed of neuron cell bodies, have different functions Below is a list of the components shown in the diagram: - Paraventricular nucleus - Anterior nucleus - Preoptic area - Suprachiasmatic nucleus - Optic chiasma - Anterior pituitary (adenohypophysis) - Posterior pituitary (neurohypophysis) - Pituitary gland - Dorsomedial nucleus - Posterior nucleus - Ventromedial nucleus - Mammillary body - Supraoptic nucleus - Median eminence Experimental heating of this hypothalamic area results in hyperventilation (stimulated by somatic motor nerves), vasodilation, salivation, and sweat-gland secretion (regulated by sympathetic nerves). These responses serve to correct the temperature deviations in a negative feedback fashion. The coordination of sympathetic and parasympathetic reflexes is thus integrated with the control of somatic and endocrine responses by the hypothalamus. The activities of the hypothalamus are in turn influenced by higher brain centers. ### Regulation of the Pituitary Gland The pituitary gland is located immediately inferior to the hypothalamus. Indeed, the posterior pituitary derives embryonically from a downgrowth of the diencephalon, and the entire pituitary remains connected to the diencephalon by means of a stalk (chapter 11, section 11.3). Neurons within the supraoptic and paraventricular nuclei of the hypothalamus (fig. 8.20) produce two hormones - antidiuretic hormone (ADH), which is also known as vasopressin, and oxytocin. These two hormones are transported in axons of the hypothalamo-hypophyseal tract to the neurohypophysis (posterior pituitary), where they are stored and released in response to hypothalamic stimulation. Oxytocin stimulates contractions of the uterus during labor, and ADH stimulates the kidneys to reabsorb water and thus to excrete a smaller volume of urine. Neurons in the hypothalamus also produce hormones known as *releasing hormones and inhibiting hormones* that are transported by the blood to the adenohypophysis (anterior pituitary). These hypothalamic releasing and inhibiting hormones regulate the secretions of the anterior pituitary and, by this means, regulate the secretions of other endocrine glands (chapter 11, section 11.3). ### Regulation of Circadian Rhythms Within the anterior hypothalamus (fig. 8.20) are bilaterally located suprachiasmatic nuclei (SCN). These nuclei contain about 20,000 neurons that function as "clock cells," with electrical activity that oscillates automatically in a pattern that repeats about every twenty-four hours. The SCN functions as the master regulator of the body's circadian rhythms (from the Latin *circa = about*; *diem = day*). These are the physiological processes including metabolism, sleep, body temperature, blood pressure, hormone secretion, and many others - that repeat at approximately 24-hour intervals. For these to function properly, the neuron clocks of the SCN must be entrained (synchronized) to the day/night cycles. Nonmammalian vertebrates-fish, amphibians, reptiles, and birds have photosensitive cells in their brains that can *** **Figure 8.19 The adult brain seen in midsagittal section** Description: The brain is seen in midsagittal section highlighting the forebrain, midbrain and hindbrain. The image contains the folllowing labeled points. - Corpus collosum - Septum pellucidum - Genu of corpus collosum - Thalamus - Anterior commissure - Hypothalamus - Optic chiasma - Infundibulum - Pituitary gland - Mammillary body - Intermediate mass - Choroid plexus of third ventricle - Splenium of corpus collosum - Pineal body - Corpora quadrigemina - Cortex of cerebellum - Arbor vitae of cerebellum - Medulla oblongata The adult brain is seen in midsagittal section. The structures are labeled in the diagram shown in (a), and the brain regions are indicated in the photograph in (b). The diencephalon (shaded red) and telencephalon (unshaded area) make up the forebrain; the midbrain is shaded purple and the hindbrain is shaded aqua. On the way to the cerebrum. For example, the *lateral geniculate nuclei* relay visual information, and the *medial geniculate nuclei* relay auditory information, from the thalamus to the occipital and temporal lobes, respectively, of the cerebral cortex. The **intralaminar nuclei** of the thalamus are activated by many different sensory modalities and, in turn, project to many areas of the cerebral cortex. This is part of the system that promotes a state of alertness and causes arousal from sleep in response to any sufficiently strong sensory stimulus. The epithalamus is the dorsal segment of the diencephalon, containing a choroid plexus over the third ventricle where cerebrospinal fluid is formed. The epithalamus also contains the pineal gland (epiphysis), which secretes the hormone melatonin that helps regulate circadian (daily) rhythms (chapter 11, section 11.6). ### Hypothalamus and Pituitary Gland The hypothalamus is the most inferior portion of the diencephalon. Located below the thalamus, it forms the floor and part of the lateral walls of the third ventricle. This small but extremely important brain region contains neural centers for hunger and thirst; the regulation of body temperature; and hormone secretion from the pituitary gland (fig. 8.20) tion, centers in the hypothalamus contribute to the regi sleep, wakefulness, sexual arousal and performance, emotions as anger, fear, pain, and pleasure. Acting its connections with the medulla oblongata of the br the hypothalamus helps to evoke visceral responses t emotional states. In its regulation of emotion, the h mus works together with the limbic system. ### Regulation of the Autonomic System Experimental stimulation of different areas of the hypc can evoke the autonomic responses characteristic of ag sexual behavior, hunger, or satiety. Chronic stimulati lateral hypothalamus, for example, can make an anim become obese, whereas stimulation of the medial hypc inhibits eating. Other areas contain osmoreceptors th late thirst and the release of antidiuretic hormone (AI the posterior pituitary. The hypothalamus is also where the body's "the is located. Experimental cooling of the preoptic-anter thalamus causes shivering (a somatic motor respo nonshivering thermogenesis (a sympathetic motor n *** I hope this detailed conversion is helpful! Let me know if you have any other requests.