Brain and Body Theme 1 - PDF

Module 3.1 Structure of the Vertebrate Nervous System 71 The Hindbrain Figure 3.8 The human brainstem The brain has th...

Module 3.1 Structure of the Vertebrate Nervous System 71 The Hindbrain Figure 3.8 The human brainstem The brain has three major divisions: hindbrain, midbrain, This composite structure extends from the top of the spinal cord into and forebrain (Figure 3.7 and Table 3.3). Some neuroscien- the center of the forebrain. The cerebral cortex surrounds the thala- tists prefer terms with Greek roots: rhombencephalon (hind- mus, pineal gland, and midbrain. brain), mesencephalon (midbrain), and prosencephalon (forebrain). You may encounter these terms in other reading. Pineal gland The hindbrain, the posterior part of the brain, consists Thalamus of the medulla, the pons, and the cerebellum. The medulla Superior and pons, the midbrain, and certain central structures of colliculus the forebrain constitute the brainstem (Figure 3.8). Inferior Midbrain The medulla, or medulla oblongata, can be regarded colliculus as an enlarged extension of the spinal cord. Just as the lower Tectum parts of the body connect to the spinal cord via sensory Tegmentum and motor nerves, the head and the organs connect to the medulla and adjacent areas by 12 pairs of cranial nerves Pons (one of each pair on the right side and one on the left), as described in Table 3.4 and Figure 3.9. The size of each cra- nial nerve varies among species. In elephants, the trigemi- nal nerve that receives sensations from the face is huge Posterolateral because it innervates the trunk, a highly sensitive structure Medulla view of brainstem for elephants (Purkart, 2022). The elephant’s trigeminal nerve is thicker than its spinal cord! Figure 3.7 Major divisions of the vertebrate brain In a fish brain, as depicted here, the forebrain, midbrain, and hindbrain are clearly visible as separate bulges. In adult mammals, the forebrain The cranial nerves originating in the medulla control grows and surrounds the entire midbrain and part of the hindbrain. vital reflexes such as breathing, heart rate, vomiting, sali- Midbrain vation, coughing, and sneezing. Because opiate receptors, Forebrain Hindbrain which suppress activity, are abundant in the medulla, opi- Olfactory bulb ates can produce a dangerous decrease in breathing and Optic nerve heart rate. The pons lies anterior and ventral to the medulla. Like the medulla, it contains nuclei for several cranial nerves. The term pons is Latin for “bridge,” reflecting the fact that in the pons, axons from each half of the brain cross to the opposite side of the spinal cord so that the left hemisphere controls the muscles of the right side of the body and the Table 3.3 | Major Divisions of the Vertebrate right hemisphere controls the left side. Brain The cerebellum is a large hindbrain structure with Area Also Known as Major Structures many deep folds. It is one of the first brain areas to start developing and one of the last to complete development Forebrain Prosencephalon (Sathyanesan et al., 2019). The cerebellum has long been (“forward-brain”) known for its contributions to the control of movement, Diencephalon Thalamus, hypothalamus and many older textbooks describe the cerebellum as im- (“between-brain”) portant for “balance and coordination.” True, people with Telencephalon Cerebral cortex, cerebellar damage are clumsy and lose their balance, but (“end-brain”) hippocampus, basal ganglia the functions of the cerebellum extend far beyond balance Midbrain Mesencephalon Tectum, tegmentum, and coordination. People with damage to the cerebellum (“middle-brain”) superior colliculus, have difficulty with timing, such as judging whether one inferior colliculus, rhythm is faster than another rhythm. Depending on the substantia nigra location and type of damage, they may have impairments Hindbrain Rhombencephalon Medulla, pons, cerebellum of learning, memory, attention, visual-spatial process- (literally, “parallelogram- ing, language, recognizing emotional expressions, or so- brain”) cial behavior (De Zeeuw et al., 2021; Ferrari et al., 2018; Copyright 2024 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Module 3.1 Structure of the Vertebrate Nervous System 73 Koziol et al., 2014). One hypothesis is that the cerebel- midbrain structures.) Another midbrain structure, the lum’s primary function is to detect sequences of events substantia nigra, gives rise to a dopamine-containing (Van Overwalle et al., 2020; Vandervert, 2018). pathway that facilitates readiness for movement. Stop & Check 7. Most of the cranial nerves connect to which brain area? The Forebrain The forebrain, the most prominent brain area for mam- See page 79 for the answer. mals and birds, consists of two cerebral hemispheres, left and right (Figure 3.11). Each hemisphere is organized to The Midbrain receive sensory information, mostly from the contralateral (opposite) side of the body. It controls muscles, mostly on As the name implies, the midbrain is between the hindbrain the contralateral side, by way of axons to the spinal cord and the forebrain, although in adult mammals the forebrain and the cranial nerve nuclei. surrounds it. The midbrain is more prominent in reptiles, The outer portion is the cerebral cortex. (Cerebrum is amphibians, and fish. The roof of the midbrain is called the a Latin word for “brain.” Cortex is a Latin word for “bark” or tectum. (Tectum is the Latin word for “roof.” The same root “shell.”) Under the cerebral cortex are other structures, in- occurs in the geological term plate tectonics.) The swellings cluding those illustrated in Figure 3.12. The thalamus is the on each side of the tectum are the superior colliculus and main source of input to the cortex. The hypothalamus is the inferior colliculus (Figures 3.8 and 3.10). Both are im- essential for control of eating, drinking, temperature con- portant for sensory processing—the inferior colliculus for trol, and reproductive behaviors. The amygdala is part of a hearing and the superior colliculus for vision. circuit that is central for evaluating emotional information, Under the tectum lies the tegmentum, the interme- especially with regard to fear. Figure 3.12 shows the posi- diate level of the midbrain. (In Latin, tegmentum means a tions of these structures in three-dimensional perspective. “covering,” such as a rug on the floor. The tectum covers Figure 3.13 is a coronal (from the front) section through the the tegmentum, but the tegmentum covers several other human brain and a view of the ventral surface of the brain. Figure 3.10 A sagittal section through the human brain Cingulate gyrus Cerebral cortex Parietal lobe Frontal lobe Thalamus Corpus callosum Tissue dividing Occipital lobe lateral ventricles Nucleus accumbens Superior and Hypothalamus inferior colliculi Midbrain Pituitary gland Pons Cerebellum Medulla Spinal cord Central canal of spinal cord (Source: Based on Nieuwenhuys et al., 1988) Copyright 2024 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Module 3.1 Structure of the Vertebrate Nervous System 75 Figure 3.13 Two views of the human brain (a): A coronal section. Note how the corpus callosum and anterior commissure provide communication between the left and right hemispheres. (b): The ventral surface. The optic nerves (cut here) extend to the eyes. Frontal lobe of Longitudinal cerebral fissure cortex Olfactory bulbs Cerebral cortex Corpus Temporal callosum lobe of Lateral cerebral Optic Dorsal ventricles cortex nerves Ventral Basal ganglia Medulla Temporal lobes Spinal cord Dr. Dana Copeland Cerebellum (a) Anterior commissure (b) (Source: Photos courtesy of Dr. Dana Copeland) Thalamus and the globus pallidus (Figure 3.15). Many authorities include other structures as well, especially the nucleus The thalamus is a pair of structures (left and right) in the accumbens. center of the forebrain. It resembles two small avocados It has long been known that damage to the basal gan- joined side by side. Most sensory information goes first to glia impairs movement, as in conditions such as Parkinson’s the thalamus, which processes it and sends output to the disease and Huntington’s disease. The basal ganglia inte- cerebral cortex. An exception to this rule is olfactory in- grate motivational and emotional behavior to increase the formation, which goes from the olfactory receptors to the vigor of selected actions. However, the role of the basal olfactory bulbs and then directly to the cerebral cortex. ganglia extends beyond movement. They are critical for Many nuclei of the thalamus receive their input from a gradual learning of skills and habits. sensory system, such as vision, process it in various ways, and transmit information to an area of the cerebral cortex, Basal Forebrain as in Figure 3.14. Another function of the thalamus relates to memory. When you hold information in working mem- A structure on the ventral surface of the forebrain, the ory, activity bounces back and forth between the frontal nucleus basalis, receives input from the hypothalamus cortex and the thalamus (Bolkan et al., 2017). and basal ganglia and sends axons that release acetylcho- line to widespread areas in the cerebral cortex (Figure 3.16). The nucleus basalis is a key system for arousal, wakeful- Hypothalamus and Pituitary Gland ness, and attention. Patients with Parkinson’s disease and The hypothalamus, a small area just ventral to the thala- Alzheimer’s disease have impairments of attention and in- mus (Figures 3.10 and 3.12), has widespread connections tellect because of inactivity or deterioration in the nucleus with the rest of the brain. Damage in the hypothalamus basalis. leads to abnormalities in motivated behaviors, such as feeding, drinking, temperature regulation, sexual behavior, Hippocampus or fighting. Because of these important behavioral effects, The hippocampus (from the Latin word meaning “sea the small hypothalamus attracts much research attention. horse”) is a large structure between the thalamus and the Partly through nerves and partly by releasing hormones, cerebral cortex, mostly toward the posterior of the fore- the hypothalamus conveys messages to the pituitary gland, brain, as illustrated in Figure 3.12. We consider the hip- altering its release of hormones (Figure 3.10). pocampus in more detail in the chapter on memory. The gist of that discussion is that the hippocampus is critical Basal Ganglia for memories, especially memories for individual events. The basal ganglia, a group of subcortical structures lateral It is also essential for monitoring where you are and where to the thalamus, include the caudate nucleus, the putamen, you are going. Copyright 2024 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 78 Chapter 3 Anatomy and Research Methods Figure 3.17 The cerebral ventricles (a) Diagram depicting positions of the four ventricles. (b) Photo of a human brain, viewed from above, with a horizontal cut through one hemisphere to show the position of the lateral ventricles. Lateral ventricles Third ventricle Posterior Lateral ventricles Anterior Thalamus Cerebral Fourth aqueduct ventricle Dr. Dana Copeland Central canal of spinal cord (a) (b) (Source: Photo courtesy of Dr. Dana Copeland) Module 3.1 | In Closing Learning Neuroanatomy The brain is a complex structure. It will help if you return 4. The central nervous system consists of the spinal cord, to review this module as you encounter structures again in hindbrain, midbrain, and forebrain. 71 later chapters. Gradually, the material will become more 5. The hindbrain consists of the medulla, pons, and cer- familiar. ebellum. The medulla and pons control breathing, heart rate, and other vital functions through the cranial nerves. Summary The cerebellum contributes to movement, timing, cer- tain types of learning and conditioning, and detecting 1. The vertebrate nervous system has two main divisions, sequences of events. 71 the central nervous system and the peripheral nervous 6. The cerebral cortex receives its sensory information, system. 66 except for olfaction, from the thalamus. Connections 2. Each segment of the spinal cord has a sensory nerve and between the cortex and the thalamus maintain informa- a motor nerve on both the left and right sides. Spinal tion in working memory. 73 pathways convey information to the brain. 68 7. The subcortical areas of the forebrain include the thala- 3. The sympathetic nervous system (one of the two divi- mus, hypothalamus, pituitary gland, basal ganglia, and sions of the autonomic nervous system) activates the hippocampus. 73 body’s internal organs for vigorous activities. The 8. The cerebral ventricles contain fluid that provides buoy- parasympathetic system (the other division) promotes ancy and cushioning for the brain. 77 digestion and other nonemergency processes. 69 Copyright 2024 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  86 Chapter 3 many of their synaptic terminals are in the dorsal horns Anatomy of the Central of the spinal gray matter. In contrast, the neurons of the ventral root are motor (efferent) multipolar neurons with Nervous System their cell bodies in the ventral horns. Those that are part of the somatic nervous system project to skeletal muscles; In the first three modules of this chapter, you learned about those that are part of the autonomic nervous system proj- the divisions of the nervous system, the cells that compose ect to ganglia, where they synapse on neurons that in it, and some of the neuroanatomical techniques used to turn project to internal organs (heart, stomach, liver, etc.). study it. This final module focuses exclusively on the anat- See Appendix I. omy of the CNS. Your ascent through the CNS will begin with a focus on the spinal cord, and then you will move up to the brain. Five Major Divisions of the Brain LO 3.10 List and discuss the five major divisions of the human brain. Spinal Cord A necessary step in learning to live in an unfamiliar city LO 3.9 Draw and label a cross section of the spinal cord. is learning the names and locations of its major neighbor- In cross section, it is apparent that the spinal cord com- hoods or districts. Those who possess this information can prises two different areas (see Figure 3.17): an inner easily communicate the general location of any destination H-shaped core of gray matter and a surrounding area in the city. This section of the chapter introduces you to the of white matter. Gray matter is composed largely of cell five “neighborhoods,” or divisions, of the brain—for much bodies and unmyelinated interneurons, whereas white the same reason. matter is composed largely of myelinated axons. (It is the To understand why the brain is considered to be myelin that gives the white matter its glossy white sheen.) composed of five divisions, it is necessary to understand The two dorsal arms of the spinal gray matter are called its early development. In the vertebrate embryo, the tis- the dorsal horns, and the two ventral arms are called the sue that eventually develops into the CNS is recognizable ventral horns. as a fluid-filled tube (see Figure 3.18). The first indica- Pairs of spinal nerves are attached to the spinal cord— tions of the developing brain are three swellings that one on the left and one on the right—at 31 different levels occur at the anterior end of this tube. These three swell- of the spine. Each of these 62 spinal nerves divides as it ings eventually develop into the adult forebrain, midbrain, nears the cord (see Figure 3.17), and its axons are joined and hindbrain. to the cord via one of two roots: the dorsal root or the Before birth, the initial three swellings in the neural ventral root. tube become five (see Figure 3.18). This occurs because All dorsal root axons, whether somatic or autonomic, the forebrain swelling grows into two different swell- are sensory (afferent) unipolar neurons with their cell ings, and so does the hindbrain swelling. From anterior bodies grouped together just outside the cord to form to posterior, the five swellings that compose the develop- the dorsal root ganglia (see Figure 3.17). As you can see, ing brain at birth are the telencephalon, the diencephalon, the mesencephalon (or midbrain), the metencephalon, and the myelencephalon (encephalon means “within the head”). These swellings ultimately develop into the five divisions Figure 3.17 A schematic cross section of the spinal cord, of the adult brain. As students, we memorized their order and the dorsal and ventral roots. by remembering that the telencephalon is on the top and Gray matter the other four divisions are arrayed below it in alphabeti- Dorsal horn White matter cal order. Dorsal Figure 3.19 illustrates the locations of the telencepha- Dorsal root Unipolar sensory lon, diencephalon, mesencephalon, metencephalon, and Dorsal root neuron myelencephalon in the adult human brain. Notice that in ganglion humans, as in other higher vertebrates, the telencepha- lon (the left and right cerebral hemispheres) undergoes the greatest growth during development. The other four divisions of the brain are often referred to collectively Multipolar as the brain stem—the stem on which the cerebral hemi- Ventral root motor Ventral spheres sit. The myelencephalon is often referred to as Spinal Ventral neuron horn nerve the medulla. M03_PINE1933_11_GE_C03.indd 86 22/01/2021 10:42  Anatomy of the Nervous System 87 Figure 3.18 The early development of the mammalian brain illustrated in schematic horizontal sections. Compare with the adult human brain in Figure 3.19. Telencephalon (cerebral hemispheres) Forebrain Diencephalon Midbrain Mesencephalon (midbrain) Metencephalon Hindbrain Myelencephalon (medulla) Spinal cord Spinal cord 100 tiny nuclei that occupies the central core of the brain Figure 3.19 The five divisions of the adult human brain. stem from the posterior boundary of the myelencephalon Forebrain to the anterior boundary of the midbrain. It is so named Telencephalon because of its netlike appearance (reticulum means “little Diencephalon net”). Sometimes, the reticular formation is referred to as the reticular activating system because parts of it seem to play a role in arousal. However, the various nuclei Midbrain Mesencephalon of the reticular formation are involved in a variety of functions—including sleep, attention, movement, the maintenance of muscle tone, and various cardiac, circulatory, and respiratory reflexes. Accordingly, Hindbrain referring to this collection of nuclei as a system can be Metencephalon misleading. Myelencephalon Metencephalon LO 3.12 List and describe the components of the Now that you have learned the five major divisions of metencephalon. the brain, it is time to introduce you to their major struc- The metencephalon, like the myelencephalon, houses tures. We begin our survey of brain structures in the myel- many ascending and descending tracts and part of the encephalon, then ascend through the other divisions to the reticular formation. These structures create a bulge, called telencephalon. the pons, on the brain stem’s ventral surface. The pons is one major division of the metencephalon; the other is the Myelencephalon cerebellum (little brain)—see Figure 3.21. The cerebellum is the large, convoluted structure on the brain stem’s LO 3.11 List and describe the components of the dorsal surface. It is an important sensorimotor structure; myelencephalon. cerebellar damage eliminates the ability to precisely Not surprisingly, the myelencephalon (or medulla), the control one’s movements and to adapt them to changing most posterior division of the brain, is composed largely conditions. However, the fact that cerebellar damage also of tracts carrying signals between the rest of the brain and produces a variety of cognitive deficits (e.g., deficits in the body. An interesting part of the myelencephalon from decision making and in the use of language) suggests a psychological perspective is the reticular formation that the functions of the cerebellum are not restricted to (see Figure 3.20). It is a complex network of about sensorimotor control. M03_PINE1933_11_GE_C03.indd 87 22/01/2021 10:42  88 Chapter 3 Figure 3.20 Structures of the human myelencephalon Figure 3.21 The human mesencephalon (midbrain). (medulla) and metencephalon. Superior colliculus Superior colliculus Periaqueductal Inferior gray colliculus Dorsal Mesencephalic Tectum reticular formation Cerebral aqueduct Tegmentum Red nucleus Pons Substantia Ventral nigra Cerebellum Reticular Medulla formation colorful structures of particular interest to biopsycholo- gists: the periaqueductal gray, the substantia nigra, and the red nucleus (see Figure 3.21). The periaqueductal gray is the gray matter situated around the cerebral Mesencephalon aqueduct, the duct connecting the third and fourth LO 3.13 List and describe the components of the ventricles; it is of special interest because of its role in mesencephalon. mediating the analgesic (pain-reducing) effects of opioid drugs. The substantia nigra (black substance) and the The mesencephalon, like the metencephalon, has two red nucleus are both important components of the sen- divisions. The two divisions of the mesencephalon are the sorimotor system. tectum and the tegmentum (see Figure 3.21). The tectum (roof) is the dorsal surface of the midbrain. In mammals, the tectum is composed of two pairs of bumps, the colliculi Diencephalon (little hills). The posterior pair, called the inferior colliculi, have an auditory function. The anterior pair, called the LO 3.14 List and describe the components of the superior colliculi, have a visual-motor function; more spe- diencephalon. cifically, to direct the body’s orientation toward or away The diencephalon is composed of two structures: the thala- from particular visual stimuli (see Gandhi & Katnani, mus and the hypothalamus (see Figure 3.22). The thalamus 2011). In lower vertebrates, the function of the tectum is is the large, two-lobed structure that constitutes the top of entirely visual-motor, and it is sometimes referred to as the brain stem. One lobe sits on each side of the third ven- the optic tectum. tricle, and the two lobes are joined by the massa intermedia, The tegmentum is the division of the mesencephalon which runs through the ventricle. Visible on the surface of ventral to the tectum. In addition to the reticular forma- the thalamus are white lamina (layers) that are composed of tion and tracts of passage, the tegmentum contains three myelinated axons. M03_PINE1933_11_GE_C03.indd 88 22/01/2021 10:42  Anatomy of the Nervous System 89 motivated behaviors (e.g., eating, sleep, and sexual Figure 3.22 The human diencephalon. behavior). It exerts its effects in part by regulating the Right release of hormones from the pituitary gland, which Left thalamus dangles from it on the ventral surface of the brain. The Bands of thalamus myelinated literal meaning of pituitary gland is “snot gland”; it was axons first discovered in a gelatinous state behind the nose of a cadaver and was incorrectly assumed to be the main source of nasal mucus. In addition to the pituitary gland, two other struc- tures appear on the inferior surface of the hypothalamus: the optic chiasm and the mammillary bodies (see Figure 3.23). The optic chiasm is the point at which the optic nerves from each eye come together and then decussate (cross over to the other side of the brain) (see Chapter 6). The decussating fibers are said to be contralateral (pro- jecting from one side of the body to the other), and the nondecussating fibers are said to be ipsilateral (staying on the same side of the body). The mammillary bodies, Figure 3.23 The human hypothalamus (in color) in relation to the optic chiasm and the pituitary gland. Hypothalamus The thalamus comprises many different pairs of nuclei, most of which project to the cortex. The general organiza- tion of the thalamus is illustrated in Appendix V. The most well-understood thalamic nuclei are the sensory relay nuclei—nuclei that receive signals from sensory receptors, process them, and then transmit them to the appropriate areas of sensory cortex. For example, the lateral geniculate nuclei, the medial geniculate nuclei, and the ventral posterior nuclei are important relay stations in the visual, auditory, and somatosensory systems, respectively. Sensory relay nuclei are not one- way streets; they all receive feedback signals from the very areas of cortex to which they project (Zembrzycki Mammillary Optic body et al., 2013). Although less is known about the other tha- chiasm lamic nuclei, the majority of them receive input from areas of the cortex and project to other areas of the cortex (see Sherman, 2007). The hypothalamus is located just below the ante- Pituitary rior thalamus (hypo means “below”)—see Figure 3.23. gland It plays an important role in the regulation of several M03_PINE1933_11_GE_C03.indd 89 22/01/2021 10:42  92 Chapter 3 Limbic System and the Basal ex. Ganglia ry LO 3.16 List and describe the components of the limbic system and of the basal ganglia. Although much of the subcortical portion of ; the telencephalon is taken up by axons project- ing to and from the neocortex, there are several large subcortical nuclear groups. Some of them are considered part of either the limbic system or. the basal ganglia system. Don’t be misled by the word system in these contexts; it implies a level of certainty that is unwarranted. It is not entirely clear exactly what these hypothetical systems do, exactly which structures should be included in them, or even whether it is appropriate to view them as unitary systems. Nevertheless, if not taken too literally, the concepts of limbic system and basal ganglia system provide a useful means of conceptualizing the organization of several sub- cortical structures. The limbic system is a circuit of midline structures that circle the thalamus (limbic means “ring”). The limbic system is involved in the regulation of motivated behaviors—including the four F’s of motivation: fleeing, feeding, fight- l ing, and sexual behavior. (This joke is as old as biopsychology itself, but it is a good one.) In addition to the structures about which you have already read (the mammillary bodies and the hip- pocampus), major structures of the limbic system include the amygdala, the fornix, the cingulate cortex, and the septum. Let’s begin tracing the limbic circuit (see Figure 3.27) at the amygdala—the almond-shaped nucleus in the anterior temporal lobe (amygdala means “almond” and is pronounced “a-MIG-dah-lah”). Posterior to the amygdala is the hippocampus, which runs beneath the thalamus in the medial temporal lobe. Next in the ring are the cingulate cortex and the fornix. The cingulate cortex is the large strip of cortex in the cingulate gyrus on the medial surface of the cerebral hemispheres, just superior to the corpus callosum; it encircles the dorsal thalamus (cingulate means “encircling”). The fornix, the major tract of the limbic system, also encircles the dorsal thalamus; it leaves the dorsal end of the hippocampus and sweeps forward in an arc coursing along the superior surface of the third ventricle and terminating in the septum and the mammillary bodies (fornix means “arc”). The septum is a midline nucleus located at the anterior tip of the cingulate cortex. Several tracts connect the septum and mammillary M03_PINE1933_11_GE_C03.indd 92 22/01/2021 10:43  Anatomy of the Nervous System 93 as the globus pallidus (pale globe). The globus pallidus is Figure 3.27 The major structures of the limbic system: amygdala, hippocampus, cingulate cortex, fornix, septum, located medial to the putamen between the putamen and and mammillary body. the thalamus. The basal ganglia play a role in the performance of Right cingulate cortex Left cingulate voluntary motor responses and decision making (see cortex Hikosaka et al., 2014). Of particular interest is a pathway Longitudinal fissure Hippocampus that projects to the striatum from the substantia nigra of the midbrain: Parkinson’s disease, a disorder character- ized by rigidity, tremors, and poverty of voluntary move- Fornix ment, is associated with the deterioration of this pathway. Another part of the basal ganglia that is of particular interest to biopsychologists is the nucleus accumbens, which is in the medial portion of the ventral striatum (see Figure 3.28). The nucleus accumbens is thought to play a role in the rewarding effects of addictive drugs and other reinforcers. Figure 3.29 summarizes the major brain divisions and structures whose names have appeared in boldface in this section Figure 3.28 The basal ganglia: striatum (caudate plus putamen), and globus pallidus. Notice that, in this view, the right globus pallidus is largely hidden behind the right thalamus Amygdala and the left globus pallidus is totally hidden behind the left putamen. Putamen Thalamus Septum Mammillary Tail of body caudate Head of caudate bodies with the amygdala and hippocampus, thereby completing the limbic ring. The functions of the hippocampus, the hypo- thalamus and the amygdala have been investigated more than those of the other limbic structures. As stated previously, the hippocampus plays a role in certain forms of memory, and the hypothalamus is involved in a variety of motivated behaviors such as eating, sleep, and sexual behavior. The amygdala, on the other hand, is involved in emotion—particularly fear. You will learn much more about these structures in later chapters. The basal ganglia are illustrated in Figure 3.28. The long tail-like caudate (caudate means “tail-like”) and putamen (pronounced “pew-TAY- men”) receive inputs from the neocortex (see Gray- biel, 2000). Together, the caudate and putamen, which both have a striped appearance, are known Globus as the striatum (striped structure). The striatum’s pallidus Nucleus major output is to a pale circular structure known accumbens M03_PINE1933_11_GE_C03.indd 93 22/01/2021 10:43  90 Chapter 3 which are often considered to be part of the hypothala- Figure 3.24 The major fissures of the human cerebral mus, are a pair of spherical nuclei located on the inferior cortex. surface of the hypothalamus, just behind the pituitary. Lateral Longitudinal Corpus The mammillary bodies and the other nuclei of the hypo- ventricle fissure callosum thalamus are illustrated in Appendix VI. Central fissure Third Telencephalon ventricle LO 3.15 List and describe the components of the telencephalon. The telencephalon, the largest division of the human brain, Lateral mediates the brain’s most complex functions. It initiates vol- fissure untary movement, interprets sensory input, and mediates complex cognitive processes such as learning, speaking, and problem solving. CEREBRAL CORTEX. The cerebral hemispheres are covered by a layer of tissue called the cerebral cortex Hippocampus (cerebral bark). Because the cerebral cortex is mainly com- posed of small, unmyelinated neurons, it is gray and is often referred to as the gray matter. In contrast, the layer Central beneath the cortex is mainly composed of large myelin- fissure ated axons, which are white and often referred to as the Lateral white matter. fissure In humans, the cerebral cortex is deeply convoluted (furrowed)—see Figure 3.24. The convolutions have the effect of increasing the amount of cerebral cortex without increasing the overall volume of the brain. Not all mammals have convoluted cortexes; most mammals are lissencephalic (smooth-brained). It was once believed that the number and size of corti- cal convolutions determined a species’ intellectual capaci- ties; however, the number and size of cortical convolutions appear to be related more to body size. Every large mammal has an extremely convoluted cortex. hemisphere-connecting tracts are called cerebral commis- sures. The largest cerebral commissure, the corpus callo- sum, is clearly visible in Figure 3.24. As Figures 3.24 and 3.25 indicate, the two major land- Journal Prompt 3.2 marks on the lateral surface of each hemisphere are the Why do you think only large mammals have extremely central fissure and the lateral fissure. These fissures par- convoluted cortices? tially divide each hemisphere into four lobes: the frontal lobe, the parietal lobe (pronounced “pa-RYE-e-tal”), the temporal lobe, and the occipital lobe (pronounced “ok- SIP-i-tal”). Among the largest gyri are the precentral gyri, The large furrows in a convoluted cortex are called the postcentral gyri, and the superior temporal gyri in the fissures, and the small ones are called sulci (singular frontal, parietal, and temporal lobes, respectively. sulcus). The ridges between fissures and sulci are called It is important to understand that the cerebral lobes gyri (singular gyrus). It is apparent in Figure 3.24 that are not functional units. It is best to think of the cere- the cerebral hemispheres are almost completely sepa- bral cortex as a flat sheet of cells that just happens to be rated by the largest of the fissures: the longitudinal divided into lobes because it folds in on itself at certain fissure. The cerebral hemispheres are directly connected places during development. Thus, it is incorrect to think by a few tracts spanning the longitudinal fissure; these that a lobe is a functional unit, having one set of functions. M03_PINE1933_11_GE_C03.indd 90 22/01/2021 10:42  Anatomy of the Nervous System 91 lobe: The postcentral gyrus analyzes sensations from the Figure 3.25 The lobes of the cerebral hemisphere. body (e.g., touch), whereas the remaining areas of cortex Longitudinal in the posterior parts of the parietal lobes play roles in per- fissure ceiving the location of both objects and our own bodies and in directing our attention. The cortex of each tempo- ral lobe has three general functional areas: The superior temporal gyrus is involved in hearing and language, the inferior temporal cortex identifies complex visual patterns, and the medial portion of temporal cortex (which is not visible from the usual side view) is important for certain kinds of memory. Lastly, each frontal lobe has two distinct functional areas: The precentral gyrus and adjacent frontal cortex have a motor function, whereas the frontal cortex anterior to motor cortex performs complex cognitive func- tions, such as planning response sequences, evaluating the outcomes of potential patterns of behavior, and assess- ing the significance of the behavior of others (see Euston, Gruber, & McNaughton, 2012; Isoda & Noritake, 2013; Precentral Central Postcentral Pezzulo et al., 2014). gyrus fissure gyrus About 90 percent of human cerebral cortex is neocortex (new cortex), also known as isocortex. By convention, the layers of neocortex are numbered I through VI, starting at the surface. Figure 3.26 illustrates two adjacent sections of neocortex. One has been stained with a Nissl stain to reveal the number and shape of its cell bodies; the other has been stained with a Golgi stain to reveal the silhouettes of a small proportion of its neurons. Three important characteristics of neocortical anat- omy are apparent from the sections in Figure 3.26. First, it is apparent that many cortical neurons fall into one of two different categories: pyramidal (pyramid-shaped) cells and stellate (star-shaped) cells. Pyramidal cells are Lateral large multipolar neurons with pyramid-shaped cell bod- fissure ies, a large dendrite called an apical dendrite that extends from the apex of the pyramid straight toward the cor- Superior tex surface, and a very long axon (see Lodato, Shetty, & temporal gyrus Cerebellum Arlotta, 2015). In contrast, stellate cells are small star- shaped interneurons (neurons with a short axon or no axon). Second, it is apparent that the six layers of neo- Frontal Parietal Temporal Occipital cortex differ from one another in terms of the size and lobe lobe lobe lobe density of their cell bodies and the relative proportion of pyramidal and stellate cell bodies that they contain. Third, it is apparent that many long axons and dendrites Still, it is useful at this early stage of your biopsychologi- course vertically (i.e., at right angles to the cortical layers) cal education to get a general idea of various functions of through the neocortex. This vertical flow of information areas within each lobe. More thorough discussions of the is the basis of the neocortex’s columnar organization: cerebral localization of brain functions are presented in Neurons in a given vertical column of neocortex often later chapters. form a mini-circuit that performs a single function (see The main function of the occipital lobes is quite Rowland & Moser, 2014). straightforward: We humans rely heavily on the analysis A fourth important characteristic of neocortical anat- of visual input to guide our behavior, and the occipital cor- omy is not apparent in Figure 3.26: Although neocortex tex and large areas of adjacent cortex perform this func- is six-layered, there are variations in the thickness of the tion. There are two large functional areas in each parietal respective layers from area to area (see Zilles & Amunts, M03_PINE1933_11_GE_C03.indd 91 22/01/2021 10:43  Module 3.2 The Cerebral Cortex 83 straight. The cells within a column have similar properties to damage to the striate cortex of the right hemisphere causes one another. For example, if one cell in a column responds to blindness in the left visual field (the left side of the world touch on the palm of the left hand, then the other cells in that from the viewer’s perspective). A person with complete column do, too. If one cell responds to a horizontal pattern cortical blindness has normal eyes and pupillary reflexes, of light at a particular location, then other cells in the column but no conscious visual perception and no visual imagery respond to the same pattern in nearby locations. (not even in dreams). People who experience eye damage become blind, but if they have an intact occipital cortex Stop & Check and previous visual experience, they can still have visual 10. Why does the thickness of laminae IV and V vary from one imagery and visual dreams (Sabo and Kirtley, 1982). In cortical area to another? short, the eyes provide the stimulus, and the visual cortex provides the experience. See page 89 for the answer. The Parietal Lobe The Occipital Lobe The parietal lobe lies between the occipital lobe and the We group the areas of cortex into four lobes named for central sulcus, a deep groove in the surface of the cortex the skull bones that lie over them: occipital, parietal, tem- (Figure 3.23). The area just posterior to the central sulcus, poral, and frontal. The occipital lobe, at the posterior the postcentral gyrus, or primary somatosensory cortex, (caudal) end of the cortex (Figure 3.22), is the main tar- receives sensations from touch receptors, muscle-stretch get for visual information. The posterior pole of the oc- receptors, and joint receptors. Brain surgeons sometimes cipital lobe is called the primary visual cortex, or striate use only local anesthesia, anesthetizing the scalp but leav- cortex, because of its striped appearance in cross section. ing the brain awake. If during this process they lightly Damage in the striate cortex causes cortical blindness in stimulate the postcentral gyrus, people report tingling sen- the related part of the visual field. For example, extensive sations on the opposite side of the body. Figure 3.22 Areas of the human cerebral cortex (a) The four lobes: occipital, parietal, temporal, and frontal. (b) The primary sensory cortex for vision, hearing, and body sensations; the primary motor cortex; and the olfactory bulb, responsible for the sense of smell. Precentral gyrus Central sulcus Postcentral gyrus (primary motor (primary cortex) somatosensory cortex) Frontal lobe (planning of Parietal lobe Motor Somesthetic movements, (body sensations) recent memory, some aspects of emotions) Prefrontal cortex Visual Auditory Olfactory bulb Olfaction Occipital lobe Audition (vision) Vision Temporal lobe (hearing, advanced visual processing) Somesthesis Movement (a) (b) (Source: for part b: Deacon, 1990) Copyright 2024 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 84 Chapter 3 Anatomy and Research Methods Figure 3.23 Approximate representation of sensory and motor information in the cortex (a) Each location in the somatosensory cortex represents sensation from a different body part. (b) Each location in the motor cortex regulates move- ment of a different body part. Precentral gyrus (primary motor cortex) Leg Hip Trun Knee Hip Nec Trun lder Hea Sho Arm w Elb rm Arm k k Fo nd Postcentral gyrus E lb d k u o rea Ha (primary o W Fi w Th nge ris somatosensory Ha Fi t Ey um rs Th nge n cortex) d No e b N um rs se Broeck b Fac Toes Eye w e Fac Lips e Genitals Teeth Lips Gums Jaw Jaw ue Tong Tongu e r nx y l Pha ina ing om llow d Swa ab ra- Int Dr. Dana Copeland (a) Somatosensory cortex (b) Motor cortex (Source: Based on Penfield and Rasmussen, 1950) The postcentral gyrus includes four bands of cells for auditory information. The human temporal lob