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Materials appearing in this book prepared by individuals as part of their official duties as U. Sapru ; case histories written by Heidi E. Includes bibliographical references and index. ISBN alk. Neurosciences—Outlines, syllabi, etc. Sapru, Hreday N. Nervous System Physiological Phenomena. Mental Disorders—physiopathology. Nervous System Diseases. WL Se ] RC S54 However, the authors, editors, and publisher are not responsible for errors or omissions or for any consequences from application of the information in this book and make no warranty, expressed or implied, with respect to the currency, completeness, or accuracy of the contents of the publication.
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However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any change in indications and dosage and for added warnings and precautions.
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It is the responsibility of the health care provider to ascertain the FDA status of each drug or device planned for use in their clinical practice. To purchase additional copies of this book, call our customer service department at or fax orders to International customers should call The final section of the text Chapters 22 to 28 concerns a variety of functions of the nervous system characterized by higher levels of complexity.
Vascular syndromes of the brainstem constitute an important review for the student on a topic that is heavily tested on USMLE examinations. These disorders have a clear relationship to abnormalities in neural and neurochemical functions and, thus, reflect an important component of neuroscience. Essential Neuroscience proved to be a highly effective tool for students and faculty.
The goal of this second edition, therefore, is to perfect the formula with which we had such success. For example, key terms and concepts of neuroscience were highlighted in bold in each chapter and explained in an extensive glossary at the end of the book.
Also in response to reader requests, we have presented Chapter Summary Tables at the end of each chapter in this new edition. These tables will not only help students review chapters as they go, but will be valuable, high-yield tools for study and review at examination time. Selected topics have been expanded where appropriate: the functional relationship, memory, and lateralization of the hippocampal formation and limbic cortex; limbic relationships of the basal ganglia especially in reference to psychiatric issues ; the development of the anterior and posterior pituitary; a discussion of prions in relation to Creutzfeldt Jacob disease; and others.
Material has also been integrated in multiple places where it would augment understanding of important concepts. Extensive cross referencing among chapters has likewise been incorporated. Although this text was originally primarily designed for medical students who study neuroscience, it can be used quite effectively by neurology residents and graduate and undergraduate university students specializing in biological sciences. In this latest edition, special topics have been reworked to better accommodate dental students.
The trigeminal nucleus, for instance, has been divided into its components for a more detailed study. Essential Neuroscience, 2nd Edition distinguishes itself from other texts as the concise, clinically relevant neuroscience text providing balanced coverage of anatomy, physiology, biology, and biochemistry. With a full array of pedagogical features, it helps students gain conceptual mastery of this challenging discipline and, we hope, foments the urge to continue its exploration.
Allan Siegel Hreday N. An overview of the structural organization of the nervous system is helpful when beginning to study the neurosciences. However, first it would be useful to define some basic terms that will be essential for understanding the anatomy of the nervous system.
Medial—lateral: Medial means toward the median plane, and lateral means away from the median plane. Anterior—posterior: Above the midbrain, anterior means toward the front of the brain, and posterior means toward the back of the brain.
At and below the midbrain, anterior means toward the ventral surface of the body, and posterior means toward the dorsal surface of the body. Rostral—caudal: Above the midbrain, rostral means toward the front of the brain, and caudal means toward the back of the brain.
At and below the midbrain, rostral means toward the cerebral cortex, and caudal means toward the sacral end or bottom of the spinal cord. Dorsal—ventral: Rostral to the midbrain, dorsal refers to the top of the brain, and ventral refers to the bottom of the brain. At the level of and caudal to the midbrain, dorsal means toward the posterior surface of the body, and ventral refers to the anterior surface of the body.
Superior—inferior: Both at positions above and below the midbrain, superior means toward the top of the cerebral cortex, and inferior means toward the bottom of the spinal cord. Other terms commonly used in neuroanatomy are: Ipsilateral—contralateral: Ipsilateral means on the same side with reference to a specific point; contralateral means on the opposite side.
Commissure and decussation: Commissure is a group of nerve fibers connecting one side of the brain with the other. Decussation is the crossing over of these nerve fibers. Neuron: A neuron is the anatomical and functional unit of the nervous system, which consists of a nerve cell body, dendrites which receive signals from other neurons , and an axon which transmits the signal to another neuron.
Nucleus: Nucleus refers to groups of neurons located in a specific region of the brain or spinal cord that generally have a similar appearance, receive information from similar sources, project their axons to similar targets, and share similar functions.
Tract: Many axons grouped together, which typically pass from a given nucleus to a common target region or to several regions, form a tract. White and gray matter: When examining the brain or spinal cord with the unaided eye, one can distinguish white and gray tissue. The region that appears white is called white matter, and the area that appears gray is called gray matter. The fixed axes for anatomical reference planes are superior—inferior and anterior—posterior.
The other axes vary according to their location within the CNS. In contrast, the gray matter consists mainly of neuronal cell bodies nuclei and lacks myelinated axons. Glial cells: These nonneural cells form the interstitial tissue of the nervous system. There are different types of glial cells, which include astrocytes, oligodendrocytes, microglia, and ependymal cells.
Details of the functions of each of these components are provided in Chapter 5. Central and peripheral nervous systems: The central nervous system CNS includes the brain and spinal cord and is surrounded and protected by three connective tissue coverings called meninges. Within the CNS are fluid-filled spaces called ventricles.
The bone of the skull and vertebral column surround the brain and spinal cord, respectively. Autonomic and somatic nervous systems: These are functional subdivisions of the nervous system in contrast to the anatomical classifications described earlier. The autonomic nervous system innervates smooth muscle and glands, whereas the somatic nervous system innervates mainly musculoskeletal structures and the sense organs of skin. To understand the function of CNS structures, it is important to be able to identify and locate them in relation to one another.
The many structures of the brain and spine may seem confusing in this initial overview, but knowing what they are is essential for developing a broader familiarity with neuroscience. It will not be necessary to memorize every structure and function in this introduction because the chapters that follow present these structures in greater detail.
We will begin with an examination of the major structures of the CNS, taking a topographical approach to the review of anatomical and functional relationships of structures in the cerebral cortex. Key structures will be identified as they appear in different views of the brain. This chapter provides an initial overview of these regions. A more detailed analysis of the structural and functional properties of the spinal cord is presented in Chapter 9 and is followed by a parallel morphological analysis of the structures contained within the medulla, pons, midbrain, and forebrain in subsequent chapters.
The spinal cord is a thin, cylinder-like structure with five regions that extend from its attachment to the brain downward. The most rostral region, which is closest to the brain, is the cervical cord and contains eight pairs of spinal nerves.
Caudal to the cervical cord lies the thoracic cord, which contains 12 pairs of spinal nerves. Next is the lumbar cord, which contains five pairs of spinal nerves. In the cervical and lumbar regions, the spinal cord is enlarged because of the presence of greater numbers of nerve cell bodies and fiber tracts, which innervate the upper and lower limbs, respectively. The brainstem, cerebellum, and cerebral hemispheres form the brain.
The brainstem can be divided into three regions: the medulla, rostral to and continuous with the spinal cord; the pons, rostral to the medulla; and the midbrain, rostral to the pons and continuous with the diencephalon. The cerebellum is positioned like a tent dorsal to the pons and is attached to the brainstem by three massive fiber groups, or peduncles. The cerebral hemispheres contain the cerebral cortex, which covers the surface of the brain and is several millimeters thick as well as deeper structures, including the corpus callosum, diencephalon, basal ganglia, limbic structures, and the internal capsule.
Thus, sensation from the left side of the body is consciously appreciated on the right side of the cerebral cortex. Similarly, motor control over the right arm and leg is controlled by neurons located on the left cerebral cortex. Lateral Surface of the Brain Four lobes of the cerebral cortex—the frontal, parietal, and temporal lobes and a portion of the occipital lobe— can be identified on the lateral surface of the brain Fig.
The lobes of the cerebral cortex integrate motor, sensory, autonomic, and intellectual processes and are organized along functional lines. For the most part, a fissure, called a sulcus, separates these lobes. In addition, pairs of sulci form the boundaries of ridges referred to as gyri. The cortex consists of both cells and nerve fibers. The cellular components constitute the gray matter of cortex and lie superficial i.
As a general rule, the nerve fibers that comprise the white matter of the cortex pass between different regions of cortex, facilitating communication between the lobes of the cerebral cortex. In addition, large components of the white matter consist of fibers passing bidirectionally between the cortex and other regions of the CNS. Frontal Lobe The first step in identifying the main structures of the lateral surface of the brain is to locate the central sulcus, which serves as the posterior boundary of the frontal lobe Fig.
This sulcus extends from near the longitudinal fissure present along the midline but not visible in the lateral view of the brain shown in Fig. Major structures include the central sulcus and the precentral primary motor , premotor, and postcentral primary somatosensory gyri. Also note the gyri situated rostral to the premotor cortex, including the orbital gyri, which mediate higher order intellectual functions and contribute to the regulation of emotional behavior.
Of the three gyri comprising the temporal lobe, the superior temporal gyrus is important for auditory functions, and the inferior and middle temporal gyri mediate complex visual functions. Different aspects of the parietal lobe located just caudal to the primary somatosensory cortex integrate a variety of higher order sensory functions; the occipital lobe contains the primary receiving area for visual impulses.
The frontal lobe, the largest of the cerebral lobes, extends from the central sulcus to the frontal pole of the brain. It extends inferiorly to the lateral sulcus. The frontal cortex also extends onto the medial surface of the brain, where it borders the corpus callosum inferiorly see Fig. At the posterior aspect of the frontal lobe, the most prominent structure is the precentral gyrus, which is bounded posteriorly and anteriorly by the central and precentral sulci, respectively Fig.
The function of the precentral gyrus is to integrate motor function signals from different regions of the brain. It serves as the primary motor cortex for control of contralateral voluntary movements. The neurons within the precentral gyrus are somatotopically organized.
Somatotopic means that different parts of the precentral gyrus are associated with distinct parts of the body, both functionally and anatomically. The outputs from the precentral gyrus to the brainstem and contralateral spinal cord follow a similar functional arrangement.
The region closest to the lateral Sylvian sulcus the inferior part of the precentral gyrus is associated with voluntary control over movements of the face and head. The neurons associated with motor control of the upper and lower limbs are found at progressively more dorsal and medial levels, respectively.
When the parts of the body are drawn in terms of the degree of their cortical representation i. The motor homunculus demonstrates how cell groups in the CNS associated with one part of the body relate anatomically to other cell groups associated with other parts of the body. In addition, the illustrative device shows the relative sizes of the populations of neurons associated with specific parts of the body.
Immediately rostral to the precentral gyrus is the premotor area premotor cortex , which extends from near the lateral fissure on to the medial surface of the brain; this region is referred to as the supplemental motor area. This cortex exercises control over movements associated with the contralateral side of the body by playing an important role in the initiation and sequencing of movements.
Immediately anterior to the premotor cortex, three parallel gyri—the superior, middle, and inferior frontal gyri—are oriented in anterior—posterior positions Fig. In the region of the middle frontal gyrus extending into the inferior frontal gyrus and immediately rostral to the premotor region, lies an area called the frontal eye fields. This region coordinates voluntary control of conjugate i. Visible are the structures situated on the medial aspect of the cortex as well as subcortical areas, which include the corpus callosum, septum pellucidum, fornix, diencephalon, and brainstem structures.
Portions of these gyri are also involved in the integration of motor processes. Far rostral to this region, an area that includes inferior orbital gyri , medial, and lateral aspects of the frontal lobe, called the prefrontal cortex, also plays important roles in the processing of intellectual and emotional events. Within the depths of the lateral Sylvian sulcus is a region of cortex called the insula, which can be seen only when the temporal lobe is pulled away from the rest of the cortex.
It reflects a convergence of the temporal, parietal, and frontal cortices and has, at different times, been associated with the reception and integration of taste sensation, reception of viscerosensations, processing of pain sensations, and vestibular functions. Parietal Lobe The parietal lobe houses the functions that perceive and process somatosensory events.
It extends posteriorly from the central sulcus to its border with the occipital lobe Fig. The parietal lobe contains the postcentral gyri, which has the central sulcus as its anterior border and the postcentral sulcus as its posterior border. The postcentral gyrus is the primary receiving area for somesthetic i. Like the motor cortex, the postcentral gyrus is somatotopically organized and can be depicted as having a sensory homunculus, which parallels that of the motor cortex.
The remainder of the parietal lobe can be divided roughly into two regions, a superior and an inferior parietal lobule, separated by an interparietal sulcus. The inferior parietal lobule consists of two gyri: the supramarginal and angular gyri.
The supramarginal gyrus is just superior to the posterior extent of the lateral sulcus, and the angular gyrus is immediately posterior to the supramarginal gyrus and is often associated with the posterior extent of the superior temporal sulcus Fig. These regions receive input from auditory and visual cortices and are believed to perform complex perceptual discriminations and integrations.
This region is essential for comprehension of spoken language. The superior parietal lobule integrates sensory and motor functions and aids in programming complex motor functions associated with the premotor cortex. Damage to this region produces CNS disturbances, such as apraxia of movement and sensory neglect see Chapters 19 and Occipital Lobe Although a part of the occipital lobe lies on the lateral surface of the cortex, the larger component occupies a more prominent position on the medial surface of the hemisphere.
Situated inferior to the lateral sulcus, the temporal lobe consists of superior, middle, and inferior temporal gyri. On the inner aspect of the superior surface of the superior temporal gyrus lie the transverse gyri of Heschl not shown in Fig.
The other regions of the temporal lobe, including the middle and inferior temporal gyri, are associated with the perception of moving objects in the visual field and recognition of faces, respectively see Chapter 26 for details. Medial Surface of the Brain The principal structures on the medial aspect of the brain can be seen clearly after the hemispheres are divided in the midsagittal plane Fig.
On the medial aspect of the cerebral cortex, the occipital lobe can be seen most clearly. It contains the primary visual receiving area, the visual cortex. The primary visual cortex is located inferior and superior to the calcarine sulcus calcarine fissure , a prominent sulcus formed on the medial surface that runs perpendicular into the parieto-occipital sulcus, which divides the occipital lobe from the parietal lobe Fig.
Located more rostrally from the occipital lobe and situated immediately inferior to the precentral, postcentral, and premotor cortices is the cingulate gyrus. Its ventral border is the corpus callosum.
Another prominent medial structure is the corpus callosum, a massive fiber pathway that permits communication between equivalent regions of the two hemispheres. The septum pellucidum lies immediately ventral to the corpus callosum and is most prominent anteriorly.
It consists of two thin-walled membranes separated by a narrow cleft, forming a small cavity cavum of septum pellucidum.
It forms the medial walls of the lateral ventricles. The septum pellucidum is attached at its ventral border to the fornix. The fornix is the major fiber system arising from the hippocampal formation, which lies deep within the medial aspect of the temporal lobe. It emerges from the hippocampal formation posteriorly and passes dorsomedially around the thalamus to occupy a medial position inferior to the corpus callosum but immediately superior Prefrontal cortex Gyrus rectus Olfactory bulb Medial olfactory stria Lateral olfactory stria Olfactory tract Mammillary bodies Optic chiasm Infundibular stalk Middle temporal gyrus Uncus Inferior temporal gyrus Inferior temporal sulcus Parahippocampal gyrus Collateral sulcus Cerebral peduncle Occipitotemporal gyrus Inferior olivary nucleus Pyramid FIGURE 1—4 Inferior surface of the brain showing the principal gyri and sulci of the cerebral cortex.
On the inferior surface, the midbrain, pons, parts of the cerebellum, and the medulla can be clearly identified. A basic function of the fornix is to transmit information from the hippocampal formation to the septal area and hypothalamus.
The diencephalon lies below the fornix and has two parts Fig. The thalamus is larger and is responsible for relaying and integrating information to different regions of the cerebral cortex from a variety of structures associated with sensory, motor, autonomic, and emotional processes.
The hypothalamus, the smaller structure, lies ventral and slightly anterior to the thalamus. Its roles include the regulation of a host of visceral functions, such as temperature; endocrine functions; and feeding, drinking, emotional, and sexual behaviors. The ventral aspect of the hypothalamus forms the base of the brain to which the pituitary gland is attached.
Inferior Ventral Surface of the Cerebral Cortex As part of our task in understanding the anatomical organization of the brain, it is useful to examine its arrangement from the inferior view. The medial aspect of the anterior part of the prefrontal cortex contains a region called the gyrus rectus Fig. Lateral to the gyrus rectus lies a structure called the olfactory bulb, a brain structure that appears as a primitive form of cortex consisting of neuronal cell bodies, axons, and synaptic connections.
The olfactory bulb receives information from the first olfactory cranial nerve and gives rise to a pathway called the olfactory tract. These fibers then divide into the medial and lateral olfactory branches called striae. The lateral pathway conveys olfactory information to the temporal lobe and underlying limbic structures, whereas the medial olfactory stria projects to medial limbic structures and contralateral olfactory structures via a fiber bundle called the anterior commissure; see Chapter Posterior Aspect of the Cerebral Cortex: Temporal and Occipital Lobes The occipitotemporal gyrus lies medial to the inferior temporal gyrus and is bound medially by the collateral sulcus.
The parahippocampal gyrus lies medial to the collateral sulcus. There is a medial extension of the anterior end of the parahippocampal gyrus called the uncus. The hippocampal formation and amygdala described below are situated deep to the cortex of the parahippocampal gyrus and uncus Figs.
These structures have a very low threshold for induction of seizure activity and are commonly the focus of seizures in temporal lobe epilepsy. In brief, CSF is secreted primarily from specialized epithelial cells found mainly on the roofs of the ventricles called the choroid plexus.
CSF serves the CNS as a source of electrolytes, as a protective and supportive medium, and as a conduit for neuroactive and metabolic products. It also helps remove neuronal metabolic products from the brain. The lateral ventricle is the cavity found throughout much of each cerebral hemisphere Fig.
It consists of several continuous parts: an anterior horn, which is present at rostral levels deep in the frontal lobe; a posterior horn, Body of lateral ventricle Posterior horn Anterior horn FIGURE 1—5 Lateral view of the positions and relationships of the ventricles of the brain. Note that the lateral ventricles are quite extensive, with different components i. The medial and lateral apertures represent the channels by which cerebrospinal fluid can exit the brain see Chapter 3 for details.
Within the diencephalon, another cavity, called the third ventricle, can be identified. It lies along the midline of the diencephalon, and the walls are formed by the thalamus dorsally and the hypothalamus ventrally.
The third ventricle extends throughout the diencephalon and communicates anteriorly with the left and right lateral ventricles through the interventricular foramen. Posteriorly, at the level of the diencephalic—midbrain border, it is continuous with the cerebral aqueduct, which allows CSF to flow from the third ventricle to the fourth ventricle Fig. Basal Ganglia The basal ganglia play an important role in motor integration processes associated with the cerebral cortex.
Damage to this region results in motor dysfunctions referred to as dyskinesias i. The most prominent structures of the basal ganglia are the caudate nucleus, putamen, and globus pallidus Figs.
Visible are the caudate nucleus, thalamus, fornix, hippocampus, and amygdala. Note the shape and orientation of the hippocampal formation and its relationship to the amygdala as well as the positions occupied by the globus pallidus and putamen, which lie lateral to the internal capsule label shown in Figure , and the thalamus, which lies medial to the internal capsule.
The caudate nucleus is a large mass of cells that is most prominent at anterior levels of the forebrain adjacent to the anterior horn of the lateral ventricle and can be divided into three components Fig. The largest component, the head of the caudate, is found at anterior levels of the forebrain rostral to the diencephalon.
As the nucleus extends caudally, it maintains its position adjacent to the body and inferior horn of the lateral ventricle but becomes progressively narrower at levels farther away from the head of the caudate. This narrow region of the caudate nucleus, distal to the head, is called the tail of the caudate nucleus.
The region between the head and tail is referred to as the body of the caudate nucleus. The body and tail of the caudate nucleus are situated adjacent to the dorsolateral surface of the thalamus.
The putamen is the largest component of the basal ganglia and is situated in a lateral position within the anterior half of the forebrain. It is bordered laterally by the external capsule, a thin band of white matter, and medially by the globus pallidus Figs. The globus pallidus has both a lateral and medial segment. It lies immediately medial to the putamen and just lateral to the internal capsule, which is a massive fiber bundle that transmits information to and from the cerebral cortex to the forebrain, brainstem, and spinal cord Figs.
Note again the relationships of the caudate nucleus and diencephalon relative to those of the globus pallidus and putamen with respect to the position of the internal capsule. The level along the rostro-caudal axis of the brain at which the section was taken is shown in the sketch of the brain at the bottom of the figure.
Hypothalamus Globus pallidus Optic tract Amygdaloid nuclei Body of caudate nucleus Stria terminalis Thalamus Head of caudate nucleus FIGURE 1—8 Schematic diagram illustrating the components of the caudate nucleus and their relationship to the thalamus, internal capsule, globus pallidus, putamen, and brainstem. Because of its anatomical proximity to the caudate nucleus, the stria terminalis, which represents a major efferent pathway of the amygdala to the hypothalamus, is included as well.
Stria terminalis to hypothalamus Putamen Diencephalon As mentioned previously, the diencephalon includes principally the thalamus, situated dorsally, and the hypothalamus, situated ventrally. The ventral border is the base of the brain, and the dorsal border is the roof of the thalamus. The diencephalon is generally considered to be bounded anteriorly by the anterior commissure Fig.
The posterior limit of the diencephalon is the posterior commissure, a fiber bundle that crosses the midline between the diencephalon and midbrain. Limbic Structures Limbic structures serve important functions in the regulation of emotional behavior, short-term memory processes, and control of autonomic, other visceral, and hormonal functions usually associated with the hypothalamus.
Several structures in the limbic system can be identified clearly in forebrain sections. Two of these structures, the amygdala and hippocampus, are situated within the temporal lobe Fig.
The amygdala lies just anterior to the hippocampus. Both structures give rise to prominent fiber bundles that initially pass in a posterodorsal direction following the body of the lateral ventricle around the posterior aspect of the thalamus and then run anteriorly, following the inferior horn of the lateral ventricle.
The fiber bundle associated with the hippocampal formation is the fornix, which is situated just inferior to the corpus callosum Fig. The fiber system associated with the amygdala is the stria terminalis and is just ventromedial to the tail of the caudate nucleus Fig. The trajectory of the stria terminalis is parallel to that of the tail of the caudate nucleus. Both fiber bundles ultimately terminate within different regions of the hypothalamus see Chapters 13, 24, and Other components of the limbic system include the cingulate gyrus, the prefrontal cortex, and the septal area.
A Dorsal view of the cerebellum indicating the positions of the anterior, posterior, and flocculonodular lobes and the midline region called the vermis. B Dorsal view of the brainstem after removal of the cerebellum. The connections of the cerebellum to the brainstem are indicated by the presence of the inferior, middle, and superior cerebellar peduncles. It is attached to the brainstem by the cerebellar peduncles, three pairs of massive fiber bundles.
One pair, the superior cerebellar peduncle, is attached rostrally to the upper pons. Another pair, the inferior cerebellar peduncle, is attached to the dorsolateral surface of the upper medulla. The third pair, the middle cerebellar peduncle, is attached to the lateral aspect of the pons Fig. The cerebellum see Chapter 21 contains bilaterally symmetrical hemispheres that are continuous with a midline structure, the vermis. The hemispheres are divided into three sections.
The anterior lobe is located towards the midbrain. Extending posterior-inferiorly from the anterior lobe is the posterior lobe, the largest lobe of the cerebellum. The flocculonodular lobe, the smallest of the three lobes, is situated most inferiorly and is somewhat concealed by the posterior lobe.
It is important to note that each of these lobes receives different kinds of inputs from the periphery and specific regions of the CNS. For example, the flocculonodular lobe primarily receives vestibular inputs, the anterior lobe receives inputs mainly from the spinal cord, and the posterior lobe is a major recipient of cortical inputs. The dorsal surface of the pons and medulla form the floor of the fourth ventricle Fig.
The walls of the ventricle are formed by the superior cerebellar peduncle, and the roof of the fourth ventricle is formed by the superior medullary velum, which is attached to the superior cerebellar peduncle on each side. In the caudal half of the medulla is the end of the fourth ventricle, the position at which the ventricle becomes progressively narrower and ultimately continuous with the central canal that continues into and throughout the spinal cord.
The position at which the fourth ventricle empties into the central canal is the obex. The part of the medulla that contains the fourth ventricle is the open medulla, and the part that contains the central canal is the closed medulla. On the dorsal surface of the caudal medulla are two protuberances, the gracile and cuneate tubercles cuneate tubercle is situated immediately lateral to gracile tubercle but is not labeled in Figure These contain relay and integrating neurons associated with ascending sensory fibers from the periphery to the medulla.
Ventral View of the Brainstem Brainstem Dorsal View of the Brainstem Two pairs of protuberances at the level of the midbrain can be seen on the dorsal surface of the brainstem Fig. The superior colliculus is more rostrally positioned and is associated with visual functions; the more Crus Cerebri.
A massive fiber bundle passes from the cerebral hemispheres into lower regions of the brainstem and spinal cord at the level of the midbrain Fig. This fiber bundle is the crus cerebri, part of the descending complex of motor pathways that communicates signals from the cerebral cortex to the brainstem and spinal cord.
Note the positions of the cerebral peduncle; basilar part of the pons; pyramid; pyramidal decussation situated immediately rostral to the cervical spinal cord ; inferior olivary nucleus, which lies lateral to the pyramid; and root fibers of cranial nerves. The neural plate continues to thicken over the following week and expands laterally. As it expands, the faster growing lateral edges of the plate accumulate in a dorsal position as neural folds Fig.
As this plate grows and widens, it forms a shallow groove along its longitudinal axis known as the neural groove Fig. The posterior end of the neural plate, which is narrower than the anterior end, will ultimately become the spinal cord, whereas the broader, anterior end will become the brain. By the third to fourth week of embryonic development, the notochord, of mesodermal origin, induces the development of the neural plate Fig. By the third to fourth week of embryonic development, there is a high rate of cell proliferation.
Panels A—D depict early development at the third and fourth weeks of gestation in which the neural plate A , neural groove B , and neural tube C are formed from the dorsal surface of the embryo. The left side of each panel depicts the developing embryo in a dorsal view, and the right side shows cross sections through the nervous system cut at the levels indicated by the arrows.
Dendrite formation 4. Gliogenesis 5. Corticogenesis 6. Neuronal migration 7. Genes, circuits and behavior 2. Human neurogenetics 3. Visual systems 4. Auditory systems 5. Olfactory systems 6. Motor systems 7. Pain and somatosensory 8. Learning 9. Cognitive neuroscience Download Link. Kindly support us by sharing this Post with your friends. You may send an email to admin cmecde.
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