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CHAPTER 2 Chapter 2 — GrossAnatomy of the Central Nervous System I. Major Components of the Nervous System A. Central Nervous System 1. Brain and spinal cord 2. Brain- initiates, controls, and regulates all functions 3. Spinal cord- sends messages to multiple body parts. B. Peripheral Nervous System 1. Sensory and motor nerves that connects to the spinal cord and brain stem 2. Somatic nervous system and automatic nervous system 3.Afferent consists of nerves and cells that transmits sensory information to the CNS from the skin muscles and organs. C. Functions of the Nervous System 1. The brain is accountable for beginning, regulating, and controlling all mental tasks as well as triggering and controlling human contact. II.Anatomy of the Human Brain A. Basic Facts 1. The brain weighs about three pounds and only accounts for 2% of body weight. 2. Telencephalon, a major division of the brain, is responsible for language cognition, emotion, personality, imagination, and consciousness. 2. The cerebrum, which is comprised of the cerebral hemispheres are the largest part of the brain consisting of gyri and sulci. a. Left Hemisphere: processes language, speech, calculation, and verbal memory b. Right Hemisphere: processes and regulates pragmatic skills and visuals and spatial concepts c. Longitudinal fissure: fissure which divides the two hemispheres along the midline 3. Major lobes/sections of the brain a. Primary Lobes 1) Frontal, Parietal, Temporal, Occipital b. Secondary Lobe 1) Insular B. Frontal Lobe 1. Controls personality and mood along with reasoning, decision making planning, and is involved with movements and regulates responsiveness along with speech, hand, and finger movements. 2. Largest lobe which contains four gyri, the pre central gyrus and three horizontal gyri. 3. Broca’s area is located in front and is responsible for language. C. Parietal Lobe 1. Concerned with spatial orientation, cross-modality integration, memory, recognition, expression of emotions and cognition. 2. Postcentral gyrus is the primary motor cortex which all bodily experienced sensations are perceived and recognizes as awareness as well as perceptual experiences. 3. Lesion in the parietal lobe would cause sensory loss including disorders of recognition along with alexia, agraphia, and aphasia D. Temporal Lobe 1. Responsible for hearing, illustrative memory, olfaction along with understanding both verbal and composed language. 2. Contains three gyri, superior, middle, and inferior 3. The lateral fissure separates the temporal lobes from the frontal and parietal lobes. 4.Alesion in the temporal lobe would cause hearing sensitivity, auditory perceptual function and skills for phonemic discrimination 5. Wernike’sArea is located here and is responsible for language. E. Occipital Lobe 1. Contains the primary (Brodmann area 17) and secondary (Brodmann area 18) visual cortical areas. F.Additional Structures of the Brain 1. Corpus Callosum- the largest horizontal fiber bundle that interconnects with most of cortical areas. a. The midsagittal surface which is an interhemispheric commissural fiber bundle, connecting both hemispheres of the brain. b. The roof of the underlying ventricular cavities is formed with the myelinated fibers of this structure. c. The corpus callosum shares memories, experiences, and actions between the two hemisphere. d. Patients who have commissurotomy (the complete sectioning of the hemispheres) has helped give functions for each hemispheres separately. 2. The pituitary gland (hypophysis)- a. Ventral to the corpus callosum. b. Secretes the hormones to regulate sexual drive, pain, emotional drive, temperature control, and metabolism. 3. Insular Lobe a. The insular cortex (isle of Reli) is deeper in the lateral fissure of the frontal, parietal, and temporal lobes. b. Related to limbic and sensorimotor functions, including gustatory functions 4. Limbic Lobe a.An older part of the brain. b. This forms a ring around the medial margins of the frontal, parietal, and temporal lobes. c. Provides the emotional drive to visceral and vegetative functions including reflexes, aggression, anxiety, and fear. d. The limbic system governs our values and decisions about perceptions and feelings, helps drive the emotion. e. Papez Circuit involves neuronal connections of the hypothalamus. limbic system, and thalamus. 5. Basal Ganglia a. Regulates motor functions, muscle tone and cortical output processing by slowing or inhibiting the activity of other loops. b. Damage to basal ganglia results in release of inappropriate behavioral movement patterns because of the disinhibition. 1) This is shown in Parkinson, Huntington disease, Tourette syndrome c. Basal ganglia structures are best seen on the horizontal or coronal sections of the brain they include the caudate nucleus, putamen, globus pallidus, claustrum, and amygdaloid nucleus. 6. Diencephalon a. Thalamus 1)Amajor function to relay sensorimotor information to the cortex, contributes to cortically mediated speech and language features. b. Hypothalamus 1) Made up of nuclei, this will communicate with the brain through to the spinal cord by neural and hormonal circuitry. 2) Serves four primary functions: autonomic, endocrine, regulatory, and drive and emotion. 3) Controls food and water intake, sexual behavior, and body temperature. 7. Brainstem a.Ashort extension of the brain that connects the diencephalon to the spinal cord. b. Made up of the midbrain, pons, and medulla oblongata (leaving out the cerebellum). 1) Midbrain i. The link between the two hemispheres and the peripheral and cranial sensory input systems. ii. Responsible for making neurotransmitters which are very important to telencephalic, diencephalic, brainstem and spinal cord functions. iii. Monitors all brain outputs 2) Pons i. The medial structure between the midbrain and medulla. ii. Contains all descending motor fibers and ascending sensory fibers, numerous cranial nuclei, the reticular formation, and transverse fibers. 3) Medulla Oblongata i. Most caudal part of the brainstem ii. Motor fibers that descend to the spinal cord and all the sensory fibers 8. Cerebellum a. The cerebellum is found to the back of the pons and medulla. b. Helps keep equilibrium in check and coordination of more skilled motor movements. c. Does not initiate motor activity. d. Cerebellar penducles 1. Superior- Brachium Conjunctivum 2. Middle- Brachium Points 3. Inferior Cerebellar Penduncles- Restiform Body 4. The lateral inferior surface of the cerebellum reveals the connections of the peduncles to the brainstem. 5.Afferents from the motor cortex by way of the pons enter through fibers of the middle cerebellar penducle 6. Fibers of the inferior cerebellar peduncle transmit proprioceptive afferent information from the trunk and limbs and the vestibular information to the cerebellum e. Input to the Cerebellum 1.Afferents from the motor cortex by way of the pons enter through fibers of the middle cerebellar peduncle. 2. Fibers of the inferior cerebellar peduncle transmit proprioceptive afferent information from the trunk and limbs and the vestibular information to the cerebellum. f. Output from the Cerebellum 1.After analyzing and synthesizing the received sensorimotor information, the cerebellum projects its corrective feedback predominantly to the opposite motor context, through the superior cerebellar peduncle. 9. Spinal Cord a. The transmission link between the brain and the body. b. Transmits motor impulses from the brain to the visceral organs and muscles and carries sensory information, such as pain, touch, temperature, and proprioception, from the body to the brain. c. The spinal cord is 42-45 cm. (16 – 18 in) long with a diameter of about 1 cm. d. Wrapped in the three meningeal layers and is housed in the bony vertebral column. e. Gray matter - all of the spinal nerve cells. Two dorsal horns and two ventricle horns. f. White matter- ascending and descending fibers g. The dorsal horns- nerve cells that receive sensory information from the body through dorsal root fibers. h. The ventral horns- contain motor nerve cells, axons leave the cord through the anterior roots to activate visceral and skeletal muscles and glands. i. Networking of Spinal Nerves • Dorsal and ventral horns contain both sensory and motor fibers • Dorsal rami serve the sensorimotor functions of the posterior trunk • Ventral rami do not go directly to body structures • Four major plexus: Cervical, Brachial, Lumbar, and Sacral 10. Ventricles a. Primary function is to circulate the CSF, which is secreted by the choroid plexus b. Four interconnected ventricles within the brain 1) Two lateral ventricles- i. Consists of the central body and three extensions: anterior, posterior, and inferior horns ii. Collateral TrigoneArea – the broader portion in the posterior floor of the lateral ventricle. 2) The third ventricle i. Narrow vertical space between the two thalami 3) The fourth ventricle ii. The tegmentum of the pons and medulla form the triangular floor of the fourth ventricle and the cerebellum forms its roof. 11. Cortical White Matter a. Projection Fibers 1) Projects through the corona radiate and coalesce in the internal capsule. 2) The sensory projection fibers collect cutaneous and proprioceptive sensation from the skin and joints and project to the CNS. b.Association Fibers 1) Provides efficient bidirectional channels for communication among cortical areas in each hemisphere. 2) Most numerous of the three types of fibers and are confined within the hemisphere. 3) The superior longitudinal fasciculus are also known as the arcuate fasciculus. b. Commissural Fibers 1) Largest bundle of fibers in the corpus callosum G. Meninges of the Brain 1) Basic Protections of the CNS a. Cushioning the CSF, the bony wall of the skull, and the vertebral column 2) Dura Mater a. The grey outer membrane consisting of dense, fibrous connective tissue, providing the maximum meningeal protection to the CNS. b. Thicker and tougher than the pia and arachnoid membranes c. Two spaces around the cranial dura: 1) Epidual: Space between the dura mater and bone 2) Subdural: space between the dura mater and the arachnoid membrane 3)Arachnoid Membrane a.Athin, nonvascular membrane between the internal pia mater and the external dura mater b. It does not adhere to the cortical surface like the pia mater. c.Arachnoid trabeculae: fibrous and elastic connective tissue 4) Pia Mater a.Athick, transparent, collagenous (connective tissue) membrane, is closely attached to the surface of the brain. b. Surrounds the blood vessels and forms the perivascular space. 5) Meningitis a. The inflammation of the membranes of the brain and spinal cord b. Caused by a viral of bacterial infection c. Causes the neck to become stiff and any stretching of the nerves causes intense pain d. The arachnoid membrane and pia mater are most commonly associated with meningitis due to their delicateness. H. Meninges of the Spinal Cord 1) Spinal Dura Mater a. Single layer meningeal membrane, lacks cranial periosteal layer; attached to foramen magnum 2) SpinalArachnoid a. Begins at the foramen magnum and extends to the cauda equina 3) Spinal Pia Mater a. Innermost protective layer, surrounds and tightly adheres to the spinal cord III. Cranial Nerves A. Cranial Nerve Facts 1. The efferent fibers of the spinal nerves innervate skeletal muscles and the visceral organs 2. The afferent fibers transmit sensory information from the skin and visceral organs to the CNS. 3. The cranial nerves start at the brainstem and innervate the muscles of the head, neck, face, larynx, tongue, pharynx, and glands. 4. Essential for speech, resonance, and phonation. B. Cranial Nerves I. Olfactory; Sensory nerve, perception of smell II. Optic; Vision III. Oculomotor Motor Nerve; Eye movement, controls muscles responsible for moving the eyeball IV. Trochlear Motor Nerve; Eye movement, controls one of the six muscles for eye movement V. Mastication; sensation in the face, orbit, and oral structures VI.Abducens; Eye movement VII. Facial; facial expression, secretion of salvia and tears, taste VIII.Acoustic; Equilibrium and audition IX. Glossopharyngeal; swallowing and taste X. Vagus; Phonation, swallowing, sensation in the pharyngeal, thoracic, and abdominal cavity XI.Accessory; Head movement and shoulder elevation XII. Hypoglossal; Tongue Movement IV.Autonomic Nervous System A. Facts of theANS 1. Regulated by the hypothalamus in the CNS 2. Consists of sensory and motor components 3. Controls the motor activity of smooth and cardiac muscles and regulates secretion glands 4. Motor components consists of: a. Sympathetic system which spends energy by stimulating organs and preparing for fight or flight. b. Parasympathetic system which conserves energy, dominant during relaxation or sleep CHAPTER 3 Chapter 3: Internal anatomy of the central nervous system Anatomical Landmarks – • There are two distinct landmarks used for visual orientation when it comes to the internal anatomy of the brain shape: Corticospinal fibers &Ventricular cavities Spinal Cords in Cross Sections – • Sacral Section – contains a thin mantle of white matter and a larger gray region with bulky ventral and dorsal horns. This section contains the dorsal lemniscal column, and the fasciculus gracilis which bring information concerning touch, pressure and limb position. • Lumbar Section – located laterally to the dorsal median sulcus and the dorsal lemniscus column. This section also mediates fine discriminative touch to the brain. • Thoracic Section – reduced amount of gray matter and enlarged amount of white matter. Mediates sensations of touch, pain, and temperature • Cervical Section – Highest volume of white matter. Dorsal horns are slender and ventral horns are large and wing shaped. The Medulla (lower part of brainstem) Caudal Medulla • The crossing of the pyramidal tract fibers accounts for the motor cortex of one side of the brain controlling the opposite side of the body. • The spinal trigeminal tract consists of CN V nerves, which meditates pain, touch, & temperature in the face. • The decussating of the sensory internal arcuate fibers and motor pyramidal fibers are two landmarks of the caudal medulla. • CNXII is the hypoglossal nerve, it controls all intrinsic and most extrinsic tongue muscles and Is an important nerve for speech production and swallowing. • The medial longitudinal fasciculus regulates head-eye coordination. It also interconnects the motor nuclei of four cranial nerves: CN III, CN IV, CN VI, and CN XI. • Middle Medulla • The principal olivary nucleus is an important relay center for motor and proprioceptive information to the cerebellum. • There are three peduncles that connect the brainstem to the cerebellum. • One of the important nuclei at this level is the nucleus ambiguous, the motor nucleus of the glossopharyngeal (CNIX) and vagus (CNX) nerves. • Rostral (High) Medulla • In this section is the cochlear nuclear complex and glossopharyngeal (CN IX) nerve. The cochlear (CN VIII) nuclear complex receives projections from cochlear region of the inner ear. The glossopharyngeal nerve mediates taste and contributes to swallowing. • Lower Pons • Appear beneath the floor of the 4 ventricle, the vestibular nuclear complex receives projections from the semicircular canals in the inner ear, and plays a role in equilibrium and head eye coordination. • The facial nerve (CN VII) innervates the muscles of facial expression & speaking. Middle Pons • The most characteristic features of the pons are interspersed corticospinal- corticopontine fibers and the crown-shaped lumen of the 4 ventricle. • The crescent shaped superior cerebellar peduncle provides cerebellar feedback to the primary motor cortex via the red nucleus. • Located ventrolaterally are fibers of the lateral lemniscus which carry auditory info from both the ears to the cortex. Pons-Midbrain junction • In this section the ventricular floor is formed, it contains important somatic and visceral nuclei. • Dorsally in this section is the trochlear nerve root, which is one of the three cranial nerves responsible for innervating the eye and is the only motor nerve that exits dorsally. Midbrain • The midbrain consists of: tectum, tegmentum, and basis pedunculi. Caudal Midbrain • The inferior colliculus is located here and is a relay center in the transmission of information from the ears to the auditory cortex; it also regulates auditory and visual reflexes. Rostral Midbrain • The superior colliculi in this section serves as the visual reflex center. • Tectobulbar and tectospinal projections to the spinal cord and brainstem motor nuclei result in the appropriate turning of the eyes, head, and body toward the sound source. • The superior colliculus and the adjacent pretecal area mediate reflexes involving intrinsic eye muscles. o It also regulates pupil constriction (Light reflex), and lens accommodation for near vision. • Cells of the substantia nigra secrete dopamine, an inhibitory basal ganglia neuro transmitter; Degeneration of dopamine is associated with Parkinsons Disease. • The medial longitudinal fasciculus regulates synergetic conjugate eye movement and coordinates head/eye movement. High Rostral Midbrain • Contains the posterior thalamus, optic tract, and edinger-Westphal nucleus. • The lateral geniculate body is the thalamic relay center for vision, and the medial geniculate body is the thalamic relay nucleus for audition. Midbrain-Diencephalon Junction • The subthalamic nucleus is a very important basal ganglia nucleus. • Both the subthalamic nucleus and substantia nigra are major regulators of movement and their dysfunction is associated with movement disorders. • The pulvinar is associated with speech. • The dysfunction of the subthalamic nucleus, an important extrapyramidal structure results in hemiballism: a neurologic condition characterized by an abrupt on set of violent and flinging movements. Coronal Section Through the Posterior Thalamus 1. Coronal Brain section shown in page.104, shows the distinction between white and gray matter with sulci and gyri markings. 2. Large fissure in the middle separating the hemispheres is the interhemispheric longitudinal fissure. 3. The body of the corpus callosum forms the roof of the lateral ventricles. 4. The splenium of the corpus callosum connects both occipital lobes. 5. Large cavities in this section are the bodies of the lateral ventricles; small cavities in the temporal lobe are the inferior horns of the lateral ventricles. 6. In the floor of the lateral ventricles is the fornix, a bundle of fibers that serves as a two-way connection between the hypothalamic structures and hippocampus. 7. Forming the medial wall of the inferior horn of the lateral ventricles is the hippocampal formation. a. Thought to serve memory functions by consolidating new information. 8. Thalamic nucleus in this section is the pulvinar 9. Ventral to the pulvinar are the geniculate bodies. b. Serve as thalamic relay centers. A. Coronal Section Through the Midthalamus 1. Emerging from the walls of the lateral ventricle is the larger body of the caudal nucleus. 2. Caudal nucleus with its long tail, is a C-shaped structure in sagittal views of the brain. a. Important nucleus, contributing to motor activity. b. May have a role in cognitive processing. 3. Forming the floor of the lateral ventricles in this section are the large gray masses of the thalamus. a. Both thalami are connected through the massa intermedia, a thalamic loose fibrous tissue. 4. In the midline between the two lateral ventricles, is the septum pellucidum. 5. Through the base of the septum courses the fornix, an important C-shaped limbic structure that connects the mamillary bodies of the hypothalamus to the hippocampus and septum and is involved in autonomic functions. 6. Located lateral to the internal capsule, the lenticular nucleus consists of the globus pallidus and putamen. 7. The globus pallidus and putamen are parts of the basal ganglia. a. Very important in regulating motor functions and muscle tone. B. Coronal Section Through theAnterior Thalamus 1. The rough, saggy, and worm-shaped structure in the lateral ventricles is the choroid plexus, which secretes cerebrospinal fluid. 2. Forming the floor of the lateral ventricles is the anterior nucleus a. Most rostral nucleus of the thalamus. 3. This nucleus receives afferents from the mammillary bodies of the hypothalamus and projects to the cingulate gyrus of the limbic lobe. 4. Along the lateral wall of the lateral ventricles is the caudate nucleus, a C- shaped structure. 5. Medial to the internal capsule is the biconvex-shaped subthalamic nucleus, which receives afferents from the lateral segment of the globus pallidus and projects to both of the palidal segments and to the pars reticulate region of the substantia nigra. C. Coronal Section Through theAnterior Commissure 1. The Head of the caudal nucleus emerges in the ventricular cavity as a larger structure than at the more caudal levels. 2. The anterior commissure is a small forebrain fiber bundle that contains bidirectional olfactory fibers and connect that temporal cortices. 3. All hippocampal projections terminate in the septum verum nuclei, which are part of the limbic system. D. Coronal Section Through theAnterior Limb of the Internal Capsule and Caudate Head. 1. Acoronal section of the forebrain at the rostral region of the basal ganglia reveals the large head of the caudate nucleus, the anterior horn of the lateral ventricles, and the anterior limb of the internal capsule. 2. The cingulum a. Abundle of mediofrontal parietal cingulate association fibers, is beneath the cingulate gyrus. E. Coronal Section Through theAnterior Horn. 1. Acoronal section of the forebrain at the genu of the corpus callosum reveals the end of the lateral ventricle and the rostral striatum. ❖ Forebrain in Horizontal Sections ➢ Removing a cm thick layer of the cerebral cortex exposes: • the longitudinal fissure • semiovale center: ➢ Removing another 1-2 cm of brain exposes Dorsal side of the corpus callosum ▪ • This section includes the genu, body, and splenium of corpus callosum ➢ More removal of the corpus callosum exposes: ▪ The subcortical structures Lateral ventricles: ▪ • Laterally located are the fibers that make up the corona radiate • Spaces on both sides of the corpus callosum mark the cavities of the lateral ventricles. • Two prominent structures on the floor of the lateral ventricles: 1. Caudate nucleus 2. Thalamus ➢ Removal of white medullary substance, caudate nucleus, and thalamus exposes: The cavity of the lateral ventricles and surrounding subcortical structures ▪ • inner temporal lobe contains slender temporal horns of the lateral ventricles. ♦ Hippocampus, amygdala, and uncus are located medially in the inferior horn. ♦ Hippocampus forms medial wall of the temporal ➢ Receives direct projections from the fornix ➢ Receives indirect projections from cingulum via parahippocampal gyrus, associated withAlzheimer disease CHAPTER 4 Chapter 4: Development of the Nervous System Human Chromosomes, Genes, and Cell Division • Human somatic cells -diploid: 44 autosomes, 2 sex chromosomes -haploid: 23 chromosomes Abnormalities in Chromosome Number • Euploid- any exact multiple of n chromosomes -triploid: 23x3 -tetraploid: 23x4 • Aneuploid- any chromosome number that is not euploid, happens during gametogenesis -Patau Syndrome: 13 chromosomes -Edwards Syndrome: 18 chromosomes -Down Syndrome: 21 chromosomes Genes and Genome • Genome -made up of 6 to 7 billion base pairs of deoxyribonucleic acid (DNA) • Gene -the sequence of chromosomal DNArequired for a functional product to be produced • Chromatin -DNAand histones (chromosomal proteins) combined Cell Division • Meiosis -reduction division that occurs during gametogenesis -chromosome number is reduced to half the usual number • Mitosis -four phases: prophase, metaphase, anaphase, telophase -leads to the formation of two sibling cells -leads to the growth of tissue which leads to development and maturation Early Human Development • Zygote -result of the union of spermatozoon and an ovum which is fertilization -undergoes repeated divisions, giving rise to the multicellular human form Gametogenesis • Nondisjunction -cause of abnormal gametes that are able to develop into a fetus which result in congenital malformations • Spermatogenesis -male sperm development begins at puberty and continues through life • Oogenesis -female egg formation begins before birth Fertilization and the First Week of Development • First and second meiotic divisions with crossover -homologous chromosomes approach each other -homologous chromosomes pair, each member of the pair consists of two chromatids -the intimately paired homologous chromosomes interchange chromatid fragments -the double-structured chromosomes pull apart -anaphase of the first meiotic division -double-structured chromosomes split at the centromere, resulting in 4 daughter cells that are different from each other Second Week of Development • Blastocyst becomes completely implanted -bilaminar embryo develops -prechordal plate develops Third Week of Development • The embryo becomes trilaminar -the three germ layers are ectoderm, mesoderm, and endoderm • The notochord is the first skeletal structure that develops and is retained in the nucleus pulpous The Central Nervous System • Development of the brain and spinal cord begins early in week 3 of gestation • Neurulation - important processes that begins during the trilaminar stage of human development and is completed by the end of week 4 Neural Plate, Neural Tube, and Neural Crest • The neuroectoderm overlying the midline notochord thickens to form the neural plate, cranial to the primitive knot • The neural tube develops into the brain and the spinal cord, and the segmentally arranged neural crest tissue develops into the cranial and spinal ganglia, nerve sheaths, postganglionic autonomic nerves Brain • Early in week 4, the rostral two-thirds of the neural tube represents the future brain, and the caudal third represents the future spinal cord • The brain flexures develop with the rapid growth and folding of the brain • The midbrain and cervical flexures develop ventrally in the midbrain region and all the junction of the hindbrain and spinal cord Prosencephalon (Forebrain)- Develops into two subdivisions: • Telencephalon -Week 4 optic vesicles form the primordial for retinas and optic nerves, the telencephalic vesicles appears dorsal and rostral to the optic vesicles. These grow into cerebral hemispheres each with anteriorly a lateral ventricle • Diencephalon -The epithalamus, thalamus, metathalamus, hypothalamus, and subthalamus develop in the walls of the third ventricle. The pituitary gland develops during weeks 4 and 5 of gestation Mesencephalon (Midbrain) • The superior and inferior colliculi form in its roof or tectum • The superior colliculi relay visual impulses; The inferior colliculi relay auditory impuses Rhombencephalon (Hindbrain)- develops into metencephalon and myelencephalon • Metencephalon -it is the region of the brainstem which nerve fibers connect to the cerebellar and cerebral cortices with the spinal cord • Myelencephalon - most caudal brain region, it is continuous with the brainstem superiorly and the spinal cord inferiorly Spinal Cord • As the neural tube begins to close, its walls thicken and stratify • Three layers- an inner spendymal cells, a middle mentle, and an external marginal- become differentiated The Peripheral Nervous System • Normal Development -Peripheral Nervous System consists of the: cranial, spinal, and the autonomic nervous system. -Suprarenal gland medulla is obtained from the postganglionic sympathetic neurons. -Some of the 12 pairs of the Cranial Nerves a. 4 are Oculomotor (CN III) b. Facial (CN VII) c. Glossopharyngeal (CN IX) d. Vagus (CN X), which belong to the cranial parasympathetic system. • Neural Tube -The motor nuclei, all cranial and spinal nerves, as well as all preganglionic neurons for the autonomic nervous system all are gained from the neural tube. -Which means the entire PNS comes from the neural tube. • Neural Crest -The spinal or dorsal root ganglia, sensory ganglia, autonomic ganglia, and postganglionic autonomic neurons all come from the neural crest. -Additionally the following also are derived from the neural crest: suprarenal medulla, the mucosal and sub-mucosal enteric ganglia, capsular cells, and Schwann cells. -Furthermore, some of the cranial ganglia neurons come about not from the neural tube but from the surface ectoderm. Clinical Correlates • Abnormal Development of the CNS -The brain and the spinal cord come to completion of neurons by week 25 of gestation; however, the cerebellum does not yet. -The next stages take place: a. synaptogenesis- begins in midgestation into the second year of life and beyond. b. Myelinohgenesis- begins at the end of the first trimester and continues to age 4. c. Embryogenesis- timing of the insult is more detrimental than the nature of the insult in causing cerebrospinal malformations. d. Teratogenesis- time specific but insult-nonspecific phenomenon. • Anencephaly -Defective fusion of the neural tube results in anencephaly, in which the cranial vault is congenitally absent. • Cranium Bifidum -Cranium Bifidum is a condition in which bone joining is prevented in the posterior midline of the skull. • Spina Bifida -Spina Bifida is failure of the dorsal part of the neural tube, which occurs in the vertebral column. -The type of spina bifida depends on the severity and tissue involvement. a. Spina Bifida Cystica- posterior vertebral arches fail to fuse b. Spina Bifida Occulta- the skin of the back is epithelialized and always shows a surface marking in the form of a dimple. -The casual displacement of cerebellar tissue through the foramen magnum isArnold- Chairimalformation. This occurs with every case of spina bifida cystica. -The two abnormalities commonly associated with syndrome are hydrocephalus and syringomyelia. This tissue protrusion results in cerebellar and medullary symptoms. On test*Hydrocephalus • Characterized by an enlarged head, a prominent forehead, brain atrophy, mental deficiency, and convulsions. • Central ventricles expand because of excessive making of cerebrospinal fluid and/or obstruction of the cerebrospinal fluid drainage passage. Microcephaly • Uncommon condition in which the brain, and calvaria, and face are small. • Infants with this condition are mentally retarded. • Primary causes are environmental disturbances, genetic abnormalities, and ionizing radiation during the critical period of CNS development. Holoprosencephaly • The incomplete development of midline structures as well as fused eyes, single nasal chamber, a single ventricle, instead of lateral ventricles, olfactory bulbs and tracts, and carpus callosum are hypoplastic or absent the brain and face are highly malformed. • Lissencephaly- defined as gross neural defect where sulci and gyri do not develop and thus the brain appears smooth surfaced. • AdditionAbnormalities- Less common structural abnormalities of the nervous system are craniorachischisis, encephalocele, meningocele, cyclopia, and agenesis of the cortex, corpus callosum, and cerebellum. Development Disabilities • Mental Retardation -Disability characterized by significant limitations both in intellectual functioning and in adaptive behaviors. -Originates before age 16 -Genetic causes include chromosomal abnormalities chromosomal abnormalities or gene mutations. -Most common preventable cause is maternal alcohol abuse. • Down Syndrome -Results from a translocation of chromosome 21 -The affected individual has three copies of this chromosome, which is also known as trisomy 21. -Clinical findings include mental retardation, retarted growth, flat high anxiety, attention deficit disorder, and phobia to loud sounds. -Acontiguous gene deletion syndrome with occurrence of 1 in 8,000 births. • ChildhoodAutism -Amental-social disorder of unknown cause characterized by abnormal development of brain circuitry that is essential for integrating social interaction and communicative skills. -Asperger syndrome is the distinctive behavioral disorders that he documented were apathy, lack of eye contact, clumsy movements, stereotyped behavior or language use, obsessive interests, and impaired ability to socially interact. • Attention Deficit Hyperactivity Disorder -One of the most common developmental disabilities. -Has serious implication for cognitive development, social interaction, and educational performance. -Condition is characterized by persistent inattention, chronic hyperactivity, and impulsivity. Abnormal Development of the PNS • Anencephalic fetuses lack optic nerves, but the eyes, although large, appear normal. • Aganglionic Megacolon -The colon is greatly dilated because of lack of muscular tone and contractile activity of the bowel segment, which causes fecal retention. CHAPTER 5 Chapter 5: Nerve Cell Physiology Neuron: • Aspecialized cell within the nervous system which transmits nerve impulses to other nerve cells. Muscle or gland cells. The Three Main Components of a Neuron: • Cell Body (Soma), Dendrites &Axon Cell Body (Soma) • The cell body contains the nucleus and the cytoplasm. • Brings information to the neuron, axon and sends information to other neurons. Dendrites (Efferent) • extend from the neuron cell body and receive messages from other neurons. • are covered with synapses formed from the ends of axons from other neurons. • Synapses: a junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter. Axon (Afferent) • Axons are elongated nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. • Some axons are covered with a fatty white substance called myelin (myelin sheath), which acts as an insulator. The myelinated axons transmit information much faster than other neurons. Central and Peripheral Nervous Systems • CNS and PNS differences: different myelin-forming cells; Schwann cell forms myelin for one internode of a nerve fiber in the PNS • PNS has endometrium, fibrous connective tissue covering for axons and CNS does not. • Nerve fiber composition: peripheral nerve fibers are held together by connective tissue that form the endoneurial membrane (does not exist in the CNS) Neuronal Pruning and Synapse Establishment • Human brain’s ability to serve speech functions is related to the neuronal growth pattern in the embryonic period. • Embryogenesis is known to an abundance of neurons in the brain. • During brain development, there are mechanisms that guide the cells that are connected through traveling axons in the brain. • When final destination is established, the neuron extends an axon with growth cones (path finders) • Growth cones navigate axonal paths through the biological environment of cellular density to connect with the target neuron. • Glycoproteins are produced by myelin-forming cells, they prevent uncontrolled axonal growth in all directions. • Only synaptic connections that survive and function are those that meet the criterion of biocompatibility on both sides. Nerve Impulse • Nerve cells communicate with one another through impulse that represent all neuronal activity. • Specific resting membrane potential depends on the cell type. • Typical neuron has low internal sodium and chloride concentration and high internal potassium concentration. • Inhibitory postsynaptic potential is if the postsynaptic cell demonstrates hyper- polarization in response to the neurotransmitter. • Membrane potential is maintained by an unequal distribution of positively charged sodium and potassium ions and negatively charged chloride ions and proteins. • Ion concentration gradient is when ions move to lower concentration of ion. • Electrical gradient is negative ions moving toward positive charges and vice versa. • Excitability is a cell response to stimuli and this response turns into a nerve impulse or action potential. • Action potential is passively conducted a short distance in the axon by sodium entering the cell membrane. Neuronal Responses to Brain Injuries • Nerve cells in the human brain are less capable of further cell division than other cell types. • Two types of degenerative changes that follow axonal sectioning -Axonal Reaction & Wallerian degeneration • Proximal segment – axonal segment still attached to the cell body • Chromatolysis is the reactive or degenerative process in individual cells. • Severity of injury may have the chromatolytic process continue for 10 to 18 days. • Neuroglial cells react to cell injury and brain tissue necrosis by multiplying and increasing in size. • Axons damaged in the CNS undergo regrowth and sprouting similar to that in the PNS. • Lack of growth protein in the CNS may be a factor in why damaged neurons don’t reconnect to the distal axonal segments and reinnervate their target structures. Axonal Reaction • First cytologic signs of changes in the cell body are swelling of the organelles and dissolution of coarse clumps of Nissl bodies into fine granules • Chromatolysis: swelling of the cell and shifting of the nucleus from its central position to the periphery • While the cell is injured and undergoing reactive or degenerative changes cellular RNA production and protein synthesis increase, as does the formation of the plasma membrane to regenerate the severed axon and to prevent the cell body from dying Wallerian Degeneration • The degeneration of the axonal part that is separated from its cell body • Distal portion swells and begins to degenerate within 12-20 hours • Axons degenerate before the myelin sheath • Within 7 days they are both broken down and gradually degenerate setting the stage for the macrophagic action of the microglia cells Neuroglial Responses • Neuroglia cells react to cellular injures and brain tissue necrosis by multiplying in number(hyperplasia) and by increasing their size(hypertrophy) • Infection-fighting neutrophils (scavenger white blood cells) arrive at the lesion site within a few days of the injury • Microglia’s are the primary scavengers of the nervous system -function is to phagocytose the cellular debris • Phagocytic cells dominate the injury site from the first week and it may take several months or even years to remove the debris of dead brain tissue Axonal Regeneration in the PNS • The sectioned nerve endings proximal to the cell body begin regeneration within 3-4 days and cannot occur unless the proximal and distal ends of the severed nerve are cleaned and attached • The Schwann cells and fibroblasts contribute significantly • There is a low probability that the regenerated axon will reach its previously attached fiber. Instead, it might attach to a different sensory or motor fiber. Axonal Regeneration in the CNS • The physiologic concept that most intrigues and frustrates health professionals is the minimal restoration of function after a lesion in the brain. • Axons severed in the CNS also undergo regrowth and sprouting similar to those in the PNS but unknown factors prevent damaged neurons from reconnecting to the distal axonal segments and reinnervating their target structures • Intrinsic differences between PNS and CNS such a protein expression may play a factor Neurotransmitters • Help regulate brain mechanisms that control cognition, language, speech, moods, attention, memory, personality, motivation and the turning of the brain and its pathways • Released at a synapse and it transmits signals across neurons • Most have more than one receptor type and may have different effects on different synapsis • More than one neurotransmitter may be secreted at a single synapse Acetylcholine • One of the primary neurotransmitters of the PNS regulating muscle activity • Also functional in the CNS but functions are more difficult to decipher • Critical in the cycle of sleep and wakefulness • Binds to receptor sites on the muscle fiber membrane and increases its permeability to sodium and potassium ions. Monoamines • Asubgroup of small-molecule transmitters derived from amino acids • Lies in the brainstem • These neurons have projections to the wider areas of the brain and participate in regulating the activity of the large portions of the CNS Dopamine • Found mainly in the upper midbrain and project ipsilaterally • The two most important projections include mesostriatal (midbrain to striatum) and mesocortical (midbrain to cortex) • Projections to the cortex and limbic structures support their involvement in cognition, emotion and motivation Norepinephrine • One of the primary neurotransmitters in the PNS • Responsible for the flight-or-fight reaction • Thought to be involved in generating paradoxical sleep and maintaining attention and vigilance • Drugs used for treatment of depression act by enhancing norepinephrine transmission Serotonin • Firing rate fluctuates with sleep and wakefulness • Thought to be involved with the overall level of arousal and slow-wave sleep • Contributes to the descending pain-control system • Low levels are thought to be associated with severe depression and mental illnesses Aminobutyric Acid (GABA) • Amajor inhibitory neurotransmitter for the CNS • Pharmaceutical agents that interact with GABAreceptors are widely prescribed for clinical conditions such as epilepsy, anxiety, and insomnia • Reduction causes an elevation of the ratio of dopamine to acetylcholine which produces abnormal movements Glutamate • Main excitatory neurotransmitter in the mammalian CNS • Mediates fast synaptic transmissions in the CNS • Produced by all excitatory neurons in the CNS • Too much can cause excessive calcium influx • Brain damage secondary to stroke or degenerative disorder may be the result of excessive release or insufficient reuptake of glutamate by astrocytes Peptides • Large molecule chemicals that can function as neurotransmitter or neuromodulators. • Most neurons also contain one of the classic small molecule transmitters. • Many peptides consist of consist of opioid-like compounds, and their projections are important in pain management. Brain Tumors • Aneoplasm refers to an uncontrolled and unregulated growth of the body tissue including glia. • Tissue involved with a tumor may retain some of its original functions or may revert to a primitive functional state. • Oncogenes: coding proteins involved with cellular growth. • angiogenesis, the formation of new blood vessels promoting growth in tumorous tissue. • Metastatic tumors arise from elsewhere in the body and spread to the brain from the body outside of the brain. • tumors in the brain are either malignant or benign. • Most malignant tumors grow fast, invade the surrounding tissue, and are fatal. • Malignancy is determined by a grading scale of (I-IV) • Astrocytoma’s, ependymoma, and oligodendroglimas are the common malignant tumors of the brain. • The meningiomas, acoustic neuromas, vestibular schwannomas, and pituitary adenomas are common benign tumors of the brain. • Symptoms of these tumors are related focally to the affected brain area but develop slowly. Multiple Sclerosis • M.S is an autoimmune central demyelinating disease • M.S has been linked to viral infections and abnormalities in the immune systems which reacts improperly to antigens causing antibodies to attack the body’s own myelin at random locations in the central nervous system. • The myelin sheath degenerates and later on the axon becomes involved • The initial sparing of axons account for the periods of remission, followed by a symptom relapse • Early symptoms could be vision loss, double vision, vertigo, loss of balance, weakness, and numbness in the limbs. • The exact antigen responsible for the immune attack seen in M.S remains unknown • Tumor necrosis factor a has also been associated with inflammation and demyelination • Most of the treatments for M.S are symptomatic • B-Interferon and Copaxone Injections have recently been used to reduce the frequency and severity of new attacks and slow the progression of the disability by inhibiting the immune process • M.S was not considered to be associated with cognitive dysfunction • Guillain-Barre Syndrome is also an autoimmune demyelinating syndrome that affects peripheral myelin; It is triggered by an infection Myasthenia Gravis • Aneuromuscular junction disorder and it is characterized by progressive fatigue and muscle weakness that worsens with exercise and improves with rest. • In this autoimmune condition, the antibodies bind with the acetylcholine receptors at the motor end plates and prevent the normal effects of acetylcholine. • Symptoms appear at any age, more prevalent in females during the first 30 years • Ptosis and diplopia are the most common early manifestations of the illness. • The first signs of the disease usually appear in the constantly used muscles. • Diagnosis is made predominately based off clinical symptoms, the presence of serum antibodies to the acetylcholine receptor, and the electrophysiologic testing. • Drug treatments consists of drugs that inhibit acetylcholinesterase, allowing a higher concentration of the acetylcholine synaptic cleft. • Myasthenic crisis is treated best by plasma-pheresis, steroids, or infusion of immunoglobulins. • Long periods of remission do occur, but some patients undergo a progressive course that may result in bulbar and respiratory paralysis. CHAPTER 6 Chapter 6 Outline – Diencephalon: Thalamus andAssociated Structures Diencephalon: ○ Located beneath the cortex ○ Composed of four parts: thalamus, epithalamus, subthalamus, hypothalamus 1. Epithalamus: concerned with diurnal and autonomic bodily functions 2. Subthalamus: important for motor functions through its connections with the brainstem, basal ganglia, diencephalic structures 3. Hypothalamus: part of the autonomic nervous system (ANS), which mediates endocrine and other metabolic states 4. Thalamus: ○ Serves as sensorimotor gateway for information projected to forebrain ○ 3 cm x 1.5 cm ○ Retains information through time and connects it with the forebrain regions ○ Three Main Important Functions: 1. Channel the projections of sensory information entering lower levels of nervous system to specific cortical areas 2. Integrate sensorimotor information and project afferents from the basal ganglia, limbic system, and cerebellum to primary and premotor cortices 3. Regulates functions of the associated cortex as well as cortically mediated cognitive functions Thalamic Structure ● Consists of three tiers of nuclei: medial, lateral, ventral ● Also contains internal medullary lamina: surrounds anterior nucleus; contains small intralaminar nuclei Anatomical Connections and Functions of Thalamic Nuclei ● Each thalamic nucleus screens definitive information from thalamic structures before transmitting to respective area of cortex ● Medial Nuclear Complex: ○ Dorsomedial Nucleus: ■ mammillothalamic tract passes beneath ■ involved with emotion, judgement and reasoning, memory, language, cognitive functions ■ surgical lesions to DM lead to anxiety-related disorders and Wernicke- Korsakoff syndrome (memory loss) ○ Midline Nuclear Complex: ■ Bridges gray matter across the third ventricle above hypothalamus ■ Important in visceral and emotional functions ● Lateral Nuclear Complex (consists of three nuclei): ○ Lateral Dorsal Nucleus: ■ Contributes to visceral-sensory integration that is needed for any behavioral responses ○ Lateral Posterior Nucleus: ■ Involved with information integration for vision, tactile, audition prior to behavioral response ○ Pulvinar Nucleus: ■ Regulation of higher mental functions including language formulation, lexical storage and processing, reading, writing ● Ventral Nuclear Complex (relays information from sensory surfaces to sensory cortex): ○ VentralAnterior Nucleus: ■ Definitive role in execution and planning of skilled and sequential movements ○ Ventrolateral Nucleus: ■ Regulation of volitional movements ■ Coordinates different aspects of motor functions ■ Damage causes abnormal (involuntary) movements ○ Ventral Posterior Nucleus ■ Relays somatosensation (pain, temperature, touch) information from body and face ○ Ventral Posterior Lateral Nucleus ■ Relays somatic information from body ○ Ventral Posterior Medial Nucleus ■ Relays sensations of taste, pain, temperature, and touch for head and face (facial sensation) ○ Lateral Geniculate Body ■ Relays sensation of vision ■ Damage causes homonymous hemianopsia (loss of vision in contralateral halves of visual fields) ○ Medial Geniculate Body ■ Fibers in ears project to primary auditory cortex ■ Constitute auditory radiations (geniculo-Heschl fibers) ■ Gives the ability to discriminate speech sounds and provides hearing sensitivity Additional Nuclei in the Thalamus ● Anterior Nucleus: ○ Protrudes as an anterior tubercle on the floor of the lateral ventricle and is surrounded by the forks of the internal medullary lamina ○ Contributes to digestive, respiratory, urogenital, emotional, and endocrine functions ○ Projects to the cingulate gyrus, an important structure in the limbic circuitry ○ Regulates the hypothalamic and limbic influence on the neocortex ○ Electrical stimulation and the removal of the nucleus induce changes in blood pressure, anxiety levels, and emotional drive ● Reticular Nucleus: ○ Consists of a thin layer of nerve cells that covers the entire lateral thalamus ○ Receives input from virtually all ascending systems, including other thalamic nuclei ○ Sends projections indirectly to the brain ○ Regulates thalamic neuronal activity participation, which influences cortical functions by inhibiting or facilitating the thalamocortical relay ● Intralaminar Nuclei: ○ The complex consists of several nuclei intersped in the core of the internal medullary lamina ○ The centromedian nucleus and parafascicular, two important intralaminar nuclei, indirectly contribute to the diffuse reticular-brain activation system ○ The complex receives afferents from the globus pallidus, vestibular nucleus, superior colliculus, and most importantly the brainstem reticular formation ○ The centromedian and parafascicular nuclei also receive cortical afferents from the motor, premotor, and prefrontal cortical areas ○ The IN system as a whole influences the excitability of the association cortex with both its intrathalamic projections and striatal collaterals to the cortex ○ The IN system is in prime position to modulate the excitability and overall function of both the cortex and basal ganglia ○ Intralaminar nuclei are known to evoke a cortical recruiting response when directly stimulated with electrical impulses ○ Stimulation of the centromedian nucleus has been noted to have positively affected human performance in involving the frontal, parietal, cingulate, and orbital areas of the association cortex Epithalamus ● Consists of two small structures ● Pineal gland: ○ Renders an inhibitory influence over gonadal (sex gland) functions ○ Secrets melatonin in response to the day-night cycle ○ Regulates diurnal rhythms of the brain ○ Controls endocrinic activity related to the sleep cycle ● Habenular Nuclei: ○ Serve autonomic functions, such as emotional experiences and drives, and possibly the sens of smell. Subthalamus ● These structures are anatomically included in the diencephalon, but are functionally related to the basal ganglia ● Refers to several nuclei between the thalamus and midbrain ● Contains primarily subthalamic nucleus and secondarily the prerubral area. ● Subthalamic nucleus: ○ Connected to the globus pallidus via bidirectional fibers ○ Makes substantial contributions to motor functions ● Prerubral area: ○ Thin area of gray matter ○ Lies in the subthalamus between the thalamic and lenticular fasciculi. ○ Serves as visuomotor coordinator by projecting to superior colliculus and pretectal. Hypothalamus ● Contains important nuclei and a tract that forms crossroads among the limbic system, brainstem, and thalamus. ● Located below thalamus ● Includes many nuclei and specific structures (optic chiasm, mammillary bodies, hypophysis, infundibular stem, and tuber cinereum) ● Its afferents and efferents use 2 modes of communication: neural and horomonal. ● Neural Impulses: ○ Using these impulses, the hypothalumus connects with the brain and spinal structures. ● Hormonal efferents: ○ Regulated by pituitary gland ○ Allows hypothalamus to communicate with the body by releasing selected proteins into the blood circulation. ○ Released proteins influence other body activities ● Hypothalamus serves three partly overlapping functions closely connected with the forebrain and the limbic system: ○ 1st: Controlling center forANS ○ 2nd: Regulating center of the endocrinic activities. ○ 3rd: Controls body temperature, water and food intake, sugar metabolism, sexual behavior, and emotional states. Cogniti
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