Cerebrum - Applied Neuroscience Overview PDF

CEREBRUM APPLIED NEUROSCIENCE OVERVIEW THE ORGANIZATION OF NERVOUS SYSTEM (Part 1)  Learning Outcome Describe the organization/functions of CNS Describe the structure/function of PNS Describe the organization/function of lymbic system Explain the brain protection (meninges...

CEREBRUM APPLIED NEUROSCIENCE OVERVIEW THE ORGANIZATION OF NERVOUS SYSTEM (Part 1)  Learning Outcome Describe the organization/functions of CNS Describe the structure/function of PNS Describe the organization/function of lymbic system Explain the brain protection (meninges/CSF/BBB) and blood supply.  Introduction Classification i. Central Nervous System - Brain, Spinal Cord ii. Peripheral Nervous System - peripheral nerves (spinal & cranial), ganglion, receptor Develoment of Central Nervous System  BRAIN Consist of 4 major parts: – Brain stem – Diencephalon – Cerebrum – Cerebellum CEREBRUM: Main functions: Seat of intelligence – It provides the ability to read, write and speak; Make calculations Compose music To remember the past Plan for the future Imagine things that have never existed before Centre of sensory perception Initiate and coordinate skeletal muscle contraction Cerebral cortex and it’s structures: Consists of cerebral cortex (gray matter), internal region of cerebral white matter and gray matter nuclei deep within the white matter. Thick : 2 – 4 mm, contains billions of neurons. This gray matter is made of cell bodies of neurons. During embryonic development, when brain size increases rapidly, the gray matter of the cortex enlarges much faster than the deeper white matter. As a result, cerebral cortex rolls and folds upon itself so that it could fit into the cranial cavity.  The folds called gyri / gyrus or convolutions. The deeper grooves between folds are known as fissures. The shallow grooves between folds are termed as sulci / sulcus. The most prominent fissure, is the longitudinal fissure which separates the cerebrum into right and left halves called cerebral hemisphere.  Within the longitudinal fissure between the cerebral hemispheres is the falx cerebri. The hemispheres are connected internally by the corpus callosum. (broad band of white matter containing axons that extend between the hemispheres)  Each hemisphere is further subdivided into five lobes. The lobes are named after the bones that cover them: – Frontal lobes. – Parietal lobes. – Temporal lobes. – Occipital lobes. – Insula A fifth part of the cerebrum, the insula, cannot be seen at the surface of the brain because it lies within the lateral cerebral sulcus, deep to the parietal, frontal, and temporal lobes. Main boundaries in cerebrum: Sulcus and fissures Central sulcus – Separates the frontal and parietal lobes. Longitudinal fissure – Separates the cerebrum into right and left hemispheres. Lateral cerebral sulcus – Separates the frontal and temporal lobes. Parieto-occipital sulcus – Separates parietal and occipital lobes. Major Gyrus of cerebrum: Precentral gyrus – Located immediately anterior to the central sulcus. – It contain primary motor area. Postcentral gyrus – is located immediately posterior to the central sulcus, contains the primary somatosensory area of the cerebral cortex.  CEREBRAL WHITE MATTER The cerebral white matter consists of myelinated and unmyelinated axons that transmit impulses. There are 3 types of tracts:- – Association tracts. – Commissural tracts – Projection tracts.  association tracts; contain axons that conduct nerve impulses between gyri in the same hemisphere.  Commissural tracts; contain axon that conduct nerve impulses from gyri in one cerebral hemisphere to corresponding gyri in the other cerebral hemisphere. 3 important commissural tracts are the: Corpus callosum (largest fiber bundle in the brain – 300 million fibers) Anterior commissure Posterior commissure  Projection tracts; contain axons that conduct nerve impulses from the cerebrum to lower parts of the CNS (thalamus, brainstem, or spinal cord) or lower parts of the cerebrum to the cerebellum. An example; is the internal capsule, which is the thick band of white matter that contains both ascending and descending axons.  Summary of Tracts projection tracts From brain to spinal cord & vice verca, forms internal capsule Commissural tracts Cross to opposite hemisphere: » Corpus callosum » Anterior and posterior commissures Association tracts Connect lobes and gyri within a hemisphere.  Cerebral lobes: Frontal The frontal lobe forms the anterior portion of each cerebral hemisphere. Extends from precentral sulcus up to the end of brain anteriorly.  It is bordered posteriorly by a central sulcus (fissure of Rolando), which passes out from the longitudinal fissure at a right angle and inferioly by a lateral sulcus (fissure of Sylvius) which exits the undersurface of the brain along its sides.  Cerebral lobes: Parietal Extend from central sulcus to parietooccipital sulcus posteriorly. The parietal lobe is posterior to the frontal lobe and is separated from it by the central sulcus.  Cerebral Cerebral lobes: lobes: Temporal Temporal The temporal lobe lies inferior to the frontal and parietal lobes and is separated from them by the lateral sulcus.  Cerebral Cerebral lobes: lobes: Occipital Occipital The occipital lobe forms the posterior portion of each cerebral hemisphere and is separated from the cerebellum by a shelflike extension of duramater called tentorium cereblli. Extends from parietooccipital sulcus to the inferior end of brain posteriorly. The occipital,parietal and temporal lobes have no distinct boundary.  Cerebral lobes: Insula A fifth part of the cerebrum, the insula – cannot be seen at the surface of the brain because it lies within the lateral cerebral sulcus, deep to the parietal, frontal and temporal lobes. Is on the lateral surface (medially) of the cerebrum Cerebral lobes and it’s functions  Cerebral lobes and it’s functions Frontal – Voluntary motor functions – Voluntary scanning movements of the eyes. – Planning, mood, smell and social judgement – Intellect – Personality – Complex learning ability – Recall of information – Initiative – Reasoning – Articulation of speech  Cerebral lobes and it’s functions Parietal – Receives and integrates sensory information. – Examples: touch, proprioception, pain, itching, tickle, temperature. – Interprets the meaning of a speech. Temporal – Areas for hearing (auditory perception) and smell (olfactory perception).  Cerebral lobes and it’s functions Occipital – Visual center of brain – Involved in visual perception – Relates present and past visual experiences and is essential for recognizing and evaluating what is seen. Functional Area of Cerebral Cortex  Functional Functional Organization Organization of of the the Cerebral Cerebral Cortex Cortex Specific types of sensory, motor and integrative signals are processed in certain regions of the cerebral cortex. Sensory areas receive sensory information and are involved in perception, the conscious awareness of a sensation. Motor areas control the execution of voluntary movements. Association areas deal with more complex integrative functions (memory, emotions, reasoning, will, judgments, personality traits and intelligence)  Brodmann’s Brodmann’s Area Area Functional area of cerebral cortex Define by German Anatomist, Dr Korbinian Brodmann Base on cytoarchitecture of the neuron in cerebral cortex. Split the cortex into 52 areas Consist of i. Motor areas (primary & association) ii. Sensory areas (primary & association)  MOTOR AREAS Motor output from the cerebral cortex flows mainly from the anterior part of each hemisphere. MOTOR AREAS  IMPORTANT MOTOR AREAS Primary motor area Broca`s speech area  Primary Primary motor motor area area (4) (4) Located in the precentral gyrus of the frontal lobe. Each region in the primary motor area controls voluntary contractions of specific muscles or groups of muscles. Electrical stimulation of any point in the primary motor area causes contraction of specific skeletal muscle fibers on the opposite side of the body. More cortical area is devoted to those muscles involved in skilled, complex or delicate movement. For instance, the cortical region devoted to muscles that move the fingers is much larger than the region for muscles that move the toes. Form corticospinal and corticobulbar/nuclear tracts  Broca’s speech area (44, 45) Located in the frontal lobe close to the lateral cerebral sulcus. (dominant hemisphere) Is involved in the articulation of speech. In most people, Broca’s speech area is localized in the left cerebral hemisphere. Neural circuits between Broca’s speech area, premotor area and primary motor area activate muscles of the larynx, pharynx, and mouth and breathing muscles. The coordinated contractions of your speech and breathing muscles enable you to speak your thoughts. In stroke patient when this areas is affected they still have clear thoughts, but are unable to form words.(...) MOTOR ASSOCIATION AREAS  Premotor area (6,8) Is a motor association area that is immediately anterior to the primary motor area. Neurons in this area communicate with the primary motor cortex, the sensory association areas in the parietal lobe, the basal ganglia and the thalamus. The premotor area deals with learned motor activities of complex and sequential nature It generates nerve impulses that cause specific groups of muscles to contract in a specific sequence, as when you write your name. The premotor area also serves as a memory bank for such movements.  Frontal eye field area (8) Is in the frontal cortex It is sometime included in the premotor area. It controls voluntary scanning movements of the eyes – like those you just used in reading this sentence. Eyes move to the opposite site simultaneously – conjugate movements. SENSORY SENSORY AREAS AREAS  Primary Primary Sensory Sensory Areas Areas Sensory information arrives mainly in the posterior half of both cerebral hemisphere in regions behind the central sulci The cortex, primary sensory areas have most direct connections with peripheral sensory receptors. Sensory areas are:- – Primary somatosensory area- postcentral gyrus. – Primary visual area- occipital lobe. – Primary auditory area- temporal lobe. – Primary gustatory area- base of the postcentral gyrus. – Primary olfactory area- temporal lobe  Secondary Secondary Sensory Sensory Areas Areas Secondary sensory areas and sensory association areas often are adjacent to the primary areas and from other brain regions. Secondary sensory areas and sensory association areas integrate sensory experiences to generate meaningful patterns of recognition and awareness. A person with damage in the primary visual area would be blind in at least part of his visual field, but a person with damage to a visual association area might see normally yet be unable to recognize her best friend.  IMPORTANT IMPORTANT SENSORY SENSORY AREAS AREAS  1. 1. Primary Primary somatosensory somatosensory area area (1,2,3) (1,2,3) Located posterior to the central sulcus of each cerebral hemisphere in the postcentral gyrus of each parietal lobe. It extends from the lateral cerebral sulcus, along the lateral surface of the parietal lobe to the longitudinal fissure and then along the medial surface of the parietal lobe within the longitudinal fissure.  Receives nerve impulse for touch, pressure, vibration, itch, tickle, temperature, pain, proprioception and is involved in the perception of these somatic sensations. The side of cortical area receiving impulses from a particular part of the body depends on the number of receptors present there rather than on the size of the body part. A larger region of the somatosensory area receives impulses from the lips and fingertips than from the thorax or hip. (sensory homunculus)  2. 2. Primary Primary visual visual area area (17) (17) Located at the posterior tip of tip of the occipital lobe mainly on the medial surface. Receives visual information and is involved in visual perception.  3. 3. Primary Primary auditory auditory area area (41,42) (41,42) Located in the superior part of the temporal lobe near the lateral cerebral sulcus Receives information for sound and is involved in auditory perception.  4. 4. Primary Primary gustatory gustatory area area (43) (43) Located at the base of the postcentral gyrus superior to the lateral cerebral sulcus in the parietal cortex. Receives impulses for taste and is involved in gustatory perception.  5. 5. Primary Primary olfactory olfactory area area (34) (34) Located in the temporal lobe on the medial aspect (and thus not visible) Receives impulses for smell and is involved in olfactory perception. ASSOCIATION ASSOCIATION SENSORY SENSORY AREAS AREAS Secondary sensory areas /sensory association areas often are adjacent to the primary areas and from other brain regions. Secondary sensory areas / sensory association areas integrate sensory experiences to generate meaningful patterns of recognition and awareness. A person with damage in the primary visual area would be blind in at least part of his visual field, but a person with damage to a visual association area might see normally yet be unable to recognize her best friend.  ASSOCIATION ASSOCIATION AREAS AREAS Consist of larger areas of the occipital, parietal and temporal lobes and anterior surface frontal lobe. Association areas are connected with one another by association tracts. 1. 1. Somatosensory Somatosensory association association area area (5,7) (5,7) Is just posterior to and receives input from the primary somatosensory area, as well as from the thalamus and other parts of the brain.  It allows to determine the expect shape and texture of an object without looking at it, to determine the orientation of one object with respect to another as they are felt, and to sense the relationship of one body part to another. Another role of the somatosensory association area is the storage of memories of past somatic sensory experiences, enabling you to compare current sensations with previous experiences. For example, the somatosensory association area allows you to recognize objects such as a pencil and a paperclip simply by touching them.  2. 2. Visual Visual association association area area (18, (18, 19) 19) Located in the occipital lobe, receives sensory impulses from the primary visual area and the thalamus. It relates present and past visual experiences and is essential for recognizing and evaluating what is seen. For example, the visual association area allows you to recognize an object such as a spoon simply by looking at it. 3. 3. Facial Facial recognition recognition area area (20,21) (20,21) Corresponding roughly to areas 20, 21 and 37 in the inferior temporal lobe, receives nerve impulses from the visual associations area. This area stores information about faces, and it allows you to recognize people by their faces. (prosopagnosia) The facial recognition area in the right hemisphere is usually more dominant than the corresponding region in the left hemisphere. 4. 4. Auditory Auditory association association area area (22) (22) Located inferior and posterior to the primary auditory area in the temporal cortex Allows you to recognize a particular sound as speech, music or noise.  5.Secondary 5.Secondary olfactory olfactory area area (11) (11) Corresponding roughly to area 11 along the lateral part of the frontal lobe Receives sensory impulses from the primary olfactory area.  This area allows you to identify odors and to discriminate among different odors. During olfactory processing, the orbital frontal cortex of the right hemisphere exhibits greater activity than the corresponding region in the left hemisphere.  6. 6. Wernicke’s Wernicke’s area area (39,40) (39,40) A broad region in the left temporal and parietal lobes (dominant hemisphere), interprets the meaning of speech by recognizing spoken words. It is active as you translate words into thoughts.  7. 7. Common Common integrative integrative area area Is bordered by somatosensory, visual and auditory association areas. It receives nerve impulses from these areas and from the primary gustatory area, primary olfactory area, the thalamus and parts of the brain stem. This area integrates sensory interpretations from the association areas and impulses from other areas, allowing the formation of thoughts based on a variety of sensory inputs. It then transmits signals to other parts of the brain for the appropriate response to the sensory signals it has interpreted.  8. 8. Prefrontal Prefrontal cortex cortex (frontal (frontal association association area) area) (9,10,11) (9,10,11) is an extensive area in the anterior portion of the frontal lobe. This area has numerous connections with other areas of the cerebral cortex, thalamus, hypothalamus, limbic system and cerebellum. Prefrontal cortex (frontal association area) The prefrontal cortex is concerned with make up of a person`s: Personality Intellect Complex learning abilities Recall of information Initiative Judgement Foresight Reasoning Conscience Intuition Mood Planning for future Development of abstract ideas. Prefrontal cortex (cont…) Damage to bilateral prefrontal cortices make a person become: – rude, – inconsiderate – Incapable of accepting advice – Moody – Inattentive – Less creative – Unable to plan for the future  SUMMARY SUMMARY FOR FOR CEREBRAL CEREBRAL LOBE LOBE FUNCTIONS FUNCTIONS Frontal – Voluntary motor functions – Planning, mood, smell and social judgement Parietal – Receives and integrates sensory information Occipital – Visual center of brain Temporal – Areas for hearing, smell, learning, memory, emotional behaviour.  SUMMARY: SUMMARY: LANGUAGE LANGUAGE Includes reading, writing, speaking and understanding words. Wernicke`s area – Permit recognition of spoken and written language and creates plan of speech. Broca`s area – Generates motor signals for larynx, tongue, cheeks and lips. – Transmits to primary motor cortex for action HEMISPHERIC HEMISPHERIC LATERALIZATION LATERALIZATION Slight anatomical differences between the right and left hemispheres exist. 2/3rd of the population, the Wernicke's area is 50% larger on the left side than on the right side. Physiological differences also exists. This functional asymmetry is termed as hemispheric lateralization. Most obvious examples are: Left hemisphere receives somatic sensory signals from and controls muscles on the right side of the body, whereas the right hemisphere receives sensory signals from and controls the left side of the body. In most people the left hemisphere is more important for reasoning, numerical and scientific skills, spoken and written language, and the ability to use and understand sign language.  The right hemisphere is more specialized for: – musical and artistic awareness; – spatial and pattern perception; – recognition of faces and emotional content of language; – Discrimination of different smells – Generating mental images of sight, sound, touch, taste and smell to compare relationships among them. HEMISPHERIC HEMISPHERIC LATERALIZATION LATERALIZATION Neuroanatomy & Physiology Basal Ganglia and its Clinical Correlation By Hermizan Halihanafiah  Anatomical Classification Neurologic structure Basal nuclei Corpus striatum Caudate nuclei and lentiform nuclei Lentiform nuclei Putamen & globus pallidus Neostriatum / striatum Caudate nuclei & putamen Amygdaloid body Amygdaloid nuclei Claustrum Claustrum  Functional Classification Nuclei Discription Corpus striatum Caudate nuclei and lentiform nuclei Subthalamic nuclei Diencephalic origin Subtantia nigra Masses of grey matter located at midbrain  Basal Ganglia Disorder Hypokinesia Hyperkinesia  Hypokinesia Parkinsonism - bradykinesia / akinesia - resting tremors / pill rolling - lead pipe regidity/cogwheel rigidity  Hyperkinesia Chorea – Huntington - Sydenham’s / St Vitus Dance Hemiballism Athetosis Dystonia Tardive dyskinesia Wilson disease – tremor, dyskinesia, rigidity Internal Capsule  Internal capsule Projection tracts (ascending and descending tracts) V shaped of white matter Located in between lenticular nuclei (laterally) and thalamic / caudate nuclei (medially)  Internal capsule It divide into: 1.anterior limb 2.Genu 3.Posterior limb 4.Retrolenticular portion 5.Sublenticular portion  Genu Refers to the flexure of internal capsule Consist of corticobulbar/corticonuclear tracts Which originate from primary motor area (head and facial areas) Terminate at the cranial somatic motor nuclei (III, IV, V, VI, VII, IX, X, XI, XII)  ANTERIOR LIMB  Located in between lenticular nuclei and caudate nuclei  Huge connection between thalamus and frontal lobe  Three major tracts formed ALIC 1.thalamocortical/thalamofrontal 2.Frontothalamic and frontopontine  Posterior Limb The largest fibers of IC Consist most of the ascending and descending tracts Located inbetween lentiform nuclei and thalamus  Contains fibers of: 1.Corticospinal tracts 2.Somaticsensory tracts (PCML, ASTT, LSTT and TTT) 3.Optic radiation from thalamus to visual cortex (occipital lobe) 4.Acoustic fibers to temporal lobes  Meninges Ventricle System and CSF Blood Brain Barrier Lymbic System 1. MENINGES Is a protective covering of the brain and spinal cord. The cranial bones and cranial meninges surround and protect the brain. The cranial meninges are continuous with the spinal meninges. Consists of 3 layers: – Dura mater (outer most) – Arachnoid mater (middle) – Pia mater (inner most) 1.1. Dura mater cranial dura mater has 2 layers and spinal dura mater has only 1 layer. 2 dural layers; periosteal and meningeal layers around the brain are fused together except where they separate to enclose the dural venous sinuses that drain venous blood from the brain and deliver it into the internal jugular veins.(p498) There is no epidural space in the brain. Blood vessels enter brain tissue pass along the surface of the brain, and as they penetrate inward, they are sheathed by a loose – fitting sleeve of pia mater. Extensions of the Dura Mater Copyright 2009, John Wiley & Sons, Inc. Extensions of the dura mater 3 extensions of the dura mater (Dural Folds) separate parts of the brain (p498): Falx cerebri – the largest dural folds, separates the 2 hemispheres of the cerebrum, lies in the longitudinal fissure and anchored anteriorly by crista galli. Falx cerebelli – separates the 2 hemispheres of the cerebellum. Tentorium cerebelli – horizontally separates the cerebrum and the cerebellum.  Dura mater Falx Cerebri Falx Cerebri Tentorium Cerebelli 1.1. Dura mater (cont…) (cont…) spinal dura mater forms a loose sheath round the spinal cord, extending from the foramen magnum to the second sacral vertebra. It encloses the filum terminale and fuses with the periosteum of the coccyx. It is an extension of the inner layer of cerebral dura mater and is separated from the periosteum of the vertebrae and ligaments within the neural canal (vertebral canal) by the epidural or extradural space, containing blood vessels and areolar tissue. Nerves enter and leave the spinal cord, pass through the epidural space. 1.2. Arachnoid mater Is a serous membrane lies between the dura and pia mater. Is separated from the dura mater by the subdural space, and from pia mater by subarachnoid space which contains cerebrospinal fluid. It passes over the convolutions of the brain and accompanies the inner layer of dura mater in the formation of the falx cerebri, tentorium cerebelli and falx cerebelli. It continues downwards to envelop the spinal cord and ends by merging with the dura mater at the level of the 2nd nd sacral vertebra. 1.3. Pia mater Is a fine connective tissue containing many minute blood vessels. It adheres to the brain, completely covering the convolutions and dipping into each fissure. It continues downwards surrounding the spinal cord. Beyond the end of the cord it continues as the filum terminale, pierces the arachnoid tube and goes on, with the dura mater, to fuse with the periosteum of the coccyx. Spinal Meninges Cranial Meninges 2. VENTRICLES Within the brain there are 4 irregular shaped cavities or ventricles containing CSF (p499): 2 lateral ventricles (right and left) 3rd rd ventricle 4thth ventricle  2.1. Lateral ventricles lie within the cerebral hemisphere, one on each side of the median plane just below the corpus callosum (p502). Anteriorly the lateral ventricles are separated from each other by a thin membrane called septum pellucidum, and they are lined with ciliated epithelium (p502).. Leteral ventricles communicate with 3rdrd ventricle by interventricular foramina (foramina of Monro). Consists network of blood capillaries called choroid plexus.  2.2. Third ventricles Is a cavity situated below the lateral ventricles between the right and left halves of the thalamus. Is a narrow cavity along the midline superior to the hypothalamus. Communicates with the 4thth ventricle by a canal, the cerebral aqueduct or aqueduct of the midbrain (Aqueduct of Sylvius). Consists network of blood capillaries called choroid plexus.  2.3. Fourth ventricles Is a diamond shaped cavity situated below and behind the 3rdrd ventricle, between the cerebellum and pons. Is continuous below with the central canal of the spinal cord and communicates with the subarachnoid space by two lateral aperture (Foramina of Luschka) and one median aperture (foramina of Magendie). CSF enters the subarachnoid space through these openings and through the open distal end of the central canal of the spinal cord. Consists network of blood capillaries called choroid plexus. 3. CEREBROSPINAL FLUID Is a colorless liquid that protects the brain and spinal cord from chemical and physical injuries. It carries oxygen, glucose and other needed chemicals from the blood to neurons and neuroglia (brain tissues). CSF continuously circulates through cavities in the brain and spinal cord and around the brain and spinal cord in the subarachnoid space (between arachnoid and pia mater) 3. CEREBROSPINAL FLUID The total volume of CSF is 80 to 150 ml in an adult. CSF contains glucose, proteins, lactic acid , urea, cations (Natt, Ktt ,Catt , Mg2t2t) and anions (Cl-- and HCO3--); it also contains some white blood cells. The CSF contributes to homeostasis in 3 main ways:- – Mechanical protection – Chemical protection – Circulation 3. CEREBROSPINAL FLUID CSF contributes to Homeostasis in three main ways: Mechanical protection Serves as shock-absorbing medium that protects the delicate tissues of the brain and spinal cord from jolts that would otherwise cause them to hit the bony walls of the cranial and vertebral cavities. The fluid also buoys the brain so that it ‘floats’ in the cranial cavity. 3. CEREBROSPINAL FLUID Chemical protection It provides an optimal chemical environment for accurate neuronal signaling. Even slight changes in the ionic composition of CSF within the brain can seriously disrupt production of action potential and postsynaptic potentials. Circulation CSF allows exchange of nutrients and waste products between the blood and nervous tissue. 3. CEREBROSPINAL FLUID 3.1. Functions of CSF provide support and protection for brain and spinal cord. Maintain a constant pressure around the brain and spinal cord. Acts as cushion of fluid that absorb shock. (shock absorber) Carries nutrient, oxygen and needed chemicals from blood to neuron and neuroglia. Carries out waste product from neuron and neuroglia to blood. 3. CEREBROSPINAL FLUID 3.2. Formation of CSF Produced at the choroid plexus, network of capillaries in the walls of the ventricles. The capillaries are covered by ependymal cells that form CSF from blood plasma by filtration and secretion. The blood-CSF fluid barrier permits certain substances to enter the CSF but excludes others, protecting the brain and spinal cord from potentially harmful blood borne substance. Figure 8.37c 3. CEREBROSPINAL FLUID 3.3. Circulation of CSF Formed in the choroid plexuses of each lateral ventricles - flows into the 3rdrd ventricle through 2 narrow, oval openings, the interventricular foramina (of Monro). More CSF is added by the choroid plexus in the roof of the 3rdrd ventricle. The fluid then flows through the aqueduct of the midbrain (cerebral aqueduct @ of Sylvius) which passes through the midbrain, into the 4thth ventricle. 3. CEREBROSPINAL FLUID 3.3. Circulation of CSF The choroid plexus of the 4thth ventricle contributes more fluid. CSF enters the subarachnoid space through 3 openings in the roof of the 4thth ventricles; a median aperture (of foramen of Magendie) and the paired lateral apertures (foramen of Luschka), one on each side. CSF then circulates in the central canal of the spinal cord and in the subarachnoid space around the surface of the brain and spinal cord. Figure 7.14 Arrows showing the flow of cerebrospinal fluid. Copyright © Elsevier Ltd 2005. All rights reserved. 3. CEREBROSPINAL FLUID 3.4. Reabsorption of CSF CSF is gradually reabsorbed into the blood through arachnoid villi, fingerlike extensions of the arachnoid that project into the dural venous sinuses, especially the superior sagittal sinus (a cluster of arachnoid villi is called an arachnoid granulation) Normally CSF is reabsorbed as rapidly as it is formed by the choroid plexuses, at a rate of about 20mL/hr (480mL/day). Because the rates of formation and reabsorption are the same, the pressure of CSF normally is constant. Summary of the formation, circulation, and reasorption of CSF Lateral Lateral ventricles ventricles Lateral Lateral ventricles ventricles choroid choroid plexuses plexuses CSF Through interventricular foramina 3rd 3rd ventricles ventricles 33rdrd ventricles ventricles choroid choroid plexuses plexuses CSF Through cerebral 44thth ventricles ventricles aqueduct 44thth ventricles ventricles choroid choroid plexuses plexuses CSF Through lateral and Median apertures Subarachnoid Subarachnoid space space Arachnoid Arachnoid villi villi of of dural dural venous venous sinuses sinuses Venous blood Heart Heart and and lungs lungs  Blood Brain Barrier (BBB) The existence of BBB protect the brain cells from harmful substances and pathogens by preventing passage of many substances from blood into brain cells. Endothelial cells of the blood vessels in the choroid plexus which are joined by tight junction form the BBB. The processes of many astrocytes press up against the capillaries and secrete chemical that maintain the permeability characteristic of tight junction. A few water soluble substances such as glucoses cross the BBB by active transport. Other substances such as creatinine, urea, and most ions, cross the BBB very slowly.  Blood Brain Barrier (BBB) Other substances such as protein and antibiotic drugs do not pass at all through BBB. However, lipid-soluble substances, such as oxygen, carbon dioxide, alcohol, and most anesthetic agents easily cross the BBB. Trauma, certain toxins, and inflammation can cause a breakdown of the BBB.  THE LIMBIC SYSTEM Part of the cerebrum and diencephalon are grouped together as a lymbic system. Lymbic refers to deep portion of the cerebrum that form a ring around the diencephalon. Sometimes called “the emotional brain”. The Limbic System THE LIMBIC SYSTEM The Limbic System The Limbic System  COMPONENTS OF THE LIMBIC SYSTEM (p 517) The limbic system includes many structures in the cerebral cortex and sub-cortex of the brain. Limbic lobe – a rim of cerebral cortex on the medial surface of each hemisphere. It includes the cingulate gyrus which lies above the corpus callosum Located in the frontal lobe of cerebrum. Cingulate gyrus : Autonomic functions regulating heart rate, blood pressure and cognitive and attentional processing The Limbic System COMPONENTS OF THE LIMBIC SYSTEM parahippocampal gyrus which is in the temporal lobe below. Parahippocampal gyrus : Plays a role in the formation of spatial memory. The hippocampus is a portion of the parahippocampal gyrus that extends into the floor of the lateral ventricle. Hippocampus : Required for the formation of long-term memories COMPONENTS OF THE LIMBIC SYSTEM Dendate gyrus lies between the hippocampus and parahippocampal gyrus. Dentate gyrus : thought to contribute to new memories and to regulate happiness. The amygdala is composed of several groups of neurons located close to the tail of the caudate nucleus (basal ganglia). Amygdala : Involved in signaling the cortex of motivationally significant stimuli such as those fear COMPONENTS OF THE LIMBIC SYSTEM The septal nuclei are located within the septal area formed by the regions under the corpus callosum and the paraterminal gyrus (a cerebral gyrus). The mammillary bodies of the hypothalamus are two round masses close to the midline near the cerebral peduncles. Mammillary body : Important for the formation of memory Two nuclei of thalamus, the anterior nucleus and the medial nucleus, participate in limbic circuits. Thalamus: The "relay station" to the cerebral cortex The Limbic System COMPONENTS OF THE LIMBIC SYSTEM The olfactory bulbs are flattened bodies of the olfactory pathway that rest on the cribriform plate. Olfactory bulb: Olfactory sensory input The fornix, stria terminals, stria medullaris, medial forebrain bundle, and mammillothalamic tract are linked by bundles of interconnectimg myelinated axons. The Limbic System  Summary:components Of The Limbic System Limbic lobe; includes the cingulate gyrus and parahippocampal gyrus and hippocampus gyrus. Dentate gyrus Amygdala Septal nuclei Mammillary bodies of the hypothalamus Anterior and medial nucleus Olfactory bulbs Fornix, stria terminals, stria medullaris, medial forebrain bundle, mammillothalamic tract. The Limbic System The Limbic System The Limbic System  FUNCTIONS OF THE LIMBIC SYSTEM The limbic system is sometimes called the emotional brain because it plays a primary role in a range of emotions, including pain, pleasure, docility, affection, and anger. It also involved in olfaction (smell) and memory. The amygdala involves fear and aggression. The hippocampus, together with other parts of the cerebrum function in memory. People with damage to limbic system structures forget recent events and cannot commit anything to memory.