ANATOMY OF THE CEREBRUM.pptx

NEUROANATOMY CEREBRUM DR PAUL A. ODEY BSc., MBBCh., MSc, LMIH, PHD in view INTRODUCTION The cerebrum is the largest part of the brain, situated in the anterior and middle cranial fossae of the skull an...

NEUROANATOMY CEREBRUM DR PAUL A. ODEY BSc., MBBCh., MSc, LMIH, PHD in view INTRODUCTION The cerebrum is the largest part of the brain, situated in the anterior and middle cranial fossae of the skull and occupying the whole concavity of the vault of the skull. It may be divided into two parts: the diencephalon, which forms the central core, and the telencephalon, which forms the cerebral hemispheres.  They are separated by a deep midline sagittal fissure, the longitudinal cerebral fissure  The fissure contains the sickle-shaped fold of dura mater, the falx cerebri, and the anterior cerebral arteries  In the depths of the fissure, the great commissure, the corpus callosum, connects the hemispheres across the midline.  A second horizontal fold of dura mater separates the cerebral hemispheres from the cerebellum and is called  POLES OF THE CEREBRUM Three somewhat pointed ends or poles can be recognised.  These are the frontal pole anteriorly, The occipital pole posteriorly, The temporal pole that lies between the frontal and occipital poles, and points forwards and somewhat downwards.  the cerebrum A coronal section through the cerebral hemispheres shows that each hemisphere has three borders:  superomedial inferolateral inferomedial Borders of the cerebrum The inferomedial border is divided into an anterior part called the medial orbital border And a posterior part called the medial occipital border. The orbital part of the inferolateral border is called the superciliary border (as it lies just above the level of the eyebrows). SURFACES OF THE CEREBRUM These borders divide the surface of the hemisphere into three large surfaces:  SUPEROLATERAL SURFACE MEDIAL SURFACE  INFERIOR SURFACE The inferior surface is further subdivided into an anterior orbital part and a posterior tentorial part. SURFACES OF THE CEREBRUM  To consider the boundaries Lobes of the cerebrum of these lobes reference has to be made to some sulci and other features to be seen on each hemisphere. On the superolateral surface of the hemisphere there are two prominent sulci. One of these is the posterior ramus of the lateral sulcus which begins near the temporal pole and runs backwards and slightly upwards. Its posterior most part curves sharply upward  The second sulcus that is Lobes of the cerebrum used to delimit the lobes is the central sulcus.  It begins on the superomedial margin a little behind the midpoint between the frontal and occipital poles, and runs downwards and forwards to end a little above the posterior ramus of the lateral sulcus. On the medial surface of the hemisphere, near the occipital pole, there is a sulcus called the parieto-occipital sulcus Lobes of the A little anterior to the occipital cerebrum pole the inferolateral border shows a slight indentation called the preoccipital notch (or preoccipital incisure). To complete the subdivision of the hemisphere into lobes we now have to draw two imaginary lines. The first imaginary line connects the upper end of the parieto- occipital sulcus to the preoccipital notch. The second imaginary line is a backward continuation of the posterior ramus of the lateral sulcus LOBES OF THE  The frontal lobe lies anterior to the central sulcus, and above CEREBRUM the posterior ramus of the lateral sulcus.  The parietal lobe lies behind the central sulcus. It is bounded below by the posterior ramus of the lateral sulcus and by the second imaginary line; and behind by the upper part of the first imaginary line.  The occipital lobe is the area lying behind the first imaginary line.  The temporal lobe lies below the posterior ramus of the lateral sulcus and the second imaginary line. It is separated from the occipital lobe by the lower part of the first imaginary line. LOBES OF THE CEREBRUM GYRI AND SULCI OF THE CEREBRUM  Gyri, so also sulci are present in human brain and brain of higher mammals.  These are called Gyrencephalic brain.  Cerebral cortex of lower mammals, birds and reptiles, presents smooth surface called Lissencephalic brain  Sulci of cerebral cortex are of variable length and depth. A suclus separates two adjacent gyri, it has two adjacent walls and floor which are lined by GYRI AND SULCI ON THE SUPEROLATERAL SURFACE OF THE CEREBRAL HEMISPHERE FRONTAL LOBE  The precentral sulcus runs downwards and forwards parallel to and a little anterior to the central sulcus.  The area between it and the central sulcus is the precentral gyrus  Anterior to the precentral gyrus is the superior and inferior frontal sulci. They divide this region into superior, middle and inferior Frontal gyri  The anterior and ascending rami of the lateral sulcus extend into the inferior frontal gyrus dividing it into three parts.  The part below the anterior ramus is the pars orbitalis; SUPEROLATERAL SURFACE OF THE CEREBRAL HEMISPHERE (TEMPORAL LOBE) TEMPORAL LOBE  The temporal lobe has two sulci that run parallel to the posterior ramus of the lateral sulcus They are termed the SUPERIOR AND INFERIOR TEMPORAL SULCI. They divide the superolateral surface of this lobe into SUPERIOR, MIDDLE AND INFERIOR TEMPORAL GYRI.  GYRI AND SULCI ON THE SUPEROLATERAL SURFACE OF THE CEREBRAL HEMISPHERE (PARIETAL LOBE) PARIETAL LOBE  The postcentral sulcus runs downwards and forwards parallel to and a little behind the central sulcus.  The area between these two sulci is the postcentral gyrus.  The rest of the parietal lobe is divided into a superior parietal lobule and an inferior parietal lobule by the intraparietal sulcus  The upturned posterior end of the posterior ramus of the lateral sulcus extends into the inferior parietal lobule  The posterior ends of the superior and inferior temporal sulci also turn upwards to enter this lobule  The upturned ends of these three sulci divide the inferior parietal lobule into three parts.  The part that arches over the upturned posterior end of the posterior ramus of the lateral sulcus is called the supramarginal gyrus.  The part that arches over the superior temporal sulcus is called the angular gyrus.  The part that arches over the GYRI AND SULCI ON THE SUPEROLATERAL SURFACE OF THE CEREBRAL HEMISPHERE (OCCIPITAL LOBE)  The occipital lobe shows three rather short sulci. One of these, the lateral occipital sulcus lies horizontally and divides the lobe into superior and inferior occipital gyri  The lunate sulcus runs downwards and slightly forwards just in front of the occipital pole. The vertical strip just in front of it is the gyrus descendens.  The transverse occipital sulcus is located in the uppermost part of the occipital lobe.  The upper end of the parieto- occipital sulcus (which just reaches the superolateral surface from the medial surface) is surrounded by the arcus parieto-occipitalis GYRI AND SULCI AND ON THE MEDIAL SURFACE OF THE CEREBRAL HEMISPHERE GYRI AND SULCI AND ON THE MEDIAL SURFACE OF THE CEREBRAL HEMISPHERE PARTS OF THE CORPUS CALLOSUM GYRI AND SULCI AND ON THE MEDIAL SURFACE OF THE CEREBRAL HEMISPHERE  The most prominent of the sulci is the cingulate sulcus which follows a curved course parallel to the upper convex margin of the corpus callosum  The area between the cingulate sulcus and the corpus callosum is called the gyrus cinguli  It is separated from the corpus callosum by the callosal sulcus.  The part of the medial surface of the hemisphere between the cingulate sulcus and the superomedial border consists of two parts.  The smaller posterior part which is wound around the end of the central sulcus is called the paracentral lobule.  The large anterior part is called the medial frontal gyrus  The part of the medial surface behind the paracentral lobule and the gyrus cinguli shows two major sulci that cut off a triangular area called the cuneus  The triangle is bounded anteriorly and above by the parieto- occipital sulcus  inferiorly by the calcarine sulcus and posteriorly by the superomedial border of the hemisphere. INFERIOR SURFACE OF THE CEREBRUM INFERIOR SURFACE OF THE CEREBRUM HEMISPHERE  GYRI AND SULCI AND ON THE INFERIOR SURFACE OF THE CEREBRAL HEMISPHERE SULCI AND GYRI ON ORBITAL SURFACE  Close to the medial border of the orbital surface there is an anteroposterior sulcus: it is called the olfactory sulcus because the olfactory bulb and tract lie superficial to it.  The area medial to this sulcus is called the gyrus rectus.  The rest of the orbital surface is divided by SULCI AND GYRI ON THE TENTORIAL SURFACE  The tentorial surface is marked by two major sulci that run in an anteroposterior direction. These are the collateral sulcus medially, and the occipito-temporal sulcus laterally.  The posterior part of the collateral sulcus runs parallel to the calcarine sulcus: the area between them is the lingual gyrus.  Anteriorly, the lingual gyrus becomes continuous with the parahippocampal gyrus  The anterior end of the parahippocampal gyrus is cut off from the curved temporal pole of the  This part of the parahippocampal gyrus forms a hook- like structure called the uncus  The area between the collateral sulcus and the rhinal sulcus medially, and the occipitotemporal sulcus laterally, is the medial occipitotemporal gyrus  The area lateral to the occipitotemporal sulcus is called the lateral occipitotemporal gyrus  SOME IMPORTANT POINTS ABOUT CEREBRAL CORTEX As per as evolution concerned, cerebral cortex indicates the highest stage of development of human brain.  Phylogenetic subdivision Archicortex: it is the most primitive part of cerebral cortex, found in lower vertebrate, in human it is represented by the parahippocampal gyrus Paleocortex: It is intermediate in evolution, In human brain it is represented by cingulate gyrus Neocortex: It is the major part of human cerebral cortex which is evolved latest, it is represented by 90% of human cortex. Structural composition of the cerebral cortex  Cerebral cortex is made up of  Neurons with chain of synapses  Neuroglia  Total number of neurons in human cerebral cortex is 14000 millions.  Neurons are arranged in stratification of layers Maximum number of layers are six (6) in neocortex. Minimum number are three (3) in archicortex Types of neurons in the cerebral cortex Types of neurons in the cerebral cortex LAYERS OF THE CEREBRAL CORTEX LAYERS OF THE CORTEX SHOWING CONNECTIONS  GROSS FUNCTION OF THE CEREBRAL CORTEX In reference to both motor commands and sensory responses, cerebral cortex possesses influence over opposite half of body. Basic functions of cerebral cortex are as follows: Perception of various sensations Reaction or response as per perception of sensation To send motor commands to opposite half of body. Various types of higher functions for mental activities, e.g. memory, intelligence, learning, thinking, etc. STRUCTURES WITHIN THE CEREBRAL HEMISPHERE The surface of the cerebral hemisphere is covered by a thin layer of grey matter called the cerebral cortex. The cortex follows the irregular contour of the sulci and gyri of the hemisphere and extends into the depths of the sulci. As a result of this folding of the cerebral surface, the cerebral cortex acquires a much larger surface area than the size of the hemispheres would otherwise allow. The greater part of the cerebral hemisphere deep to the cortex is occupied by white matter within which are embedded certain important masses of grey matter. Immediately lateral to the third ventricle there are the thalamus and hypothalamus (and certain smaller masses) from the diencephalon. More laterally there is the corpus striatum which is derived from the telecephalon It consists of two masses of grey matter, the caudate nucleus and the lentiform nucleus A little lateral to the lentiform nucleus we see the cerebral cortex in the region of the insula Between the lentiform nucleus and the insula there is a thin layer of grey matter called the claustrum The caudate nucleus, the lentiform nucleus, the claustrum and some other masses of grey The white matter that occupies the interval between the thalamus and caudate nucleus medially and the lentiform nucleus laterally is called the internal capsule. It is a region of considerable importance as major ascending and descending tracts pass through it. The white matter that radiates from the upper end of the internal capsule to the cortex is called the corona radiata. The two cerebral hemispheres are interconnected by fibres passing from one to the other. These fibres constitute the commissures of the cerebrum. The largest of these is the corpus callosum  WHITE MATTER OF THE CEREBRUM White matter of cerebrum are huge number of myelinated nerve fibers of different diameter with associated neuroglial cells It forms a compact mass situated in the central core of cerebrum deep to cortex. In contrast to the term of cortical gray matter, white matter is referred as medullary substance  The compact bundle of fibers in white matter may be restricted within cerebral hemisphere CLASSIFICATION OF WHITE MATTER  Bundles of white matter are classified into following three groups  ASSOCIATION, COMMISSURAL AND PROJECTION FIBERS  1) Association fibers are the fiber bundles which interconnect different areas of same cerebral hemisphere. But these may be restricted in one lobe or may extend from one lobe to another  So these fibers do not cross midline and do not go to any subcortical centers.  Broadly, association fibers are classified into following two groups  A) Short association fibers: These are restricted to one of the lobes of cerebral hemisphere.  B) Long association fibers: These fibers extend from one lobe to another in the form of bundle. They are present in the form of following names :  I) Uncinate fasciculus  II) Cingulum  III) Superior longitudinal fasciculus  IV) Fronto-occipital fasciculus  V) Inferior longitudinal fasciculus  2) Commissural fibers: Commissural fibers interconnect identical areas of two cerebral hemispheres  So these fibers cross the midline but do not extend to any center below cerebral cortex  These fibers, which are also known as interhemispheric fibers, are present in the form of bundles. The bundles are known as commissures. Name of important commissures are: I. Corpus callosum II. Anterior commissure III. Habenular commissure IV. Posterior commissure V. Hippocampal commissure. Corpus callosum Corpus callosum is the largest and most compact bundle of commissural fibers. This thick bundle of fibers crosses the midline across the bottom of median longitudinal fissure of brain to interconnect almost all the identical area of two Corpus callosum Callosal commissure ANTERIOR COMMISSURE  Anterior commissure is a compact bundle of myelinated nerve fibers crossing midline horizontally.  It crosses in front of anterior column of fornix being embedded in a thin layer of gray matter called lamina terminalis  It connects the two temporal lobe of the cerebral hemisphere across the midline Habenular commissure Habenular commissure is a thin bundle of fibers passing transversely through proximal lamina of pineal stalk. These fibers primarily interconnect neurons of Habenular nucleus of both side of the diencephalon POSTERIOR COMMISSURE  Posterior commissure is a thin bundle of fibers which cross the midline through distal lamina of pineal stalk.  It connects identical areas of both sides which are as follows: 1. Superior colliculus 2. Pretectal nucleus  commissure (commissure of the fornix)  As per the name, hippocampal commissure is made up bunch of fibers which interconnect hippocampal formation of both sides.  3) PROJECTION FIBERS  These fibers are vertically disposed in the central nervous system  These are the fibers by which cerebral cortex is connected to many centers ranging from the level Just below the cortex which are commonly termed as subcortical centers.  It is clear therefore, projection fibers connect cerebral cortex with subcortical TYPES OF PROJECTION FIBERS  Corticofugal fibers: These are efferent outflow from cerebral cortex to subcortical centers which are at the following level  Corpus striatum: These are components of basal ganglia which are submerged collection of gray matter embedded in central core of white matter of cerebrum. Fibers are called corticostriate fibers  Thalamus: Corticothalamic fibers  Various centers in brainstem: These fibers either project to some specific nuclei, e.g.corticorubral, corticonigral, corticopontine  Corticopetal fibers: These are afferent fibers projecting into cerebral cortex from various centers  All incoming (afferent) projection fibers initially terminate in thalamus. After relay, from thalamus corticopetal projection fibers reach cerebral cortex  cerebral cortex and thalamus are connected by fibers of both way directions.  These fibers connecting thalamus with all the four lobes of cerebrum are called thalamic radiation 1. Anterior thalamic radiation: Connecting frontal lobe. 2. Superior thalamic radiation: Connecting parietal lobe. 3. Posterior thalamic  Some areas of the cerebral Functional areas of cortex can be assigned specific the cerebral cortex functions. These areas can be defined in terms of sulci and gyri. Various authors have worked out ‘maps’ of the cerebral cortex indicating areas of differing structure. The best known scheme is that of Brodmann who represented different areas by numbers. In the year 1909, Brodmann classified these areas from number 1–47 and thereby called Brodmann’s area.  The motor area of classical Motor Area description is located in the precentral gyrus on the superolateral surface of the hemisphere , and in the anterior part of the paracentral lobule on the medial surface. It corresponds to area 4 of Brodmann (and possibly to the part of area 6 which lies in the precentral gyrus, Specific regions within the area are responsible for movements in specific parts of the body.  Stimulation of the MOTOR AREA paracentral lobule produces movement in the lower limbs. The trunk and upper limb are represented in the upper part of the precentral gyrus, while the face and head are represented in the lower part of the gyrus. MOTOR HOMONCULUS  The premotor area is located just anterior to the motor area. PREMOTOR AREA  It occupies the posterior parts of the superior, middle and inferior frontal gyri The part of the premotor area located in the superior and middle frontal gyri corresponds to areas 6 and 8 of Brodmann The part in the inferior frontal gyrus corresponds to areas 44 and 45 and constitutes the motor speech area (of Broca) Stimulation of the premotor area results in movements, but these are somewhat more intricate than those produced by stimulation of the motor area.  Closely related to the premotor area there are two specific areas of importance. One is the motor speech area of Broca, mentioned above; and the other is the frontal eye field  The motor speech area of Broca lies in the inferior frontal gyrus (areas 44 & 45).  Injury to this region results in inability to speak (aphasia) even though the muscles concerned are not paralysed. These effects occur only if SENSORY AREA The sensory area of classical description is located in the postcentral gyrus It corresponds to areas 1, 2, and 3 of Brodmann. It also extends onto the medial surface of the hemisphere where it lies in the posterior part of the paracentral lobule Responses can be recorded from the sensory area when individual parts of the body are stimulated. A definite representation of various parts of the body can be mapped out in the sensory area.  The areas concerned with VISUAL AREAS vision are located in the occipital lobe, mainly on the medial surface, both above and below the calcarine sulcus (area 17). Area 17 extends into the cuneus, and into the lingual gyrus. Area 17 is continuous, both above and below, with area 18 and beyond this with area 19. Areas 18 and 19 are responsible mainly for interpretation of visual impulses reaching area 17: they are often described as psychovisual areas. AUDITORY AREA The acoustic area, or the (ACOUSTIC) area for hearing, is situated in the temporal lobe. It lies in that part of the superior temporal gyrus which forms the inferior wall of the posterior ramus of the lateral sulcus The acoustic area lies in the anterior transverse temporal gyrus (area 41) and extends to a small extent onto the surface of the hemisphere in the superior temporal gyrus (See areas 41, 42 ).  APPLIED ANATOMY Lesions of area 4 of Brodmann will cause loss of function of voluntary muscles (paralysis) of opposite half of body. It is grossly manifested by paralysis of contralateral upper and lower limbs. It is called hemiplegia. Motor dysfunction caused by lesion of premotor area is called apraxia which is characterized by impairment of skillful movements of voluntary muscles, even if primary motor area is normally functioning.  APPLIED ANATOMY (STROKE) A cerebrovascular accident (also known as a stroke) is defined clinically as “an abrupt loss of focal brain function lasting more than 24 hours due to either spontaneous haemorrhage into brain substance or inadequate blood supply to part of the brain i.e. ischaemia (thrombosis, embolism)“.  APPLIED ANATOMY Damage to the cerebrum in this matter can give rise to a range of clinical signs. The exact nature of the functional deficit that arises depends on the specific lobe that has been affected: Frontal lobe – a diverse range of presentations, often personality and behavioural changes occur and an inability to solve problems develops. Parietal lobe – typically presents with attention deficits e.g. contralateral hemispatial neglect syndrome: where the patient does not pay attention to the side of the body opposite to the lesion.  APPLIED ANATOMY Temporal lobe – presents with recognition deficits (agnosias) e.g. auditory agnosia: patient cannot recognise basic sounds, prosopagnosia: failure to recognise faces. Occipital lobe – visual field defects: contralateral hemianopia or quadrantanopia with macular sparing. Global lesions – severe cognitive deficits (dementia), patients cannot answer simple questions such as their name, today’s date, where they are etc.  THANKS FOR LISTENING