Nervous System Lecture Notes PDF

NERVOUS SYSTEM SYSTEM COORDINATOR: DR. CECILLE ESPINO BLOCK 3 MODULE 1 (LECTURES 7-9) BASIC BIOMEDICAL SCIENCES I NOT FOR SALE | DO NOT UPLOAD I...

NERVOUS SYSTEM SYSTEM COORDINATOR: DR. CECILLE ESPINO BLOCK 3 MODULE 1 (LECTURES 7-9) BASIC BIOMEDICAL SCIENCES I NOT FOR SALE | DO NOT UPLOAD IN ONLINE SITES ------------------------------------------------------------------------------------------------------------------------------------------------------- LECTURE #7: CEREBROVASCULAR SYSTEM AND BLOOD SUPPLY BRANCHES OF THE CEREBRAL PORTION OF THE SPINAL CORD AND MENINGES Ophthalmic Artery By: Roland Mark Gigataras, MD (PRE-RECORDED) o Arises as the internal carotid artery (ICA) emerges from the cavernous BLOOD SUPPLY TO THE BRAIN (ARTERIES OF THE BRAIN) sinus o Enters the orbit through the optic canal below and lateral to the optic nerve o It supplies the eye and other orbital structures Posterior Communicating Artery (PCom) o Originates from the ICA close to its terminal bifurcation o It runs posteriorly above the oculomotor nerve to join the posterior A patient facing towards the right side and the neck has been dissected to cerebral artery, thus forming part of the circle of Willis show the paired arteries (internal carotid artery and vertebral artery) 2 Internal Carotid Arteries (right and left) 2 Vertebral Arteries (right and left) They lie within the subarachnoid space Branches anastomose on the inferior surface of the brain to form the circle of Willis Left internal carotid which will terminate as the interior and the middle cerebral arteries. Before its termination, there is a branch called the posterior communicating artery which communicates the internal carotid o The aortic arch is found in the bottom (imagine patient is facing you) with the posterior cerebral artery. It forms this arterial circle called the o From the aortic arch, there is a brachiocephalic artery which arterial circle of Willis. bifurcates to the right common carotid. From the right common Choroidal Artery carotid, it becomes the right internal carotid artery. o Also originates from the ICA close to its terminal bifurcation o The left common carotid branches directly out from the arch of the o It passes posteriorly close to the optic tract, enters the inferior horn aorta. The left common carotid will bifurcate into the left internal and of the lateral ventricle, and ends in the choroid plexus left external carotid arteries. o It gives off numerous small branches to surrounding structures, o The right internal carotid artery and the left internal carotid artery including the crus cerebri, the lateral geniculate body, the optic will both go up to supply blood to the brain tract, and internal capsule INTERNAL CAROTID ARTERY Begins at the bifurcation of the common carotid artery, where it usually possesses a localized dilatation, called the carotid sinus It ascends the neck and perforates the skull base by passing through the carotid canal of the temporal bone It then runs horizontally forward through the cavernous sinus and emerges on the medial side of the anterior clinoid process by perforating the dura mater. 1st pic: Left side and is very close to the termination of the ICA. The choroidal artery will go on to supply the choroid plexus of the lateral ventricle which will produce CSF. 2nd pic: View of the patient’s brain from below, and the brain is sectioned at the level of the choroidal artery Anterior Cerebral Artery o The smaller terminal branch of the ICA Right Internal Carotid Artery- at the beginning, there is a carotid sinus o It runs forward and medially superior to the optic nerve and enters the and the right carotid internal artery ascend the neck, enters the temporal longitudinal fissure of the cerebrum (the fissure that separates the bone, passes forward, and then superiorly to enter the brain. left and right brain) It now enters the subarachnoid space by piercing the arachnoid mater o It is joined to the ACA (anterior cerebral artery) of the opposite side by It turns posteriorly to the region of the medial end of the lateral cerebral the anterior communicating artery. sulcus Here it divides into the anterior and middle cerebral arteries (terminal branches) View of patient’s brain from below (CT scan view) showing left anterior cerebral artery and anterior communicating artery o It curves backward over the corpus callosum, and finally, View of patient’s brain from below and the terminal ends of the internal anastomoses with the posterior cerebral artery carotid artery are seen. The right internal carotid artery is seen from o The cortical branches supply all the medial surface of the cerebral below and will branch out into its terminal branches- the anterior cerebral cortex as far back as the parieto-occipital sulcus artery and the middle cerebral artery 1  o They also supply a strip of cortex 2.5 cm wide on the adjoining lateral The patient is facing towards your left side. There is a brain retractor placed surface on the left temporal lobe, so the middle cerebral artery and its branches o The ACA thus supplies the “leg” area of the precentral gyrus can be seen. The MCA supplies almost the whole lateral surface of the  The ACA supplies the medial surfaces of the brain cerebral hemisphere except for the areas supplied by the ACA. o Central branches enter the anterior perforated substance and supply the lentiform, caudate nuclei, and the internal capsule View of patient’s brain from the front (patient is facing you). A retractor is placed on the right frontal lobe and another retractor on the left frontal View of the brain with the patient facing towards you. There is a coronal lobe separating the hemispheres. The ACA are seen on the right and the section that is done and at the level of the MCA. There are central left side in the interhemispheric fissure. The right ACA supplies the medial (perforating) branches that go out at about 90° to supply the deep basal surface of the hemisphere while the left ACA supplies the medial surface of ganglia, the caudate nucleus, and the internal capsule. These branches the left frontal lobe up to about 2.5 cm lateral. These are the areas are small and are usually the ones affected in hypertensive patients. These supplied by the ACA. The anterior communicating (“ACOM”) artery is the branches can bleed. one communicating the right and left. VERTEBRAL ARTERY A branch of the first part of the subclavian artery Ascends the neck by passing through the foramina in the transverse processes of the upper six cervical vertebrae It enters the skull through the foramen magnum and pierces the dura mater and arachnoid to enter the subarachnoid space Side view of the patient’s brain. The left cerebral hemisphere has been removed and the medial surface of the right cerebral hemisphere is seen. The branches are supplying the medial surface of the cerebral hemisphere up to the area of the parietooccipital sulcus. o A group of central branches pierces the anterior perforated substance and helps to supply parts of the lentiform and caudate nuclei and the internal capsule. 1st pic: Subclavian artery which gives rise to the vertebral artery, which passes through the transverse foramina of the cervical vertebrae, which enters the foramen magnum and become subarachnoid in location to supply the brain It then passes upward, forward, and medially on the medulla oblongata At the lower border of the pons, it joins the vessel (vertebral artery) of the opposite side to form the basilar artery 2nd pic: View of the patient's brain from below (patient is lying supine with the feet toward you). The vertebral artery is seen which enters the skull and it An illustration of the areas supplied by the anterior cerebral artery. will join with the other vertebral artery at the pons to form basilar artery  Middle: The view is like in the CT scan machine (view of patient’s BRANCHES OF THE CRANIAL PORTION brain from below). The hatch areas are seen supplied by the anterior Meningeal Branches cerebral arteries. o Small branches  Upper Left: The patient is facing towards your right side. The o Supply bone and dura in the posterior cranial fossa hatched (shaded) portion is the area supplied by the ACA.  Upper Right: The patient is facing to the left. The left cerebral hemisphere is seen and the shaded area supplied by the left ACA.  Lower Left: The patient is facing towards your left side. The left cerebral hemisphere is removed and the medial surface of the right cerebral hemisphere are seen with the area supplied by the ACA.  Lower Right: The patient is facing to your right. The left medial surface of the left cerebral hemisphere are seen and the areas The patient is facing toward the left, and seen here are the brain stem and shaded are the areas supplied by the ACA. the left cerebellum Middle Cerebral Artery Posterior Spinal Artery o The largest branch of the ICA o May arise from the vertebral artery, or from the posterior inferior o Runs laterally in the lateral cerebral sulcus cerebellar artery (PICA) o Cortical branches supply the entire lateral surface of the hemisphere, o It descends on the posterior surface of the spinal cord close to the except for the narrow strip supplied by the ACA, the occipital pole, and posterior roots of the spinal nerves the inferolateral surface of the hemisphere, which are supplied by the posterior cerebral artery 2  Vertebral artery gives rise to the posterior spinal artery which goes down BRANCHES OF THE BASILLAR ARTERY near the posterior nerve roots Pontine Arteries Anterior Spinal Artery o Numerous small vessels that enter the substance of the pons o Formed from a contributory branch from each vertebral artery near its termination o The single artery descends on the anterior surface of the medulla oblongata and spinal cord and is embedded in the pia mater along the anterior median fissure Small arteries from the basilar artery which supplies the substance of the pons. This is a closer view showing the circle of Willis and pontine arteries Labyrinthine Artery o A long narrow artery that accompanies the facial and vestibulocochlear nerves into the internal acoustic meatus and supplies the inner ear 1st pic: Vertebral artery will also give rise to the anterior spinal artery which goes down the anterior median fissure of the spinal cord 2nd pic: A view like in the CT scanner. Contributory branches from both the right are and the left vertebral arteries are seen, they join together to form the single anterior spinal artery which goes down the spinal cord Posterior Inferior Cerebellar Artery (PICA) o The largest branch of the vertebral artery Branches out of the vertebra and goes together with the 7th and 8th nerve o It passes on an irregular course between the medulla and the towards the ear cerebellum Anterior Inferior Cerebellar Artery (AICA) o It supplies the inferior surface of the vermis, the central nuclei of o Passes posteriorly and laterally and supplies the anterior and inferior the cerebellum, and the undersurface of the cerebellar parts of the cerebellum hemisphere o A few branches pass to the pons and the upper part of the medulla o It also supplies the medulla oblongata and the choroid plexus of oblongata the fourth ventricle 2nd pic (Side view, facing left side): Goes out of the basilar artery and goes around the pons to supply the inferior cerebellum 1st pic (Inferior view): It arises from the vertebra and goes around the Superior Cerebellar Artery medulla and supplies the cerebellum o Arises close to the termination of the basilar artery 2nd pic (Side view): The PICA goes around the medulla and supplies the o It winds around the cerebral peduncle and supplies the superior inferior surface of the cerebellum surface of the cerebellum Medullary Arteries o It also supplies the pons, pineal gland, and the superior medullary o Very small branches that are distributed to the medulla oblongata vellum Medullary arteries will also arise from the vertebral artery and go into the It is near the termination of the basilar artery substance of the medulla Posterior Cerebral Artery BASILAR ARTERY o Curves laterally and backward around the midbrain and is joined by Formed by the union of the two vertebral arteries the posterior communicating artery from the ICA Ascends in a groove on the anterior surface of the pons o Cortical branches supply the inferolateral and medial surfaces of the At the upper border of the pons, it divides into the two posterior cerebral temporal lobe, and the later and medial surfaces of the occipital lobe arteries o Supplies the visual cortex in the occipital lobe o Central branches pierce the brain substance and supply parts of the thalamus and lentiform nucleus, the midbrain, the pineal, and the medial geniculate bodies o A choroidal branch that enters the inferior horn of the lateral ventricle and supplies the choroid plexus o It also supplies the choroid plexus of the third ventricle CT scan view of patient’s brain. 2 vertebral arteries are seen joining to form into a single basilar artery, which will also terminate as the right and left cerebral artery, and forms part of the circle of Willis 3  It is joined by the posterior communicating artery branch from the ICA. It Under normal conditions, the local blood flow is mainly controlled by the goes around the midbrain to supply the occipital lobe concentrations of carbon dioxide, hydrogen ions, and oxygen present in the nervous tissue. A rise in the carbon dioxide and hydrogen ion concentrations and the lowering of oxygen tension bring about a vasodilatation o If the neurons (nerve cells) are very active, they will utilize a lot of glucose and oxygen, and there will be a rise in the metabolic waste products (carbon dioxide and hydrogen ions). o If the neurons are very active, they will require more oxygen and blood, which causes vasodilation so that the neurons will be supplied with more blood and oxygen CRANIAL VENOUS SINUSES Areas supplied by the Posterior Cerebral Artery (PCA)  A: Patient is facing to your right and the areas supplied by the posterior cerebral artery are seen.  D: Patient is facing to your left side. The left cerebral hemisphere is removed, and the medial surface of the right cerebral hemisphere, and the areas supplied by the right PCA are seen.  C: Patient is lying supine (like in the CT scan machine) where his/her feet are toward you. The brain can be seen from below, and the posterior cerebral artery supplying the inferior surface of the occipital In this view, the patient is facing toward the left side, with cerebral lobes and temporal lobes are seen. CIRCLE OF WILLIS hemispheres removed. An arterial circle that lies in the interpeduncular fossa at the base of the The falx cerebri can be seen, and in the superior margin is the superior brain. sagittal sinus, where cerebral veins will drain. Formed by the anastomosis between the two internal carotid arteries There is an inferior sagittal sinus in the free margin of falx cerebri. and the two vertebral arteries. The straight sinus communicates the inferior sagittal to the confluence of sinuses. From the confluence, the blood will drain down to the transverse sinus, then to the sigmoid sinus, then finally into the internal jugular vein. Superior and inferior petrosal sinuses drain this area and communicate with the sigmoid sinus. VEINS OF THE BRAIN No muscular tissue in their very thin walls, and they possess no valves. The Anterior communicating artery, Anterior cerebral artery, Emerge from the brain and lie in the subarachnoid space Internal carotid artery, Posterior communicating artery, Posterior They pierce the arachnoid mater and the meningeal layer of dura cerebral artery (PCom), and Basilar artery all contribute to the circle They drain into the cranial venous sinuses The circle of Willis allows blood that enters by either internal carotid or EXTERNAL CEREBRAL VEINS vertebral arteries to be distributed to any part of both cerebral hemispheres Variations in the sizes of the arteries forming the circle are common, and the absence of one or both posterior communicating arteries has been reported Superior Cerebral Vein o Pass upward over the lateral surface of the cerebral hemisphere and empty into the superior sagittal sinus o Drain blood from the brain, and empty in the superior sagittal sinus A closer look of the arterial circle of Willis. Imagine the patient is lying supine with their feet toward you and you are looking up at the patient’s brain. o The circle is composed of the branches of the internal carotid, the anterior cerebral, the middle cerebral, and the posterior communicating artery, and from the vertebral artery, it becomes the The patient is facing left, the dura has been incised and retracted upwards, basilar artery and the posterior cerebral arteries. and the superior cerebral veins are seen draining the superior sagittal sinus. o In front are the anterior communicating artery and the same arteries Superficial Middle Cerebral Vein on the other side. o Drains the lateral surface of the cerebral hemisphere o The blood from the left internal carotid can go around the circle to o Runs inferiorly in the lateral sulcus (also called Sylvian fissure) and supply the area of the right middle cerebral artery because of the circle empties into the cavernous sinus of Willis. Blood from the right vertebral artery can go to the circle and supply the area of the left middle cerebral artery. NERVE SUPPLY OF CEREBRAL ARTERIES Cerebral arteries receive a rich supply of sympathetic postganglionic nerve fibers. Fibers are derived from the superior cervical sympathetic ganglion. Stimulation of these nerves causes vasoconstriction 4  The superficial middle cerebral vein goes inferiorly and anteriorly to empty The brain is supplied by the 2 internal carotid arteries and 2 vertebral into the cavernous sinus, which is just beside the carotid arteries. arteries. Deep Middle Cerebral Vein The arterial circle of Willis permits blood to flow forward or backward o Drains the insula and is joined by the anterior cerebral and striate veins across the posterior communicating artery if the internal carotid artery to form the basal vein or vertebral artery is occluded. o Located deep into the superficial middle cerebral vein It also permits blood to flow across the midline when the internal carotid artery or vertebral artery on one side is occluded. Once the arteries enter the brain substance, no further anastomoses occur. The most important factor in forcing the blood through the brain is the arterial blood pressure This is opposed by o Raised intracranial pressure Basal Vein  If BP is low, then blood cannot be pushed up into the brain o Ultimately joins the great cerebral vein of Galen, which in turn drains  If there is brain tumor or hematoma in the skull, this could raise the into the straight sinus. intracranial pressure and oppose the blood flow o o Increased blood viscosity  If there is increase in RBCs, then it will make it difficult for blood to be pushed up to the brain o Narrowing of vascular diameter  If the vessels are narrowed, it will be difficult for blood to flow up Cerebral blood flow remains remarkably constant in spite of changes in the general blood pressure CEREBRAL AUTOREGULATION This autoregulation is accomplished by a compensatory lowering of the INTERNAL CEREBRAL VEINS cerebral vascular resistance when the arterial pressure is decreased, Two in number and a raising of the vascular resistance when the arterial pressure is Formed by the thalamostriate vein and choroid vein at the increased. interventricular foramen The diameter of the cerebral blood vessels is the main factor contributing The 2 veins run posteriorly in the tela choroidea of the third ventricle to the cerebrovascular resistance. They unite beneath the splenium of the corpus callosum to form the While it is known that they are innervated by sympathetic post-ganglionic great cerebral vein of Galen, which empties the straight sinus nerve fibers and can respond to norepinephrine, they apparently play little or no part in the control of cerebrovascular resistance in normal human beings. The most powerful vasodilator influence on cerebral blood vessels is an increase in carbon dioxide or hydrogen ion concentration A reduction in oxygen concentration also causes vasodilatation. A cerebral blood flow of 50 to 60 ml per 100gm of brain per minute is considered normal ARTERIES OF THE SPINAL CORD 3 small arteries o 2 posterior spinal arteries o 1 anterior spinal artery Reinforced by small segmentally arranged arteries that arise from outside the vertebral column and enter the vertebral canal through the intervertebral foramina These vessels anastomose on the surface of the cord and send Frontal view showing the ventricles of the brain and the deep veins. They branches into the substance of the white and gray matter. will join together to form the internal cerebral vein which runs in the tela Considerable variation exists as to the size and segmental levels at choroidea, the roof of the third ventricle, and they will drain into the great which the reinforcing arteries occur. cerebral vein of Galen, and it empties into the straight sinus POSTERIOR SPINAL ARTERIES DEEP VEINS OF THE BRAIN They arise either directly from the vertebral arteries inside the skull, or indirectly from the posterior inferior cerebellar arteries Each artery descends on the posterior surface of the spinal cord close to the posterior nerve roots and gives off branches that enter the substance of the cord They supply the posterior one-third of the cord Top view, brain sectioned axially. Anterior septal vein joins with superior thalamostriate vein to become the internal cerebral vein (runs in the tela choroidea or roof of the third ventricle) → will drain into the great cerebral vein of Galen→ drains to the straight sinus→ confluence of sinuses. CEREBRAL CIRCULATION Posterior spinal arteries are going down with the posterior spinal roots The blood flow to the brain must deliver oxygen, glucose, and other They are small in the upper thoracic region. nutrients to the nervous tissue The first three thoracic segments of the spinal cord are particularly It must remove carbon dioxide, lactic acid, and other metabolic vulnerable to ischemia should the segmental arteries in this region be byproducts. occluded. 5  ANTERIOR SPINAL ARTERY Formed by the union of 2 arteries, each of which arises from the vertebral artery inside the skull. Descends on the anterior surface of the spinal cord within the anterior median fissure. Branches enter the substance of the cord and supply the anterior two- thirds of the spinal cord. The anterior medullary artery (artery of Adamkiewicz) is coming from the left side of the patient VEINS OF THE SPINAL CORD The blood drains into six tortuous longitudinal channels that communicate superiorly within the skull with the veins of the brain and venous sinuses Anterior spinal artery coming from the vertebral arteries and going down They drain mainly into the internal vertebral venous plexus the anterior median fissure of the cord In the upper and lower thoracic segments of the spinal cord, this artery may be extremely small Should the segmental arteries be occluded in these regions, the fourth thoracic and first lumbar segments of the spinal cord would be particularly liable to ischemic necrosis SEGMENTAL SPINAL ARTERIES OR FEEDER ARTERIES At each intervertebral foramen, the longitudinally running posterior and anterior spinal arteries are reinforced by small segmental arteries on Spinal canal and the internal vertebral venous plexus are seen which is both sides a network of veins draining the spinal cord They are branches of arteries that lie outside the vertebral canal. LECTURE #8: INTELLECTUAL FUNCTIONS o Deep cervical arteries (neck) By: Maria Cecilia Alvarez-Espino, MD, FPLS, FPSP (PRE-RECORDED) o Intercostal arteries (thoracic area) PHYSIOLOGIC ANATOMY OF THE CEREBRAL CORTEX o Lumbar arteries (lumbar area) The functional part of the cerebral cortex is a thin layer of neurons Each segmental artery gives rise to anterior and posterior radicular covering the surface of all the convolutions of the cerebrum arteries that accompany the anterior and posterior nerve roots to the spinal cord. This layer is only 2 to 5 millimeters thick, with a total area of about one quarter of a square meter The total cerebral cortex contains about 100 billion neurons The cerebrum is the biggest portion of the brain Front view (left) and back view (right) of the cord. Anterior spinal artery are The thickness of the cortex varies from 1.5 to 4.5 mm and is thickest seen and the different segmental spinal arteries are seen helping to over the crest of a gyrus and thinnest in the depth of a sulcus. supply the anterior spinal artery The cerebral cortex, like gray matter elsewhere in the CNS, consists of a mixture of nerve cells, nerve fibers, neuroglia, and blood vessels. Seen are the various gyrus/gyri and sulcus/sulci. In the middle of the 2 cerebral hemispheres would be the longitudinal fissure, and as pointed by A close up view of the intercostal artery in the thoracic area and it gives rise the arrow is the central sulcus. This is a very important landmark to be able to a spinal branch that will go with the nerve roots. There is anterior to locate the sensory and motor portions of the cerebrum. The lateral radicular artery helping the anterior spinal artery and there are posterior sulcus will identify the frontal, parietal, and part of the occipital portion from radicular arteries which helps supply the posterior cord as well the temporal area of the cerebrum. The transverse fissure will separate the The number and size of these segmental arteries vary considerably from cerebrum from the cerebellum. one individual to another. NERVE CELLS OF THE CEREBRAL CORTEX Great Anterior Medullary Artery of Adamkiewicz Pyramidal Cells o One large and important feeder artery o Are named from the shape of their cell bodies o Arises from the aorta in the lower thoracic or upper lumbar vertebral o Most of the cell bodies measure 10 to 50 μm long levels o Axon arises from the base of the cell body and o Usually unilateral either terminates in the deeper cortical layers or, o In the majority, it enters the spinal cord from the left side more commonly, enters the white matter of the o Clinical significance: It may be the major source of blood to the lower cerebral hemisphere as a projection, association, or two-thirds of the spinal cord commissural fiber. 6  Giant Pyramidal Cells LAYERS OF THE CEREBRAL CORTEX o Also known as Betz cells o Cell bodies measure as much as 120 µm o Found in the motor precentral gyrus of the frontal lobe o The apices of the pyramidal cells are oriented toward the pial surface of the cortex o From the apex of each cell, a thick apical dendrite extends upward toward the pia, giving off collateral branches Stellate Cells o Sometimes called granule cells o Because of their small size, are polygonal in shape, and their cell bodies measure about 8 µm in diameter o These cells have multiple branching dendrites and a relatively short axon, which terminates on a nearby neuron. Fusiform Cells o Have their long axis vertical to the surface and are 1. Molecular Layer concentrated mainly in the deepest cortical layers o The most superficial layer o Dendrites arise from each pole of the cell body o Consists mainly of a dense network of tangentially oriented nerve o The inferior dendrite branches within the same fibers cellular layer, while the superficial dendrite ascends o Derived from the apical dendrites of the pyramidal cells and toward the surface of the cortex and branches in the fusiform cells, the axons of the stellate cells and cells of Martinotti superficial layers. 2. External Granular Layer o The axon arises from the inferior part of the cell body o Contains large number of small pyramidal cells and stellate cells and enters the white matter as a projection, association, o The dendrites of these cells terminate in the molecular layer, and the or commissural fiber. axons enter deeper layers, where they terminate or pass on to enter Horizontal Cells of Cajal the white matter of the cerebral hemisphere o Are small, fusiform, horizontally oriented cells found in the most 3. External Pyramidal Layer superficial layers of the cortex o Composed of pyramidal cells, whose cell body increases from the o A dendrite emerges from each end of the cell, and an axon runs superficial to the deeper borders of the layer parallel to the surface of the cortex, making contact with the dendrites o The apical dendrites pass into the molecular layer and the axons of pyramidal cells. enter the white matter as projection, association, or commissural fibers NERVE FIBERS OF THE CEREBRAL CORTEX 4. Internal Granular Layer Can be arranged tangentially or radially o Composed of closely packed stellate cells o There is high concentration of horizontally arranged fibers known collectively as external band of Baillarger, which has 2 parts:  Inner Band of Baillarger- dense horizontal plexus of myelinated fibers in the 5th layer of the cerebral cortex  Outer Band of Baillarger- dense horizontal plexus coursing in the Tangential Fibers 4th layer of cerebral cortex o Run parallel to the cerebral surface  Band of Gennari- greatly thickened outer band of Baillarger o Are responsible for connecting the areas of the cortex between 5. Internal Pyramidal Layer (Ganglionic) themselves o Contains very large and medium-sized pyramidal cells o Are distributed across the whole thickness of the cortex o Stellate and Martinotti cells are also found scattered among the o The tangential fibers are most concentrated in layers 4 and 5, which pyramidal cells are referred to as the outer and inner bands of Baillarger o Contain large number of horizontally arranged fiber that form the Inner o The bands are particularly well developed in the sensory areas due Band of Baillarger to the high concentration of the terminal parts of the thalamocortical o In the motor cortex of the precentral gyrus, the pyramidal cells of this fibers layer are very large called Betz Cells o These cells account for 3% of the projection fibers of the Corticospinal or Pyramidal Tract 6. Multiform Layer (Layer of Polymorphic Cells) o Majority of the cells are fusiform, many of the cells are modified pyramidal cells with triangular or ovoid bodies o The cells of Martinotti also are conspicuous Not all areas of the cerebral cortex possesses six layers o Heterotypical areas of the cortex in which the basic six layers cannot be recognized o Homotypical possess six layers oThe outer band of Baillarger (also called the stria of Gennari) is so There are 2 Heterotypical Areas thick that it can be seen with the naked eye o Granular type o Because of this, the visual cortex in the walls of the calcarine sulcus is  Well-developed and contain densely package stellate cells. sometimes called the “striate cortex”  Layers 2 and 4 are well-developed, while 3 and 5 are poorly Radial Fibers developed. o Run at right angles to the cortical surface  Layers 2 through 5 merge into a single layer of predominantly o This includes the afferent entering projection, association, and granular cells commissural fibers which terminate within the cortex, and the axons  Found in the postcentral gyrus, in the superior temporal gyrus, of stellate, pyramidal, and fusiform cells which leave the cortex to and in parts of the hippocampal gyrus become projection, association, and commissural fibers of the white matter of the cerebral hemisphere 7  o Agranular type  Giant Pyramidal Cells of Betz  Layers 2 and 4 are practically absent  Largest neurons in the CNS  The pyramidal cells in layer 3 and 5 are densely packed and are very  Concentrated most highly in the superior part of the precentral large gyrus and paracentral lobule  Found in precentral gyrus and other areas in the frontal lobe  Giving rise to most corticobulbar and corticospinal fibers which give rise to large numbers of efferent fibers that are  2 Division of Precentral area associated with motor functions  Posterior Regions CEREBRAL CORTEX  Referred as motor area, primary motor area, or Brodmann The cerebral cortex is organized into vertical units or columns of area 4. functional activity, measuring about 300 to 600 µm wide  Occupies the precentral gyrus extending over the superior In the sensory cortex, each column serves a single specific sensory border into the paracentral lobule. function. Such a functional unit extends through all 6 layers from the  Anterior Regions cortical surface to white matter  a.k.a. premotor area, secondary motor area, or Brodmann Each unit possesses afferent fibers, internuncial neurons, and area 6. efferent fibers  Also parts of area 8, 44, and 45. Afferent fibers may synapse directly with an efferent neuron or may  Occupies the anterior part of precentral gyrus and posterior involve vertical chains of internuncial neurons parts of superior, middle, and inferior frontal gyri. A single vertical chain of neurons may be involved in isolation, or the wave of excitation may spread to adjacent vertical chains through short axon granular cells The Horizontal cells of Cajal permit activation of vertical units that lie some distance away from the incoming afferent fibers The spread of incoming information serving one sensory modality laterally from one column to an adjacent column or to columns some distance away, may permit the individual to start the process of understanding the nature of sensory input o Primary Motor Areas  One of the principal brain areas involved in motor function  Generates neural impulses that control the execution of voluntary movements of the body  If this area is electrically stimulated, it produces isolated movements on the opposite side of the body as well as contraction of the muscle groups concerned with the performance of a specific movement  Receives numerous afferent fibers from the premotor area, the sensory cortex, the thalamus, the cerebellum, and the basal ganglia  At the primary motor cortex, motor representation is arranged in an orderly manner, inverted.  The toes are represented at the top of the cerebral hemisphere, while the mouth is represented at the bottom of the hemisphere, closer to the lateral sulcus. CEREBRUM  These representations lie along a fold in the cortex called the central The Cerebrum is the largest part of the brain sulcus. It is divided into 4 sections, called lobes:  Some body parts may be controlled by partially overlapping regions o Frontal of cortex. o Temporal o Parietal o Occipital Frontal Lobe o It is considered as the emotional control center and the home of our personality. o The frontal lobe controls higher level thinking: Reasoning, Planning, Language, Long-term memory, Impulse control, Problem solving, Emotions, Judgement, Motor function, Initiation, Social/Sexual Behavior o Precentral Area  Situated in the precentral gyrus  Includes the anterior wall of central sulcus and the posterior parts of o Premotor Area superior, middle, and inferior frontal gyri  Has no giant pyramidal cell of Betz  Extend over the superomedial border of the hemisphere into  Electrical stimulation produces muscular movements similar to paracentral lobule those obtained by stimulation of the primary motor area however, it requires stronger stimulation to produce the same degree of movement  Receives numerous inputs from the sensory cortex, the thalamus, and the basal ganglia.  Function is to store program of motor activity assembled as the result of past experience  It projects directly to the spinal cord and therefore may play a role in the direct control of behavior, with a relative emphasis on the trunk muscles of the body 8   Premotor Cortex  Frontopontine fibers also connect this area to the cerebellum  Damage to the premotor area results in the loss of the motor skills through pontine nuclei. in that region  Muscle strength and the ability to perform the discrete individual movements are not hindered  Neurons relearning the skill would require practice  Functions:  Concerned with the makeup of the individual’s personality  Plays a role as a regulator of the persons depth of feelings  It also exerts its influence in determining initiative and judgement of individual. Parietal Lobe o Responsible for sensation, body position, o Supplementary Motor Area (Area 6) speech, and language  Location: Medial frontal gyrus on the medial surface of the o 3 parts: hemisphere and anterior to paracentral lobule  Primary somesthetic area  Functions: Stimulation of this area results in movement of  Secondary somesthetic area contralateral limb.  Somesthetic Association area  Removal of SMA produces no permanent loss of movements.  Premotor and supplementary motor areas are also involved in higher-order motor planning and project to primary motor cortex  Planning of complex movements  Mental rehearsal of movements  Learning movement sequence  Lesions in these areas do not produce severe movement deficit but rather deficit in motor planning The primary, secondary, and sensory association areas would be located post centrally (after the central sulcus). o Primary Somesthetic Area (Primary Somatic Sensory Cortex S1)  Occupies the postcentral gyrus on the lateral surface and posterior part of the paracentral lobe on the medial surface  Receives projection fibers from ventral posterior lateral and ventral o Frontal Eye Field posterior medial nuclei of the thalamus  This cortical region controls the voluntary movements of the eyes  For the most inferior part of the lateral surface, it is represented by  Engaged when we look quickly at something, as in moving our eyes the pharyngeal region, tongue, and jaws followed by the face, fingers, to follow a moving target hands, arm, trunk, and thigh  For the posterior part of the medial surface, it is represented by the leg, foot areas, anal, and genital regions  The size of the cortical area distributed to each body part is based on the functional importance and the number of sensory receptors present in it  Even if most sensations are from the contralateral (opposite) side, some from oral region heads to the same side (ipsilateral) while those from the pharynx, larynx, and perineum head to both sides  Afferent fibers excite the neurons in layer IV then the signal spreads towards the surface of the cerebral unit and into deeper layers  Location:  From layer VI, large numbers of axons leaves the cortex and passes Extend forward from the facial area of the precentral gyrus into the to lower sensory relay stations of the thalamus, medullary oblongata, and the spinal cord which provides sensory feedback that serves to middle frontal gyrus  Parts of area 6, 8, and 9 modulate the intensity of the sensory input o Motor Speech Area of Broca  The anterior part of the postcentral gyrus receives a large number of  Location: afferent fibers from muscle spindles, tendon organs, and joint receptors which is analyzed by the vertical columns of the sensory  Inferior frontal gyrus between the anterior and ascending rami and also posterior rami of lateral fissure. cortex passed on to the primary motor cortex which influences the  Brodmann area 44 and 45 skeletal muscle activity o Secondary Somesthetic Area (Secondary Somatic Sensory  Destruction results in paralysis of speech (motor aphasia) in which the language is understood but it cannot be expressed in speech or Cortex C2) writing  Located in the superior lip of the posterior limb of the lateral fissure o Prefrontal Cortex  Face area lies most anterior while leg area lies posteriorly  Body is bilaterally represented with the contralateral side dominant  Location:  Anterior half of cingulate gyrus (Brodmann areas 9, 10, 11, 12)  Many sensory impulses come from the primary area and many  Large number of afferent and efferent pathways connect to this signals are transmitted from the brainstem area.  Neurons respond to brief stimuli like brush strokes or tapping of the skin 9  o Somesthetic Association Area  Area 41- granular type of cortex  Occupies the superior parietal lobule extending onto medial surface  Area 42- homotypical and is mainly an auditory associated area  Many connections with other sensory areas in the cortex o Secondary Auditory Area (Auditory Associated Cortex)  Main function is to receive and integrate different sensory modalities  Situated posterior to the primary auditory area in the lateral sulcus  It not only receives information concerning the size and shape of an and in the posterior temporal gyrus (Brodmann Area 22) object but also relates this to past experiences which will lead to the o Sensory Speech Area of Wernicke interpretation of the information that may lead to recognition  Localized in the left dominant hemisphere Occipital Lobe  Connected to the Broca’s area by a bundle of nerve fibers called arcuate fasciculus o Primary Visual Cortex (Brodmann Area 17)  Is situated in the walls of the posterior part of the calcarine sulcus and occasionally extends around the occipital pole onto the lateral surface of the hemisphere. The visual cortex receives fibers from the temporal half of the ipsilateral retina and the nasal half of the contralateral retina  The macula lutea, which is the central area of the retina and the 1st pic: Whatever spoken word you hear will be received in the auditory area for most perfect vision, is represented on the cortex in the cortex. This will move to the Wernicke’s area where the sound is posterior part of Brodmann area 17 and accounts for one-third of the comprehended. The Wernicke’s area through the arcuate fasciculus, the visual cortex word that was herd will proceed to the Broca’s speech area, which will then  The visual impulses from the peripheral parts of the retina terminate be passed on to the Brodmann area 4 (where the motor cortex is) so that in concentric circles anterior to the occipital pole in the anterior part whatever word that was herd will be spoken. of area 17 2nd pic: Whatever you read will be processed in the visual cortex, and through the angular gyrus, would go into the Wernicke’s area where there will be comprehension of the written word. From the Wernicke’s area, it will then go to the Broca’s area and to the Brodmann area 4 (Primary motor area) so that you will be able to speak the written word. OTHER CORTICAL AREAS Taste Area (Brodmann Area 43) o Situated at the lower end of the postcentral gyrus in the superior wall of the lateral sulcus and in the adjoining area of the insula (Brodmann area 43) Occipital area showing the areas of the contralateral vision and bilateral o Ascending fibers from the nucleus solitarius probably ascend to the vision, which is in the visual cortex ventral posteromedial nucleus of the thalamus, where they synapse o Secondary Visual Cortex (Brodmann Area 18 and 19) on neurons that send fibers to the cortex.  Surrounds the primary visual area on the medial and lateral surfaces Vestibular Area of the hemisphere; it is known as Brodmann Areas 18 and 19 o Situated near the part of the postcentral gyrus concerned with  This area receives afferent fibers from area 17 and other cortical sensations of the face areas, as well as from the thalamus o Lies opposite the auditory area in the superior temporal gyrus  Occipital eye field is thought to exist in the secondary visual area o Concerned with appreciation of the positions and movements of the in humans head in space  Stimulation produces conjugate deviation of the eyes, especially to o Movements of the eyes and the muscles of the trunk and limbs are the opposite side. The occipital eye fields of both hemispheres are influenced in the maintenance of posture through its nerve connected by nervous pathways and also are thought to be connections. connected to the superior colliculus  Example: When you ask a person to walk in a single line rapidly with Temporal Lobe the eyes closed, you will see that the person will be swaying. Insula o Area of the cortex that is buried within the lateral sulcus and forms its floor o Posterior part is granular o Anterior part is agranular o Important for planning or coordinating the articulatory movements necessary for speech o Primary Auditory Area (Brodmann Areas 41 and 42)  Includes the gyrus of Heschl  Situated in the inferior wall of lateral sulcus 10  Lesions of the Motor Cortex o Lesions of the primary motor cortex in one hemisphere result in paralysis of the contralateral extremities, with the finer and more skilled movements suffering most. Destruction of the primary motor area (Brodmann area 4) produces more severe paralysis than destruction of the secondary motor area (area 6). o Destruction of both areas produces the most complete form of contralateral paralysis. o Lesions of the secondary motor area alone produce difficulty in the performance of skilled movements, with little loss of strength. o The Jacksonian epileptic seizure is due to an irritative lesion of the The insula is seen from the underneath/bottom of the brain. It cannot be primary motor area (area 4). It is a partial seizure that begins in one seen on the top portion. part of the body such as the side of the face, the toes on one foot, or ASSOCIATION AREAS the fingers on one hand. The jerking movements then spread to other Each sensory system has its own association areas on the cerebral muscles on the same side of the body. This type of seizure is cortex associated with a lesion or defect in the area of the cerebral cortex o Each primary sensory area sends information to its own cortical that controls voluntary movement. association areas, which are next to their primary areas Muscle Spasticity o A discrete lesion of the primary motor cortex (area 4) results in little change in the muscle tone. o However, larger lesions involving the primary and secondary motor areas (areas 4 and 6), which are the most common, result in muscle spasm. o The explanation for this is that the primary motor cortex gives origin to corticospinal and corticonuclear tracts, and the secondary motor cortex gives origin to extrapyramidal tracts that pass to the basal The processing that occurs in the sensory association areas is the basis ganglia and the reticular formation. of complex mental processes associated with each sense  The corticospinal and corticonuclear tracts tend to increase o For example, the visual association area on the lower part of the muscle tone, but the extrapyramidal fibers transmit inhibitory temporal lobe plays a primary role in your ability to recognize faces, impulses that lower muscle tone. dogs, cars, trees, etc., whereas the primary visual cortex is required o Destruction of the secondary motor area removes the inhibitory for detecting basic features of the visual world: edges, light and dark, influence, and consequently, the muscles become spastic. location, etc. Destruction of the Frontal Eyefield Higher Order Association Areas o Destructive lesions of the frontal eye field of one hemisphere cause o Carries out complex mental processes not associated with any the two eyes to deviate to the side of the lesion and an inability to turn particular sense the eyes to the opposite side. o Each sensory and motor association areas sends signals to higher o The involuntary tracking movement of the eyes when following moving order association areas, which combine this information to form the objects is unaffected, because the lesion does not involve the visual basis of the highest mental processes cortex in the occipital lobe. o Area for Naming Objects o Irritative lesions of the frontal eye field of one hemisphere cause the  In the most lateral portions of the anterior occipital lobe and posterior two eyes to periodically deviate to the opposite side of the lesion. temporal lobe is an area for naming objects.  The names are learned mainly through auditory input, whereas the physical natures of the objects are learned mainly through visual input.  In turn, the names are essential for both auditory and visual language comprehension (functions performed in Wernicke’s area located immediately superior to the auditory “names” region and anterior to the visual word processing area).  It is important for the Wernicke’s area to be intact because this is where you have the comprehension of both spoken and written words. o Limbic Association Area  This area is found in the anterior pole of the temporal lobe, in the ventral portion of the frontal lobe, and in the cingulate gyrus lying deep in the longitudinal fissure on the midsurface of each cerebral hemisphere.  It is concerned primarily with behavior, emotions, and motivation. Lesions of the Association Areas o Agnosia  The loss of the interpretation of a certain sensation  A rare disorder whereby a patient is unable to recognize and identify Destruction to the Motor Speech Area of Broca objects, persons, or sounds using one or more of their senses o Destructive lesions in the left inferior frontal gyrus result in the loss of despite otherwise normally functioning senses ability to produce speech, that is, expressive aphasia. The patients, o Behaviors cannot be executed properly and normally however, retain the ability to think the words they wish to say, they can o Contralateral neglect write the words, and they can understand their meaning when they see o Cannot form any new explicit memories or hear them. o Lack of ability to remember and relate things over time o Motor Speech Centre o Diminished attention span  Area 44 and 45 (Broca’s area) o Abstract reasoning disappears  Speech centers (motor and sensory) may be transferred to right hemisphere in child up to 6-8 years (in case of cerebral injury) 11  Destruction to the Sensory Speech Area of Wernicke Destruction of the Prefrontal Cortex o Destructive lesions restricted to the Wernicke speech area in the o It is now generally agreed that destruction of the prefrontal region does dominant hemisphere produce a loss of ability to understand the not produce any marked loss of intelligence. spoken and written word, that is, Receptive Aphasia o It is an area of the cortex that is capable of associating experiences o Since the Broca area is unaffected, speech is unimpaired, and the that are necessary for the production of abstract ideas, judgment, patient can produce fluent speech. However, the patient is unaware of emotional feeling, and personality. the meaning of the words he or she uses and uses incorrect words or o Tumors or traumatic destruction of the prefrontal cortex result in the even nonexistent words. The patient is also unaware of any mistakes. person’s losing initiative and judgment. The patient no longer conforms to the accepted mode of social behavior and becomes careless of dress and appearance.  Most alcoholics have destruction of the prefrontal cortex, that is why they lose their conformity to accepted mode of social behavior. They become unruly and negligent of their appearance. When there is a destructive lesion in the motor speech area of Broca, there will be expressive aphasia. If it will be on the sensory portion of the Wernicke’s area, there will be receptive aphasia. o According to the National Aphasia Association, people with Wernicke's aphasia can frequently produce speech that sounds normal and grammatically correct. Large area for behavior and judgement, attention, and emotional responses o The actual content of this speech makes little sense. Non-existent and o The Prefrontal Cortex and Schizophrenia irrelevant words are often included in the sentences that these  The prefrontal cortex has a rich dopaminergic innervation. individuals produce.  It has been shown with PET scans that the blood flow in the o Symptoms of Wernicke's aphasia include: prefrontal cortex in schizophrenic patients is challenged, with the  Making up meaningless words executive type of functions much less than in normal individuals.  Producing sentences that do not make sense  Speaking in a way that sounds normal but lacks meaning  Difficulty repeating words or phrases  Being unaware of problems with speech o Individuals with Wernicke's aphasia have difficulty understanding spoken language but are able to produce sounds, phrases, and word sequences. Frontal Leukotomy and Frontal Lobectomy o While these utterances have the same rhythm as normal speech, they o Frontal leukotomy and frontal lobectomy are surgical procedures that are not a language because no information is conveyed. This type of have been used to reduce the emotional responsiveness of patients aphasia affects both spoken and written language. with obsessive emotional states and intractable pain. Destruction to the Motor and Sensory Speech Areas o Past experiences is not recalled and the possibilities of the future are o Destructive lesions involving both the Broca and Wernicke speech not considered; thus, introspection is lessened. areas result in loss of the production of speech and the understanding o A patient suffering severe pain, such as may be experienced in the of the spoken and written word, that is, Global Aphasia. terminal stages of cancer, will still feel the pain following frontal o Patients who have lesions involving the Insula have difficulty in lobectomy. pronouncing phonemes in their proper order and usually produce sounds that are close to the target word but are not exactly correct. Lesions of the Sensory Cortex o Lesions of the primary somesthetic area of the cortex result in contralateral sensory disturbances, which are most severe in the distal Destruction to the Dominant Angular Gyrus parts of the limbs. o Destructive lesions in the angular gyrus in the posterior parietal lobe o Crude painful, tactile, and thermal stimuli often return, but this is (often considered a part of the Wernicke area) divide the pathway believed to be due to the function of the thalamus. The patient remains between the visual association area and the anterior part of the unable to judge degrees of warmth, unable to localize tactile stimuli Wernicke area. accurately, and unable to judge weights of objects. Loss of muscle o This results in the patient being unable to read (Alexia) or write tone may also be a symptom of lesions of the sensory cortex. (Agraphia). o Lesions of the secondary somesthetic area of the cortex do not o This so-called angular gyrus area is needed to make meaning out of cause recognizable sensory defects. the visually perceived words. In its absence, a person can still have Lesions of the Somesthetic Association Area excellent language comprehension through hearing but not through o Lesions of the superior parietal lobule interfere with the patient’s ability reading to combine touch, pressure, and proprioceptive impulses, so he or she is unable to appreciate texture, size, and form. o This loss of integration of sensory impulses is called astereognosis. For example, with the eyes closed, the individual would be unable to recognize a key placed in the hand. o Destruction of the posterior part of the parietal lobe, which integrates Angular areas seen in the posterior area of the parietal lobe. When there are somatic and visual sensations, will interfere with the body. The destructive lesions in the angular gyrus, you will lose the comprehension in individual may fail to recognize the opposite side of the body as his or your reading 12  her own. The patient may fail to wash it or dress it or shave that side of the face or legs. Lesions of the Primary Visual Area o Lesions involving the walls of the posterior part of one calcarine sulcus result in a loss of sight in the opposite visual field, that is, crossed homonymous hemianopia. It is interesting to note that the central part of the visual field, when tested, apparently is normal. The so- called macular sparing is probably due to the patient’s shifting eyes very slightly while the visual fields are being examined. o Lesions of the upper half of one primary visual area- the area above the calcarine sulcus- result in inferior quadrantic hemianopia, whereas lesions involving one visual area below the calcarine sulcus result in superior quadrantic hemianopia. o Lesions of the occipital pole produce central scotomas. The most common causes of these lesions are vascular disorders, tumors, and injuries from gunshot wounds. The characteristics of a person who has a dominant left hemisphere and  Central scotomas are blind spots in the center of the visual field. In dominant right hemisphere. the early stages, it will cause slight nuisance. As the scotomas CEREBRAL CORTICAL POTENTIALS become larger and increase in number, this will be more alarming to the patient. Electrical recordings taken from inside neurons of the cerebral cortex show a negative resting potential of about 60 mV. Lesions of the Secondary Visual Area o Lesions of the secondary visual area result in a loss of ability to The action potentials overshoot the zero potential. rec