Neuroscience: The Cerebrum PDF

Both the central nervous system and the peripheral nervous system have major subdivisions. The closeup COURSE OUTLINE of the brain s...

Both the central nervous system and the peripheral nervous system have major subdivisions. The closeup COURSE OUTLINE of the brain shows the … as seen from the midline. I. Divisions of the Human Nervous System II. The Brain III. The Cerebral Hemispheres A. Surfaces B. Poles and Lobes IV. Sulci on the Lateral Surface V. Gyri on the Lateral Surface VI. Sulci on the Medial Surface VII. Gyri on the Medial Surface VIII. Sulci on the Inferior Surface IX. Gyri on the Inferior Surface A. Limbic System Illustration B. Basal Ganglia Components Figure 2. Layers of the scalp X. Difference Between an MRI and a CT Scan I. DIVISIONS OF THE HUMAN NERVOUS SYSTEM Central Nervous System ○ The brain and the spinal cord Peripheral Nervous System ○ The nerves outside the brain (cranial nerves) and spinal cord (spinal nerves) ○ Two Division of the PNS: Somatic Nervous System - the nerves that convey messages from the sense organs to the CNS (sensory/afferent) and from the Figure 3. Meninges CNS to the muscles and glands (motor/efferent) Autonomic Nervous System - a set of The brain and spinal cord are protected by meninges neurons that control the heart, the intestine Three (3) Layers and other organs ○ Dura mater - outermost, tough, continuous with periosteum ○ Arachnoid mater - middle layer, spider web appearance ○ Pia mater - innermost; not visible to the naked eye; connected to the brain Figure 1. The human nervous system Figure 4. Meninges 1  Figure 6. Choroid plexus The CSF circulates throughout the ventricles, down the central canal of the spinal cord and throughout the subarachnoid space. CSF is reabsorbed back into the blood primarily at the venous sinuses found within the dura mater. Figure 5. Falx cerebri and tentorium cerebelli Subarachnoid space - where CSF is found Continuation … Ventricles - canals that contain CSF, lined by The dura mater helps keep the brain in position ependymal cells, some portions of the ventricles and the cerebral spinal fluid (CSF) helps cushion (ependymal cells) become highly specialized / protect the brain vascular structures (choroid plexus). Ependymal cells in the choroid plexuses will produce the CSF. EXTENSIONS OF THE DURA MATER All ventricles are lined by ependymal cells but not 1. Falx cerebri - between the left and the right all have choroid plexus. hemisphere There should be a balance between the amount of CSF produced and the amount excreted everyday. 2. Tentorium cerebelli - separates the cerebrum from Overproduction/ decrease in excretion: ventricles the cerebellum and brainstem will enlarge ○ Above this is the supratentorial: ○ Hydrocephalus - enlargement of ventricles Cerebrum due to obstruction in the flow/ failure of CN I (olfactory) excretion/ overproduction of CSF. CN II (optic) ○ Below this is the infratentorial: Cerebellum Brainstem and cranial nerves - Midbrain: CN III, IV - Pons: CN V, VI, VII, VIII - Medulla oblongata: CN IX, X, XI, XII 3. Septum pellucidum - separates the anterior aspect of the left and right lateral ventricles Where does the fluid come from? Choroid plexus on ventricle walls Figure 7. Cerebrospinal fluid flow 2  Example: corpus callosum connects hemispheres Inner layer: fibers coming from the neurons from the gray matter ○ Gray matter outer layer (neurons stain darker) Cerebral cortex Cerebrum: outer gray, inner white Spinal cord: inner gray, outer white Figure 8. The brain Figure 9. The sections of the brain Figure 11. Basic components of the CNS The basic components of the CNS include the: It is the largest part of the forebrain ○ Cerebrum It is highly developed in human ○ Diencephalon It is derived from the telencephalon. ○ Cerebellum The two cerebral hemispheres are incompletely ○ Brain Stem separated by the median or greater longitudinal ○ Spinal Cord fissure (largest fissure in the cerebrum) They are connected by the corpus callosum II. THE BRAIN Each hemisphere has a cavity called the lateral ventricle. Septum pellucidum - separates the anterior horns of the lateral ventricles Figure 10. Basic components of the CNS Figure 12. Coronal section of the cerebrum III. THE CEREBRAL HEMISPHERES The surface is made of: ○ Gyri: ridges/ convolutions in any of the four lobes ○ Sulci: grooves/ invaginations, not contain brain substance, divide four lobes into smaller subsections/ smaller lobes Layers of the Cerebrum ○ White matter Fiber tracts inside the gray matter Figure 13. Development of the brain 3  Each hemisphere has 3 poles: ○ Frontal pole CEREBRUM: SURFACES ○ Occipital pole ○ Temporal pole Also, each hemisphere has 4 lobes: ○ Frontal lobe - the only lobe that has a motor function ○ Temporal lobe - sensory ○ Parietal lobe - sensory ○ Occipital lobe - sensory IV. SULCI ON THE LATERAL SURFACE Figure 14. Surface of the cerebrum Each hemisphere has ○ 3 surfaces ○ 3 poles ○ 4 borders ○ 4 lobes (frontal, parietal, temporal, occipital) A. CEREBRUM: SURFACES The Three Surfaces: Figure 16. Brain sulci ○ Lateral or Superolateral: Convex and related to the skull vault Lateral sulcus or fissure / Sylvian fissure ○ Medial ○ Separates the frontal and parietal lobes from the Flat and vertical and related to the falx temporal lobe cerebri and median longitudinal fissure Central sulcus /central sulcus of Rolando/ ○ Inferior Rolandic sulcus Divided into orbital and tentorial parts by ○ Begins from the superomedial border ½ inch the stem of lateral sulcus behind the midpoint between the frontal and Orbital surface - free, lying on the frontal occipital poles. bone, above the eyes ○ It descends downward and forward making an Tentorial surface - lying on top of the angle about 70° with the vertical line. tentorium cerebelli, so not every part of the ○ It stops slightly above the lateral sulcus inferior frontal lobe is on top of the ○ Divides the frontal from the parietal lobe tentorium cerebelli Pre-central: a finger breadth anterior & parallel to B. CEREBRUM: POLES AND LOBES the central sulcus Post-central: a finger breadth behind & parallel to the central sulcus Superior & inferior frontal sulci (dividing the frontal lobe into three: superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus) Superior & inferior temporal sulci (dividing the temporal lobe into three: superior temporal gyrus, middle temporal gyrus, inferior temporal gyrus) Intraparietal sulcus (dividing the parietal lobe into two: superior parietal lobule, inferior parietal lobule) Lunate sulcus - occipital lobe Figure 15. Lobes and poles of the cerebrum 4  Figure 17. Gyri on the Cerebrum and the Central Sulcus Figure 19. Sulci on the medial surface CALLOSAL SULCUS V. GYRI ON THE LATERAL SURFACE ○ just above the corpus callosum CINGULATE SULCUS ○ one inch above and parallel to the callosal sulcus PARIETO-OCCIPITAL SULCUS ○ begins in the upper border 4cm in front of the occipital pole ○ it ends at the meeting of calcarine & post calcarine sulci ○ Separates occipital from the parietal lobe CALCARINE ○ begins below the splenium then passes backwards and upwards to meet the parieto-occipital sulcus then continuous as the postcalcarine sulcus ○ Divide occipital lobe into two: Cuneus - higher lobe Lingual gyrus - lower lobe POST CALCARINE SULCUS ○ it is an extension of the calcerine VII. GYRI ON THE MEDIAL SURFACE Figure 18. Brain gyri and sulci Precentral gyrus: ○ between central and precentral sulcus ○ primary motor cortex or the Brodmann area 4 Postcentral gyrus: ○ between central and postcentral sulcus ○ Area 3, 1, 2 (Primary somatosensory cortex) Superior, middle & inferior frontal gyri ○ Inferior frontal gyrus is divided into: orbital - triangular - opercular parts Superior, middle & inferior temporal gyri Figure 20. Gyri on the Medial Surface Superior & inferior parietal lobules ○ Inferior parietal gyrus is divided into: Cingulate gyrus a. Supramarginal gyrus - more anteriorly ○ between the callosal & cingulate sulci located ○ Part of the limbic system b. Angular gyrus Paracentral lobule ○ it is the continuation (medially) of the VI. SULCI ON THE MEDIAL SURFACE precentral & postcentral gyri Precuneus 5  ○ behind the paracentral lobule Gyrus rectus Cuneus ○ medial to the olfactory sulcus ○ between the parieto-occipital & postcalcarine Orbital gyri sulcus ○ anterior, posterior, medial, and lateral, orbital *Limbic lobe is sometimes considered as the fifth gyri lobe Lateral occipitotemporal gyrus VIII. SULCI ON THE INFERIOR SURFACE ○ lateral to occipitotemporal sulcus Parahippocampal gyrus ○ medial to collateral sulcus ○ for emotions: part of limbic system ○ medial to hippocampus (memory and learning) Lingual gyrus ○ between collateral & calcarine sulci Uncus ○ Anterior end of the Parahippocampal gyrus ○ it is the smell center Figure 21. Sulci on the Inferior Surface ○ Part of the limbic center ○ Olfactory is a major part of the limbic system Olfactory sulcus because the sense of smell carries emotional ○ close and parallel to the medial orbital margin component Orbital sulcus ○ Close to midbrain ○ irregular H-shaped lateral to olfactory sulcus ○ Compresses midbrain when the compression in ○ divides into 4: the brain is high. (Herniation which can lead to Anterior orbital comatose) Posterior orbital Medial orbital Lateral orbital Stem of lateral sulcus ○ it divides the inferior surface into orbital and tentorial parts Rhinal sulcus ○ a short sulcus on the temporal pole Collateral sulcus ○ behind the rhinal sulcus and extend to the occipital pole Figure 23. Patterns of cerebral and cerebellar herniation Occipitotemporal sulcus ○ lateral to the collateral sulcus A. ILLUSTRATIONS OF THE LIMBIC SYSTEM ○ it extends from temporal to occipital poles ○ divides into two: Medial occipital temporal gyrus Lateral occipital temporal gyrus IX. GYRI ON THE INFERIOR SURFACE Figure 24. Limbic System Limbic lobe cannot be delineated grossly because it consists of scattered lobes/areas/structures on the medial aspect that collectively constitute the limbic system. Figure 22. Gyri on the Inferior Surface 6  From Cerebrum: Cingulate Gyrus, X. DIFFERENCE BETWEEN MRI & CT SCAN Parahippocampal Gyrus, Hippocampus, I. Magnetic Resonance Imaging (MRI) Amygdaloid Body (reward center, addiction) MRI (Magnetic resonance imaging) Diencephalon: Thalamus, Hypothalamus Longer procedure, makes more noise, not for Olfactory bulb claustrophobics B.COMPONENTS OF BASAL NUCLEI/ GANGLIA uses magnetic field, radiofrequencies reacts with body metal detailed structures, differentiated normal from abnormal MRI (Intensity) ○ White (hyperintensity) ○ Black (hypointensity) ○ T1 (csf black in lateral ventricle) ○ T2 (csf white) II. Computed Tomography (CT) Scan Faster, less noise, bigger hole Uses x-ray Exposure to ionizing radiation Figure 25. Coronal View of the Basal Ganglia Better for bone structures, gives overall picture Reported as Density Basal Ganglia - telencephalic derivative; A functional ○ White (hyperdensity) system consists of five components: - Bone - Blood 3 Telencephalon ○ Black (hypodensity) ○ Caudate Nucleus - Air - CSF ○ Globus Pallidus Brain will appear grayish. Globus Pallidus interna In between bone and CSF color is black. Globus Pallidus externa Between the Gray Matter will be a little less gray ○ Putamen - most laterally placed compared to white matter. 1 Diencephalon ○ Subthalamus 1 Mesencephalon ○ Substantia Nigra (Dopamine) Internal Capsule - convergence of all white matter tracts coming from the cerebral cortex. Located between the thalamus and other portions of basal ganglia laterally. What happens if there is a problem in the Basal Figure 26. MRI Basics Ganglia? It will not give you weakness but affects modulation of movements (E.g. Parkinson’s -dopamine lacking in the substantia nigra.) A person with this condition is characterized by stoop posture, no facial expression, no arm swing, tremors at hand, and feet together in slow steps that go faster when walking till they fall. Figure 27. CT Scan vs. MRI 7  Figure 29. CT Scan Negatoscope - used to read negative films of CT scans. CT Scan results - Orbit should be on the top left portion of the negatoscope. Figure 28. Comparison of MRI and CT Scan Figure 30. MRI Scan Sagittal View of Brain Figure 31. MRI Axial Section Midbrain three portions Centrum semiovale - refers to all white matter ○ Posterior:Tectum-has 4 corpora quadrigemina coming from the cortex that will eventually go down divided into Inferior Colliculi (hearing) and Lateral Ventricles - appear as black due to CSF Superior Colliculi (vision) Choroid Plexus - whitish image inside lateral Sylvian Aqueduct - consists of CSF appearing as ventricles due to blood content black Internal Capsule - where all fibers from Centrum Septum Pellucidum - a Dural Derivative that lights Semiovale will converge up in the image, between the left and right hemispheres; within the lateral ventricles Reference(s): Splittgerber, (2019). Snell’s Clinical Neuroanatomy (8th edition) Falx Cerebri - Outside of lateral ventricles Philadelphia: Wolters Kluwer 8