Neuroscience 1 - Neuroglial Cells and Cerebral White Matter PDF

NEUROANATOMY NEUROGLIAL CELLS & CEREBRAL WHITE MATTER DR. ALLAN VIADO 1A...

NEUROANATOMY NEUROGLIAL CELLS & CEREBRAL WHITE MATTER DR. ALLAN VIADO 1A Table 1. Neuroglial cells present in the Central and Peripheral OUTLINE Nervous system. I. Neuroglial cells Central Nervous System Peripheral Nervous System II. Classifications of Neuroglial Cells Astrocytes Schwann cells A. Astrocytes Oligodendrocytes Satellite cells B. Microglial cells Ependymal cells C. Ependymal cells Microglial cells 1. Ependymocytes 2. Tanycytes A. ASTROCYTES 3. Choroidal epithelial cells from Greek word “astron” which means a “star” D. Oligodendrocytes Most abundant, largest, versatile, highly branched glial cells E. Schwann cells (branching processes that extend in all directions) F. Satellite cells Cling to neurons and cover capillaries III. Global Aphasia IV. Cerebral White Matter FUNCTIONS: A. Commissure Fibers - with their branching processes, form a supporting B. Association Fibers framework for the nerve cells and nerve fibers C. Projection Fibers - electrical insulators preventing axon terminals from influencing neighboring and unrelated neurons - barriers for the spread of neurotransmitter substances I. NEUROGLIAL CELLS released at synapses - take up excess K+ ions from the extracellular space so that Glial cells/supporting cells they may have an important function during repetitive Metabolic and mechanical support for neurons firing of a neuron Unlike neurons, they undergo mitosis - store glycogen within their cytoplasm they comprise about half the total volume of the brain and - serve as phagocytes by taking up degenerating synaptic spinal cord; 10X more abundant than neurons (billions) axon terminals - replacement gliosis (following the death of neurons due to Primary Brain Tumors disease, astrocytes proliferate and fill in the spaces - when control over capacity of reproduction is lost previously occupied by the neurons) - Astrocytoma/Oligodendroglioma/Ependymoma/ - play an important role in the structure of the blood-brain Ganglioglioma barrier - Grade I-IV - responsible for scar formation - Astrocytoma is considered histologically to be the most - energy metabolism benign glioma, and glioblastoma multiforme is considered - guide migration of young neurons during development the most malignant II. CLASSIFICATIONS OF NEUROGLIAL CELLS B. MICROGLIAL CELLS derived from macrophages outside the nervous system Phagocytes – phagocytize neuronal debris and microorganisms which is part of the inflammatory response “Policemen” of the Nervous system o protection from viruses and mcgs o proliferate in the site of lesion and become antigen presenting cells, which together with the invading T lymphocytes confront invading organisms smallest of the neuroglial cells Trans 3 |Abero, Rizel Chlo Anne 1 of 4  Neuroanatomy NEUROGLIAL CELLS & CEREBRAL WHITE MATTER scattered throughout the central nervous system D. OLIGODENDROCYTES analogue of Schwann cells (PNS) in the CNS responsible for the formation of the myelin sheath of nerve fibers o provides the axons with an insulating coat and greatly increases the speed of nerve conduction along these axons o 1 oligodendrocyte : 60 axons surround nerve cell bodies unlik Schwann cells, they are not surrounded by a basement membrane (neurilemma) C. EPENDYMAL CELLS line the cavities of the brain and the central canal of the spinal cord form a single layer of cells that are cuboidal or columnar in shape and possess microvilli and cilia o movements of cilia contribute to the flow of the cerebrospinal fluid 1. Ependymocytes line the ventricles of the brain and the central canal of the spinal cord and are in contact with the cerebrospinal fluid assist in the circulation of the cerebrospinal fluid within the cavities of the brain and the central canal of the spinal cord 2. Tanycytes line the floor of the third ventricle overlying the median eminence of the hypothalamus transport chemical substances from the cerebrospinal fluid to the hypophyseal portal system 3. Choroidal Epithelial cells cover the surfaces of the choroid plexuses sides and bases of these cells are thrown into folds held together by tight junctions which prevents the leakage of cerebrospinal fluid into the underlying tissues involved in the production and secretion of cerebrospinal fluid from the choroid plexuses E. SCHWANN CELLS also known as Lemmocytes analogue of oligodendrocytes in the PNS wrap individually around the shaft of peripheral axons, forming a layer of myelin sheath along segments of the axon o 1 Schwann cell : 1 axon with a neurilemma (basal lamina) Schwann cell membrane – composed primarily of lipids; the lipid serves as an insulator thereby speeding the transmission rate of action potentials along the axon F. SATELLITE CELLS analogue of astrocytes in the PNS wraps around nerve cell bodies in the sensory (dorsal root ganglia) and autonomic (sympathetic and parasympathetic) ganglias regulates the microenvironment in these ganglias Trans 3 |Abero, Rizel Chlo Anne 2 of 4  Neuroanatomy NEUROGLIAL CELLS & CEREBRAL WHITE MATTER nutrient supply/structural function more research ongoing to study their function III. GLOBAL APHASIA problem with both receptive and expressive language B. ASSOCIATION FIBERS (spoken and written language) connect various cortical regions within the same combined with auditory and visual comprehension deficit hemisphere deficit in language production, comprehension and may be divided into short and long groups repition Damage: left cerebral hemisphere = perisylvian cortex Short association fibers including Broca’s and Wernicke’s area - lie immediately beneath the cortex and connect adjacent gyri - run transversely to the long axis of the sulci most commonly due to thrombotic stroke (main left middle cerebral artery trunk) Long association fibers may still be able to express themselves through facial - collected into named bundles that can be dissected in a formalin- expression, gestures and intonation (preserved right hardened brain hemisphere) o uncinated fasciculus - connects the first motor speech area and the gyri on the inferior surface of the frontal lobe with the cortex of the pole of the temporal lobe IV. CEREBRAL WHITE MATTER o cingulum - long, curved fasciculus lying within the white myelinated nerve fibers of different diameters supported matter of the cingulate gyrus by neuroglia o superior longitudinal fasciculus - largest bundle of nerve provides conduit for extensive communications fibers; connects the anterior part of the frontal lobe to the via (mostly) myelinated axon fibers bundles into tracts occipital and temporal lobes o Commissural fibers o inferior longitudinal fasciculus - runs anteriorly from the o Assocation fibers occipital lobe, passing lateral to the optic radiation, and is o Projection fibers distributed to the temporal lobe o fronto-occipital fasciculus - connects the frontal lobe to the A. COMMISURAL FIBERS occipital and temporal lobes connect corresponding regions of the two hemispheres corpus callosum - largest commissure of the brain - connects the two cerebral hemispheres o rostum o genu o body o splenium Trans 3 |Abero, Rizel Chlo Anne 3 of 4  Neuroanatomy NEUROGLIAL CELLS & CEREBRAL WHITE MATTER C. PROJECTION FIBERS Consist of afferent and efferent fibers Internal capsule - compact band of fibers at the upper part of the brainstem - flanked medially by the caudate nucleus and the thalamus and laterally by the lentiform nucleus o anterior limb o posterior limb Corona radiata - fibers that emerged superiorly from between the nuclear masses - radiate in all directions to the cerebral cortex - spray of projection fibers from precentral gyrus - combines with sensory fibers traveling to sensory cortex REFERENCE Snell, R.S. Clinical Neuroanatomy, 7th Edition, 2010. Trans 3 |Abero, Rizel Chlo Anne 4 of 4