Histology of the Nervous System: Cellular Diversity and Its Locations

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LIBORIO NETO, Adail Orrith [1]

LIBORIO NETO, Adail Orrith. Histology of the Nervous System: Cellular Diversity and Its Locations. Multidisciplinary Scientific Journal. Edition 8. Year 02, Vol. 05. pp. 74-93, November 2017. ISSN:2448-0959

ABSTRACT

The nervous system is basically bruised by one of the four basic types of tissues of the body, the nervous tissue, being distributed throughout the body. It is formed by neurons and the glia or neuróglia cells, which have origin in the ectoderm. However, the nervous system is also composed of modified cells of the conjunctive and epithelial tissue. All these cells are grouped, forming the Nervous System, which is divided into Central Nervous System (brain and spinal cord, protected by the meninges) and Peripheral Nervous System (nerve ganglia and nerves). This bibliographic review aims to explain the morphological characteristics, different cell types and locations of the cells and structures that constitute the nervous system, thus demonstrating the extension, diversity, flexibility and significance of the cells of this system and its interactions with the other systems that constitute the human body.

Key words: Nervous, Glia, Neurons, Neuroglia, Marrow, Ganglion, Nerve, Meninges, Histology.

1. INTRODUCTION

Nervous tissue is distributed throughout the body, interconnecting and forming a communication network, which constitutes the nervous system. Anatomically, this system is divided into: central nervous system (CNS), formed by the brain, neural constituents of the photoreceptor system and spinal cord, and peripheral nervous system (SNP), formed by nerves and aggregates of nerve cells called ganglia. The nerves are mainly composed of prolongations of the neurons located in the CNS or nervous ganglia. Nerve tissue has two major components: neurons, cells usually with long extensions, and various types of glia or neuróglia cells, which support the neurons and participate in other important functions. (JUNQUEIRA, CARNEIRO, 2013)

2. MATERIALS AND METHODS

The main histology and neuroanatomy books available in Brazil were analyzed: JUNQUEIRA; CARNEIRO, Basic Histology, 12th Ed .; GARTNER; HIATT, Treaty of Histology in Colors, 2nd Ed .; KIERSZENBAUM, B. L. Histology and cell biology: an introduction to pathology. 3rd Ed .; Machado, ABM. Functional neuroanatomy, 3rd Ed .; MONTANARI, Histology – Text, Atlas and Script of Practical Classes – Graduation Series – 2 Ed .; Gray's Anatomy – 29 Ed. As well as articles in the area of ​​histology consulted in the database Scielo and Google Scholar.

3. THE NERVOSA CELL

Neurons present complex morphology, but almost all have three components: dendrites, cell body or pericardium, and axon. The dimensions and shape of nerve cells and their extensions are very variable. In general, nerve cells are large, and the cell body can measure up to 150 μm.  (JUNQUERIA; CARNEIRO, 2013) The shape of the cell body varies according to the location and functional activity of the neuron. (MONTANARI, 2006)

The nucleus is large, spherical or ovoid and clear, because of loose chromatin, with one and sometimes two or three prominent nucleoli. In female neurons, a corpuscle corresponding to the sexual chromatin can be observed, associated with the nucleolus or the inner face of the nuclear membrane. As first described by Barr, it is also called Barr's corpuscle. (MONTANARI, 2006)

The rough endoplasmic reticulum is well developed and there is abundance of free ribosomes, which confers basophilia to the cytoplasm, even in the form of granules. Before the advent of electron microscopy, these basophilic granules were called Nissl corpuscles. The name is due to the German neurologist Franz Nissl, who described them in the early twentieth century. The eucrotic nucleus, prominent nucleolus and abundance of rough endoplasmic reticulum and ribosomes are related to the intense activity of the cell in protein synthesis. (MONTANARI, 2006)

The Golgi, also involved in the synthesis of these substances and their packaging, is bulky and is usually located close to the nucleus. The smooth endoplasmic reticulum is abundant and, just below the plasma membrane, forms hypoelemal cisterns. Mitochondria, present throughout the neuron, are related to the high energy requirement, especially for the electrochemical gradients of the nerve impulse. (MONTANARI, 2006)

Lysosomes are numerous due to the intense renewal of the plasma membrane and other cellular components. With aging, residual corpuscles containing lipofuscin are concentrated, which can compress the organelles and nucleus, affecting their activities. (MONTANARI, 2006)

Lipid droplets can be found and represent a reserve of energy or, in large numbers, may be due to a failure in lipid metabolism. Pigments containing iron may be observed in certain CNS neurons and also accumulate with age. Melanin granules are present in certain CNS and PNS neurons. The cytoskeleton is composed of actin filaments, intermediate filaments (neurofilaments), microtubules and motor proteins, such as dynein and kinesin (MONTANARI, 2006). It is very organized and maintains the shape of the cell, supports the extensions and allows the transport of organelles and substances. (MONTANARI, 2006) Dendrites are afferent endings, that is, they receive stimuli from the environment, from sensory epithelial cells or from other neurons. Most nerve cells have numerous dendrites, which considerably increase the cell surface, making it possible to receive and integrate impulses brought by numerous axon terminals of other neurons. (MONTANARI, 2006)

The composition of the cytoplasm of the base of the dendrites, close to the pericary, is similar to that of the cell body; However, the dendrites do not present Golgi complex. The vast majority of impulses arriving at a neuron are received by small projections of dendrites, pimples, or gemstones. Gemstones, measuring 1 to 3 μm in length and less than 1 μm in diameter, are usually formed by an elongated part attached to the dendrite and terminated by a small dilatation. They are the first place to process the nerve impulses that reach the neuron. This processing mechanism is located in a complex of several proteins attached to the inner surface of the postsynaptic membrane. Gemstones participate in the plasticity of neurons related to adaptation, memory and learning. These lemons are dynamic structures with morphological plasticity based on actin protein, a component of the cytoskeleton that is related to the formation of synapses and their functional adaptation, even in adults. (JUNQUEIRA; CARNEIRO, 2013) The axon is an efferent extension of the neuron. It drives the impulses to another neuron, the muscle or glandular cells. It is generally slender and much longer than dendrites and has a constant diameter. According to the neuron, the axon can measure from 1 to 20μm in diameter and from 1mm to 1.5m in length. (MONTANARI; 2006) Each neuron contains only a single axon, which is a cylinder of variable length and diameter depending on the type of neuron. Generally, the axon originates from a cellular body structure, called the implantation cone. Neurons whose axons are myelinated, the part of the axon between the cone of implantation and the beginning of the myelin sheath is called the initial segment. This segment receives many stimuli, both excitatory and inhibitory, from which the result can give rise to an action potential whose propagation is the nerve impulse. (JUNQUEIRA, CARNEIRO, 2013)

4. TYPES OF NEURONAL CELLS

PURKINJE CELL

Purkinje cells belong phylogenetically to the cerebellar neocortex, evolving more recently and with a cytoarchitecture characterized by three layers: molecular, Purkinje and granular. The Purkinje cell is the dominant element in the cerebellar information process and may exhibit degenerative changes in senescence that can be noticed by simple staining methods such as H & E. (I.R.A., et al., 2001).

ASTROCIDE

They are the largest and most numerous cells of the CNS glial. They present a starred morphology, due to the prolongations, which gives rise to its name (from the Greek astron, star). They have a large, ovoid or slightly irregular nucleus, with loose chromatin and central nucleolus. The cytoplasm contains the glial fibrillary acidic protein (GFAP), an exclusive intermediate filament of these cells in the CNS. Astrocytes communicate with each other by gap junctions. They show basal lamina. The star shape of the astrocytes is not evident in the sections stained by HE, and special methods such as silver impregnation by the Golgi method or immunoperoxidase are required, showing GFAP. (MONTANARI, 2006) These cells have bundles of intermediate filaments constituted by the glial acid fibrillar protein, which reinforce the cellular structure. Astrocytes bind the neurons to the blood capillaries and the pia mater. Astrocytes with less numerous and longer prolongations are called fibrous astrocytes and are located in the white matter; the protoplasmic astrocytes, found mainly in the gray matter, present a greater number of prolongations that are short and very branched (JUNQUEIRA, CARNEIRO, 2013)

Astrocytes provide physical and metabolic support to CNS neurons and contribute to the maintenance of homeostasis. They secrete interleukins and growth factors, such as fibroblast growth factor (FGF), epidermal growth factor (EGF), and tumor necrosis factor β (TNF-β), which are important for the morphogenesis of neighboring neurons. the differentiation of astrocytes and the response of these cells to traumatic or pathological events. (MONTANARI, 2006)

OLIGODENDRÓCITOS

The oligodendrocytes are smaller than the astrocytes and their nuclei are irregular and densely stained. One function of oligodendrocytes is axonal myelination in the CNS. (KIERSZENBAUM, 2012) They are located in the gray matter and white matter of the CNS. The electron microscope shows rough endoplasmic reticulum, ribosomes and mitochondria in abundance, and the presence of Golgi and microtubules, but there are no intermediate filaments or basal lamina. (MONTANARI, 2006)

SCHWANN CELLS

Schwann cells have the same function as oligodendrocytes, but are located around the axons of the peripheral nervous system. Each Schwann cell forms myelin around in a single axon segment. (Junqueira, Carneiro, 2013) Schwann cells are elongated, with elongated nuclei, poorly developed Golgi and few mitochondria. They contain GFAP and are surrounded by the outer blade. They do not have extensions and their own body, giving up to more than 50 turns, envelop the axon and form the myelin nervous fiber (MONTANARI, 2006)

MICRÓGLIA

The microglia cells are small and elongated, with short and irregular lengthening. These cells can be identified on hematoxylin-eosin-stained histological blades because their nuclei are dark and elongated, contrasting with the spherical nuclei of the other glial cells. Microglial cells are phagocytic and derive from precursors brought from the bone marrow through the blood, representing the mononuclear phagocytic system in the central nervous system. They participate in inflammation and repair of the central nervous system. When activated, microglial cells retract their prolongations, take the form of macrophages and become phagocytic and antigen presenting. The microglia secretes various cytokines regulating the immune process and removes cellular debris arising in the lesions of the central nervous system. (JUNQUEIRA; CARNEIRO, 2013) Microglial cells have the following characteristics:

  1. They are cells derived from the mesoderm, whose primary function is phagocytosis.
  2. They are considered as immune protectors of the brain and spinal cord.
  3. They interact with neurons and astrocytes and migrate to sites of dead neurons where they proliferate and phagocyte the dead cells.
  4. During the histogenesis in the embryo, the microglia cells discard an excess of neurons and non-viable glial cells, eliminated by apoptosis. (KIERSZENBAUM, 2012)

<strong> CELLS IN BASKET </ strong>

The cerebellar cortex has three distinct layers. In the molecular layer is formed by star cells and cells in basket. These have large dendritic tree and both are inhibitory. The axons of basket cells form basket-like terminal branches of about 5 to 8 sums of Purkinje cells, thus receiving that name. This layer is also formed by parallel fibers. (MACHADO, 2006)

<strong> CEREBELLAN GRANULUS CELLS </ strong>

The granulosa cells are the smallest neurons in the body. Its small nucleus resembles that of a lymphocyte, and the nucleolus, when present, is barely evident. The rosy spaces between granulosa cells are complex synapses called cerebellar glomeruli. In the glomerulus, an axon called mossy fiber ends in a small bulb, which makes synapses with dendrites of nearby granular cells and dendrites of Golgi cells. (MACHADO, 2006)

<strong> BRAIN GRANULAR CELLS </ strong>

Granular cells are the major interneurons of the cortex. They have dendrites branching close to the cell body, and a short axon that connects to nearby cells. They also receive synapses from the vast majority of the axons that reach the cortex and are therefore the main cortical receptor cells. Granular cells exist in all layers, but predominate in layers II and IV or external and internal granular, considered the main receptor layers. (MACHADO, 2006)

<strong> EPENDIMARY CELLS </ strong>

The eppendima is represented by the simple cubic epithelium that lines the surface of the brain ventricles and the central canal of the spinal cord. The ependyma consists of two types (1) ependymal cells and (2) tanicites. Ependymal cells form a simple cubic epithelium, lining the cavities of the brain ventricles and the central canal of the spinal cord. These cells differentiate from germinal or ventricular cells of the embryonic neural tube. The apical domain of ependymal cells contains abundant microvilli and one or more eyelashes. Desmosomes unite adjacent ependymal cells. The basal domain is in contact with astrocytic extensions. (KIERSZENBAUM, 2012)

<strong> TANICITOS </ strong>

Tanicites are specialized ependymal cells with basal extensions that extend between astrocytic prolongations to form terminal legs over blood vessels. (KIERSZENBAUM, 2012) The term tanicite was created by Horstmann in 1954 when he described a distinct structural feature of the glial cells present in the hypothalamus, which was the presence of a single basal process, which protrudes along the interior of the hypothalamus. (LUIZ, 2011) These are special cells with long extensions that will selectively allow the transfer of regulatory substances between the cerebrospinal fluid and the middle eminence. Its extensions interdigitate with the vessels, facilitating the crossing of the middle blood-brain barrier and the action on the production of hormones produced at the pituitary level. (LOURENÇO, FORTUNATO, 2005)

<strong> GOLGI CELLS </ strong>

Golgi cells are neurons that have the cell body in the superficial part of the granular layer, i.e., closest to the Purkinje layer. Its dendrite is directed to the molecular layer where it arborizes in all directions, and not in a single plane like the dendrite of the cells of Purkinje. The Golgi cell axon terminates in the cerebellar glomeruli, where it has inhibitory influence. (MACHADO, 2006)

<strong> PITUICITOS </ strong>

The pituicytes are located in the nervous pars of the posterior pituitary interspersed with demyelinated axons and Herring corpuscles. The pituicytes have an irregular and branched shape that resembles another type of glial cell: the astrocyte. Like astrocytes, its cytoplasm has characteristic intermediate filaments made of glial fibrillary acidic protein (GFAP). (WEI, ZHAO; LIU; WANG, JU; 2009)

<strong> GLIA DE MULLER </ strong>

Müller's glia, or Müller's cells, are a type of retinal glial cells. They are found in the retina of vertebrates and have supporting role of retinal neurons. They are the type of glial cell most commonly found in the retina. They are found throughout the thickness of the neural retina. The main function of Müller cells is to maintain the stability of the extracellular medium through the regulation of K * uptake, neurotransmitter uptake, debris removal, glycogen storage, electrical isolation of neurons and mechanical support of the neural retina. (REICHENBACH et al., 2009)

<strong> GLIA DE BERGMANN </ strong>

Bergmann's astrocytes, whose cell bodies are in the Purkinje cell layer, launch parallel extensions that sweep the molecular layer of the cerebellum, ending in the leaf leptomeninge with horn-like expansions reminiscent of 'sucking feet' (endings of astrocytes in pots). (MACHADO, 2006)

<strong> PYRAMID NEURON </ strong>

The pyramidal cells have a triangular cell body, which varies from 10 to 80 micrometers in diameter. The cell body gives rise to a single thick dendrite apical and multiple basal dendrites. The apical dendrite rises toward the cortical surface, sharpens and branches more superficially, ending in a tuft of small terminal branches on the most superficial blade, the molecular layer. (GOSS, 1998) They can be small, medium, large and giant (these, the pyramidal cells of Betz of the motor cortex). Pyramidal cells can be found in all layers, but predominate in layers III and V or pyramidal external and internal, considered the main effector layers of the cortex. (MACHADO, 2006)

<strong> CABAL INTERSTICAL CELL </ strong>

The interstitial cell of Cajal (or simply Cajal cell) is a type of cell found in the gastrointestinal tract. It serves as a pacemaker that triggers bowel contraction. They can trigger slow waves. These cells are characterized by having an undeveloped contractile apparatus, but many mitochondria. The cell body is fusiform, with little cytoplasm and a large oval nucleus. (Mostafa RM, Moustafa YM, Hamdy H; 2010)

<strong> HORIZONTAL CABAL CELL OR CAJAL-RETZIUS CELL </ strong>

The horizontal cells of Cajal have dendrites and axon in horizontal direction, constituting the tangential fibers of the molecular layer. They participate in the intracortical circuitry of association of the cerebral cortex. (MACHADO, 2006) The Cajal-Retzius cell is a neuron of the human embryonic marginal zone of the brain. They are reelin producing neurons in the human embryo that show, as salient characteristic, ascending radial processes that connect the Pia Mater and a horizontal axonic plexus located in the deep margin zone. (GUNDELA et al., 1999).

<strong> STARCELL CELLS </ strong>

The stellate cells are the second most numerous cell type in the neocortex and, for the most part, occupy the IV lamina. They have relatively small multipole cell bodies. Several primary dendrites profusely covered with spicules are irradiated by various variables from the cell body. Their axons branch out amid the gray matter predominantly in the vertical plane. Star cells probably use glutamate as the neurotransmitter. (GOSS, 1998)

<strong> CANDELABRO CELLS </ strong>

Chandelier cells have a variable morphology, although most are ovoid or fusiform and their dendrites originate from the upper and lower poles of the cell body. Axonal arborization, which emerges from the pericardium or a proximal dendrite, is characteristic and identifies these neurons. Few cells are found on the most superficial laminae (II and IIIa). They have descending axons, deeper cells (laminae IIIe and IV) have ascending axons and intermediate neurons (IIIb) often both. The axons branch off near the cell body of origin and terminate in numerous vertically oriented cords that follow along with the axonal implantation cones of the pyramidal cells with which they make synapses. (GOSS, 1998)

<strong> FUSIFORMES NEURONS </ strong>

Bipolar or spindle cells are ovoid with a single ascending dendrite and a single descending dendrite, which originate from the upper and lower poles, respectively. These primary dendrites branch out sparsely and their branches follow vertically to produce a narrow dendritic tree, which can extend through most of the cortical thickness. Commonly, the axon originates from one of the primary dendrites and rapidly branches out to give the vertically elongated, horizontally confined axonal afforestation that closely resembles the dendritic tree in extension. (GOSS, 1998)

<strong> NEURONES IN DOUBLE BUBBLE </ strong>

Double-tufted cells or double-tufted cells are found on blades II and III and their axons traverse blades II and V. Generally, these neurons have two or three major dendrites, which give rise to a superficial or deep dendritic tuft. A single axon usually originates from the oval or fusiform cell body and rapidly divides into an ascending branch and a descending branch. These branches undergo extensive collateralization, but axonal afforestation is confined to a perpendicular but horizontally confined roller. (GOSS, 1998)

<strong> NEUROGLIFORM NEURON </ strong>

The main recognizable neuronal type is the neurogliform or spider web. These small spherical cells are found mainly on slides II and IV, depending on the cortical area. Seven to ten thin dendrites typically radiate from the cell body, some branching once or twice to form a spherical dendritic field body. The delicate axon originates from the cell body or a proximal dendrite. Almost immediately, it branches profusely amidst the vicinity of the dendritic field to produce a spherical axonal afforestation of up to 350 micrometers in diameter. (GOSS, 1998)

<strong> MARTINOTTI CELLS </ strong>

They exist in most blades, being small, multipolar, with localized dendritic fields and long axons. Preferably located in layers IV to VI, whose axon in ascending direction branches in the most superficial layers, especially in layer I. (MACHADO, 2006)

<strong> 5. MEDULA </ strong>

The spinal or spinal cord is an elongated portion of the central nervous system that continues with the brainstem. It begins at the time in the first cervical vertebra and ends at the height of the first lumbar vertebrae. (P.A. Abrahamsson, 2007) The spinal cord is a flat, cylindrical mass of neural tissue that lies within the vertebral canal. The white matter of the spinal cord is located externally and the gray matter more internally. The gray matter of the marrow has a shape of the letter H. This substance forms four expansions called spinal horns. These horns, two are posterior sensitive and two are anterior motors. The ends of the horns thin and reach the medullary surface at the height of the posterior lateral grooves. The anterior horns are rounded, dilated and contain bulky neurons (motors). The marrow also has numerous nerve cells with unmyelinated fibers, astrocytes, oligodendrocytes and microglia. The white matter of the marrow has a median anterior cleft. The medullary white matter halves are united by the anterior commissure and the majority consists of myelin fibers. (da CRUZ, 2009) The spinal cord is an important organ of communication between the organism and the encephalon. Significant sets of axons pass through the white matter of the marrow, transmitting information from the organism to the brain and information from the brain to neurons located in the marrow and located outside the marrow. (P.A. ABRAHAMSOHN, 2007)

<strong> 6. GANGLIOS </ strong>

The ganglia are aggregates of cellular bodies of neurons located outside the central nervous system. They differ in two types of ganglia: sensitive and autonomous. Sensors are found in the dorsal root of the spinal nerves and in the cranial nerves of the trigeminal, facial, glossopharyngeal, and vagus nerves. Autonomous patients include the ganglia of the autonomic sympathetic and parasympathetic system, as well as the enteric nervous system (myoenteric and submucosal plexus). (BRANCALHÃO, TORQUATTO, RIBEIRO, OLGUÍN, 2016)

The sensory ganglion has a connective tissue capsule that represents the continuation of the epineurium. They are formed by pseudounipolar neurons, the axon being myelinated. Each cell body is surrounded by satellite cells similar to Schwann cells, with the support function. Already in the autonomic ganglion is the postganglionic neuron, which is multipolar and has a massive cell body, cytoplasm with basophilic granulations and prominent nucleolus. This neuron receives the myelin fibers (white communicating branch) of the preganglionic neuron located in the spinal cord or in the brainstem. The axon of the postganglionic neurons is most often amyelinic (gray communicating branch) and is directed to the effector organ. Each neuron is surrounded by satellite cells (less than in the sensory ganglia) and by connective tissue. Like the sensory ganglion, the autonomic ganglion also has a capsule of connective tissue. (BRANCALHÃO, TORQUATTO, RIBEIRO, OLGUÍN, 2016)

<strong> 7. NERVOS </ strong>

The clustering of nerve fibers into bundles in the peripheral nervous system is called the nerve. On the thin nerves there may be only a bundle while in the more caliber nerves there may be several bundles. Because of the color of myelin and collagen, the nerves are whitish except for nerves with only unmyelinated fibers. The nerves establish communication between the nerve centers, the organs of the sensibility and the effectors, like muscles and glands. The fibers that carry the information obtained in the environment and the interior of the body to the CNS are afferent, and those that carry impulses from the CNS to the effector organs are efferent. The nerves that only have afferent fibers are called sensory, and those with efferent fibers, motors. Most nerves, however, have fibers of both types, and these nerves are mixed. The nerve-supporting tissue is composed of an outer fibrous layer of dense connective tissue, the epineurium, which lines the nerve and fills the spaces between the bundles of nerve fibers. Each of these beams is covered by a multilayer sheath of flattened, juxtaposed cells, the perineurium. The perineural sheath cells are joined by occlusive junctions, constituting a barrier to the passage of many macromolecules and an important mechanism of defense against aggressive agents. Within the perineural sheath are the axons, each surrounded by the sheath of Schwann cells, with its basal lamina and a connective sheath consisting mainly of reticular fibers called the endoneurium. (JUNQUEIRA, CARNIERO, 2013)

<strong> 8. MENINGES </ strong>

The central nervous system is contained and protected in the cranial cavity and vertebral canal, being surrounded by membranes of connective tissue called meninges. The meninges are formed by three layers, which, from the outside to the inside, are the following: dura mater, arachnoid and pia mater. (Junqueira and Carneiro, 2013). The pia mater (from the Latin, pia, soft, mater, mother) is the innermost meningeal, lying on the limiting glia, the layer of astrocyte extensions that covers the nervous tissue. It consists of a layer of pavement epithelial cells of mesenchymal origin, meningothelial cells, and loose vascular connective tissue. It involves the blood vessels entering into the nervous tissue, resulting in perivascular spaces, but disappears before they become capillaries. The pia mater remains with the perineurium of the nervous fascicles. Pliaptic folds covered by the epidermis form the choroid plexuses of the third and fourth ventricles and the lateral ventricles. (MONTANARI, 2006)

The arachnoid (Greek, spider-like, arachnoid) is composed of avascularized dense connective tissue (although blood vessels pass through it) and meningothelial cells on the surfaces. The region adjacent to the pia mater is trabeculated, and the cavities correspond to the subarachnoid space, through which the main arteries and veins of the brain enter and exit. The arachnoid has, in some places, expansions that pierce the dura mater and terminate in the venous sinuses: the arachnoid villi. (MONTANARI, 2006)

The dura mater (from the Latin, hard, hard, mater, mother), the outermost meninge, is a thick and resistant layer. In the skull, it is adjacent to the periosteum and in the spinal cord it is separated from the periosteum of the vertebrae by the epidural space, which contains loose connective tissue with adipose cells and a venous plexus. It consists of dense connective tissue and the meningothelial cells on the inner surface and, in the case of the spinal column, also on the outer surface. (MONTANARI, 2006)

<strong> FINAL CONSIDERATIONS </ strong>

The nervous system is one of the most diversified systems of the human body because it consists of a network of communication of the organism, formed by a set of organs of the human body that have the function of capturing the stimuli of the environment and interpreting them. In this way, he elaborates answers, which can be given in the form of movements, sensations or findings. The nervous system consists of different cell types which perform various functions depending on their location. Not only is it formed by neuronal cells, the human nervous system is also composed of connective tissue and epithelial cells, which are not the majority but play the primary role in homeostasis. From the data collected by this work, it is seen that the knowledge of the cells and tissues that compose the nervous system is of paramount importance. Therefore, it is integrated with other systems, commanding, executing, sending and receiving stimuli. The present work sought to contribute to a deeper understanding of the normal morphology of the nervous system and its functional aspects. In addition, it ensured a greater understanding of the subject allowing a better understanding of the microscopic view of the cells. Because the injury that can occur to these cells and tissues influences the quality of life and well-being of the affected individual.

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<sup> [# $ sg2_dp11] [1] </a> </ sup> Student. Academic of Medicine of the Federal University of Rio de Janeiro Campus Macaé (UFRJ)

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