The spinal cord is a long, tubular structure made up of nervous tissue, that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord; the brain and spinal cord together make up the central nervous system. In humans, the spinal cord begins at the occipital bone where it passes through the foramen magnum, meets and enters the spinal canal at the beginning of the cervical vertebrae; the spinal cord extends down to between the second lumbar vertebrae where it ends. The enclosing bony vertebral column protects the shorter spinal cord, it is around 45 cm in men and around 43 cm long in women. The spinal cord has a varying width, ranging from 13 mm thick in the cervical and lumbar regions to 6.4 mm thick in the thoracic area. The spinal cord functions in the transmission of nerve signals from the motor cortex to the body, from the afferent fibers of the sensory neurons to the sensory cortex, it is a center for coordinating many reflexes and contains reflex arcs that can independently control reflexes.
It is the location of groups of spinal interneurons that make up the neural circuits known as central pattern generators. These circuits are responsible for controlling motor instructions for rhythmic movements such as walking; the spinal cord is the main pathway for information connecting the brain and peripheral nervous system. Much shorter than its protecting spinal column, the human spinal cord originates in the brainstem, passes through the foramen magnum, continues through to the conus medullaris near the second lumbar vertebra before terminating in a fibrous extension known as the filum terminale, it is about 45 cm long in men and around 43 cm in women, ovoid-shaped, is enlarged in the cervical and lumbar regions. The cervical enlargement, stretching from the C5 to T1 vertebrae, is where sensory input comes from and motor output goes to the arms and trunk; the lumbar enlargement, located between L1 and S3, handles sensory input and motor output coming from and going to the legs. The spinal cord is continuous with the caudal portion of the medulla, running from the base of the skull to the body of the first lumbar vertebra.
It does not run the full length of the vertebral column in adults. It is made of 31 segments from which branch one pair of sensory nerve roots and one pair of motor nerve roots; the nerve roots merge into bilaterally symmetrical pairs of spinal nerves. The peripheral nervous system is made up of these spinal roots and ganglia; the dorsal roots are afferent fascicles, receiving sensory information from the skin and visceral organs to be relayed to the brain. The roots terminate in dorsal root ganglia, which are composed of the cell bodies of the corresponding neurons. Ventral roots consist of efferent fibers that arise from motor neurons whose cell bodies are found in the ventral gray horns of the spinal cord; the spinal cord are protected by three layers of tissue or membranes called meninges, that surround the canal. The dura mater is the outermost layer, it forms a tough protective coating. Between the dura mater and the surrounding bone of the vertebrae is a space called the epidural space; the epidural space is filled with adipose tissue, it contains a network of blood vessels.
The arachnoid mater, the middle protective layer, is named for its spiderweb-like appearance. The space between the arachnoid and the underlying pia mater is called the subarachnoid space; the subarachnoid space contains cerebrospinal fluid, which can be sampled with a lumbar puncture, or "spinal tap" procedure. The delicate pia mater, the innermost protective layer, is associated with the surface of the spinal cord; the cord is stabilized within the dura mater by the connecting denticulate ligaments, which extend from the enveloping pia mater laterally between the dorsal and ventral roots. The dural sac ends at the vertebral level of the second sacral vertebra. In cross-section, the peripheral region of the cord contains neuronal white matter tracts containing sensory and motor axons. Internal to this peripheral region is the grey matter, which contains the nerve cell bodies arranged in the three grey columns that give the region its butterfly-shape; this central region surrounds the central canal, an extension of the fourth ventricle and contains cerebrospinal fluid.
The spinal cord is elliptical in cross section, being compressed dorsolaterally. Two prominent grooves, or sulci, run along its length; the posterior median sulcus is the groove in the dorsal side, the anterior median fissure is the groove in the ventral side. The human spinal cord is divided into segments. Six to eight motor nerve rootlets branch out of right and left ventro lateral sulci in a orderly manner. Nerve rootlets combine to form nerve roots. Sensory nerve rootlets form off right and left dorsal lateral sulci and form sensory nerve roots; the ventral and dorsal roots combine to form one on each side of the spinal cord. Spinal nerves, with the exception of C1 and C2, form inside the intervertebral foramen; these rootlets form the demarcation between the peripheral nervous systems. The grey column, in the center of the cord, is shaped like a butterfly and consists of cell bodies of interneurons, motor neurons, neuroglia cells and unmyelinated axons; the anterior and posterior grey column present as projections of the grey matter and are known as the horns of the spinal cord.
Together, the gr
A Rosenthal fiber is a thick, worm-like or "corkscrew" eosinophilic bundle, found on H&E staining of the brain in the presence of long-standing gliosis, occasional tumors, some metabolic disorders. Its presence is associated with Alexander's disease, they are seen in the context of fucosidosis. Pilocytic astrocytoma is the most common primitive tumor in pediatric patients; the fibers are found in astrocytic processes and are thought to be clumped intermediate filament proteins. Their components include glial fibrillary acidic protein. Neuropathology Mini-Course. Chapter 9 - Tumors of the Nervous System Doctor's Doctor - Brain and Spinal Cord Isolation of a major protein component of Rosenthal fibers
Glial fibrillary acidic protein
Glial fibrillary acidic protein is a protein, encoded by the GFAP gene in humans. Glial fibrillary acidic protein is an intermediate filament protein, expressed by numerous cell types of the central nervous system including astrocytes and ependymal cells during development. GFAP has been found to be expressed in glomeruli and peritubular fibroblasts taken from rat kidneys Leydig cells of the testis in both hamsters and humans, human keratinocytes, human osteocytes and chondrocytes and stellate cells of the pancreas and liver in rats. First described in 1971, GFAP is a type III IF protein that maps, in humans, to 17q21, it is related to its non-epithelial family members, vimentin and peripherin, which are all involved in the structure and function of the cell’s cytoskeleton. GFAP is thought to help to maintain astrocyte mechanical strength, as well as the shape of cells but its exact function remains poorly understood, despite the number of studies using it as a cell marker. Glial fibrillary acidic protein was named and first isolated and characterized by Lawrence F. Eng in 1969.
Type III intermediate filaments contain three domains, named the head and tail domains. The specific DNA sequence for the rod domain may differ between different type III intermediate filaments, but the structure of the protein is conserved; this rod domain coils around that of another filament to form a dimer, with the N-terminal and C-terminal of each filament aligned. Type III filaments such as GFAP are capable of forming both heterodimers. GFAP and other type III IF proteins cannot assemble with keratins, the type I and II intermediate filaments: in cells that express both proteins, two separate intermediate filament networks form, which can allow for specialization and increased variability. To form networks, the initial GFAP dimers combine to make staggered tetramers, which are the basic subunits of an intermediate filament. Since rod domains alone in vitro do not form filaments, the non-helical head and tail domains are necessary for filament formation; the head and tail regions have greater variability of structure.
In spite of this increased variability, the head of GFAP contains two conserved arginines and an aromatic residue that have been shown to be required for proper assembly. GFAP is expressed in the central nervous system in astrocyte cells, it is involved in many important CNS processes, including cell communication and the functioning of the blood brain barrier. GFAP has been shown to play a role in mitosis by adjusting the filament network present in the cell. During mitosis, there is an increase in the amount of phosphorylated GFAP, a movement of this modified protein to the cleavage furrow. There are different sets of kinases at work; this specificity of location allows for precise regulation of GFAP distribution to the daughter cells. Studies have shown that GFAP knockout mice undergo multiple degenerative processes including abnormal myelination, white matter structure deterioration, functional/structural impairment of the blood–brain barrier; these data suggest that GFAP is necessary for many critical roles in the CNS.
GFAP is proposed to play a role in astrocyte-neuron interactions as well as cell-cell communication. In vitro, using antisense RNA, astrocytes lacking GFAP do not form the extensions present with neurons. Studies have shown that Purkinje cells in GFAP knockout mice do not exhibit normal structure, these mice demonstrate deficits in conditioning experiments such as the eye-blink task. Biochemical studies of GFAP have shown MgCl2 and/or calcium/calmodulin dependent phosphorylation at various serine or threonine residues by PKC and PKA which are two kinases that are important for the cytoplasmic transduction of signals; these data highlight the importance of GFAP for cell-cell communication. GFAP has been shown to be important in repair after CNS injury. More for its role in the formation of glial scars in a multitude of locations throughout the CNS including the eye and brain. In 2016 a CNS inflammatory disorder associated with anti-GFAP antibodies was described. Patients with GFAP astrocytopathy developed meningoencephalomyelitis with inflammation of the meninges, the brain parenchyma, the spinal cord.
About one third of cases were associated with various cancers and many expressed other CNS autoantibodies. There are multiple disorders associated with improper GFAP regulation, injury can cause glial cells to react in detrimental ways. Glial scarring is a consequence of several neurodegenerative conditions, as well as injury that severs neural material; the scar is formed by astrocytes interacting with fibrous tissue to re-establish the glial margins around the central injury core and is caused by up-regulation of GFAP. Another condition directly related to GFAP is a rare genetic disorder, its symptoms include mental and physical retardation, enlargement of the brain and head and seizures. The cellular mechanism of the disease is the presence of cytoplasmic accumulations containing GFAP and heat shock proteins, known as Rosenthal fibers. Mutations in the coding region of GFAP have been shown to contribute to the accumulation of Rosenthal fibers; some of these mutations have been proposed to be detrimental to cytoskeleton formation as well as an increase in caspase 3 activity, which would lead to increased apoptosis of cells with these mutations.
GFAP therefore plays an important role in the pathogenesis of Alexander disease. Notably, the expression of some GFAP isoforms
A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image, taken on a microscope but is only magnified less than 10 times. Micrography is the art of using microscopes to make photographs. A micrograph contains extensive details of microstructure. A wealth of information can be obtained from a simple micrograph like behavior of the material under different conditions, the phases found in the system, failure analysis, grain size estimation, elemental analysis and so on. Micrographs are used in all fields of microscopy. A light micrograph or photomicrograph is a micrograph prepared using an optical microscope, a process referred to as photomicroscopy. At a basic level, photomicroscopy may be performed by connecting a camera to a microscope, thereby enabling the user to take photographs at reasonably high magnification. Scientific use began in England in 1850 by Prof Richard Hill Norris FRSE for his studies of blood cells.
Roman Vishniac was a pioneer in the field of photomicroscopy, specializing in the photography of living creatures in full motion. He made major developments in light-interruption photography and color photomicroscopy. Photomicrographs may be obtained using a USB microscope attached directly to a home computer or laptop. An electron micrograph is a micrograph prepared using an electron microscope. Micrographs have micron bars, or magnification ratios, or both. Magnification is a ratio between the size of an object on its real size. Magnification can be a misleading parameter as it depends on the final size of a printed picture and therefore varies with picture size. A scale bar, or micron bar, is a line of known length displayed on a picture; the bar can be used for measurements on a picture. When the picture is resized the bar is resized making it possible to recalculate the magnification. Ideally, all pictures destined for publication/presentation should be supplied with a scale bar. All but one of the micrographs presented on this page do not have a micron bar.
The microscope has been used for scientific discovery. It has been linked to the arts since its invention in the 17th century. Early adopters of the microscope, such as Robert Hooke and Antonie van Leeuwenhoek, were excellent illustrators. After the invention of photography in the 1820s the microscope was combined with the camera to take pictures instead of relying on an artistic rendering. Since the early 1970s individuals have been using the microscope as an artistic instrument. Websites and traveling art exhibits such as the Nikon Small World and Olympus Bioscapes have featured a range of images for the sole purpose of artistic enjoyment; some collaborative groups, such as the Paper Project have incorporated microscopic imagery into tactile art pieces as well as 3D immersive rooms and dance performances. Close-up Digital microscope Macro photography Microphotograph Microscopy USB microscope Make a Micrograph – This presentation by the research department of Children's Hospital Boston shows how researchers create a three-color micrograph.
Shots with a Microscope – a basic, comprehensive guide to photomicrography Scientific photomicrographs – free scientific quality photomicrographs by Doc. RNDr. Josef Reischig, CSc. Micrographs of 18 natural fibres by the International Year of Natural Fibres 2009 Seeing Beyond the Human Eye Video produced by Off Book - Solomon C. Fuller bio Charles Krebs Microscopic Images Dennis Kunkel Microscopy Andrew Paul Leonard, APL Microscopic Cell Centered Database - Montage Nikon Small World Olympus Bioscapes Other examples
Nervous tissue called neural tissue or nerve tissue, is the main tissue component of the nervous system. The nervous system regulates and controls bodily functions and activity and consists of two parts: the central nervous system comprising the brain and spinal cord, the peripheral nervous system comprising the branching peripheral nerves, it is composed of neurons, or nerve cells, which receive and transmit impulses, neuroglia known as glial cells or glia, which assist the propagation of the nerve impulse as well as provide nutrients to the neurons. Nervous tissue is made up of different types of nerve cells. An axon is the long stem-like part of the cell. Bundles of axons make up the nerves in the PNS and tracts in the CNS. Functions of the nervous system are sensory input, control of muscles and glands and mental activity. Nervous tissue is composed of neurons called nerve cells, neuroglial cells. Four types of neuroglia found in the CNS are astrocytes, microglial cells, ependymal cells and oligodendrocytes.
Two types of neuroglia found in the PNS are Schwann cells. In the central nervous system, the tissue types found are white matter; the tissue is categorized by its neuroglial components. Neurons are cells with specialized features that allow them to receive and facilitate nerve impulses, or action potentials, across their membrane to the next neuron, they possess a large cell body, with cell projections called an axon. Dendrites are thin, branching projections that receive electrochemical signaling to create a change in voltage in the cell. Axons are long projections that carry the action potential away from the cell body toward the next neuron; the bulb-like end of the axon, called the axon terminal, is separated from the dendrite of the following neuron by a small gap called a synaptic cleft. When the action potential travels to the axon terminal, neurotransmitters are released across the synapse and bind to the post-synaptic receptors, continuing the nerve impulse. Neurons are classified both structurally.
Functional classification: Sensory neurons: Relay sensory information in the form of an action potential from the PNS to the CNS Motor neurons: Relay an action potential out of the CNS to the proper effector Interneurons: Cells that form connections between neurons and whose processes are limited to a single local area in the brain or spinal cordStructural classification: Multipolar neurons: Have 3 or more processes coming off the soma. They include interneurons and motor neurons. Bipolar neurons: Sensory neurons that have two processes coming off the soma, one dendrite and one axon Pseudounipolar neurons: Sensory neurons that have one process that splits into two branches, forming the axon and dendrite Unipolar brush cells: Are excitatory glutamatergic interneurons that have a single short dendrite terminating in a brush-like tuft of dendrioles; these are found in the granular layer of the cerebellum. Neuroglia encompasses the non-neural cells in nervous tissue that provide various crucial supportive functions for neurons.
They are smaller than neurons, vary in structure according to their function. Neuroglial cells are classified as follows: Microglial cells: Microglia are macrophage cells that make up the primary immune system for the CNS, they are the smallest neuroglial cell. Astrocytes: Star-shaped macroglial cells with many processes found in the CNS, they are the most abundant cell type in the brain, are intrinsic to a healthy CNS. Oligodendrocytes: CNS cells with few processes, they form myelin sheaths on the axons of a neuron, which are lipid-based insulation that increases the speed at which the action potential, can travel down the axon. NG2 glia: CNS cells that are distinct from astrocytes and microglia, serve as the developmental precursors of oligodendrocytes Schwann cells: The PNS equivalent of oligodendrocytes, they help maintain axons and form myelin sheaths in the PNS. Satellite glial cell: Line the surface of neuron cell bodies in ganglia Enteric glia: Found in the enteric nervous system, within the gastrointestinal tract.
In the central nervous system: Grey matter is composed of cell bodies, unmyelinated axons, protoplasmic astrocytes, satellite oligodendrocytes and few myelinated axons. White matter is composed of myelinated axons, fibrous astrocytes, myelinating oligodendrocytes, microglia. In the Peripheral Nervous System: Ganglion tissue is composed of cell bodies and satellite glial cells. Nerves are composed of myelinated and unmyelinated axons, Schwann cells surrounded by connective tissue; the three layers of connective tissue surrounding each nerve are: Endoneurium. Each nerve axon, or fiber is surrounded by the endoneurium, called the endoneurial tube, channel or sheath; this is a thin, protective layer of connective tissue. Perineurium; each nerve fascicle containing one or more axons, is enclosed by the perineurium, a connective tissue having a lamellar arrangement in seven or eight concentric layers. This plays a important role in the protection and support of the nerve fibers and serves to prevent the passage of large molecules from the epineurium into a fascicle.
Epineurium. The epineurium is the outermost layer of dense connective tissue enclosing the nerve; the function of nervous tissue is to form the communication network
Astrocytes known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. The proportion of astrocytes in the brain is not well defined. Depending on the counting technique used, studies have found that the astrocyte proportion varies by region and ranges from 20% to 40% of all glia, they perform many functions, including biochemical support of endothelial cells that form the blood–brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, a role in the repair and scarring process of the brain and spinal cord following traumatic injuries. Research since the mid-1990s has shown that astrocytes propagate intercellular Ca2+ waves over long distances in response to stimulation, similar to neurons, release transmitters in a Ca2+-dependent manner. Data suggest that astrocytes signal to neurons through Ca2+-dependent release of glutamate; such discoveries have made astrocytes an important area of research within the field of neuroscience.
Astrocytes are a sub-type of glial cells in the central nervous system. They are known as astrocytic glial cells. Star-shaped, their many processes envelop synapses made by neurons. Astrocytes are classically identified using histological analysis. Several forms of astrocytes exist in the central nervous system including fibrous and radial; the fibrous glia are located within white matter, have few organelles, exhibit long unbranched cellular processes. This type has "vascular feet" that physically connect the cells to the outside of capillary walls when they are in proximity to them; the protoplasmic glia are the most prevalent and are found in grey matter tissue, possess a larger quantity of organelles, exhibit short and branched tertiary processes. The radial glial cells are disposed in planes perpendicular to the axes of ventricles. One of their processes abuts the pia mater, while the other is buried in gray matter. Radial glia are present during development, playing a role in neuron migration.
Müller cells of the retina and Bergmann glia cells of the cerebellar cortex represent an exception, being present still during adulthood. When in proximity to the pia mater, all three forms of astrocytes send out processes to form the pia-glial membrane. Astrocytes are macroglial cells in the central nervous system. Astrocytes are derived from heterogeneous populations of progenitor cells in the neuroepithelium of the developing central nervous system. There is remarkable similarity between the well known genetic mechanisms that specify the lineage of diverse neuron subtypes and that of macroglial cells. Just as with neuronal cell specification, canonical signaling factors like Sonic hedgehog, Fibroblast growth factor, WNTs and bone morphogenetic proteins, provide positional information to developing macroglial cells through morphogen gradients along the dorsal–ventral, anterior–posterior and medial–lateral axes; the resultant patterning along the neuraxis leads to segmentation of the neuroepithelium into progenitor domains for distinct neuron types in the developing spinal cord.
On the basis of several studies it is now believed that this model applies to macroglial cell specification. Studies carried out by Hochstim and colleagues have demonstrated that three distinct populations of astrocytes arise from the p1, p2 and p3 domains; these subtypes of astrocytes can be identified on the basis of their expression of different transcription factors and cell surface markers. The three populations of astrocyte subtypes which have been identified are 1) dorsally located VA1 astrocytes, derived from p1 domain, express PAX6 and reelin 2) ventrally located VA3 astrocytes, derived from p3, express NKX6.1 and SLIT1 and 3) and intermediate white-matter located VA2 astrocyte, derived from the p2 domain, which express PAX6, NKX6.1, reelin and SLIT1. After astrocyte specification has occurred in the developing CNS, it is believed that astrocyte precursors migrate to their final positions within the nervous system before the process of terminal differentiation occurs. In medical science, the neuronal network was considered the only important function of astrocytes, they were looked upon as gap fillers.
More the function of astrocytes has been reconsidered, they are now thought to play a number of active roles in the brain, including the secretion or absorption of neural transmitters and maintenance of the blood–brain barrier. Following on this idea the concept of a tripartite synapse has been proposed, referring to the tight relationship occurring at synapses among a presynaptic element, a postsynaptic element and a glial element. Structural: They are involved in the physical structuring of the brain. Astrocytes get their name because they are "star-shaped", they are the most abundant glial cells in the brain that are associated with neuronal synapses. They regulate the transmission of electrical impulses within the brain. Glycogen fuel reserve buffer: Astrocytes contain glycogen and are capable of gluconeogenesis; the astrocytes next to neurons in hippocampus store and release glucose. Thus, astrocytes can fuel neurons with glucose during periods of high rate of glucose consumption and glucose shortage.
A recent research on rats suggests there may be a connection between this activity and physical exercise. Metabolic support: They provide neurons with nutrients such as lactate. Glucose sensing: associated w