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Clinical Anatomy. Applied anatomy for students and junior doctors. Harold Ellis. ELEVENTH EDITION. SOFTbank E-Book Center Tehran, Phone: Library of Congress Cataloging-in-Publication Data Snell, Richard S. Clinical anatomy by regions / Richard S. Snell. – 9th ed. p. ; cm. Includes index. Anatomy one of the most difficult subject in the medical world. One can not easily remember structures, bones name, muscle names.

Olson should be commended for an excellent fast effort. I highly recommend this book for physicians who must care for patients exposed to toxins and for anyone interested in a well-written, concise overview of toxicologic principles. Edward J. By Richard S. Snell, MD, tw, and Mark S. Smith, MD.

The tail of sperm consists of a very long cilium called flagellum. It encircles the entire cell like a belt. It merges with surrounding connective tissue. Stereocilia are found in sites where fluid secretion and resorption take place.. It is visible under the electron microscope. The basal lamina of the basement membrane provides a barrier between the underlying connective tissue and the epithelial cells.

The cells exhibit two domains. It is composed of reticular tissue. Desmosome macula adherens is punctate or spot-like in appearance on light microscopy. Gap junction nexus is seen only by electron microscope. Its ground substance consists mainly of laminin. It means that the cells have free apical surface and basal surface directed towards basement membrane. It is synthesized by fibroblasts.. The chemical components of plasma membranes are different in the two domains as per the functional requirements.

The patients suffer from respiratory symptoms caused by the accumulation of dust and other particulate matter inhaled from atmospheric air Structural Specializations for Absorptive Functions i.

Clinical insight. Basement Membrane in Diseases i. Structural Specialization for Protection The cilia are present in epithelia. Basement Membrane The basement membrane is a structure that supports the epithelium. Chapter Polarity The basal lamina is composed of type IV collagen fibers. The basement membrane thickens in pathologic conditions like nephropathies kidney diseases and Contd.

Cell Junctions Intercellular contact is served by means of intercellular junctions. Under the light microscope. Microvilli are the infoldings of apical plasma membrane to increase the surface area. The gap junctions allow passage of small molecules between neighboring cells and thus allow cell to cell communication. The cancer cells from adenocarcinona developing from epithelium invade the basement membrane to spread outside the primary site.. The cilia project from the apical surface of the cells from the basal bodies.

Functions of Basement Membrane i. The basal lamina is the layer in contact with the epithelial cells which synthesize it. They are visible under electron microscope. The basal lamina can filter noncellular materials. The reticular lamina is visible in sections prepared for light microscopy. In the kidneys. The hemidesmosomes spot like in appearance attach the epithelial cells to the basement membrane. The reticular lamina is the deeper layer. Tight junction zonula occludens is located close to the luminal surface of the epithelium.

It forms an effective barrier of paracellular absorption in the absorptive epithelia and in transitional epithelium. The stereocilia are long microvilli but are non-motile. On lateral surface of the cells. When examined under electron microscope it shows two distinct layers. It also encircles the entire cell. The cells of intestinal epithelium have very high rate of mitosis. It lines the gall bladder.

The mesoderm gives origin to endothelium lining the blood vessels.. It consists of multiple layers of cells of which superficial cells are flat squamous and basal cells are cuboidal in shape. A thickened basement membrane is visible under light microscope with routine haematoxylin and eosin staining. There are shorter and taller cells. Thus it is clear that young cell population is in the basal layers and the oldest cells are in the superficial layers. Classification of Epithelium The epithelium is classified according to the number of cell layers into simple epithelium and compound or stratified epithelium.

An intact basement membrane is an indication that the cancer is localized to the primary site. While examining the tissue biopsy from primary site of cancer arising from epithelium epithelioma. The intervening rows of cells are polyhedral. The endoderm gives origin to epithelium of gastrointestinal tract and of respiratory tract including lung alveoli.

The taller cells bear cilia. The function of this epithelium is diffusion of gases and fluids.. All cells rest on basement membrane but the nuclei of the cells are at varying levels giving false impression of stratification.

Cell Turn Over The epithelial cells undergo mitosis to renew old cells. The epithelium is derived from endoderm. Pseudostratified ciliated columnar with goblet cells lines the respiratory tract from nasal cavity to intrapulmonary bronchi.

The ectoderm gives origin to the epidermis. In this epithelium. Simple Epithelium i. The stratified compound epithelium is composed of more than one layer of cells stacked on each other.

Nourishment The epithelium is avascular. Simple columnar ciliated epithelium is found in uterine tube and uterus. This epithelium also known as respiratory epithelium is suited for respiratory passages as the cilia dispel the foreign particles inhaled in the air and the mucus secreted by goblet cells traps the foreign particles not dispelled by cilia.

It forms the moist surfaces that are protective in function. There is migration and gradual transformation of new cells into polyhedral cells and finally into flat cells. The simple epithelium is composed of a single layer of cells resting on a basement membrane. Simple columnar epithelium is composed of columnar cells. At places. Embryologic insight. It is composed of a row of cube shaped cells resting on the basement membrane. It is characterized by keratinization of superficial cells.

The basal cells are capable of mitosis to produce new cells. Simple columnar epithelium with goblet cells is found in small and large intestines. This is known as cell turn over.

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If the basement membrane is broken it is an indication that cancer cells have begun spreading from the primary site. The cells in all layers have nuclei. Simple cuboidal epithelium lines the thyroid follicles.

Its function is to provide protection against abrasion. Stratified squamous keratinized epithelium is found in epidermis of skin. Stratified squamous non-keratinized epithelium is found in cornea. Stratified Epithelium i. Simple squamous epithelium lines the lung alveoli. Stratified columnar epithelium lines the spongy part of male urethra and the main ducts of large salivary glands and large ducts of mammary glands. Serous-watery fluid containing protein example parotid and lacrimal glands ii.

Under the light microscope it shows cuboidal basal cells. The exocrine glands consist of secretory units which synthesize secretion and ducts by which they let out their secretion. It is structurally adapted to provide a permeability barrier to water and salts in urine. Classification of Exocrine Glands According to number of cells i. The surface cells which are exposed to the urine are large and facetted umbrella cells.

Depending on the type of secretion i. In chronic vitamin A deficiency transitional epithelium of urinary bladder may change into stratified squamous variety. Apocrine in which the secretory product accumulates in apical cytoplasm and is expelled out by pinching of the apical plasma membrane e. Depending on the shape of the secretory units i. The fusiform vesicles along with plaques merge into the surface plasma membrane providing a reserve membrane during stretching.

Multicellular e. Holocrine in which the cell after filling with secretory product dies and is expelled along with its contents e. Alveolar or acinar if secretory units are shaped like small bags iii Tubulo-alveolar combination of the above two shapes 3. In the undistended state. Mixed example. The apical cytoplasm contains microfilaments and fusiform membrane bound vesicles enclosing uroplakin plaques.

The seminiferous epithelium in the testis is also regarded as a special type of stratified cuboidal epithelium. Depending on the mode of their secretion i. The endocrine glands release secretion hormone directly into blood capillaries. The cells in middle layers are polygonal or rounded.. Unicellular e. Glandular Epithelium The glands may consist of a single cell or aggregations of epithelial cells specialized for secretory function. From the basal to the superficial aspect.

Metaplasia Transformation of one type of epithelial tissue into another type is known as metaplasia or metaplastic change. It lines the renal calyces. Chapter drying. Simple tubular or coiled tubular when the secretory units are shaped like small tubes ii. In the distended state. In cigarette smokers. Stratified cuboidal epithelium lines the ducts of sweat glands.

The stratified squamous epithelium of esophagus may change into simple columnar with goblet cells intestinal type in a condition called Berret esophagus which may lead to cancer.

The death of the cells to produce secretion is called apoptosis programmed cell death. Subtypes of Multicellular Exocrine Glands 1. Mucous-viscous secretion containing mucus example. There are several layers of columnar cells. Depending on duct pattern i. Transitional epithelium is a special type of epithelium lining the urinary passages. Merocrine eccrine in which secretory product is expelled out by exocytosis e. Their luminal surface is covered with modified plasma membrane.

This epithelium in the thick or glabrous skin of palms and soles is composed of five layers. It consists of two layers of cuboidal cells. On light microscopy. Chemically the ground substance is mainly composed of glycosaminoglycans GAG. The pigment cells or melanocytes of connective tissue are found in iris and choroid layer of eyeball. It is here that collagen fibrils are polymerized to form collagen fibers in the extracellular compartment.

Their cytoplasm is filled with basophilic granules. Basic Components The connective tissue consists of three basic components: Their main function is phagocytosis by ingestion of foreign substances. The surfaces of active fibroblasts show characteristic scalloping coves.

The ground substance is amorphous and transparent having the properties of a viscous solution or a highly hydrated thin gel. Ground Substance The connective tissue is composed of abundant ground substance. Fibers collagen. Migrant Cells i. The fat droplet stains orange on staining with Sudan III. They are characterized by well-developed rough endoplasmic reticulum accounting for basophilic cytoplasm. They are large in size. The mast cells increase their number in allergic or hypersensitivity reactions.

The mast cells are usually found in close relation to the blood vessels. The fibroblasts are the most common type. They are firm and do not stretch. It is widely distributed in the body. A special type of fibroblast known as myofibroblast shows properties of both fibroblast and smooth muscle cell.

The granules contain histamine vasoactive agent. Intercellular material or ground substance or matrix iii.

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Connective Tissue Fibers Collagen Fibers The collagen fibers are the white fibers of connective tissue. In inflammation of any organ it is the connective tissue that acts as a battle ground for the infecting agents and immune cells of the connective tissue.

They develop from monocytes of the circulating blood. The connective tissue cells and fibres are embedded into it. The fibroblasts are metabolically very active cells as they synthesize the three types of fibers and the ground substance.

They provide. On routine staining. The eccentrically placed nucleus has characteristic cart wheel or clock face appearance due to distribution of the chromatin in the form of four or five clumps subjacent to nuclear envelope. The myofibroblasts play a significant role in wound contraction during healing. This appearance resembles a signet ring.

The plasma cells are derived from the B lymphocytes. Water or tissue fluid might accumulate in the extracellular spaces in case of venous stasis or lymphatic stasis causing edema.

The plasma cells produce antibodies. They are stellate or spindle-shaped cells with little cytoplasm. The lipid droplet is so large that it pushes the cytoplasm and the nucleus to the periphery of the cell. They store neutral fat triglycerides in the form of a single lipid droplet in their cytoplasm.

The adipocytes or lipocytes or fat cells are large in size average size 50 microns. Connective tissue cells both resident and wandering ii.

The impaired structure and function of the connective tissue result in some disorders of connective tissue. The macrophages are also known as histiocytes. The electron microscopic appearance of fibroblasts reveals characteristics of protein secreting cells. The ground substance allows free exchange of nutrients and gases between the cells of tissues and the blood in the capillaries.

These large cells have round nuclei and abundant acidophilic cytoplasm rich in lysosomes. The white blood cells that are found in connective tissue are the lymphocytes. They develop from embryonic mesenchymal cells. The mast cell granules on staining show metachromasia. They show irregular contours or ruffles of plasma membrane.

The Golgi complex is pale on regular staining. Schwann cells and epithelial cells. The collagen fibers are composed of a protein called collagen. The tropocollagen molecules aggregate to form collagen fibrils. Here the lysine and proline are hydroxylated Contd. Steps in intracellular and extracellular synthesis of collagen Chapter tensile strength to the tissues their strength is comparable to that of steel cables.

The polypeptide chains coil around each other to form a triple helix except at the terminals where th chain remains uncoiled. Extracellular Synthesis of Collagen Fig. They appear pink on staining with eosin. The collagen fibers are visible on light microscopy. The proline. Genetic Disorders of Collagen Synthesis Defective collagen encoding genes cause autoimmune disorders in which immune responses destroy the collagen fibers. The soluble procollagen is converted into nonsoluble tropocollagen by cutting the uncoiled terminals.

The packaging of procollagen molecules takes place in Golgi apparatus for transportation out of the cells. The deficiency of vitamin C scurvy with resultant defective collagen leads to widespread effects like bleeding gums. Examples of autoimmune disorders are rheumatoid arthritis and osteogenesis imperfecta. The collagen is also secreted by non connective tissue cells like smooth muscle cells. Intracellular Synthesis of Procollagen Fig. Clinical insight.. This forms the soluble procollagen molecules.

The collagen fibers aggregate into wavy bundles. Individual fibers do not branch.. Biosynthesis and Secretion of Collagen The collagen is secreted by fibroblasts in connective tissue.

They are mainly produced by fibroblast but other cells like reticular cells in bone marrow and lymphoid tissues. The structures that are rich in elastic fibers tunica media of aorta. They are produced by fibroblasts.

Yellow Elastic Tissue This tissue is composed predominantly of elastic fibers. It is subdivided into two types. Type II fibers are found in hyaline and elastic cartilages and cornea. They occur in loose areolar tissue. This is found in ligamenta flava which connect the laminae of adjacent vertebrae. Dense connective tissue iii. They are composed of an amorphous core of elastin. Yellow elastic tissue iv. This tissue is rich in ground substance and poor in fibers and connective tissue cells.

They are designated by Roman numerals according to their order of discovery. Because of their affinity to silver salts the reticular fibres are called argyrophilic fibers. Loose or areolar connective tissue ii. The type I are widely distributed in the body. They occur in spleen. Type III fibers are reticular fibers.

Reticular Tissue The reticular tissue is a network of reticular fibers and fibroblasts and reticular cells subtype of fibroblasts. It lies underneath the epithelia forming lamina propria of mucous membranes and in submucosa of hollow organs. Adipose tissue vi. The individual fibers branch and anastomose. They are smallest and very delicate. Dense Connective Tissue This type is composed predominantly of collagen fibers.

It is found in reticular layer of dermis. Loose Connective Tissue This type is the most abundant connective as it forms stroma of the organs and tunica adventitia of blood vessels. A tendon consists of parallel collagen fibers and fibroblasts. They stain poorly with ordinary hematoxylin and eosin stains. Myxomatous connective tissue embryonic connective tissue Elastic Fibers The elastic fibers impart elasticity to the tissues.

They are the main component of reticular lamina of basement membranes. The dense regular connective tissue is characterized by densely arranged fibers. The reticular fibers give support to the nerve fibers. Reticular connective tissue v. With silver stains they appear black.

Type I fibers are found in fascia. The collagen fibers are regularly oriented and are arranged in bundles. The regular dense connective tissue is found in tendons. Type I to type IV fibers are very common. A longitudinal section of tendon consists of bundles of collagen fibers and parallel rows of elongated nuclei of fibroblasts that are compressed between collagen fibers. The patients are liable to develop aortic aneurysm.

The elastic fibers do not form bundles. They are highly refractile. The dense irregular connective tissue is characterized by many collagen and elastic fibers running in irregular orientation.

The tendons attach the muscle belly to the bone or cartilage. Myxomatous mucoid Connective Tissue It is characterized by abundant ground substance. Adipose Tissue Types of Muscle Tissue The adipose or fatty tissue contains a collection of fat cells adipocytes.

They differ in distribution.. They have the potential to differentiate into myofibroblasts and fibroblast and can give rise to new blood vessels.

Each muscle fiber is encircled by a delicate connective tissue covering called endomysium. The brown adipose tissue is more widely distributed in fetuses and newborn. They are described as voluntary as they contract under the influence of motor neurons of somatic nervous system or in other words. The nucleus is in the cell center and cell organelles are spread out in the cytoplasm. The white adipose tissue is found in adult and the brown adipose tissue is found in fetus and newborn..

Numerous muscle fibers aggregate and are held together by means of well-organized connective tissue to form muscle bundles or fascicles. The main function of the muscle is contraction to perform mechanical work like locomotion. The adipose tissue is of two types. Microscopic Structure of Muscle Fiber The muscle fiber is an elongated multinucleate syncytium.

There are numerous mitochondria. The fibers are hardly visible and fibroblasts assume star shape. It provides warmth. The myofibroblasts are modified fibroblasts involved in wound healing. The connective tissue provides routes for the nerves and blood vessels to reach the individual muscle fiber.

The cell nucleus is flat and pushed by the lipid droplet to the periphery. The flattened nuclei Chapter provides a soft structural framework to support the cells of lymph nodes. The pericytes are small fusiform cells around the capillaries and venules. Each bundle is covered by another connective tissue covering called perimysium. In the fetus. The brown adipose cells brown adipocytes are small polygonal cells and are called multilocular because their cytoplasm is filled with multiple lipid droplets.

These proteins are filamentous in nature and hence. In addition. They are myoepihelial cells. In adult. Skeletal muscle ii.

The myoepithelial cells are found around the secretory units in salivary gland. Smooth muscle. The white adipose cells white adipocytes are larger in size and are called unilocular because their cytoplasm is filled by a single large lipid droplet. There are other contractile cells in the body not belonging to muscular tissue but having actin and myosin filaments. The mitochondria are few in number and are dispersed in the peripheral rim of cytoplasm.

The muscle fibers aggregate to form a muscle. They are also known as striated because their cells show cross striations when examined under a light microscope.

In the adult. The jelly like viscous ground substance is rich in hyaluronic acid. In response to their functions. It functions as store house of energy. Its cytoplasm is called sarcoplasm and plasma membrane is called sarcolemma. Many such bundles are held together to form a muscle like for example deltoid muscle by an outer common connective tissue covering called epimysium.

Cardiac muscle iii. The white fat is widely distributed in the subcutaneous tissue in the body. Organization of Muscle Fibers in a Skeletal Muscle The basic unit of a muscle is a long muscle cell called muscle fiber. There are three types of muscular tissue in the body: Skeletal Muscle The skeletal muscles are so called because by and large they attach to the bones and cartilages.

The calcium ions act on actin and myosin filaments causing contraction of muscle. The thoracodorsal nerve contains axons of anterior horn cells of C6.

I band is bisected by a thin dark line called Z line. The T tubules transmit the wave of depolarization to membranes of terminal cisternae at triads. Functions of Muscle Triad i. It is the basic contractile unit of the striated muscle. The cross striations of cardiac muscle are not as prominent as found in skeletal muscle.

The sarcoplasm is filled with structural and functional subunits of muscle fibers called myofibrils. The nucleus is centrally placed. A sarcomere is the segment of a myofibril between adjacent Z lines. A bands show light area in the middle called H band. This may be due to less number of myofibrils and more amount of cytoplasm with abundant mitochondria in cardiac myocytes. At this site. Muscle Triad The EM appearance of muscle fiber reveals that at A-I junctions of each myofibril there is a triad consisting of invaginated sarcolemma T tubule flanked on upper and lower sides by terminal cisternae of sarcoplasmic reticulum.

Nerve Supply of Skeletal Muscle and Motor Unit The nerve and the accompanying blood vessels supplying the skeletal muscle enter the muscle at a specific point called neurovascular hilum.

The muscle cells are joined end-to-end at junctional specializations called intercalated discs. The dark bands are A anisotropic bands and the light bands are I isotropic bands.

The contraction beating of the heart is initiated inherently by the pacemaker located in sinuatrial node. They branch and anastomose with myocytes of adjacent fibers. The muscle fibers are disposed parallel to each other. Electron Microscopy of Intercalated Disc The intercalated discs are located between the ends of two contiguous myocytes.

One motor neuron and the muscle fibers supplied by it constitute one motor unit. This triggers the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.

It resembles skeletal muscle structurally in having cross striations. The myofibrils are surrounded by special type of smooth endoplasmic reticulum called sarcoplasmic reticulum. The number of muscle fibers is smaller in motor units of muscles which are involved in fine and precise movements for example in extraocular muscles. C7 and C8 segments of spinal cord. When the contraction ceases. Cross Striations The characteristic cross striations of muscle fibers are due to the presence of alternating light and dark bands composed of above mentioned contractile proteins arranged in regular pattern on the myofilaments.

The T tubules carry the signals of depolarization from the surface sarcolemma into the deeper part of muscle fibers. Microscopic Structure of Cardiac Muscle Cardiac myocytes muscle cells are short uninucleated cells. It resembles smooth muscle functionally in being involuntary. They have a transverse part corresponding to the step of staircase and a longitudinal part corresponding to the connection between the two steps.

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Cardiac Muscle The cardiac muscle is present in the heart. From this we understand that one axon of anterior horn neuron supplies several muscle fibers. The branches are compactly arranged and have the same parallel orientation like the parent fiber. It functions under the control of both sympathetic and parasympathetic nerves. It also contains other cell organelles and inclusions. The fascia adherens and desmosomes are seen in the transverse part of the disc.

The information is received. In isometric contraction. Depending on the actions of the muscles. On lifting a heavy suitcase. The gap junctions are present in longitudinal part of the disc. Pennate comb like muscles are characterized by muscle fascicles that are disposed at an oblique angle to the line of contraction of the muscle. The sensory fibers of the peripheral nerves carry the external and internal sensations to the neurons or nerve cells of CNS.

Schwann cells and synapses. The flexors and extensors of carpus flexor carpi radialis and extensor carpi radialis and extensor carpi radialis longus and brevis and extensor carpi ulnaris contract simultaneously to stabilize the wrist joint when long flexor or extensor muscles of the digits contract.

In unipennate muscle. Additional Features of Skeletal Muscles 1. It occurs in the wall of blood vessels. They help to rapidly transmit force of contraction from one cell to another. They provide electrical coupling of cells. Fixator is the muscle that contracts isometrically to stabilize the prime mover. In multipennate muscle. The neurons are the Chapter gap junctions.

Microscopic Structure of Smooth Muscle The smooth muscle fibers are elongated cells with broad central part and tapering ends. There are three types of pennate muscles. The type of muscle contraction depends on whether the joint moves or not. The basic components of the nervous tissue are the neurons. The acidophilic sarcoplasm contains myofibrils. Antagonist is the term used for a muscle that opposes the action of a prime mover as exemplified by contraction of triceps brachii the extensor of elbow during flexion movement of that joint.

A network of delicate reticular fibers envelops the muscle fibers to bind the cells to each other and the gap junctions join the neighboring cells to facilitate intercellular transmission of electric impulse. Prime mover is the main muscle that performs a particular action. In this way. In isotonic contraction.

In bipennate muscle. The arrangement of muscle fibers may be different according to the functional needs. Synergist is the term used for a muscle. The oval or elongated nucleus is located in the central part of the cell. The response or the command of the CNS is taken to the effector organs muscle. The muscle fibers show remarkable variation in length depending on the site. The autonomic ganglia and nerves belong to sympathetic and parasympathetic divisions of autonomic nervous system.

The examples of fixator muscles are quadratus lumborum which fixes the 12th rib during inspiration facilitating contraction of diaphragm and rhomboid muscles fixing the scapula during overhead abduction of arm. Bipolar Neurons Fig. They are specialized for reception of stimuli. The neuroglia cells serve to support the neurons and their processes in CNS while Schwann cells and satellite cells serve similar function in PNS.

It contains a euchromatic in which chromatin is uncoiled and active and vesicular nucleus with prominent nucleolus. The neurons are arrested in Go phase of cell cycle. They are involved in protein synthesis. Microscopic Structure of Multipolar Neuron The body of neuron is called perikaryon. Neurons give off radiating processes from their cell bodies. Upper motor neurons UMN belong to CNS as their cell bodies are located in the motor area of cerebral cortex and their long axons become the corticospinal fibers.

Multipolar Neurons Fig. Their axons leave the CNS to supply the skeletal muscles via peripheral nerve. These fibers terminate on anterior horn cells of Fig. The absence of centriole is responsible for inability of the neurons to divide.

Their cell bodies are located in ventral horn of spinal cord and in cranial nerve nuclei in brainstem. The synapse is a site of close contact between two neurons for easy transmission of information from neuron-to-neuron.

It is found only in the early stages of embryonic development. Sensory neurons receive stimuli from external and internal environment. Classification of Neurons According to the Number of Processes Unipolar Neuron A neuron with a single process is called unipolar neuron.

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They are found in retina. These neurons are found in sensory ganglia of dorsal roots of spinal nerves and cranial nerves also called dorsal root ganglia.

The giant pyramidal cell of Betz is an example of UMN. Types of neurons depending on the number of cell processes Note multipolar neuron with one axon but large number of dendrites.

They are found in gray matter of central nervous system spinal cord. The Nissl bodies are basophilic and are dispersed through out the cytoplasm and in the dendrites but absent in axon hillock and axon. Pseudounipolar Neurons Fig. The area of cell body that gives origin to axon is called axon hillock. The neurons of the mesencephalic nucleus of trigeminal nerve belong to this category. These processes are of two types. According to the Location of Neuronal Cell Body i.

Motor neurons conduct impulses to skeletal muscles neurons of ventral horn of spinal cord. The cytoplasm shows characteristic Nissl bodies rough endoplasmic reticulum studded with ribosomes.

Lipid rich plasma membranes of oligodendrocytes in CNS for example in optic nerve and Schwann cells in PNS for example in sciatic nerve tightly wrap around the axon several times with the help of mesaxon by which the axon is suspended from the plasma membrane surrounding it.

Schwann cells lemnocytes or peripheral glia are derived from neural crest. The node of Ranvier or nodal gap denotes the limit of adjacent Schwann cells.

The axons transmit action potential. This forms the myelin sheath. Axons are either myelinated or nonmyelinated. Axons terminate by forming synapses with other neurons.

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Ependymoma is the tumor arising from ependymal cells. They regulate ionic milieu in CNS. Myelin sheath is interrupted at regular intervals at nodes of Ranvier in the peripheral nerve. Tumors of Neuroglia i. Ependymal cells produce CSF in ventricles of brain. Synapse is the specialised site of interneuronal contact for cell-to-cell transmission of nerve impulse.

The synaptic vesicles release the neurotransmitter into synaptic cleft. Neuroglia cells in CNS i. Microglia are derived from mesenchymal cells.

Oligodendrocytes or Schwann cells line up in rows along the length of the axon outside the myelin sheath. Guillain Barre syndrome GBS is disorder in which the peripheral nerves lose their myelin sheath. Oligodendroglioma arises from oligodendrocytes. They myelinate nerve fibers in PNS. Schwannoma of acoustic nerve is an intracranial tumor seen at cerebellopontine angle Chapter ii. Faulty Myelination i. The glia cells play a role equivalent to connective tissue in other organ systems of the body.

Schwannoma is the growth of Schwann cells encircling peripheral nerves. There is only one axon per cell and usually it is long. All cytoplasmic contents of the cell body except the Golgi complex are present. Satellite cells capsular gliocytes are present in ganglia.

Multiple sclerosis MS is disorder of brain and spinal cord in which the oligodendrocytes undergo degeneration leading to demyelination of nerve fibers which form white matter.

Lysosomes are prominent feature of the cytoplasm. The cell bodies also contain microtubules and microfilaments for internal support. Axons arise from cell bodies at axon hillock and lack Nissl bodies. Several concentric layers of plasma membrane and its lipid around the axon give the axon an appearance of a Swiss roll.

Neuroglia Cells in PNS i. The synapse consists of three parts. Dendrites are the cell processes that are close to cell body. Oligodendrocytes with few processes are derived from neural tube. As soon as the neurotransmitter comes in contact with plasma membrane of postsynaptic neuron. They contain hydrolytic enzymes necessary for phagocytosis. They form the motor fibers of peripheral nerves. The symptoms include muscle weakness. Astrocytes fibrous and protoplasmic types are derived from neural tube.

Astrocytoma is a tumor arising from astrocytes. The terminal bouton contains vesicles filled with neurotransmitter. This results in slow transmission of nerve impulses causing muscle weakness and abnormal sensations starting in the legs and spreading towards arms and upper body.. The myelin sheath is necessary for insulation of nerve fiber so that nerve impulse can jump from node-to-node for speed of transmission saltatory conduction.

Cognitive symptoms include weak memory and low problem solving capacity. They tend to branch and are capable of forming a dendritic tree for networking with processes of other neurons. They myelinate nerve fibers in CNS. The myelinated fibers impart white color to the white matter in CNS.

The cytoplasm of axon is called axoplasm and its plasma membrane is called axolemma. They are non-neuronal cells in CNS. The glia cells are capable of mitotic cell division throughout life. Aging neurons show cell inclusions. The synaptic cleft is a narrow extracellular space between the two neurons. The matrix is. The unique feature of chondrocytes is that they retain capacity to divide and continue to secrete the matrix. Elastic cartilage iii.

The hyaline cartilage has a tendency to calcify and ossify as age advances. Once the chondroblasts are surrounded by matrix they become mature chondrocytes. By appositional process new cartilage is added to the surface of old cartilage by the cells of perichondrium. The nourishment is provided by perichondrial blood vessels by a process of diffusion through ground substance.

By interstitial process new cartilage is added internally to the old cartilage by chondrocytes. It is covered with perichondrium. It contains homogeneous matrix. The inner cellular layer contains a row of undifferentiated perichondrial cells that have a potential to turn into chondroblasts if occasion demands.

The matrix of hyaline cartilage contains type II collagen fibers. The cartilage consists of chondroblasts and chondrocytes. The outer covering of the cartilage is known as perichondrium. Just close to the perichondrium there is a layer of chondroblasts that secrete the ground substance. Histological Types of Cartilage i.

The ground substance consists of sulfated glycosaminoglycans and proteoglycans with a large proportion of hyaluronic acid. General Features i. Hyaline cartilage ii. The hyaline cartilage appears transparent like a glass. The perichondrium is composed of two layers called inner cellular and outer fibrous. It is found in the adults in nose.

The outer fibrous layer contains dense irregular connective tissue and plenty of blood vessels and sensory nerves. When chondrocytes divide. The cartilage grows by interstitial and appositional processes. The cartilage is avascular. Fibrocartilage Hyaline Cartilage It is the most commonly occurring cartilage in the body. It is basophilic and exhibits metachromasia. Contrary to our usual thinking. That is why the bone is a storehouse of calcium and phosphorous.

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This way they bring about destruction and resorption of hard Chapter divisible into territorial and intererritorial according to the location and intensity of staining. The processes of adjacent osteocytes meet each other inside canaliculi at gap junctions. The osteocytes are mature form of osteoblasts.

Bone Cells i.. The fibrocartilage lacks perichondrium. Fibrocartilage This cartilage is found in secondary cartilaginous joints like symphysis pubis and manubriosternal joint as intraarticular plate of fibrocartilage joining the articulating bones. Golgi complex and mitochondria as they secrete type I collagen fibers and ground substance of bone matrix osteoid.

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The elastic cartilage looks yellow in color in fresh state due to presence of abundant yellow elastic fibers in its matrix. The type I collagen fibers are arranged in large interlacing bundles. The osteoblasts are the bone forming cells. The cells appear closely placed as intercellular ground substance is lesser than in hyaline cartilage. The chondrocytes are present as single row between the collagen bundles. Components of Osseous Tissue Like any other connective tissue. The osteocytes are metabolically active.

During bone development. They are present in the cellular layers of periosteum and endosteum. The fibrocartilage consists of minimum ground substance. A disservice to the hand has been to depict it as a flat structure, thumb out, as in the dissection table.

In the real state, as we all know, the wrist is slightly dorsiflexed, the MCFs and the IFs slightly flexed, and the 1st web at about 90 degrees to the other web spaces. Strength and precision are attributes of the human hand. Strength is delivered primarily by the long flexors and extensors, but a hand without intrinsic muscles, while maintaining its strength, is only useful as a hook.

But the all-important forearm pronation and supination are provided by the distal radioulnar joint, the humeroradial and, to a lesser extent, the humeroulnar joints. The neutral position of the wrist is thumb up. In pronation, or palm down, the distal ulnar head becomes more prominent while the radius, with the triangular ligament attached, has fallen palm down. This makes the extensor carpi ulnaris ECU tendon to appear in the ulnarmost portion of the wrist.

Once again thumb up, the ECU tendon is felt to overlap dorsally the distal ulnar head. Now in supination, or palm up, the ECU tendon appears between the distal ulnar head and the radius. The cases that follow highlight clinically relevant aspects of the hand that are only rarely discussed during rheumatology training. Upper panel. The collateral ligament is relaxed. Note tibrocartilaginous palmar plate in the palmar aspect of the joint. Lower panel. The lateral collateral ligament becomes taut in flexion.

Palmar Fascia The palmar fascia is a triangle shaped, tough sheet of connective tissue placed deep to the skin in the palm of the hand Fig. Skin displacement during grip is prevented by fibrovascular septae with loculated fat in between that link the skin to the palmar fascia.

This arrangement resembles closely to the plantar fat pad. The superficial fibers of the palmar fascia fan out from palmaris longus and continue in the fingers as the pretendinous band, the spiral fibers and the lateral digital sheet.

All of these structures, as well as the vertical septae that link the palmar fascia to the skin, are important in the pathogenesis of Dupuytren's contracture. The fascia that covers the thenar and hypothenar muscles, 8,9 in contrast to the thick and complex palmar fascia, is thin and adherent to muscle. There is a superficial, transverse muscle that can be seen to bulge in the hypothenar eminence which originates in the palmar fascia and inserts in the skin. This is palmaris brevis.

On the one hand it deepens the cupping of the hand when we drink from it. The longitudinal fibers derive from palmaris longus tendon. Note the transverse fibers of palmaris brevis, a subcutaneous musle at the hypothenar eminence. The palmar fascia is located near the palmar surface.

It is connected to the dermis by fibrous strands that loculate tiny fat lobules. Septae connect the deep aspect of the palmar fascia to the deep fascia that overlies the metacarpals and the interosseous muscles the insert shows the site of the section. Digital Flexor Sheaths Participants will have traced on their hands the full length of the digital flexor sheaths. They should understand the role of the restraining fibrous structures that maintain the tendons in close vicinity to bone and prevent bowstringing during flexion of the digits, the anular and cruciform pulleys.

Resulting swelling and chondroid changes in both the pulley and the tendon lead to nodule formation and the trigger phenomenon. Because finger flexor muscles are stronger than extensors trigger fingers are usually caught in flexion. A permanent flexor deformity may result in late, unrelieved cases. An additional restraining fibrous structure is the palmar aponeurosis pulley which is comprised of transverse fibers of the palmar fascia. This restraint, which is of marginal importance in normals, helps at preventing bowstringing when the A1 or the A2 pulley is cut.

The thumb has 3 anular pulleys and an oblique pulley. The thumb A1 pulley, as in the fingers, overlaps the MCP joint. We would like to add that when the MCP joint ligaments are weakened, as in rheumatoid arthritis, the pull of the A1 pulley on the palmar plate and the base of the proximal phalanx in forceful finger flexion may be such as to cause palmar subluxation of the joint.

This is a simplified rendition of the fibrous digital pulleys. The proximal pulley, A1, inserts in the palmar plate and in the transverse metacarpal ligament that binds neighboring palmar plates. Proximal Extension of the Flexor Synovial Sheaths The proximal extension of the synovial flexor tendon sheaths, which are contained in the digital flexor sheaths, will now be shown Fig. The synovial sheath of the long flexor of the thumb, also known as radial bursa, also traverses the palm and the carpal tunnel and extends into the distal forearm.