anat2241-lecture-summary.pdf

lOMoARcPSD|8900360 ANAT2241 - Lecture Summary Histology: Basic and Systematic (University of New South Wales) Studocu is not sponsored or endorsed by any college or university Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Structur...

lOMoARcPSD|8900360 ANAT2241 - Lecture Summary Histology: Basic and Systematic (University of New South Wales) Studocu is not sponsored or endorsed by any college or university Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Structural Organisation  Epithelial tissue is present in two forms 1. Sheets of cells that cover external surfaces (skin, lining of digestive/ respiratory/ cardiovascular tracts, pleura, peritoneal and pericardial membranes etc.) 2. Glands (exocrine and endocrine) originate from epithelial cells     Epithelial cells are close to each other with space between membranes and small amounts of intercellular material (glycosaminoglycan – acts as a cement) Junctional complexes  between epithelial cells. Hold adjacent cell membranes together All epithelial cells sit on a basement membrane, separating them from underlying connective tissue Epithelium is avascular and depends on diffusion of substances across basement membrane MAIN FUNCTIONS OF EPITHELIUM  Protection of underlying tissues from abrasion, injury, dehydration, invasion.  Regeneration in skin wound healing and renewal of the lining cells of the uterus following menstruation and in the replacement of cells lining the GI tract (every 4 to 6 days).  Secretion by glandular epithelial cells of products into the blood (hormones), ducts and hollow organs (acids and enzymes), or onto the skin (sweat and sebum).  Absorption lipids in the SmIn. and selective re-absorption in kidney tubules (sodium).  Detection sensations taste buds, retina of eye, specialized hair cells in the ear.  Lubrication by various types of glandular epithelial cells, which secrete mucus and help the movement of food along the alimentary tract. Mesothelial cells, lining the closed body cavities, secrete a thin serous fluid that prevents friction between organs e.g. heart, lungs.  Excretion by epithelial cells, which filter waste products from the blood and then excrete them as urine or sweat.  Diffusion of gases (O2/CO2) by squamous epithelium (endothelium) of capillaries in the lungs. CLASSIFICATION OF EPITHELIA  Classified according to 3 characteristics 1. Number of cell layers (simple or stratified) 2. Shape of cells (squamous, cuboidal, columnar) 3. Presence of surface features (cilia, microvilli, keratin)   Simple Found on adsorptive and secretory surfaces May have surface specializations (E.g. microvilli and cilia) Squamous  Single layer of tightly packed, flattened cells  Location: lining blood and lymph vessels (endothelium), lining of pleural, peritoneal and pericardial cavities (mesothelium), alveoli, and loops of Henle.  Function: Thin and functions where an exchange of gases (alveoli), fluids (loop of Henle), nutrients, or metabolites occurs. Cuboidal Single layer polygonal-shaped cells with a centrally placed nucleus  Location: lining tubules or ducts (kidney tubules, salivary glands, pancreas for enzyme production, thyroid follicles for hormone production, ovary  Function: secretory, absorptive, protection Columnar  Cells appear tall  Nuclei located basally in a single row  May have microvilli on apical surface of cells (small intestine) or cilia (oviducts, efferent ductules, small bronchi, paranasal sinuses)  Location: small intestine, inner lining of gall bladder, larger ducts of glands, stomach lining, uterus and oviducts.  Function: reabsorption of water from bile, secretion of enzymes and mucus and absorption of nutrients and fluids, protection. Pseudostratified Columnar  Appears stratified but is a single layer of cells.  All cells in contact with basement membrane, but only some reach surface of epithelium.  Because the cells are of different heights, their nuclei are located at different levels, giving the impression of a stratified epithelium  Location: urethra, epididymis and larger excretory ducts of glands.  A ciliated form is found lining most of the trachea and primary bronchi, the auditory tube, and the nasal cavity. Function: secretion (mucus), lubrication, transportation (mucus), and protection. Stratified Squamous (Non-Keratinized)  Composed of several layers  thick. Only deepest layer in contact with basement membrane  Deepest cells are cuboidal, surface cells are squamous  Because surface cells are nucleated – nonkeratinized  Location: lining of mouth, oral pharynx, oesophagus, vocal cords and vagina.  Function: protection, secretion (mucus) Stratified Squamous Keratinized  Similar to non-keratinized except superficial layers are composed of dead cells whose nuclei and cytoplasm have been replaced with keratin  Location: skin epidermis.  Function: protection Stratified Cuboidal  2+ layers of cuboidal cells  Location: lining ducts of sweat glands.  Function: absorption, secretion.  Epithelium    Stratified Protective function Degree of stratification is related to kinds of physical stresses to which the surface is exposed Classified according to the shape of the superficial (surface) cells Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Transitional Epithelium BASOLATERAL AREA  2 regions – lateral plasma membrane and basal plasma membrane  Each region possesses its own junctional specialisations and receptors for hormones and neurotransmitters Stratified Columnar  Composed of a low polyhedral to cuboidal deeper layer in contact with the basement membrane and a superficial layer of columnar cells.  Location: conjunctiva of the eye, large excretory ducts of glands and the cavernous urethra.  Function: secretion, absorption, and protection  Located solely in the urinary system – lines urinary tract from the renal calyces to the urethra  Composed of 5+ layers of cells – those that are located basally are either low columnar or cuboidal cells  Superficial cells of the empty bladder are large, occasionally bi-nucleated and exhibit scalloping that bulge into the lumen  become squamous and epithelium things when bladder is stretched  Function: protection, distensibility Lateral Plasma Membrane Specialisations  Terminal bars  where epithelial cells contact each other. Classified into 3 types 1. Zonula Occludens (Tight Junctions) Prevent movement of membrane proteins from the apical domain to the basolateral domain. Fuse plasma membranes of adjacent cells disallow water-soluble molecules from passing between cells. 2. Zonula Adherens Below the zonulae occludens, join cell membranes and maintain cell-to-cell adherences 3. Desmosomes (Macula Adherens) "spot weld-like" junctions along lateral cell membranes of simple epithelia and throughout cell membranes of stratified squamous epithelia, esp. in epidermis. SURFACE MODIFICATIONS Apical Surface (top of cell)  Site where secretory products are delivered for release into surrounding micro-environment  Several surface modifications include microvilli, stereocilia, cilia, and flagella. Microvilli    Stereocilia   Cilia   Flagella   Projections of cytoplasm (plasma membrane) from the top surface of these cells Example: The striated border of intestinal absorptive cells and brush border of the kidney proximal tubule cells. In intestinal epithelia, where absorption occurs, microvilli increase (up to x30) the surface area of cells. Long microvilli (not cilia) found in epididymis, vas deferens and on sensory hair cells of the cochlea (inner ear). These non-motile structures in the epididymis function to increase the SA (absorbing fluid surrounding the sperm), whereas in the hair cells of the ear they function in signal generation. Motile projections (diameter 0.2 μm/length 7-10 μm) from surface of certain epithelial cells (e.g. trachea, bronchi and in oviduct). Specialized to function in propelling mucus (trachea) and other structures (fertilized ovum by the oviduct) over the surface of the epithelium via rhythmic wavelike oscillations. Resemble cilia but are longer and wider and occur singly as free cells  E.g. spermatozoa. By whip like action, aid in moving sperm. Basal Plasma Membrane/Basal Lamina Specialisations  Anchor basal plasma membrane to basal lamina  Acellular supportive structure (20-100nm thick)  Secreted by epithelium resting on it  Located at boundary between epithelium and underlying connective tissue  Composed mainly of Type IV collagen, laminin, and proteoglycans.  The basal lamina with a deeper layer, the reticular lamina of the CT (reticular fibres and ground substance) is the "basement membrane" of light microscopy  All epithelia supported by basement membrane  Epithelial cells dependent on diffusion of oxygen and metabolites from underlying tissues Functions  Diffusion barrier to protect movement of harmful substances into blood  Provides elastic support for protection against trauma from hard, rough materials Gap Junctions (Nexus, Communicating Junctions)  Gap junctions allow intercellular communication by passage of ions and small molecules between adjacent cells CLINICAL CONSIDERATIONS  Epithelium may undergo metaplasia (abnormal change in the nature of a tissue) transforming into another epithelial form  Pseudostratified ciliated columnar epithelium of the bronchi of heavy smokers may undergo squamous metaplasia  transforming into stratified squamous to resist continuous abrasion Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Glands  Glands: Epithelial invaginations into underlying CT forming secretory units Function  Glandular epithelia make their product intracellularly by synthesis of macromolecules and stored in vesicles (secretory granules)  May be: hormone (mucin) from goblet cells sebum from sebaceous glands enzymes from exocrine part of the pancreas  Glandular epithelium can remove metabolic wastes (E.g. through sweat glands) Compound  Compound tubular  Brunner’s glands of duodenum  Compound acinar  pancreas  Compound tubulo-acinar types  salivary glands, mammary, prostate and seminal vesicles Classification Glands can be classified on:  Organisation (endocrine/exocrine)  # of cells involved  Having ducts  Branching of ducts  Material secreted and manner in which secreted 1.    EXOCRINE GLANDS These glands maintain their continuity with the epithelial surface via a duct Exocrine glands put products through ducts that open into lumen of an organ or onto the skin Classified as unicellular or multicellular Unicellular  Simplest form as isolated secretory cells in epithelium (goblet cells), amongst the simple columnar epithelia lining the digestive tract (small intestine) and pseudostratified columnar epithelium of the respiratory tract (trachea)  Mucous lubricates the passage of materials protecting the lining along parts of the GIT  In respiratory system, it moistens the air and traps inhaled dust and other pollutants and antigens Multicellular  Gland composed of 1+ cell and drained by a series of ducts  Classification into simple or compound multicellular is by the morphology of their ducts and the shape of the secretory portion Tubular  straight or coiled Acinar  grapelike Alveolar  flask like Ducts (non-secretory portion)  Simple: Single duct which does not branch.  Compound: Several ducts which branch. Simple  Simple tubular (large intestine, stomach body, uterine endometrium)  Simple coiled tubular (sweat glands)  Simple branched tubular (pylorus of the stomach, oesophageal glands)  Simple branched acinar (sebaceous glands). Architecture  Larger multicellular glands are surrounded by CT capsule sending septa (strands of CT) into the gland  subdividing it into smaller compartments  lobes and lobules  Septa  where blood vessels, lymphatics, nerves, and ducts enter and leave the gland. Also provides structural support  Location of ducts in a gland may be: Interlobar (between lobes) Intralobar (within lobes) Interlobular (between lobules) Intralobular (within lobules). Secretion Types  Glands can be classified according to type of material secreted Mucous (E.g. goblet cell)  Mucinogen and large glycosylated proteins which swell to become gel-like protective lubricants (mucin) Serous (E.g. in pancreas and salivary glands  Watery and rich in enzymes Mixed (E.g. sublingual and submandibular salivary glands)  Contains acini (secretory units) that produce mucous secretions as well as acini that produce serous secretions  Some mucous acini have serous demilunes that secrete serous fluid Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Mixed Endocrine/Exocrine Glands  Glands that contain both endocrine and exocrine secretory units (E.g. pancreas) Exocrine portion secretes its product (digestive enzymes) into duct Endocrine secretes product (hormones) into blood Myoepithelial (Basket) Cells  Secretory units of some glands have myoepithelial cells between glandular cells and the basal lamina  Long cytoplasmic processes extend from body of the cell around the secretory unit and by their contraction, express products from the secretory units into the ducts.  Found in sweat, mammary and salivary glands.  These cells are epithelial in origin, but function like a muscle (myo-) by contracting with actin filaments. Mode of Secretion Eccrine –  Merocrine  Apocrine  Holocrine     2.    Process of exocytosis Most common form of secretion (E.g. salivary glands) Involves top of the cell being punched off with portion of the cytoplasm  becomes part of the secretory product (lipid droplet) Remainder of cell repairs itself and continues to secrete milk in mammary gland Involves discharge of the whole cell with disintegration of the entire cell to release the secretory product Occurs in sebaceous glands Basal cells multiply to replace lost cells  gland continues to secrete sebum ENDOCRINE GLANDS Arise from epithelium sheet and lose their connections with surface  lack ducts to leave isolated islands of epithelial secretory tissue within other tissues These glands secrete hormones directly into blood Hormones empty into tissue spaces  enter blood and lymphatics for distribution to target organs/tissues Major endocrine glands include adrenal, pituitary, thyroid, parathyroid, pineal gland, ovaries, testes Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Connective Tissue – Components  Connective tissue (CT) has cells and extracellular materials  fibres, ground substance, tissue fluid  Ground Substance (GS)  Ground substance  Fibres and cells of CT are embedded in gel of variable viscosity  Composed of glycosaminoglycans (GAG) Hyaluronic acid is the main GAG. Because of its capacity to bind water, it is responsible for changes in the permeability and viscosity of the CT  GS plays role in preventing or retarding the spread of microorganisms and toxic materials at sites of infection  Tissue fluid (mainly water) is loosely bound to GS forming a medium passage of materials through the CT and for the exchange of metabolites (nutrients, waste etc.) with the circulation Lymphocytes    placed nuclei in which chromatin may be distributed along the nuclear envelope forming the "clock face" nucleus. Produce immunoglobulins (antibodies) that form a defence against infection Cells that have come from the blood into CT Responsible for initiating cell mediated immune response (T cells) or when activated, differentiate to form plasma cells, which provide humoral immunity (B cells). Have small dark nucleus and little cytoplasm. Fibres  The fibres in CT are collagen, reticular and elastic produced by fibroblasts. Cells Fibroblasts      Mast Cells   Plasma Cells  Most common CT cells Flattened cells with elliptical nuclei that contain 1-2 nucleoli Cell body looks stellate with cytoplasmic processes extending along CT fibres Elaborate precursors of collagenous, reticular and elastic fibres Produce ground substance Macrophages Large, ovoid cells (20-30 μm) with large granules in the cytoplasm Cytoplasm contains Heparin (anticoagulant) Histamine (causes vasodilation and increases permeability of capillaries so excess plasma enters the CT spaces, causing swelling) ADULT CONNECTIVE TISSUE TYPES  General CT divided into loose or dense according to how fibres are packed    Phagocytosing cells Responsible for removing particulate matter and assisting in the immune response. Originate in bone marrow, circulate in the blood as monocytes, and migrate into the CT where they perform their functions. Loose CT (areolar)  Can be classified further on basis of special properties of their constituents (E.g. adipose, reticular tissue)  Fewer fibres but more cells and matrix  Characterised by ground substance and tissue fluid housing the CT cells as well as some undifferentiated cells  Scattered through ground substance are loosely woven collagen, reticular and elastic fibres  Location  widely distributed, filling in spaces just deep to the skin, below mesothelial lining of body cavities, in the adventitia of blood vessels, and respiratory tract.  Function  Binds organs and organ components. Because this tissue lies immediately beneath the epithelia of the digestive and respiratory tracts, it is where the body first attacks antigens and bacteria. Ovoid in shape with eccentrically Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Reticular CT  Forms delicate networks and support of various organs  0.5-2.0m diameter  Type III collagen embedded in loose CT  Location  embryonic CT, around fat and smooth muscle cells and a fine supporting mesh in the liver, lymph nodes, and spleen. Elastic CT  Loose bundles of elastic fibres with some collagen and cartilage in between.  Elastic fibres are coiled, branching fibres 0.2-1.0 μm in diameter, and stretch up to 150% of their resting length.  Location  dermis, lungs, elastic cartilage and large blood vessels. Dense CT  Contains more fibres but less matrix and fewer cells than loose CT Dense Regular CT  Fibres are arranged in parallel bundles for tensile strength in 1 direction.  Fibroblasts occur in rows parallel to the collagenous bundles and are the only cells present with little ground substance  Location  tendons, ligaments and aponeuroses. Dense Irregular CT  Contains thick collagenous bundles, irregularly woven into a compact meshwork resisting stress and producing tensile strength from different directions.  Among collagen fibres is a network of elastic fibres and cells such as fibroblasts, mast cells, macrophages.  Location: dermis of skin, the sheaths of nerves, and the capsules of spleen, testes, ovary, kidney, and lymph nodes. Dense Regular Elastic CT  Possesses branching elastic fibres arranged parallel to each other with only a few collagen fibres forming networks.  Location  large blood vessels, ligamentum flava, of the spine, and the suspensory ligament of the penis. Connective Tissue – Types FUNCTIONS OF CT  Transport  CT carry blood vessels and lymphatics, mediate the exchange of metabolites (nutrients, wastes, gases) between tissues and the blood.  Support  ligaments, tendons and rigid forms (bone, cartilage). Cartilage forms temporary skeleton of foetus.  Repair  scar tissue formation after injury.  Defence  phagocytes (macrophages), antibodies (plasma cells), inflammatory response (mast cells, ground substance viscosity).  Storage  fats (lipids), bone (calcium).  Packing  space between epithelium, muscle, and glands. EMBRYONIC CONNECTIVE TISSUE Mesenchyme  Loose, spongy tissue  Forms packing between structures of the embryo  Spindle mesenchymal cells in a gel-like amorphous matrix containing a few scattered reticular fibres Multi potential  can give rise to any of the adult forms of CT Mucoid  Loose CT found in parts of the embryo – esp. in umbilicus (Wharton’s Jelly… idk sounds gross)  Has large stellate-shaped fibroblasts and jelly-like matrix (mainly hyaluronic acid) with sparse collagen fibres SPECIAL FORMS OF CONNECTIVE TISSUE Adipose Tissue  Adipose cells  adipocytes  Derived from undifferentiated mesenchymal cells which then store and metabolise fat  Represent 15-20% body weight in males, 25% in females  2 types White Fat Downloaded by Joseph Ha ([email protected])   More than brown in number and distribution Signet ring shape (50-150um) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Flat peripherally located nucleus and a thin ring of cytoplasm. Rest of cell filled by a single, large droplet of lipid (unilocular) which is free in the cytoplasm and is composed of glycerol esters and fatty acids. Location:  Mainly in adults  Men  fat stored in subcutaneous tissue of neck, shoulders, buttocks, abdominal wall, around kidneys and in bone marrow.  Women  fat is largely stored in breasts, buttocks, hips, lateral thighs, around the kidneys and bone marrow. Function: Storage depot, production of energy, insulation, packing material and shock-absorbing pads in the palms of the hands, soles of the feet, around the eyeball and kidneys.  Cells are smaller than white fat but show centrally placed round nuclei with a cytoplasm filled with numerous small droplets of lipid (multilocular)  Brown Fat Location:  Foetus and newborn mammals, some hibernating animals. Especially in the interscapular and inguinal regions, some found in the adult E.g. mainly around the aorta. Cartilage Function:  Thermoregulation.  Semi-rigid form of CT for support, resisting mechanical stresses (shock absorber) and smooth movement  Has cells, fibres and ground substance.  Together, the fibres and ground substance form the matrix.  Physical properties of ground substance gives the firm consistency to cartilage and enables it to withstand pressure and shearing forces.  The collagen and elastic fibers embedded in the ground substance provide tensile strength and elasticity.  Cartilage has no nerve or blood supply of its own and no lymphatics. Nourishment is derived by diffusion of materials through the matrix from blood vessels in adjacent tissues. Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC CELLS Chondrogenic cells  Spindle-shaped derived from mesenchymal cells. They have an ovoid nucleus with 1-2 nucleoli. These cells can differentiate into chondroblasts as well as into osteoprogenitor cells. Chondroblasts  Derived from 2 sources: mesenchymal cells within the centre of chondrification and chondrogenic cells of the inner cellular layer of the perichondrium. Chondrocytes  Chondroblasts surrounded by matrix, which they manufacture and maintain. These cells can resume active protein synthesis if they revert back to chondroblasts. MATRIX  Cartilage matrix contains: Collagen (40%), Proteoglycans, Glycoproteins, ECF.  The GS and fibers of matrix form a framework that resists tensile forces.  The matrix is subdivided into two regions: 1. Territorial matrix (stains deeper, sulphate groups on the GAG’s) around each lacuna or isogenous group (a 50μm wide band, poor in collagen and rich in chondroitin sulfate). 2. Interterritorial matrix (stains lighter, less sulphate groups on GAG’s), which is the bulk of the matrix rich in type II collagen and poorer in proteoglycans than territorial matrix. PERICHONDRIUM  Mesenchymal cells at the periphery of cartilage form fibroblasts. These cells make collagenous CT  perichondrium  1.  2.    Two layers Inner region Cellular (chondrogenic)  composed of cells which differentiate into chondroblasts and begin to make matrix Outer region Fibrous (elastic, collagen, fibroblasts, blood vessels) and also contains chondroblasts which have been pushed out as a result of inner growth The perichondrium is vascular, and its vessels supply nutrients to the cells of cartilage. In areas where the cartilage has no perichondrium (E.g. articular surfaces of a synovial joint) the cartilage cells receive their nutrients from the synovial fluid that flows in joint surfaces. CARTILAGE FORMATION  Starts with the differentiation of embryonic mesenchymal cells to form chondroblasts, which make ground substance and fibrous extracellular material.  Secretion of extracellular material traps each chondroblast in a space or lacuna within the cartilaginous matrix  Each chondroblast then undergoes mitotic divisions to form a small group of mature cells (chondrocytes) separated by extracellular material.  These cluster (isogenous groups) of 2-4+ cells in lacunae  the offspring of a single cell. Types of Cartilage Growth Interstitial Growth  Results from proliferation of young chondrocytes which divide and lay down new matrix to produce an expansion of cartilage from within  Occurs in young cartilage to allow expansion and lengthens bone  Articular cartilage (hyaline type at the synovial joint surface) lacks a perichondrium and grows only by interstitial growth Appositional Growth   Downloaded by Joseph Ha ([email protected]) Growth at the periphery where chondrogenic cells in the perichondrium differentiate into chondroblasts, forming a new layer of cartilage around the periphery of the existing cartilage This growth increases the width of the cartilage lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC 3 Types of Cartilage Based on Fibres Present in Matrix Type Description Hyaline  Common type  Has ground substance, type II collagen fibres (40% of matrix) and small groups of chondrocytes Elastic    Fibrocartilage (fibrous cartilage)        Downloaded by Joseph Ha ([email protected]) Location  Nasal septum, larynx, tracheal rings, bronchi, sternal ends of the ribs, the skeleton of the foetus, epiphyseal (growth plate) in growing bones. Is a variety of hyaline cartilage except it also contains elastic fibres between type II collagen fibre bundles It has a perichondrium whose outer fibrous layer is rich in elastic fibre Grows by apposition  Transition between dense CT and hyaline cartilage Matrix consists of cartilage cells enclosed within lacunae The cartilage cells lay singly, in pairs or short rows between bundles of dense collagen fibers Unlike the other two types, fibrocartilage does not possess a perichondrium, has a small amount of matrix in the vicinity of the cells and has bundles of type I collagen Chondrocytes are aligned in alternating parallel rows with the thick bundles of collagen, which cope with the tensile forces. Chondrocytes of fibrocartilage usually arise from fibroblasts that begin to make proteoglycans. As the ground substance surrounds the fibroblast, the cell becomes trapped in its own matrix and differentiates into a chondrocyte.    Where support with flexibility is required The ear pinna, auditory tube, epiglottis and parts of the laryngeal cartilages (cuneiform). Where support and tensile strength is needed Intervertebral discs, menisci, pubic symphysis lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC   Bone Formation and Joints  Occupy shallow depressions, (Howship's lacunae). Ruffled border (infolded plasma membrane) is that part of the cell that is directly involved in the resorption of bone. Bone  Specialised connective tissue BONE FUNCTIONS  Framework  support for skeleton  Protection  Brain and spinal cord, lungs and heart  Serve as lever for the muscles which attach to them via tendons  Reservoir for minerals  calcium, magnesium etc. PERIOSTEUM  Vascular, fibrous layer which surrounds bone except over articular surfaces  2 layers Outer Layer    Inner Layer   BONE MATRIX  Extracellular matrix (ground substance and fibres) Inorganic Materials  65%  E.g. calcium phosphate, calcium carbonate, magnesium, sodium, potassium, bicarbonate, fluoride, citrate, sulfate, and hydroxide) Gives bone rigidity and hardness Organic Material  35%  Type I collagen which gives bones slight flexibility  Ground substance E.g. GAG’s with proteins (proteoglycans) which contain sulfates (chondroitin and keratin) which gives bone resilience BONE CELLS Osteoprogenitor (osteogenic) cells Osteoblasts Osteocytes Osteoclasts   From embryonic mesenchyme Differentiates into osteoblasts Made of collagen with some elastic fibers Thin layer distributes vascular and nerve supply to bone From the outer layer, fine bundles of collagenous fibers (Sharpey’s) penetrate the underlying bone at intervals to attach the periosteum, especially at sites of attachment of tendons and ligaments. Cellular (osteogenic layer, osteoprogenitor cells) that gives rise to new bone. Endosteum  Lining of central cavity of a bone. A thin CT of osteoprogenitor cells and osteoblasts BONE MATRIX DEVELOPMENT 1. Bone starts as osteoid, which is collagen and GAG’s with no minerals. 2. Bone becomes mineralised (immature, primary or woven bone). It is the first bone to appear in development and in repair after fractures. 3. Bone starts to remodel as the adult form (mature, secondary, lamellar). MATURE BONE ORGANISATION  2 types of mature bone  dense and cancellous Location  Inner cellular layer of the periosteum, lining Haversian canals, endosteum (lining of the medullary cavity)  Derived from osteoprogenitor cells  Form and grow new bone by synthesis of the organic components of the bone matrix Location  On surfaces of existing bone tissue where they deposit the new bone matrix (osteoid), which contains no minerals  Later mineralisation occurs and the tissue  new bone  Osteoblasts extend processes with neighbouring osteoblasts for molecular transport  Flat cells with small cytoplasmic processes  Aid in the maintenance of bone tissue and the storage of minerals  Each osteoblast becomes surrounded by secreted matrix; and once this occurs, the cell is known as an osteocyte (mature bone cell), and the space it occupies is a lacuna.  Radiating out in all directions from the lacuna are tunnel-like spaces (canaliculi), which house cytoplasmic processes of the osteocytes.  Canaliculi allow transfer of nutrients, and wastes between the osteocytes and the blood.  Large, motile, multinucleated cells (150 μm diam), contain up to 50 nuclei.  Cells break up and resorb bone. 1.         2.  Dense (Compact) Edge of bone Haversian systems AKA osteons  complex of 4-20 concentric, bony lamellae surrounding a central canal (AKA Haversian canal)  20-100um diameter The canal contains blood vessels, with a few unmyelinated nerve fibers, loose CT, and flattened osteogenic and osteoblast cells that line the lumen of the canal. Osteocytes are in lacunae located within or between the lamellae. A second arrangement of lamellae is found between the osteons, (interstitial lamellae). These are remnants of older, partially resorbed Haversian systems. A third arrangement (circumferential lamellae) are rings of bone around the entire bone, beneath the periosteum. Canaliculi  Radiating from the lacunae are tiny channels Processes of the osteocytes enter these canals and communicate with adjacent osteocytes where an exchange of gases occurs, nutrients are supplied to the cells, and metabolic wastes are eliminated. The Haversian canals communicate with the marrow cavity, the periosteum, and with each other via the transverse Volkmann's canals, which run at right angles to the long axis of the bone. Each osteon has a cement line of calcified ground substance with some collagen fibers. Spongy Bone  Cancellous Bone NOT organised into Haversian systems but is a meshwork of thin bars (lamellae) or trabeculae of bone lining the marrow cavity  Spaces within latticework are filled with bone marrow Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC  Trabeculae houses osteocytes in lacunae that are fed by diffusion from the marrow cavity  Blood and Nerve Supply  Bones have periosteal vessels which penetrate the bone of the diaphysis of long bones and divide into branches that enter the Haverian systems  Supply osteocytes embedded in the calcified matrix. Larger vessels pierce the epiphysis to supply the spongy bone and the midshaft to supply the medullary cavity.  Small myelinated and unmyelinated nerves go into the Haversian canals.  Periosteum contains many pain fibers, which makes it sensitive to injury e.g. a blow on the tibia. resorbed, and replaced by bone (all the cartilage is replaced by bone) Found in long and short bones, pelvis, and vertebrae. DEVELOPING BONE REGION AT THE EPIPHYSEAL PLATE  Epiphyseal plate  Area between shaft and epiphysis  Proliferation occurs at epiphyseal plate. Replacement takes place at diaphyseal plate  Series of 5 zones beginning at the centre of the disk and go toward diaphysis Zone of Reserve Cartilage (resting zone)  Chondrocytes through the matrix are mitotically active producing hyaline cartilage. Zone of Proliferation  Zone of Maturation and Hypertrophy  Chondrocytes proliferate and form stacks of cells that parallel the direction of bone growth Chondrocytes mature, hypertrophy and accumulate glycogen in their cytoplasm. No mitosis occurs. Chondrocytes die and cartilage matrix becomes calcified impregnated with calcium and phosphorus. Zone of Calcification and Cell Death Zone of Ossification        Blood vessels invade spaces left by dying chondrocytes carrying osteoprogenitor cells from the periosteum Differentiate into osteoblasts which elaborate matrix that becomes calcified on the surface of calcified cartilage. As matrix calcifies, some osteoblasts are entrapped as osteocytes  bone trabeculae are formed. Coalescence of trabeculae creates spongy bone. Resorption of spongy bone by osteoclasts in the centre of the diaphysis enlarges the medullary cavity. HISTOGENISIS OF BONE DEVELOPMENT  Bone development is mesodermal in origin  If the tissue is membrane like (a sheet of mesenchyme of loose CT) it is intramembranous bone formation  If bone replaces cartilage that is largely resorbed before bone is formed  endochondral (intracartilaginous) bone development. Intramembranous Bone Formation  Mesenchyme directly to bone  Flat bones  skull, mandible, clavicle Endochondral Bone Formation  Process of bone formation occurs in two steps 1. A miniature hyaline cartilage model is formed in the region where bone is to grow within the embryo 2. Cartilage model grows appositionally and interstitially and serves as a structural scaffold for bone development. SUMMARY OF HISTOCHEMCAL PROCESSES FOR BOTH MODEL OF BONE FORMATION 1. Osteoblasts secrete osteoid with NO minerals. 2. Formation of primary bone whereby osteoid is mineralized. 3. Formation of secondary bone as compact or spongy types. GROWTH Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Interstitial  length   Appositional  width  Due to interstitial growth of the epiphyseal cartilage Growth continues until 20 years of age Epiphyseal plate closes (cartilage replaced by bone)  growth in length stops. Appositional growth from surface and resorption by osteoclasts of the inner shaft so that marrow space can be enlarged JOINTS  Classified according to degree of movement between bones of the joint Synarthroses Syndesmosis  Little to no  Union of bones by dense CT movement  Tibiofibular and radioulnar joints BONE REMODELING  Continual remodelling occurs in response to forces  E.g. Teeth growing in jaw bones  Bone deposited due to traction and resorbed due to pressure  Young bone  deposition > bone resorption  Adult bone  bone deposition = bone resorption Synchondrosis  Junction by cartilage  IV discs and symphysis pubis Synostosis  Joint united by bone  Skull sutures Diarthroidal Downloaded by Joseph Ha ([email protected]) Synovial  Knee, hip, shoulder  Great freedom of movement and have a CT capsule around a joint cavity held by ligaments  Joint has articular cartilage (hyaline) with no perichondrium  Capsule lined (except over articular surfaces) with a cellular, vascular, folded synovial membrane made of loose CT, which secretes a viscous, lubricating, synovial fluid lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Blood      Blood  specialised type of loose CT Ground substance  fluid (plasma) Fibres  strands of fibrin, only found in blood clot formation Cells  erythrocytes and leukocytes in the plasma. Other constituents of plasma  non-cellular blood platelets (thrombocytes), for blood coagulation, lipid droplets (chylomicrons) and specific proteins (immunoglobulins). The average adult has about 5 L of blood in circulation. BLOOD FUNCTIONS Transport Gases, nutrients, electrolytes, wastes, hormones, antibodies, cells and particles Protection Against pathogenic agents by cells of immune system Control Body temp through changes in circulation pH balance Maintained by buffers which neutralise acids and bases Fluid balance Maintained between cells for their normal functioning    When blood is exposed to air, it clots  trapping cells in a jellylike mass. The clear, straw-coloured fluid that remains is serum, which differs from plasma by the absence of fibrin. If blood is prevented from clotting by adding an anticoagulant (heparin) and then centrifuged, 3 layers form. Top layer  plasma. Middle layer  buffy coat has leukocytes and platelets, and is about 1% of the column. Lower layer  RBCs PLASMA  Slightly alkaline fluid that transports and is a solvent of nutrients of the body  Transports dissolved gases (CO2), electrolytes, waste materials, regulatory substances (hormones and enzymes) Proteins  Proteins are main component of nutrients  Albumin  most common protein. Role is maintain osmotic pressure of blood or blood vessel wall  Other proteins are globulins (alpha, beta, gamma, immune) and fibrinogens  Specific proteins (immunoglobulins) recognize and attach to foreign molecules (antigens), blocking the invasion of harmful organisms  Example  Bacteria. BLOOD CELLS – ERYTHROCYTES  Function  transport O2 from lungs to cells and return CO2 to be exhaled.  Lose nucleus and organelles during maturation in order to increase efficiency. Filled with haemoglobin  Flexible cell membrane  enables it to traverse capillaries smaller than its diameter.  Life span ~ 120 days.  2,500,000 RBCs lost per second and same number of new cells must enter the blood in the same period to maintain normal haematocrit.  Some senile cells are destroyed by phagocytosis in liver/bone marrow, but most are phagocytosed in the spleen.  Polysaccharide layer (glycocalyx) covers external surface of membrane, which contains blood group antigens, important in matching blood for transfusions, as well as an antigen for the Rh blood factor. Shape  Round  Biconcave disk  8.5 x 2.5μm in size. BLOOD CELLS – LEUKOCYTES  Contain nucleus and cytoplasmic organelles  Arise mostly in red bone marrow and lymphoid tissue and enter blood when mature  Pass through capillary walls by amoeboid movement into the tissue spaces to carry out functions (phagocytosis, immune reactions, wound repair, and control of infections)  Less numerous than RBCs. ~ 5,000-9,000/mm3 of blood for women ~ 6,000 -10,000 for men. Neutrophils 55-70% Eosinophils 1 - 4%, Basophils, 0.5 - 1%, Lymphocytes 25 - 40%, Monocytes 2-8% Classification  2 main classes exist based on type of cytoplasmic granules and morphology of nucleus Granular w/ 1+ lobe per nucleus  polymorphonuclear Non-granular w/ no nucleus lobulation  mononucleuar Granular Leukocytes Neutrophils  Most common WBC  Additional neutrophils escape from capillaries into tissue spaces or internal cavities Become phagocytes  ingesting bacteria and particulate matter (E.g. Carbon) Attracted to site of infection by chemotaxis and move by amoeboid movement to infected area  Engulf bacteria and release hydrolases which lyse surrounding cells  ~ 10-14μm diameter with multi-lobed nucleus (3 to 5 ovoid lobes) connected by strands of chromatin.  Cytoplasm filled with granules containing alkaline phosphatase and bactericidal proteins (phagocytins)  destroy bacteria after ingested by neut. Eosinophils Lifespan  6 hrs - few days.  Orange/red granules  1.0um diameter which can partially obscure bi-lobed nucleus  Granules are lysosomes containing peroxidase, histaminase, hydrolytic enzymes (similar to granules of neutrophils)  Slightly larger than neutrophils (11-15 μm).  May increase in parasitic infestations, chronic infections and most allergic reactions.  Sluggish amoeboid movement through capillary walls into tissue spaces, in the intestinal mucosa.  Show limited phagocytic activity against bacteria but phagocytize antigen antibody complexes. Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Basophils Lifespan  8 - 12 days.  Number about 0.5-1% of circulating WBCs.  10-12μm diameter.  Identified by presence of many basophilic granules, scattered over the large bilobed nucleus, usually obscuring its outline. The particles contain serotonin, histamine, and heparin.  Slightly phagocytic and collect at infection sites.  Produce about 50% of histamine in blood and play a role in allergy control. Lifespan  Few hours - few days. Non-granular Leukocytes Lymphocytes  Most numerous of non-granular  15-17um diameter  A few lysosomal granules may be present  Nucleus that nearly fills the cell, leaving a thin rim of cytoplasm.  Circulate through spleen, thymus, lymph nodes, and diffuse lymphoid tissue.  Mount an immune response by direct cell attack or via antibodies. Monocytes Platelets  Thrombocytes Lifespan  Hours - years.  “Macrophages” of blood  On passing through capillary wall, they enter loose CT and become tissue macrophages  Spherical and large  14-24um diameter  Large bean-shaped nucleus  Cytoplasm contains a few lysosomal granules Lifespan  Months  Fragments of cytoplasm from megakaryocytes (giant cells in red bone marrow).  Biconvex disks  2-4 μm diameter.  Concentration in blood ranges from 200,000-400,000/mm3.  Remain in peripheral blood for ~ week before removed in the lungs and spleen by phagocytosis.  Function in sealing small tears in blood vessels and in blood clotting. Lifespan   5 - 10 days. Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Muscle  Muscle cells allow locomotion, constriction and pumping movements by changing their length and developing tension Types of Skeletal Muscle Fibers: Red, White, Intermediate Red Fibres  Small with much myoglobin (oxygen transporting proteins that resemble haemoglobin)  Many mitochondria, oxidative enzymes  Represent slow twitch fibers adapted to slow repetitive contractions White Fibres   Large, less myoglobin, fewer mitochondria, poor in oxidative enzymes Represent fast twitch fibers adapted to rapid short lived forces. Intermediate fibres   Features of both types. Most muscles have a mixture of the 2 types Light Microscopy of Skeletal Muscle Fibers  Mainly composed of longitudinal arrays of cylinder- shaped myofibrils,  1-2μm diameter.  Extend entire length of cell, packed so densely that nuclei and cytoplasm are pushed to periphery  The ordered parallel arrangement of myofibrils is responsible for cross-striations (light/dark banding)  Dark bands  A bands (anisotropic with polarized light)  Light bands  I bands (isotropic). Structure  The centre of each A band is occupied by a pale area, the H band, which is bisected by a thin M line.  Each I band is bisected by a thin dark line, the Z disc (Z line).  The region of the myofibril between 2 successive Z disks, is a sarcomere, (2.5 μm long/the contractile unit of skeletal mm fibers). Terminology Sarcolemma Sarcoplasm Sarcoplasmic reticulum Muscle cell Fascicle Myofibril Myofilament Muscle membrane Cytoplasm Smooth ER Muscle fibre (the cell is longer than wide) Parallel muscle fibre bundles Bundle of contractile protein in a cell Contractile proteins TYPES OF MUSCLE – SKELETAL (STRIATED / VOLUNTARY)  Attached to bones or skin (E.g. biceps, hamstrings, etc.)  Myoblasts line up end to end and fuse to form myotubes which become packed with the contractile elements (myofibrils).  Specific arrays of myofilaments, the proteins (actin, myosin) responsible for the contractile capability of the cell.  Muscle fibers arranged parallel to each other, capillaries in-between. Skeletal Muscle Fibre (cell)  Long, cylindrical and multinucleated  10-100um diameter  Nuclei located peripherally, possessing 1-2 nucleoli Ultrastructural (EM) Organization of Myofibrils  Parallel, interdigitating thick and thin myofilaments can be seen under EM  Thick filaments (15nm diam, 1.5μm long) are composed of myosin. Each myosin molecule is composed of 2 identical heavy chains and 2 pairs of light chains. Heavy chains resemble two golf clubs, whose rod-like polypeptide chains are wrapped around each other in a helix.  Thin filaments (7nm diam., 1μm long) composed primarily of actin, with tropomyosin and troponin involved in muscular contraction.  There are regions of each sarcomere, on either side of each Z disk, where only thin filaments are present (correspond to the I band).  A band  region of each sarcomere that encompasses entire length of the thick filaments.  H band  zone in middle of A band, has no thin filaments  During contraction, individual thick and thin filaments do not shorten; instead, the two Z disks are brought closer together as the thick and thin filaments slide past each other (Huxley’s sliding filament theory). This reduces the width of I and H bands without altering the width of the A band.  The process of contraction obeys the "all-or-none law" in that a single muscle fibre will either contract or not as a result of stimulation.  Strength of contraction (E.g. biceps)  due to no. muscle fibers that undergo contraction. Motor Nerve Ending (Motor end plate, Neuromuscular Junction)  Specialized region on skeletal mm fibers where a motor nerve terminates.  Motor fibers  myelinated axons of neurons, which pass in the CT of the muscle.  The terminal of each arborized twig becomes dilated and overlies the motor end plate of individual muscle fibers. Function: Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC  Transmit stimulus from nerve fibre to muscle cell via release of neurotransmitters from nerve terminal vesicles across the synaptic cleft. TYPES OF MUSCLE – SMOOTH MUSCLE (UN-STRIATED / INVOLUNTARY) Location  Walls of blood vessels and hollow organs (digestive, respiratory, urinary, etc.) and the dermis of skin (arrector pili mm). Light Microscopy of Smooth Muscle Fibers  Fusiform and elongated  Length ~ 20μm-200μm, diam. 5-6μm).  Centrally placed nucleus with 2+ nucleoli.  Cell surrounded by a fine collagen and reticular fibre network  endomysium.  No cross striations. Usually form sheets of different thicknesses (walls of the intestine), or they may also occur as individual cells or small bundles (in the intestinal villi). Control of Smooth Muscle Contraction  The all-or-none law does not apply.  The entire cell or only a portion of the cell may contract at a given instant.  The regulation of contraction in smooth mm depends on Ca ions from both the sarcoplasmic reticulum and extracellular fluid. Control mechanism of contraction differs striated as smooth mm thin filaments have no troponin.  Myosin molecules assume different configuration and light chains are different Innervation of Smooth Muscle  Neuromuscular junctions are not as specifically organized as those of skeletal mm.  The synapse occurs as axonal swellings that contain synaptic vesicles, housing norepinephrine for sympathetic or acetylcholine for parasympathetic innervation.  Respond to hormones (E.g. uterine mm response to oxytocin in late pregnancy) Intercalated Discs  Highly specialized end-to-end junctions formed by cardiac mm cells at the site of a Z line.  Intercalated discs have areas of low resistance allowing rapid spread of impulse from cell to cell. Purkinje Conducting Fibers  Large modified muscle cells filled with glycogen and mitochondria.  Function as specialized conducting cells of the AV bundle in the heart.  2+ nuclei. Connective Tissue Association  Epimysium  Dense collagenous CT. Surrounds skeletal muscle  Perimysium  less dense collagenous CT Derived from epimysium Surrounds fascicles of muscle fibers and endomysium Composed of reticular and fine collagen fibers surrounds each muscle cell.  The CT binds muscle units so as to integrate the contraction.  Cardiac mm and smooth mm have CT sheaths and endomysium. Location Skeletal Attached to bones Long and cylindrical Multinucleated Heavily striated Cardiac Wall of heart (myocardium)  Branching  Intercalated discs  Single nuclei  Light striated Smooth Walls of hollow organs, vessels, respiratory tracts  Spindle-shaped  Branching networks  Non-striated Characteristics  Control action Voluntary  Produces movements at joints  Stimulated by nervous systems  Contracts/relaxes quickly Involuntary  Pumps blood out of heart  Self-excitory but influenced by nervous system and hormones Involuntary  Peristalsis  Contracts and relaxes slowly. May sustain contraction Gap Junctions None as muscle fibres stimulate independently Present as ID Present Connective tissue components    TYPES OF MUSCLE – CARDIAC MUSCLE (STRIATED / INVOLUNTARY) Location  Found only in the heart (myocardium). General Description  Myocardium consists of a network of branching cardiac mm cells arranged end to end.  Fibers are separated from each other by CT sheets (endomysium) that have blood vessels, nerves, and the conducting system of the heart.  Capillaries form a rich network surrounding every cardiac mm cell.  Heart mm differs from skeletal and smooth mm in that it possesses an inherent rhythmicity as well as the ability to contract spontaneously. Light Microscopy Cardiac Muscle Fibers  Resting lengths of individual cardiac mm cells vary  ~15μm diameter, 80μm long  Centrally placed nucleus, occasionally 2 nuclei present.  Packed myofibrils exhibit banding pattern identical to skeletal mm.  Each sarcomere has the same substructure as skeletal mm;  mode and mechanism of contraction are identical. Downloaded by Joseph Ha ([email protected]) Endomysium, Perimysium, Epimysium  Endomysium  Endomysium lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Nervous Tissue THE NERVOUS SYSTEM Classification in Central Nervous System and Peripheral Nervous System  CNS  spinal cord and brain  PNS  links the CNS with structures in the periphery of the body from which it receives sensory information and to which it sends controlling impulses THE NEURON  Neuron  smallest functional unit of the nervous system  Highly polarised, terminally differentiated cells  Soma (cell body) and cytoplasmic processes (nerve fibres, or neurites) Soma   Consisting of a nucleus and the surrounding cytoplasm. Known as perikaryon Dendrites  Neurites conducting information towards the cell body Axons  Neurites conducting information away from the cell body Synapses  Cell-cell connections between neurons and between neurons and nonneural cells such as muscle cells. Information between cells is transferred via neurotransmitters  Nissl granules  Nissl substance    Representing rough ER Reticulum  irregularly shaped masses of basophilic material scattered through cytoplasm of the cell and the dendrites Absent from axons COMPONENTS OF THE CNS  Organisation into horizontal layers  laminated appearance  6 layers that differ in neuronal populations The Cortex  Cortical neurons  5 main types exist Pyramidal and stellate being most numerous  Triangular shaped pyramidal cell bodies range from 10-50um in diameter projecting a dendrite apically and a single axon towards deeper cortical layers  >15 billion neurons in cerebral cortex The Cerebrum – Uniform trilaminar organisation  ¾ the size of cerebral cortex Outer Molecular Layer  Pale stained zone with relatively few neuron bodies  Contains network of branching dendrites of Purkinje fibres (neuropil) Middle Monolayer  Single row of uniformly arranged Purkinje cells  Large neuron bodies on the outer surface of the granule layer Inner Granule Layer  Densely packed, small neurons  Only nucleus seen as there is very little cytoplasm  Several short dendrites on each cells and one axon extending into the molecular layer  Axons establish multiple synaptic contacts with dendritic spines of Purkinje cells NEURONAL CONNECTIVITY IN THE SPINAL CORD Meninges  The outer covering of the brain and spinal cord  Organisation Dura matter Arachnoid mater Pia mater Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC Paccinian Corpuscle Meissner’s Corpuscle Muscle Spindle          Present in the skin and deep tissue (surrounding joints and mesentery) Sensitivity for mechanical distortion Present in the skin Particularly in the dermal papillae of the fingertips Sensitivity for fine or discriminative touch Present in skeletal muscle Sensitivity to muscle stretch Particularly abundant in muscles involved in fine, skilled movements Important in the control of muscle tone and movement Nerve Endings – Effector Endings  Occur in association with muscle and secretory cells  Neuromuscular junction (motor endplate)  Motor axons branch and innervate a number of different skeletal muscle fibres  The axon that innervates these fibres together with the fibres, constitute a motor unit STRUCTURE OF FASCICLE  Peripheral nerves consist of 1+ bundles of nerve fibres.  Each fascicle contains mixture of fibres which can be efferent (motor) or afferent (sensory)  Perineurium  acts as an elective metabolically active diffusion barrier PLEXUS  Structures in which nerve fibres are redistributed without synapses to form other peripheral nerves (E.g. Auerbach’s and Meissner’s plexus) COMPONENTS OF THE PNS  Nerve endings  Peripheral nerves  Plexuses  Peripheral ganglia Nerve Endings – Sensory Endings  Exteroceptors  occur superficially in the skin and respond to nociceptive (painful) stimuli, temp, touch and pressure  Interoceptors  occur in viscera  Proprioceptors  occur in muscles, joints and tendons and provides awareness of posture and movement Auerbach’s (myenteric) Plexus  Part of enteric nervous system  Present in between longitudinal and circular layers of the muscularis externa in the gastrointestinal tract (oesophagus, stomach and intestine)  Controls gastrointestinal tract motility  Parasympathetic and sympathetic input Meissner’s Plexus  Plexus of submucosa  secondary plexus derived from the Auerbach’s plexus  Lies in submucosa coat of the intestine  Parasympathetic input  Finer nerve bundles than those of Auerbach’s plexus Structural Classification Unencapsulated or “free” nerve endings  Consist of the terminal branches of sensory nerve fibres lying free in the innervated tissue  Mediate thermal and painful sensations Structural Classification - Encapsulated nerve endings  Surrounded by a structural specialisation of non-neuronal tissue  The combination of nerve and its encapsulation referred to as corpuscle Downloaded by Joseph Ha ([email protected]) lOMoARcPSD|8900360 ANAT2241 – HISTOLOGY: BASIC AND SYSTEMATIC - Contains pseudounipolar sensory neurons No synapses between neurons in the ganglion Large central nuclei Peripheral processes have receptors Central processes go to brain and spinal cord Surrounded by satellite cells GLIAL CELLS Function  Non-conductive cells with diverse structural, protective and nutritive roles  Glia control the extracellular environment of the brain  Buffer many biochemical processes which occur in neurons  Process energy sources for neurons and are involved in the “clean-up” and reprocessing of neurotransmitters at every synapse  Response to injury  Take part in building the blood brain barrier Types  Ependymal cells  Oligodendrocytes/Schwann cells  Astrocytes  Microglia AUTONOMIC NERVOUS SYSTEM  Control of visceral organs, smooth muscle and glands  Two antagonising systems Sympathetic division Parasympathetic division Ependymal cells  Remnants of embryonic neuro-epithelium  Formation of a closely packed cuboidal or columnar epithelium lining the ventricles of the brain and the central canal of the spinal cord  Luminal surface directly in contact with Cerebrospinal Fluid (CSF)  Cells possess apical microvilli and sometimes motile cilia  In the choroid plexus these cells also serve a secretory role and secrete components of the CFS  Possess structural and enzymatic characteristics needed for scavenging and detoxifying many substances in the CFS Ganglion  Ganglion  cluster of neuronal cell bodies located outside CNS Autonomic Ganglia  Peripheral motor ganglia of the ANS  Contain cell bodies of postsynaptic neurons that conduct nerve impulse to smooth muscle, cardiac muscle and glands  Synapses between presynaptic and postsynaptic neurons in autonomic ganglia Sensory Ganglia  Lies outside CNS  Contains cell bodies of sensory nerves that carry impulses into CNS  No synapses between neurons Astrocytes  Derived from neural ectoderm  Stellate shape  Maintenance of homeostasis  Their thin processes terminate on neuronal cells or blood vessels in CNS  Building of blood brain barrier  Cytoplasm contains tightly packed intermediate filaments unique to glial cells  Glial fibrillary acidic proteins (GFAP)  Form a structural syncytium in CNS via gap junctions  Control the ionic milieu by taking up potassium ions and they regulate GABA  Inactivate neuro