Histology - Part 1 PDF by Professor Zakaria Abd-EL Hamid
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Cairo University
Zakaria Abd-EL Hamid
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This textbook, "Histology Part 1", by Professor Zakaria Abd-EL Hamid, is intended for medical students. It provides a detailed explanation of cell biology, blood, and tissue structure and function, with an emphasis on the inter-relationship between structure and function at different levels of resolution.
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HISTOLOGY Part F o r Medical Students New Edition With Coloured Plates And Electron Micrographs By Professor Zakaria Abd - ELHamid Microvilli C...
HISTOLOGY Part F o r Medical Students New Edition With Coloured Plates And Electron Micrographs By Professor Zakaria Abd - ELHamid Microvilli Cell Ribosomes ~---~~l~~~~ J ~Hflitfiiii!IH;.._-i---N ucl eo l u s Smooth Endoplasmic t- ;\1itochondria Reticulum One Cell For Medical Students Q»art 1) By Professor Zakaria Abd - AL Hamid M. B., B. Ch., D. M. Sc., M. D Professor of Histology Faculty of Medicine Cairo University New Edition With Coloured Plates and Electron Micrographs All Rights Reserved To The Author 'I l Preface * *This Text-Book of Histology is the outcome of ftfty years of experience in teaching medical students and is written primarily for them. It is sufficiently detailed to satisfy the requirements of the undergraduates as well as the postgraduates. The new edition of this book was prepared with the same objectives as those of the original work. The most apparent changes in this book were the inclusion of a number of electron micrographs and their accompanying text. Emphasis was laid upon the inter-relationship between structure and function, not only at the level of resolution obtained with the optical microscope but also at the ultra-structural level. Another obvious change in this new edition was the inclusion of the chapter of genetics, and genomic studies. Genetics today, is penetrating into all fields of medicine. Its rapidly expanding methodology is enabling research workers to find answers to many questions. Our attention, therefore, becomes more focused on normal and abnormal cell divisions and on chromosomal as well as on genomic studies. In addition to the considerable changes and additions to the text, a conscious effort has been made to increase both the quality and number of illustrations. The new coloured illustrations are original and are of the kind that seem to be the most helpful guide to students when actually examining their slides. In presenting this book, I would like to express my appreciation for the help and encouragement that I have received from my wife. Dr. Zakaria Abd - AL Hamid CONTENTS Page Introduction................................................................................................................................................... I Microscopy......................_....................................................................................._............................... I Microtechnique.........................-...............................................-.............._.................................. III Types of Stains _...........................................-..................................................................................... VIII The Cell............................................................................................................................................................. 1 The Cell Organelles............................................................................................................._.......... 2 The Cell inclusions........................................................................................................................... 20 The Nucleus........................................................................................................................-.....-..... 21 Genetics............................................................................................................................................................ 29 Cell Division......................................................................................................................................... 29 Mitosis............................................................_......................................................................................... 30 Meiosis........................-......-......_.............................................................................................................. 32 Abnormalities In Cell Division.......................................................................................... 35 Human Chromosomes................................................................................................................. 35 Chromosomal Aberrations...................................................................................................... 38 The Sex Chromosomes................................................................................................................ 39 The Genome......................................................................................................................................... 41 Blood Groups........................................................................................................................................ 43 Rhesus Factor...................................................................................................................................... 45 The Blood..................................................................................................................................................... 46 Red Blood Corpuscles................................................................................................................. 46 Leucocytes.............................................................................................................................................. 51 Blood Platelets.................................................................................................................................... 61 Development Of Blood Cells.................................................................................................... 63 Tissues Of The Body......................................................................................................................... 71 Epithelial Tissue.................................................................................................................................... 71 Simple Epithelium.......................................................................................................................... 71 Stratified Epithelium.................................................................................................................... 74 Glandular Epithelium.................................................................................................................. 78 Neuro Epithelium........................................................................................................................... 81 Connective Tissue................................................................................................................................ 83 Connective Tissue Proper.......................................................................................................... 83 List Of Practical Histology Slides Plate Page Tendon (white fibrous C. T.).........._.......................................... m._....................... 4 93 Umbilical Cord (mucoid C. T.).................................................................................... 4 94 Costal Cartilage (hyaline cartilage)................................................-................... 6 97.Ear Pinna (elastic fibro-cartilage) ---·-·----·---· 6 98 White-FibroCartilage.................................-···-···-·-·······--·-·-····--····-·-·--····--···· 6 99 Compact Ground Bone............................................................."".......................................... 100 Compact Decalcified Bone ------------·--·-·-·---·------ 6 103 Spongy Bone (rib) ------·--·-------·-----·--·-·-·--·..... 7 Growing Bone (cartilagenous ossification) ·-.......................................... 7 107 Skeletal Muscle (T. S.) ·--·----.. 8 111 Skeletal Muscle (L. S.) -..--·--·-·-......................................-................. 8 111 Cardiac Muscle and Valve....................................................._........................................ 8 117 Moderator Band ---·---·-·-......-............................... 8 118 Nerve Trunk (Hx and E) -----·---·-·-·-·--·----·.......... 9 Nerve Trunk (osmic acid) ·-·-·--·----·--·---·--·..·-·-·--·-·-·-- 125 Spinal Ganglion 9 125 Sympathetic Ganglion ·----·-·-·----..-.......................................................... 9 126 Bone Marrow ·--·--···-·-·--·--····-·--·-·-................................--........................._. 13 63 Skin (tip of finger) -----·-·--·--·-·--·--·--·-------·-·--· 10 138 Skin (scalp) -----·-·--·---·---·-....................................·---..·-···-· 10 144 Medium-sized Artery and Vein...-......- -..·----·-...-...........-............... 11 Aorta..................- -........--·---- 11 Basilar Artery ___...._............-.............................................................................................. 11 149 Coronary Artery.......................................................................................................................... 150 Inferior Vena Cava.._____.._..............-..........................................--·--· 11 151 Lymph Node............................................................................................................_.................. 12 156 Spleen --·--·--·-·-····-·-·---·-··-·---·-·-·············-·-····--····--·--·-·--·-····-·..·· 12 159 Tonsil..................................................-.................................................................... 12 ThymUS.................-...........................-...m ·-·-····-··.. ""················-·······............................. 13 164 Trachea................................................................................................................................................ 14 171 Adult Lung...................................................................................................................................... 14 Foetal Lung...................................................................................................................................... 14 High Power Slides Plate Golgi apparatus in nerve cells..................................................................................................... 1. ept'd'd G101g~. apparat us tn 1 ymts..................................................................................................... 1 Mitochondria in muscle cells (Iron Hx)............................................................................. 1 Glycogen in liver cells (Best's carmine stain).............-............................................. 1 Nissl granules in nerve cell (Toluidine blue stain) 1 Pigment granules in cells of skin.............................................................................................. 1 Exogenous and endogenous granules in macrophages................................ 1 Mucous, Serous and Pancreatic Acini........................................................................... 3 Different Types of Epithelium........_........................................_.......-........................................ 3 Motor-end plate (Silver)..............._.................................................................................-.............. 9 Muscle spindle (T. S.)......................................................................................................................... 13 Pacinian Corpuscle 13 Has sail's corpuscle..................................................................".............-............................................... 13 Megakaryocyte..................................................................................................-..................................... 13 Mast cells (Toluidine Blue Stain)...............................................'"...................-.................. 13 Blood leucocytes (on the cover of this book) and in plate 10 Electron Micrographs Page Cell Membrane 3 Mitochondria............................................................................................................................................... 9 Rough Endoplasmic Reticulum................................................................................................ 11 Smooth Endoplasmic Reticulum............................................................................................. 11 Golgi Apparatus........................................................................................................................................ 12 Centriole 17 Slides Stained With Special Stains Plate Fat cells stained with Sudan black........................................................................................ 1 Lymph node stained with silver to demonstrate reticular tissue................. 5 Spleen stained with silver to demonstrate reticular tissue............................. 5 Spinal ganglion stained with silver........................................................................................ 9 Sympathetic ganglion stained with silver....................................................................... 9 Aorta stained with Verhoff to demonstrate elastic tissue................................. 13 Aorta stained with orcein to demonstrate elastic tissue............................. 5 Nerve trunk (osmic acid stain).........................................................................................Page 125 Introduction Histology: involves the study of the microscopic structure of the cells, tissues and organs. The Cells: are bound together to form different tissues. The Tissues: are combined together to form different organs. Several Organs: having correlated functions are grouped to form Systems. In the study of histology, it is important for the student to understand the various types of microscopes and the different methods used in preparation of tissues, and the different methods used for staining cells, tissues and organs. Microscopy Several types of microscopes are used to study the detailed structures of the organs. The Resolving Power of a microscope is a measure of the capacity of the microscope to separate clearly two points close together. The resolving power of the light microscope is about 0.2 micrometer. The resolving power of the Electron Microscope is 0.2 nanometer. The most important units of measurements used in Histology are: One centimeter (em)= 10 millimeters (mm). One millimeter (mm) = 1000 micrometers = I 000 microns (u). One micrometer (one micron)= 1000 nanometer (nm). One nanometer (nm) = 10 Angstrom= 10 A0 Types of Microscopes 1. The Light Microscope (LIM) In this microscope, we use the day light or electric light as a source of illumination. The light is focused on the lens of the condenser by a mirror. The Optical System of The Light Microscope Consists of: a) The Eye Pieces which are near the eye. They are of different magnifying powers: 5, I0 or 15 This means that the eye piece magnifies the object either 5 times, 10 times, or 15 times respectively. b) The Objective lenses are near the object to be examined. Types of Objective Lenses: Coarst Adjuslmtnl -Tube 1. Low Power Objective ( I0). 2. High Power Objective (45). FiDe Adj uSimtDI 3. Oil Immersion Objective (100). This lens.()bjectlv~ when used, should be immersed in a drop of cedar oil. This oil should be put on the covcrslide overlying the objec t to be examined. How can we calculate the magnification of a histological section? We multiply the power of the used eyepiece (1 0 for example) by the power of tP.e The Light Microscope used objective lens (45 for example). So, the magnification of this examined histological section will be: I 0 x 45 = 450 times. 2. The Transmission Electron tnicroscope (E/M) - In this mi croscope, a heam of electrons is used as a sou rce of illumination. -The magniliL:d image is rccei\cJ on a lluorcsccncc screen or on a phutugr. phic plat~. - The ElM g!ves a ve1) high magmfi~aLion. lt magni ries object. up tu 100.000 times. 3. The scanning Electron Microscope It is a special type of electron microscope by which we obtain a 3 dimensional image for the examined parts as red hlood corpuscles and cilia of certain cells. Red Blood Corpuscles Und er Scanning E/M JI 4. The Atomic Force Microscope It magnifies the examined fresh tissues up to 500.000 times. 5. The Ultraviolet Microscope - In this microscope, the source of light is a beam of ultraviolet rays. The image is received on a fluorescence screeen. - The magnifying power of this microscope is up to 4000 times. 6. The Fluorescence Microscope The source of light in this microscope is the ultraviolet rays which are harmful to the eye, so a filter should be inserted in its eyepiece. The fluorescent substances in the examined tissues will shine by giving off visible light. It is used to study the chemical components of the tissues. 7. The phase Contrast Microscope It is used to examine fresh tissues or living cells growing on a culture media. The Basic Techniques Used For Preparation Of Tissues For Histological Studies 1. Microtechniques. 2. Tissue culture. 3. Spreading of blood films, bone marrow and tissue smears. 1. Microtechniques These are the different types of techniques used to prepare sections from organs. 1. The paraffin technique, (is the most commonly-used method). 2. The celloidin technique, (is the most perfect used method). 3. The freezing technique, (is the most rapid used method). N.B. The Microtechniques are used to prepare tissues for microscopic examination for learning purposes and to differentiate between normal and cancer tissues before, during and after operations. m A- The Paraffin Technique In this method, soft and hard paraffin are used. The following steps are followed in paraffin techniques: 1. Obtaining the tissue from the body:- A very small fresh piece of tissue is cut out from the examined organs immediately after death or from patient before doing operation. 2. Fixation of tissues prevent tissue autolysis, The obtained tissue is put in a chemical fluid called fixative as formalin and the process is called fixation. Functions and characteristics of a good fixative - It hardens the tissue by coagulating its protein. - It prevents putrifaction and stops the autolytic changes by killing the bacteria. - It preserves the tissue in a condition similar to that existing during life. - It facilitates the process of cutting, staining and microscopic examination. 3. Washing: The fixed tissues are washed in running tap water to remove the fixative. 4. Dehydration: it is the process of gradual extraction and removal of water from the fixed tissue. It is done through the following steps: Putting the fixed tissue in 50% alcohol, then in 70% alcohol, finally in 100% alcohol (absolute alcohol). 5. Clearing: By this process, the tissue becomes translucent. The tissues are treated with clearing agents as xylol or benzol to remove alcohol. 6. Impregnation: The fixed tissue is put in melted soft paraffin. 7. Embedding In Hard Paraffin: The tissue is then embedded in hard paraffin to form a block ready for sectioning. 8. Sectioning Or Cutting Of The Paraffin Block By The Microtome. 9. Mounting: The obtained thin paraffin sections arc then put on clean glass slides smeared with glycerine. The sections are now ready to be stained. Advantages Of The Paraffin Technique -Paraffin technique takes a short time for its preparation. - It gives serial sections which are important for research. -It gives very thin sections, easy to be stained and to be examined. -Paraffin sections are very easy to be stained with different stains. IV Disadvantages of Paraffin Technique - The used fixative dissolve the fat content of the cells during preparation. - The used fixatives and heat may change the normal structure of tissues. - It is not used in demonstrating the enzyme activities in tissues. B - The Celloidin Technique In this technique we use celloidin substance instead of paraffin. - It is used to prepare large sections from the eye ball and brain stem. - In celloidin technique, fixation, and washing steps are similar to those used in paraffin technique. - Dehydration And Clearing are done in absolute alcohol and ether for 2 days. - Impregnation and embedding are done first in thin celloidin (7.5%) and then in thick celloidin (15%). - Celloidin blocks are preserved in 70% alcohol. - Sectioning of a celloidin block is done by a special microtome. - The obtained thick celloidin sections are stained in watch glasses. Advantages Of Celloidin Technique - It gives perfect and clear sections to demonstrate tissue details. - The use of no heat preserves the normal structure of the tissues. - It is used to prepare sections from large organs as eye and brain. Disadvantages Of Celloidin Technique - Celloidin technique takes about one month for its preparation. -No serial sections can be otained because the sections are thick and separated. - The celloidin sections are very difficult to be cut and to be stained. C- The Freezing Technique - In this method, the fresh or fixed tissues are frozen, hardened and are cut with a freezing microtome in the cryostat apparatus within few minutes. v Advantages Of Freezing Technique -It is a quick method used during operations for rapid diagnosis of tumours. -It is used in histochemistry to demonstrate enzyme activities in cells. Disadvantages Of Freezing Technique - It gives non-serial separated and fragmented sections. -It gives thick sections very difficult to be cut and to be stained. 2 - Tissue culture This is a special rechnique by which living cells of the body (e. g. blood cells or tissue cells) are isolated and allowed to live, to divide and to grow outside the body. This is done by incubating living cells and tissues in special media. Medical Uses Of Tissue Culture:- !. Used in studying chromosomal patterns of individuals (karyotyping). 2. Used in diagnosis of certain tumours and in the different researches of cancer. 3. Used in cultivation of bacteria, and viruses, in order to prepare different vaccines. How To Stain A Paraffin Section? - Paraffin technique is the most commonly used method in histological preparations. - The prepared paraffin sections are usually stained with the most commonly used stains which are the Hematoxylin and Eosin (HX & E) stains. These Are The Steps To Be Followed In Staining Of a Paraffin Section With Hematoxylin and Eosin (HX & E). 1. Identify the face of the slide upon which the paraffin section is present by scratching the paraffin and then label the slide face which contain paraffin. 2. Dissolve the paraffin by putting the slide in xylol solution for 3 minutes. 3. Replace Xylol by putting the slide in absolute alcohol for 3 minutes. 4. Bring The Section Down To Water by putting the section in descending grades of alcohol (in 100% alcohol, then in 90%, then in 70% alcohol and finally in distilled water) 3 minutes in each step. This process is called hydration of the section. 5. Stain The Section In Hematoxylin For 7 Minutes. This basic stain will stain the nuclei and the basophilic structures of the cytoplasm with a blue colour. VI 6. Put T he Slid e In Tap \ Vater for 5 minutes in order lO blue the ~ection. 7. Put The Slide In Eosin Fm· One M.inute. This is an acidic stain. it stains the acidophilic structures of the cytoplasm wi th red colour. 8. \Vash In Distilled water For 3 1\tlinutes. 9. Dehydrate the slide in ascending grades of alcohol. Put it for one minute in 70% alcohol. then for 3 minutes in 90% and for another 3 minu te. in I OOlk alcohol. (:iD) I Drop 01 Canada BaJlm And Covtr. )~ Rapid Mounlln I.___ _ __. 8 J.,_,.. ''"'"" f or Otarlaa J mla. aQ ~ t -8 ,... '··· 8t :- ~ '"'" \\-·\~ \:) Jmln. 8t ;;- I.. ~- j ~ ~ ~! aV Jmla. Jmla. 7mia. lli11JI. J IIlia. 8 jJ c!' ~~ Smia. _/ ~ CiD - - - Staining Of Paraffin Sections --)~ I 0. Put the slide in xylol in order to clear it from alcohol and to allow it to be mi scible with Canada balsam. Leave the slide in xylol until you put a drop of Canada balsam on a clean cover slip. I I. l\1ounting the section in Canada balsam by removing quickly the slide from xylol with its race dowm,·ards and rut it on the cover slip. 12. Examine the stained. ection and identify the structure~ pre ent in it. Precautions To Be Taken During Staining Of A Paraffin Section: I. Make sure that the slide contai ning the section is facing you. 1. Xylol and water should never be mixed (if mixed they will form a milky solution). 3. Never allow the section to become dry in between two successive steps. Types Of S tains I. Acidic stain: a.s Eosin stain, Ora.1gc G. ~l nd Acid Fuscin. They stain the alkaline structure~ or the cytoplasm (as protein ) with a red colour. VII 2. Basic Stain: as Hematoxylin, Toluidine blue and Methylene blue. They stain the acidic structures of cytoplasm and the nucleus with a blue colour. The cytoplasm is usually alkaline in reaction in non-secretory cells, so it takes the acidic stain as Eosin. Thus it is acidophillic in staining, (it likes the acidic stains). The nucleus is rich in nucleic acids, thus it is constantly acidic in reaction, so the nucleus takes the basic stains as Hematoxylin. It is basophilic in staining (it likes the basic stains). 3. Neutral stain: as Leishman stain which is usually used to stain blood cells. It acts as a fixative for the blood film. It stains both the nuclei and cytoplasm of the white blood cells. It is commonly used to stain blood films. 4. Vital stain as neutral red or trypan blue stains: by these vital stains, we can stain living cells· inside the living body as the staining of reticulo-endothelial phagocytic cells by injecting th·e dye into living animals. 5. Supravital staining is the staining of living cells outside the body, like the staining of the reticulocytes (immature red blood cells) with brilliant cresyl blue. 6. Metachromatic staining as the staining of mast cells with toluidine blue stain. This stain reacts with the mucopolysaccharides which are present in the granules of mast cells. This reaction will give rise to appearance of a new violet colour not related to the original blue colour of the stain. N. B. The Orthochromatic stains react with the contents of the cells but they give the same colour of the stain. 7. Physical stain: as Sudan III which stain fat cells with orange colour. 8. Trichrome Stains: Each trichrome stain involves three types of stains as: a) Hematoxylin Van Gieson Stain: It stains collagen fibres with red, muscles with yellow, nuclei with blue and epithelium with yellow colours. b) Mallory Stain: It stains collagenous and reticular fibres with blue, smooth muscles with yellow, and elastic fibres with red colours. c) Azan Stain: It stains muscles red, reticular fibres with blue, and the nuclei red. d) Masson's Trichrome Stain: It stains collagenous and reticular fibres with green colour, nucleus with blue black and cytoplasm with red colour. 9. Silver Methods to stain collagenous and reticular fibres with dark brown. - Iron: It can be demonstrated in tissues by potassium ferrocyanide. - Bilirubin: It shows a blue reaction with ferric chloride. VIII -Melanin: It shows a blue reaction with potassium ferrocyanide. - Mucopolysacharides: They give a red colour with P. A. S. Stain. - Hyaluoronic acid: shows a blue colour with Alcian blue stain. - Reticular Fibres: are demonstratated by silver methods. - Elastic Fibres stain brown with Orcein: and stain black with Verhoeff. - Collagenous Fibres: give green colour with Masson's stain. - Lipid: Fat can be stained orange with Sudan III, or black with Sudan black. - Ncurones: can be stained brown with silver stain. - DNA =Deoxyribonucleic Acid: can be stained red with Feulgen reaction. - RNA =Ribonucleic Acid: can be stained blue with basic dyes. - Methyle-Grcen Pyronin Stain: gives a blue colour with DNA and a red colour with RNA. - Alkaline Phosphatase Enzymes: can be demonstrated by Gomori 's method. -Acid Phosphatase Enzymes: can be stained by Azo-dye method. - Succinic Dehydrogenase Enzyme: can be identified by Tetrazolium method. Immunocytochemistry - Immunocytochemistry: Tissues containing antigens are incubated in solutions containing labelled antibodies to these antigens. Combination of antigens and antibodies gives a coloured reaction on the examined tissue. This method is used to localize hormonal receptors on different cells and used also as tissue markers to detect cancer cells. FISH Technique - Fluorescent In Situ Hybridization (FISH) Technique: It is used to localize the sites of the genes on chromosomes. The previously prepared labelled radioactive DNA probes are used as antibodies to be hybridized with specific regions on chromosomes which are previously exposed to high ph in order to locate the positions of the different genes. The chromosomal region that binds to the radioactive probe during hybridization step are visualized by auto radiography. Localization of the sites of normal and diseased genes on the different chromosomes, are called Genomic Studies. IX The Cell Detinition: The Cell is the structural and funct ional unit of the body organ s. T he Cells arc bound together to form ti ssues. the tissues, arc combi ned to form organs. Several organs hav ing interrelated functions constitute the different systems of the body as: digesti ve system. urinary system. etc. Functions of Cells: The cells in the body perform many functions as: secre tion. excreti on. respiration. absorption. conduction. contrac ti on. sensati on and regulat ion of the other body functions. Size of cells: The different hody cells va ry in size. Some cells arc very small as certain cells of' the ce rebellum. whi le oth ers nrc very large as th e musde ce ll s The majority o f body cell s are medium-sized. Shape of cells: The different body cells vary in shape. Some cells arc rounded other. arc oval. flat. cubical or columnar in shape. Eu-ka ryot ic cells contain nuclei, Pro-karyotic cells conta in no nuclei. tructure of cells: Each cell is compo ed of the follo wing two main parts: I. T he Cytoplasm. cma 2. The Nucleus. lysosome~ / Endoplasmic Go l~tl Reticulum -........... Apparatus Nucleus Centriole- N udHr Envelo ~ Nucleolus C bromalln lcrofllaments And mlcrotub ules Cell Membrane Intercell u lar ju nctions A Diagram Of Cell Components - 1- The Cytoplasm The cytoplasm is formed of the following four main components: I. Cytoplasmic Matrix or Cell sap: It is a colloidal gel-like solution of pro- teins, lipids, carbohydrates, minerals, enzymes, small molecules and ions. 2. Cytoplasmic Organelles (Cell Organoids): They Are of Two Types: a) Membranous Cytoplasmic Organelles: They are small permanent organs which are enclosed in membranes. They perform important functions in each cell. b) Non-membranous Cytoplasmic Organelles. They are special cell components which are not enclosed in membranes. 3. Cytoplasmic Cytoskeleton: They form a supportive network within the cytoplasm, these are: Microtubules, Microfilaments and Intermediate filaments. 4. Cytoplasmic Inclusions (Cell Inclusions): They are temporary components of certain cells. They are usually an · accumulation of stored food as: glycogen and fat or an accumulation of pigments as: carbon and melanin. Cell Organelles The term Organelle means small Organ, each Organelle performs certain functions which are essential for the life and metabolism of each cell. The Cell Organelles are also called cell Organoids. They are.classified into: I.-Membranous Cytoplasmic Organelles which are covered by membranes. 2. Non-Membranous Cytoplasmic Organelles which are not covered by membranes. The Membranous Cytoplasmic Organelles Are Characterized By: - They are present in all nucleated cells. - They are permanent components of the cytoplasm. - They contain enzymes that participate in ·Cellular metabolic activities. - They are enclosed in membranes. The Membranous Cell Organelles Are The Following: 1. The Cell Membrane or plasma membrane. 2. The Mitochondria. 3. The Golgi Apparatus. 4. The Lysosomes. 5. The Endoplasmic Reticulum (Rough and Smooth Types). 6. Peroxisomes. 7. Endosomes =Newly-formed lysosomes. 8. Coated Secretory Vesicles. The Non-Membranous Cytoplasmic Organelles. They are not covered by membranes as: Ribosomes, centrioles, microtubules, microfilaments, cilia and flagella. -2- The Membranous Cell Organelles 1. The Cell Me1nbrane Definition: ll is the ou termost covering of the cytopla. m. It is also named Plasmalemma or Plasma membrane. Functions: They have multiple fu nctions to different body cells. Thickness: Its thickness ran ges from 8 to I 0 nanometer (8 to I 0 nm). With T he Light Microscope (LIM): l t ca nnot be demonstrated because it is very thin. E/M Of 2 Adjacent Cell membranes \ Vith The Electron l\1icroscope (ElM); it appears as if it is formed of three layer. , therefore it is ca lled tri-lamella r membrane. Its outer and inner layers appear as dark line ~. while its middle layer appears as a light area. Staining: The coat of cell membrane i. stained red wi th PAS stain. Molecular Structure of The Cell Membrane: It is formed of lipids, proteins a nd carbohydrates molecule covered by cell receptors. T he Lipid, Protein and Carbohydrate l\lolecules Are Present In the Following Arrangcment In the Cell Membrane: Outer Surface of The Cell Cell Receptor ___ ' G lycoprotein -- --__ - Glycolipid Cell G lycocalyx } Coat Hydrophilic Lipid ___ ~ -Q 0 ~~ Small lnlrinslc Prolein Hydrophobic Lipid · ---~ I II I 1 111~ C holesterol -- -- --- - -- - - Large IntrinsJc Protein -- Phospholipid.-- glands. e) \ Valery secretory glands: as sweat glands. f) Waxy secretory glands: as glands of extern al ea r. g) Cellular secretory glands: as tes tis and ovary. 4. Accord ing to the s hape and branching of the secretory part of the glands and the shape and branching of their duomyosin, They extend from the Z line till the middle of the dark band (They terminate just before, the middle of the dark hand therfore, the middle of the dark band appears light and is called H-zone). - 112 - Sarcolemma - ,, ~_____..__....., Skeletal Mu scle (L.S.) T.S. L.S. Smooth Muscle Fibres T.S. In Moderator Band C.T.~ ~ __,. -;: ' -:=·.. - ~Valve ,. _ - - ~ ---...:...- ,.,. _._ _....r ' ,· I , ~r. E ndocardium ~ '.: - -... -..... -. ':... I _..- ~-.,. - : -- ,.,. - - B. V·':,..1.. , ·'' ,.-.. · · ·. '· · T S I n Ca rd1ac. " -: -: -;x : , ,., , -........ -..... , ,...;::...-.. :. ,~ · -:.· - -_.. -... , , ,,,, , ,. ·.· MuscleFabres ·.... ,, ,·. ' '._,,.... '... '..... ·.- ;. _, ,~,,',, '. ,, ·..... ~ ,. ·. -·· _._.. ~ =:.. ·. · · ·. ,.. :.....- - _-:......... :..._:.: ,. ~-.: - ,· Oblique =. _. :. -----_...... -- ,-- - - - 4 0 - - -;.... ;..... , 0 -.. __ -.. ;. :- -.. :,,... : - -- , Cardiac Ftbres -:.... , , Epicardi urn '.. · - - - -.. - ,.. ·.... --... -...... : :--- -- ,..~4.,, """' - : -... - -- - - 411-- - - , Wall Of Heart (Cardiac M uscle A nd Valve) [Pla te 8] 2. Thick Filaments or Myosin Skeletal Muscle filaments which are formed of - -....T. Epimysium protein known as Myosin. They C.T. Perimysium extend in the dark bands only. Each myosin molecule has a head called Heavy Meromyosin and a tail called Light Meromyosin. Both ends of the thick filament are free, while the thin filament has only one free end and the other end is attached to the Z-Iine. N.B The dark band, therefore, R Dark Band appears darker because it contains the two types of filaments (the thick z Light Band and thin filaments). The light band appears light, because it contains one type of filaments (the thin filaments). z Contraction Of Muscles Thin Filament When a nerve impulse reaches the Thick Filament muscle, acetylcholine is released at its motor-end plate. Acetylcholine Structure Of Skeletal Muscle cause depolarization of sarcolemma and T -tubules. Depolarization of T-tubules causes 1---r--r--....-----r--f z -, I release of calcium ions from the I I sarcoplasmic reticulum. The released ~HI l Sarcomere During calcium causes gliding of the thin 1 Relaxation I fi1aments over the thick filaments. I The thin filaments thus slide 1-'--.L-..--L----L-4 z J towards the middle of the sarcomere. This will result in pulling the two Z-lines behind them z., during contraction. During relaxation,· calcium ions return again to the sacroplasmic reticulum.....................L-&-L-.-...&.-f H z r 1 Sarcomere During...J Contraction - 113- Electron Microscopic Structure Of Sarcolemma The Triad of Tubular System - The sarcolemma is the cell membrane of a muscle cell (muscle fibre). - It plays an important role in conducting the wave of excitation to the myofibrils through the presence of three types of tubules called The Triad of Tubular System. The Triad Of Tubular System 4. Includes: One Transverse T. Tubule Triad (3 Tubules) Sarcoplasmic Reticulum Surrounded By Two Sarcoplasmic Triad Tubular System Tubules: 1. The T-Tubule: It is a transverse tubule which runs transversely in the muscle fibre. These T-tubules encircle the myofibrils like collars. - The T-tubules are formed by invagination ~f the sarcolemma. They extend transversely through the sarcoplasm. The cavity of each T-tubule is continuous with the exterior. 2. Two Sarcoplasmic Tubules: These tubules are the modified longitudinal parts of the smooth endoplasmic reticulum of each muscle fibre. - They run transversely in each muscle fibre and each two sarcoplasmic tubules surround one transverse T-tubule. The three tubules (one T-tubule and the surrounding two sarcoplasmic tubules) are called triad tubular system. The Role of Tubular System in Muscular Contractions: - The T -tubules and the surrounding Two Sarcoplasmic Tubules control muscular contractions by regulating the concentration of calcium ions within the myofibrils of skeletal muscles. Calcium ions facilitate the interaction between actin and myosin filaments. Types of Skeletal Muscle Fibres Muscles contain pigmented protein called myoglobin. Myoglobin is red in colour similar to haemoglobin of RBCS. According to the amount of myoglobin, the type of innervation and the mode of contraction, the muscle fibres of skeletal muscles are classified into: -114- 1. Type 1: Red Muscle Fibres: They have large amounts of myoglobin, mitochondria and cytochrome. They have small diameters. They can sustain contraction for a long time without fatigue. Their energy is derived from oxidation of fatty acids. 2. Type II: White Muscle Fibres: They have small amounts of myoglobin and few mitochondria. They have wide diameters. Their contractions are quick, but they become fatigued easily. Their energy is derived from glycolysis. 3. Type III Intermediate Muscle Fibres: They have intermediate characters between red and white fibres. N.B.: Human Muscles contain the three types of muscle fibres. Cohenheim's Areas: These are formed by the collections of myofibrils inside the sarcoplasm forming groups of myofibrils separated with the sarcoplasm. Development and Regeneration of Skeletal Muscles In the embryo muscle fibres develop from Mesodermal Myoblast Cells. In adults, they regenerate from satellite cells present outside the sarcolemma Growth of muscles and repair of torn muscles occur by the proliferation of the satellite cells which are stem cells present outside the sarcolemma and can differentiate into myoblast cells then into new muscle fibres. Changes at the Musculo-Tendonous Junctions: -The C.T. epimysium, perimysium, and the sarcolemma are firmly attached and continuous with the C.T. of the tendon. -The muscle fibres stop abruptly at the junction of the muscle with its tendon. 3. Cardiac Muscles The heart is formed of two thin atria and two thick ventricles. The cardiac muscle forms the main wall of the heart and is known as myocardium. The wall of the heart is formed of the following 3 layers: 1. Epicardium 2. Myocardium 3. Endocardium l.The Epicardium: It is the visceral layer of the pericardium. It is a serous membrane formed of: Simple squamous epithelium and a layer of C. T. which contains; fat cells and the branches of the coronary vessels. 2.The Endocardium which lines the heart from inside. It is formed of the following four layers from inside outwards: a) Simple squamous endothelial cells joined together by tight junctions. b) Subendothelial layer of loose connective tissue. - 115- c) Dense elastic and cc!lzgenous membranes. d) Loose C.T. layer containing blood capillaries and Purkinje muscle fibres. 3. The Myocardium: It forms the main walls of the heart. It is formed of continuous joined chains of cardiac muscle fibres. Characteristics Of Cardiac Muscle Fibres Cardiac Muscle Fibres are formed of individual muscle cells joined together end to end by cell junctions. The fibres are surrounded by connective tissue endomysium which contains blood capillaries and lymphatics. - Cardiac muscle fibres have small diameters. They branch and join each other forming a continuous sheet. They contract spontaneously (involuntary m action). Cardiac Muscle Fibres - Striation: They have irregular striations. -Nuclei are large, central in position and oval in shape. Most of the cardiac cells contain one nucleus, but some of them may have two nuclei. - The Sarcolemma: It is the covering cell membrane of muscle fibres, it is thin. - The Cytoplasm: It is granular acidophilic sarcoplasm and is rich in: glycogen, mitochondria and lipochrome granules. These lipochrome granules increase in number in old age as well as in brown atrophy of the heart (Aging Granules). ElM Picture of the Cardiac Muscle Fibres: - They are rich in myofibrils which are of variable diameters. -The myofibrils branch and anastomose with each other. -The myofibrils are surrounded with many mitochondria, glycogen granules, lipid droplets and with many Golgi saccules. - Cardiac Muscle Fibres are characterized by the presence of a Diad System instead of the presence of a triad system. - The Diad System is formed of one transverse T -tubule surrounded with One tubule of the endoplasmic reticulum. The T-diad Tubules are present at the level ofZ-lines -The cardiac muscle fibres are traversed at intervals by dark staining discs which extend across the fibres and are called Intercalated Discs. -116- The Intercaiated Discs - Individual cardiac muscle fibres are composed of several elongated cells. - Each cell has a central nucleus, therefore, the cytoplasm of the cardiac muscle fibres is not syncytium (the cytoplasm of each cell is isolated from the other). - The cardiac muscle fibres are joined end to end by the intercalated discs. - These discs are cell membranes, they prevent cytoplasmic continuity between the different segments. They are present at the level of Z-lines of cardiac fibres. -Each Disc has longitudinal and transverse portions (Stepwise). - There are three types of junctional complex at the intercalated discs which are: 1. Desmosomal junction, to prevent separation of cardiac muscle cells. 2. Adherens junction, to connect myofibrils of cardiac muscle cells. 3. Gap junction, to transmit impulses to all cardiac muscle cells. - Cardiac muscles of the ventricles are larger in diameter than those of the atria. - More T -diad system are present in the atrial than in the ventricular muscles. - The atrial muscle fibres secrete Atrial Naturetic Diuretic Factor which regulates the electrolytes and can lower the blood pressure. N. B.: Cardiac muscle fibres have no satellite cell, they cannot divide, nor regenerate after injury. They heal by fibrous tissue. Cardiac Muscles are mesodermal in origin. They are innervated by autonomic nervous system and are involuntary in action following "the all or non law". They have the ability to undergo rhythmic contraction. Valves of The Heart are formed of dense C.T. rich in elastic and collagenous fibres and are covered by simple squamous endotheliun. Phagocytic histiocyte celJs are present in its C.T. to engulf micro-organisms. The Fibrous Skeleton Of the Heart is formed by dense fibrous tissue. It is present at the junctions of the two atria with the two ventricles. Cardiae muscles and valves arc attached to this fibrous skeleton. Obliqu~ C:trdial' Fihrl'S Cardiac Muscle And Valve - 117 - The Conducting System Of The Heart It is formed of modified cardiac muscle cells that are specialized to generate and to conduct cardiac impulses to all heart muscles. The Conducting System Of The Heart Consists of: I. Sino- atrial node in the right atrium. It is the pace maker of the heart. 2. Atrio - ventricular node present in the inter - atrial septum. 3. Atrio-ventricular bundle of His: It branches into right and left bundles. 4. Right and left bundle branches: The right branch is called Moderator Band. Each of The previous parts of The conducting system.is formed of: - Cardiac muscle fibres with few myofibrils and many mitochondria. -They arc surrounded with vascular connective tissue. - Nerve fibres are present between these muscle fibres. The Moderator Band It is a bundle of cardiac muscle fibres through which the right branche of the atrio - ventricular bundle travers the cavity of the right ventricle to reach the lateral wall of the heart. It is well - developed in the heart of the sheep. The Moderator Band is formed of: Cardial muscle bundles, some fat cells, blood capillaries, Purkinje Musscle Fibres and bundles of nerve fibres. Delicate branches from the nerve fibres come in contact with the Purkinje muscle fibres, but nerve cells are not present in the moderator band. Characteristics Of Purkinje Muscle Fibres - The atrio - ventricular bundle and its branches are composed of elongated cells called. Fat Cells\,,._....,~~ T.S In Purkinje Muscle Fibres....... Purkinje cardiac muscle fibres. - These Purkinje fibres branch in the ventricular wall under the endocardium T.S.ln transm1ttmg the cardiac Cardiac Muscle Fibres impulses 5 times faster than the cardiac muscle fibres. T.S. In A Moderator Band - 118- -They are larger in diameter than the cardiac fibres. - They are paler in colour than the cardiac fibres. - They are usually grouped into bundles which are surrounded by C. T. sheath. - Each Purkinje fibre is formed of separate, short, thick, elongated cylindrical cells. - The sarcolemma of Purkinje fibres is thin and irregular. - The cytoplasm of the Purkinje muscle is granular and rich in glycogen. It has few myofibrils which are peripherally situated. The myofibrils are arranged parallel to the sacolemma. - Purkinje fibres have no Diad or Triad tubular systems. -The intercalated discs are absent in the Purkinje muscle fibres. - Purkinje muscle fibres have eccentric nuclei and many gap junctions. - Purkinje fibres are richly supplied with nerves and with non-anastomosing end arteris. The fibres are non-striated. The following table shows the differences between the three types of muscles: The Differences Between The Three Types of Muscles Smooth, Skeletal and Cardiac Smooth Muscles Skeletal Muscles Cardiac Muscles Action involuntary voluntary involuntary Site in the viscera Attached to bone in the heart Shape of fibres spindle-shaped cylindrical cylindrical Striations non-striated well striated non-clear striations Sarcolemma very thin very thick very thin Sarcoplasm pale cytoplasm red and pale cytoplasm red cytoplasm Size small in size large in size medium-sized Branching non branching fibres branch in face and tongue branching and anastomosing Length of fibres from 30-500 microns variable form continuous sheet Diameter of fibres Up to 10 microns up to 100 microns up to 25 microns Nuclei single and central multiple and peripheral central nuclei Intercalated Discs absent absent present Myofibrils with no sarcomeres regular sarcomcres irregular sarcomeres Triad of tubular system absent present presence of diad system Satellite cells absent present absent Regeneration from the pericytes from satellite cells cannot regenerate - 119- Nervous Tissue The nervous system of the body includes: l. Central nervous system: It consists of the brain and the spinal cord. 2. Peripheral nervous system: It consists of cranial nerves, spinal nerves. gang I ia, nerve endings and glial cells. ---.Dendrites The Neuron The neuron is the structural and functional unit of the nervous system. It is formed of a nerve cell with all its processes which are the dendrites ', and the axon. ' '....... Axon Hillock Characteristics Of A Nerve Cell: - The size of nerve cells ranges from 4 microns as the granular cells of the __ Axon cerebellum and up to 100 microns as the pyramidal cells of the cerebrum. - The cell membrane of the nerve cell is - !'lucleus of Schwann Cell very thin. - The nucleus of the nerve cell is vesicular (open-face type). It is very __ Node Of Ranvier rich in nuclear fluid. It is spherical in shape and central in position. It has a very thick nuclear membrane and very clear nucleolus. - The cytoplasm of the nerve cell contains all cell organoids and cell --Terminal End inclusions, but with no centrioles. One Neuron - The cytoplasm is rich in microtubules, neurofilaments and microtilaments. - The cyto(Jlasm of nerve cell is rich in Nissl Granules or Nissl Bodies. - Nissl Granules are specific basophilic bodies consisting of masses of rough endoplasmic reticulum with their attached ribosomes. - ThcJ' arc known as chromophil substance because they like certain stains. - They may uisuppear from their nerve cells during degeneration of neurones and the condition is known as chromatolysis. - 120- -Nissl granules are not pesent in axon and not present near the nuclear or cell membranes. - Nissl granules share in the formation of protein of the nerve cells. - They help in nutrition and in carrying the memory of nerve cells. - They can be stained by toluidine blue or by hematoxlin stains. - Golgi Apparatus in nerve cell is well-developed, it surrounds the nucleus. - Mitochondria are present in the body and processes of nerve cell. - Centrioles: They are not present in mature nerve cells, therefore they cannot divide. - Centrioles may be found in young nerve ce11s to form neurofilaments. - The cell inclusions of the nerve cells arc: - Glycogen granules which are imprortant for the function of nerve cells. - Melanin Pigments and fat droplets may be present in some nerve cells. - Yellowish lipofuscin granules are also present and may increase in old age. Classification Of Neurones Different Types Of Nerve Cells Stellate Pyramidal Pyriform Pseudo-U nipo,lar Bipolar Multipolar I. Neurones Are Classified According To The Shape Of Their Nerve Cells Into: I. The Unipolar Neurones: -They have only one process which branch to act as dendrites. - They are found in the amacrine cells of the retina. 2. Pseudo-unipolar Neurones: These neurones are bipolar, but their two processes form aT-shaped division. One branch act as an axon and the other act as dendrite. These neurones are present in: the spinal ganglia and in the mesencephalic nucleus of trigeminal nerve. 3. Uipolar Neurones: These neurones are spindle-shaped cells. They have an axon at one pole and a dendrite at the other pole. Bipolar Nerve Cells are Present in: - Bipolar nerve cells in the retina of the eye. -In the spiral ganglia of the internal ear. - In the vestibular ganglia of the internal ear. - In the olfactory epithelium of the nose. - 121 - 4. Multipolar Neurones: They are subdivided into the following 3 subtypes. a) Stellate-shaped or polygonal neurones: which are present in the anterior horn cells of the spinal cord and in the sympathetic ganglia. b) Pyramidal neurones: They are Pyramidal in shape, present in the cerebral cortex. c) Pyriform neurones: Are flask-shaped as Purkinje cells of cerebellum. II. Neurones Are Classified According To Their Functions Into: 1. Sensory Neurones as neurones of dorsal root ganglia. 2. Motor Neurones as neurones of anterior horn cells. 3. Inter Neurones which connect neurones together as in Retina. III. Neurones Are Classified According To The Length of their Axons Into: Golgi Type 1 Neurones: They have long axons as neurones of cerebral. cortex, their axons form the tracts in the brain and spinal cord. Golgi Type 2 Neurones: They have short axons as neurones of Retina. The nerve cell processes are the axon (efferent) and the dendrites (afferent). Differences Between Axon and Dendrites The Axon The Dendrites 1. It is a single process. 1. Usually multiple processes. 2. Usually it is thin and long. 2. Usually short and thick. 3. It has a uniform diameter along its 3. Thier thickness decreases gradually length. towards its end. 4. It branches at its end but may give 4. Have many fine side projections also collateral branches which arise called spines or gemmules. at right augles. 5. It contains neurofibrils but no Nissl 5. They contain Nissl granules and granules. neurofibrils. 6. Two types of axonal transport exist: 6. They receive impulses from other Antegrade and Retrograde. neurones via their synapses. The Axon It is formed of a cytoplasm known as axoplasm containing mitochondria, neurofibrils and neurotubules: ll is surrounded with a membrane known as axolemma. The axon hillock is the conical expansion of the axon at its origin from the nerve cell. it has no Nissl granules but it is rich in neurofibrils. - 122- Types Of Nerve Axons According To Their Covering Sheathes The axons may be naked or may be covered with: myelin sheath or with neurolemma or with both. On tracing any axon of an anterior horn cell of the spinal cord from origin to its termination, we can notice the following types of nerve axons: 1. Naked nerve axons without a myelin sheath and without a neurolemma as those axons in the grey matter and the terminal parts of axons at its motor-end plate in the muscles. 2. Nerve fibres which are covered with myelin sheath but without neurolemma e. g. the nerve axons in the white matter and also the optic nerve. Peripheral Nerve 3. Nerve fibres which are covered with myelin sheath and are covered also. with neurolemma. e.g.. the Pre-Gangliomc. F'b ~~ 7 sll·GIIlngJuooic Fa'bre 1 res penpheral somattc axons outstde the Types Of Nerve Fibres spinal cord. 4. Nerve fibres which are covered with neurolemma but are not covered with myelin sheath, e.g. the post ganglionic sympathetic nerve axons. The Myelin Sheath - It is a fatty tubular covering around the axon. - It is formed by neurolemma! cells which surround the peripheral nerves. In the brain it is formed by neuroglia cells (oligodendroglia). - It is composed of cholesterol, fatty acids and phospholipids. -The myelin sheath is white in colour. - It is interrupted at intervals by the nodes of Ranvier and by Lantermann's clefts. - At the node of Ranvier, the axon is not covered by myelin sheath. - Lantermann's clefts are the areas of discontinuities in the myelin sheath. These clefts facilitate the passage of Myelinated Nerve Fibre nutrition from Schwann cells to the myelin sheath. 123 Functions of Myelin Sheath: It protects the axon. IL accelerates conduction of nerve impulse. It also isolates nerve impulses. The Neurolemmal Cells Or Schwann Terminal Cells Pre synaptic - They are formed of a chain of Schwann Membrane cells around the myelin sheath. Synaptic Cleft - Each cell corresponds to an internodal segment.... and it comes in contact with the axon at the nodes of Ran vier. - Each cell has an oval nucleus and a ~--rtlffVpostsynaptic basophilic neuroplasm. membrane: - The Schwann cell in order to form the myelin sheath around the axon, it -====EIM==S=t=ru=c=t=u=re=o=fa=S=y=na=p=s=e== encircles the axon and rotates several times around it forming a series of rings of phospholipids. These rings will be the myelin sheath. Function of Neurolemmal Cells: I. They isolate nerve impulses. Formation oa· Myel~n Sheuah 2. They help in regeneration of neurones after injuries. 3. They form the myelin sheath around axons. The Synapse - Definition: It is the point of contact between the processes of the neurones. - In the synapse, there is no cytoplasmic continuity between neUI·ones. -Synapses may be Excitatory (facilitatory) or Inhibitory. -Chemical synapse transmit impulses through neurotransmitters. - Electrical Synapse transmit ionic signals very rapid as in retina. Types of Synapses a) Axo-dendritic Synapse: In which there is a contact between the axon of one neuron and the dendrites of another neuron. b) Axo-somatic Synapse: In which there is a contact between an axon of one neuron and a cell body of another neuron. c) Axo-axonic Synapse: Contact between the axons of 2 neurones. d) Dendro-dendrtic: Contact between dendrites of 2 neurones. - 124- ElM Structure of a Chemical Synapse: It is formed of the following: 1. Terminal Bouton: It is the terminal end-bulb of the axon. It is rich in these neuro-transmitters: Acetylcholine, Catecholamine and Dopamine. 2. Pre synaptic Membrane: is the membrane of the terminal end bulb of axon. 3. Synaptic Cleft: is the distance between Pre and Post-synaptic membranes. 4. Postsynaptic membrane: It is the cell membrane which belongs to the dendrites of the other neuron. It contains neurotransmitter receptors. 5. Gemmules or Spines: They are small projections which arise from the pre and post synaptic membranes. Functions of the Synapse: The arrival of a nerve impulse at the synapse will cause the discharge of the chemical transmitter into the synaptic cleft which either excites or inhibits the post-synaptic membrane. The Structure Of A peripheral Nerve Trunk The nerve trunk is formed of collections of axons arranged in bundles bound together by C.T. The whole nerve trunk is surrounded by C.T. fascia called epineurium. The C.T. around each axon is called endoneurium or Henl's sheath. In aT. S. of a nerve tmnk stained by hematoxylin and Eosin, alcohol will Perineurium dissolve the myelin sheath. Each nerve fibre shows a centrally stained axon surrounded by an empty space Myelin Sheath of the dissolved myelin, then a rim D of Schwann cell cytoplasm stained T.S. In A Nerve Trunk (Osmic Acid) pink (see plate 9). In a T.S. of a nerve trunk stained with osmic acid, the myelin sheaths will appear as black circles (Osmic acid stains only the myelin sheath). Nerve Ganglia A nerve ganglion is formed of nerve cells and nerve fibres surrounded by C.T. There are two types of ganglia: spinal and autonomic ganglia. The autonomic ganglia are of two types: sympathetic and parasympathetic ganglia. - The Spinal Ganglia are present Spinal GaagUon beside the spinal cord at its both sides. - They act as relay for sensations. - 125- - They are formed of pseudo-unipolar nerve cells. The axon of each nerve eel! forms a convolution called a glomerulus. - Each nerve cell is surrounded by many supportive satellite cells. - The ganglion is covered by thick capsule. - The Sympathetic Ganglia are present as sympathetic chain or as isolated ganglia in the different regions of the body. - They act as relay for the different motor functions arising from the spinal cord in order to distribute the autonomic orders to the different body organs. - They are formed of multipolar stellate-shaped nerve cells. - The nerve cells are surrounded by few satellite cells. Differences Between Spinal And Sympathetic Ganglia Spinal Ganglia Sympathetic Ganglia l. Present mostly at the dorsal roots of 1. Present mostly at the sympathetic the spinal cord. chain. 2. Covered by thick C. T. capsule. 2. Covered by thin C. T. Capsule. 3. Formed of pseudo-unipolar nerve 3. Formed of multipolar stellate shaped cells. nerve cells. 4. The cells may be large or small 4. All the cells are mostly of the small (20-120 microns). size (30 microns). 5. The cells are arranged in groups or 5. The cells are scattered. (not present rows. in groups). 6. The groups of cells are separated by 6. The nerve cells are separated by myelinated nerve fibres. non-myelinated nerve fibres. 7. The cells are rounded in shape in 7. The cells are irregular in shape in cross section. cross section. 8. Each ganglion contains few nerve 8. Each ganglion contains many nerve cells. cells. 9. The axon of each nerve cell is 9. There is no intra cellular glomerulus convoluted at its beginning in the because the nerve cells are nerve cell forming a glomerulus in multipolar and their axons are not its cytoplasm. convoluted. 10. There are more satellite cells l 0. Less number of satellite cells around each nerve cell. around each nerve cell. 11. There is no synapse between the 11. Synapse is present between the neurones. neurones. 1 12. It is poor in blood supply. 12. It is rich in blood supply. 126 The Neuroglia There is no C. T. in th e central nervous system; instead there arc the neurogli a. They form the supporting tissue between the neuroncs of the C. N. S. Neuroglia ca n be stained with silver or with gold chloride Neuroglia Are Classified Into: 1. The Neuroglia Proper, they are of 3 types: a) Macroglia or Astrocytes (protoplasmic and fibrous). b) Microglia or mcsoglia (mesodermal in origin). c) Oligodendroglia (with few dendrites). 2. Other Types of Supporting Neuroglia-like Cells Present In Nervous Tissue: a) Ependymal Cells : These are the simple cuboidal ciliated cells which line the cemral canal of the spinal cord and brai n ventricles. They are derived from the spongioblast cells. They form the Ccrcbro Spinal Fluid (C. S. F.). b) Satellite Cells : They are the small cells which surround the nerve cells of the brain and of the ganglia. They are of nutriti ve functions to nerve cells. c) Schwann or Ncurolemmal Cells. T hey are present around the axons of the peripheral nerves, they form the myelin sheath. They help in regeneration of cut nerves. d) Spongioblast Cells: They are primitive embryonic cells which can differentiate into neuroglia cells. c) Tanacytc cells which surround the neuroncs of Hypotha lamu.;. The Neuroglia Proper 1. Macroglia or Astrocytes = Star-Shaped Cells They are the largest type of neuroglia. T here a rc 2 Types of Astrocytes: (1) Protoplamic Astrocytes. (2) F ibrous astrocytcs. a) Protoplasmic Astrocytes: - They are ectodermal in origin (ari sing fro m spongioblasts). - T hey arc present in the grey matter· of the C. N. S. - T hey arc branched cells wi th multiple short thick processes. Protoplasmic As trocy te 127 - ll1eir cytoplasm as well as their processes are rich in cytoplasmic granules known as gliosomes which are considered as lysosomes. - Astrocytes communicate with one another by gap junctions, therefore information can flow from one cell to another. - Astrocytes influence the activity of neurones through the secretion of opioid substance called Enkephalin. - Astrocytes contain centrosomes, so they can divide. -They have neither axons nor Nissrs granules. -They have large rounded darkly-stained nuclie. - Their processes end on B.V. by foot-like expansions known as vascular end feet or sucker processes. b) Fibrous Astrocytes: They are similar to protoplasmic astrocytes but: - They are present in the white matter of C. N.S. -Their cytoplasm as well as their processes are rich in straight neuroglia fibres. - Thier cytoplasm is non-granular. - They have long, slender, smooth processes that branch infrequently. 2- Microglia Or Mesoglia: ·ibrous Astroc~·tc -They are mesodermal in origin=mesoglia. -They are present in grey and white matter. - They are small spindle-shaped cells with few short processes. - They have neither centrosomes nor N iss)' s granules. -They have flat oval darkly-stained nuclei. - They have an amoeboid movement and may change into macrophages. -They are phagocytic cells durinnI:: inflammation and during degeneration and regeneration of neurones. They eat foreign bodies. so they are called "Police Man of The Brain". - They play a defensive role during AIDS disease. - 128- Unipolar !'l erve Cells - I @ Spinal Ganglion (Silver Stain) Spinal Ganglion (H x & E) Scattered Small Multipolar :"erve Cells Sympathetic Ganglion (Silver Stain) Epineurium Neurolemma Axo~ Muscle Fibre Motor End Plate (Silver) T.S In Nerve T runk (Hx & E) [Plate 9] 3. Oligodendroglia - They are present in the grey and white matter. - T'hey are small branched cell s with large deeply stained nuclei. They contain centrioles. - Their processes are few, short and thi ck. - They are ectodermal i n ori gin. Oligodendroglia - They form myelin sheaths around C. N. S. nerves. - T hey are supportive, nutriti ve and insul ators for brain nelll·ones. F unctions Of Neuroglia I. They support the neurones. Th ey form th e bl ood brain barriers. 2. Th ey form the myelin sheath around axons (as the oligodendroglia). 3. T hey act as insulator beLween neurones (separating the neurones). 4. They have a nutritive functi on for neurones (as macroglia and satellite cells). 5. They defend again st inn arnrnations of neUI·ones (as microglia). 6. They hel p in regeneration of neurones (as oli godendrog lia and microglia). 7. T hey secr ete the C.S.F. (as the ependymal cells). 8. T hey secrete E nkephalin to influence neuronal activities. Degeneration And Regeneration Of Neurones Cutting of an axon of a neuron by a knife, trauma or infecti on w ill result in: I. Retrograde degeneration in its ner ve cell. 2. Traumatic degeneration at the site of injury. 3. \Vallerian degeneration at the peripheral pa rt of the axon. Retrograde Degeneration: These are the changes which occur in 1he nerve cell as a result of partial cutting of its axon. The changes arc in: the shape. size. nucleus. cell organoids and cell inclusions of the nerve cel l. C han ges in ner·ve cell: It swells. loses its dendrites. becomes O\ al 111 'Types Of Neuronal Degeneration s shape and small 111 s1ze. its cytopl asm becomes pal e. - 129 - The nucleus: It becomes pyknotic, eccentric in position and its nuclear membrane disappears. Degeneration of other nuclear components occur. Chromatolysis: It is the process of degeneration and disappearance of Nissl granules. Nissl granules: They are very sensitive to any toxin and to mild injuries. They break into small particles, they disappear completely from the nerve cells after 15 - days. These changes in the Nissl granules can be observed by methylene blue or by hematoxylin stains. Neurofibrils as well as Golgi apparatus degenerate gradually and finally disappear (they can be stained by silver). If the axon is completely cut, it will lead to complete death of the nerve cell especially if no regeneration takes place. Wallerian Degeneration These are the changes that occur in the axon, myelin sheath and neurolemma after partial cutting of the axon of one neuron. 1. Changes in the axon: The neurofibrils of the axon are swollen at interrupted areas giving the axon a beaded appearance. Later on, the axon begins to break into amall pieces of different lengths which can be stained by silver. 2. Changes in the myelin sheath: The myelin sheath is segmeneted to form fermentation chambers. Finally, the normal shape of the myelin sheath is changed into droplets of neutral fat and oleic acids. The myelin can be stained by osmic acid. The nodes of Ranvier will become widen and the inter-nodal segments retract and become irregular in shape. 3. Changes in the neurolemma: The neurolemmal cells increase in size and their nuclei divide by mitosis. Later on, the. cells form a tubular cord around the myelin sheath helping in regeneration of the cut neurones. N. B.: TraUJnatic degeneration: It is a rapid process of Wallerian degeneration occuring at th~ site of injury with the same previous changes. Regeneration Of Neurones Regeneration depends upon the degree of nerve injuries and upon these conditions: -Whether the axon is partially or completely cut. It also dpends upon the distance between the two cut ends. - Whether the wound is infected or not. - Whether the neurolemma is intact or not. -130 If there is no infection in a partially cut axon and if the neurolemma is intact; regeneration starts in the nerve cell by resuming its normal shape and contents. The neurofibrils of the central stump will grow to be connected with the distal cut end of the nerve to complete nerve regeneration. N. B. There are Other Types of Nerve Degenerations as: 1. Retrograde Transport Degeneration: When nerve axons are infected with Rabies or Herpes viruses, Retrograde Transport of these viruses occour through the axons of certain neurones causing infections to these neurones Therefore, Retrograde Transport Degenertion occurs to these infected neurones. 2. Transneuronal Degeneration: The neurones are functionally connected with each other by the synapse. If we isolate any neuron by cutting its dendrites, So, it will be disconnected from the other neurones. Therfore, it will receive no stimuli from the other neurones. In this case, transneuronal degeneration will occur in its axon. Nerve Endings These are special nervous structures present in certian areas of the body and are classified according to their functions into: Receptors and Effectors.. The receptors The receptors receive sensory impulses from outside the body or from the tissues in which they are present. These Receptors Include: 1. Receptors For Special Sense As: a) Photoreceptors of vision by the retina of the eyes. b) Audioreceptors of hearing by the organ of Corti of the ear. c) Chemoreceptors of' smell by the olfactory epithelium of the nose.. d) Chemoreceptors of taste by the taste buds of the tongue. e) Reception of changes in the posture and different movements of head and body by the crista ampularis and macula utriculi of the internal ear. 2. Receptors For Cutaneous Sensibility (Exteroceptors): a) Pain sensation by free nerve endings. b) Temperature sensation by Krause bulb, Ruffini organ and free nerve endings. c) Touch sensation by Merkel's disc, Meissner's corpuscle and free nerve endings. 3. Receptors For Deep Pressure and Vibration Sense (proprioceptors): a) From skin, muscles and wall of organs by Pacinian corpuscles. b) From muscles, tendons and joints by muscle spindles and tendon spindles. 4. Receptors from the wall of viscera (Visceroceptors) to transmit autonomic sensation from the stomach, bladder.. etc. to the central nervous system. - 131 - The Exteroceptors 1. Receptors In The Epithelial Tissue Non - Capsulated Receptors a) Free or Bare - Nerve Endings These endings are fo rmed of non myelil~ated sensory nerve fibres. They branch inbetween the epithelial cells. Sites: epidermis of s]
