Tissue : The living fabric
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TISSUE : THE LIVING FABRIC
The group of cells, when combine together to perform a specific function are known as tissue. There are four types of tissues.A group of cells similar in form, structure and embryonic origin which coordinate to perform a specific function alongwith their intercellular material is called a simpler tissue, while a group of cells that differ in their structure and function but coordinate to perform a specific function is called a compound tissue.
1. Epithelial tissue
Epithelial tissue was first termed by “Ruysh”
Characteristics
1. These are a single celled layer which are closely packed to each other. 2. Intercellular secretion is absent. 3. Cells rest upon basement membrane. 4. Cells are connected to each other by Desmosomes. 5. The basement membrane constitutes Lipids, mucopolysaccharides and connective tissue. 6. The free surface of cells may be smooth or may have fine hair-like cilia, stereo cilia and microvilli. 7. True epithelial tissue arises embryonically from either the ectoderm or the endoderm. 8. Epithelial cells possess the power of division and regeneration. Function of epithelial tissues. 1. Epithelial cells perform the function of protection, secretion, absorption, respiration, ultrafiltration and sensation. 2. Epithelial cells are made up of three germinal layer (Ectoderm + Mesoderm + Endoderm) 3. Epithelial layer protects the underlying tissue and helps in material exchange at the surface across the epithelial tissue. 4. Formation of exoskeleton. - 38 -
Tissue : The living fabric
Presence of Epithelial Tissue
These tissues are a continuous layer which cover the external surface of the animal body and Lumen surface and visceral organs, body cavities and blood vessels. Lining of some hollow organs are moist because of mucous secreted by epithelial cells.
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Tissue : The living fabric
Epithelial tissue are of two types (A) Simple Epithelial Tissue : 1. Simple epithelial tissue is of single layered tissues which rest upon the basement membrane. 2. It occurs on the secretory and absorptive surfaces. (B) Compound Epithelial Tissue : It consists of more than 2 layers and the deepest layer rest on the basement membrane. Being multilayered, it doesn’t perform the role of secretion or absorption but functions as protective layer against mechanical, chemical, thermal and osmotic stress. It is of two types. (1) stratified (2) Transitional
Tissue : The living fabric
Tissue : The living fabric
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2. Transitional Epithelial Tissue
These are thinner and more stretchable stratified epithelial cells. They have a single layer of cuboidal cell at the base and 2-3 middle layer of large polygonal cells. The cell of the topmost layer, superficial is large, broad, rectangular or oval. These are present in inner surface of the urinary bladder and ureters they help in expansion of the urinary bladder and accommodate urine while on stretch. It prevents loss of water from blood to urine.
Tissue : The living fabric
GLANDS Glands are group of cell performing the function of secretion . These are usually cuboidal shape. These have Zymogen granules in the cytoplasm are responsible for secretion. TYPES OF GLANDS I. Based on the kind of secretion and duct present : Glands are of two types (1) Exocrine (2) Endocrine Exocrine : E.g.. Salivary gland, Tear gland, gastric gland, intestinal gland. These Glands have duct (or) tubes which conduct their secretion to the respective site of action. Endocrine gland : Endocrine glands are those group of cells which secretes some chemical substance called Hormones that pass in to the blood stream (or blood vessel). Endocrine glands are also known as Ductless gland e.g.. Pituitary gland, thyroid, parathyroid, Adrenal etc.
2. Based on number of cells glands are of two types. (i) Unicellular glands : Occurs as single cells, example- Internal lining of the large instestine, two varieties of cells may be distinguished in this lining, namely the goblet or mucus secreting cells. - 43 (ii) Multicellular glands : The cells of the glandular part are some what cubical large and contain zymogen granules in their protoplasm. Multicellular glands divided into simple or compounds glands. Examplesweat glands, gastric glands, etc.
Tissue : The living fabric
3. Based on the shape and complexity The exocrine glands are of two main types : (1) simple gland (2) Compound gland.
Various forms of simple exocrine glands. Compound gland : These are branched system of ducts, exocrine in nature. These have tubes and Sacs or both and are present in duodenum, pancreas and submandibular salivary gland.
Tissue : The living fabric
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44 4. Based on the Mode of Secretion Exocrine glands are of three types : (1) Merocrine (Epicrine) (2) Apocrine (3) Holocrine. (i) Merocrine (or) Epicrine : Secretion occurs by diffusion e.g. Sweat glands, Salivary gland, Liver. (ii) Apocrine gland : Secretion Occurs from the apical part by squeezing gland. Eg. Mammary gland. (iii) Holocrine gland: Entire cell is filled with secretion. When cell die (or) disintegrate they discharge Secretion. Eg:.Sebaceous gland. 5. Base on the nature of Secretion Exocrine glands are of three types : (i) Mucous glands : In mucous glands, the secretion is in the form of mucous fluid such as mucopolysaccharides, as in the goblet cells in the intestine. These cells are called mucous cells or mucocytes. (ii) Serous glands : In serous glands, the secretion is in the form of a clear, watery fluid containing enzymes. The cells are termed serocytes. Examples, sweat glands, intestinal and parotid glands. (iii) Mixed glands : These glands secrete both serous and mucous secretions. These glands have both mucocytes and serocytes. Examples – gastric glands and pancreatic glands. CONNECTIVE TISSUE
Characteristics
Tissue : The living fabric 1. Connective tissue are the group of cells which provide structure, frame work and support of two different part of the organ of body 2. Connective tissue plays vital role in tissue repair. fat storage, transmission of blood vessel etc. 3. It has large amount of insoluble proteins which may be transparent or fibre containing fluid. 4. It is found in between different tissues & organs. 5. It originates from the embryonic mesoderm. 6. It comprises three basic components, cells, fibres & matrix. Function 1. Join one tissue to another in the organs. It binds skin with muscles & muscles with the bones. 2. Isolating sheath, supports, stores fat & insulate the body against heat loss. 3. Transport, defence & scavenging. 4. Shock proof cushion around kidney & eyeballs. 5. Packing material (areolar tissue), Repair (collagen fibres), formation of blood corpuscles (bone marrow).
1. Connective Tissue Proper A. Loose Connective tissue– Subdivided into 3 types. (i) Areolar tissue, (ii) Adipose Tissue, (iii) Reticular tissue. (I) Areolar Tissue
Tissue : The living fabric -These are simplest connective tissue occurs beneath the epithelial layer of hollow body organs skin, and walls of Arteries and veins Areolar tissue are made up of three types of cells : 1. Fibroblast 2. Macrophages / Histocytes 3. Mast cells (a) Fibroblast cell 1 Fibroblasts are the principle cells of the connective tissue. 2 These are irregularly shaped flat cell with long protoplasmic surfaces 3 These are also known as Fibrocytes. 4 These are the largest cells of the connective tissue with the branching processes. 5 Cytoplasm is rich in R.N.A. 6 Fibroblast are of two types due to presence of the kind of protein they have (i) Collagen. (ii) Elastin. (i) Collagen : Collagen have high tensile strength. (ii) Elastin : They have high power of elasticity due to which they prevent displacement and injury. (b) Macrophages : Macrophages are large amoeboid cells which are phagocytic in nature. They are also known as Scavengers cells. They ingest germs, microbes, debris and foreign matter they are responsible for phagocytosis (c) Mast cells : Large ovoid, irregular cells They store inflammation producing substances such as Histamine in dense granules. Histamine are released from the mast cells by providing defence mechanism during allergic conditions. There are three types of chemicals produced by Areolar cells (or) mast cells (1) Histamine : Vasodilator (2) Serotonin : Vasoconstrictor (3) Heparin : anticoagulant (which does not allow blood to clot within the body) (ii) Adipose Tissue : These are connective tissue beneath the skin, surrounding kidneys, mesenteries and bone marrow etc. These are spherical or oval cell called Adipocytes.
Tissue : The living fabric
The main function of cell is to store fats. Fats are narrowed into annular layer beneath plasma membrane Adipocytes syntheses, store and metabolizes fats. They prevent heat loss, heat insulating layer and acts as cushion. (iii) Reticular Tissue : It is found in lymph nodes, bone marrow & the spleen. Stelate shaped, the meshes of reticular tissue are filled with lymphocyte. (tissue & these meshes of tissue are called lymphoid tissue & those forms the stroma of red bone marrow are called myeloid tissue. The reticular cells and phagocytic cell play an important role in the defence mechanism of the body.
B. Dense Connective tissue : Subdivided into three types : (i) White fibrous tissue, (ii) Tendons, (iii) Ligaments.- 48 (i) White fibrous tissue : These are bundles of white fibres. They are densely packed. They have high tensile strength usually present at the joints between the skull bones to make them immovable. They have less flexibility. Eg. Duramater of the brain, capsule of the eye ball, septa of spleen etc.
(ii) Tendon : Tendons are very dense strong fibrous connective tissues which have thick parallel bundles. These are present at the attachments of skeletal muscles to a bones (muscle to a bone) (iii) Ligaments : These are fibrous connective tissues whose ground substance are densely crowded with collagen fibres which run to various directions. Ligaments joins (or) connects bones at a joint and holds their position.
Tissue : The living fabric
Tendon 1. Tendon is made up of white fibrous tissue with thick parallel band of collagen fibre 2. It forms a strong inextensible attachment 3. Tendon connects skeletal muscles to bone 49 –
Ligament It is made up of yellow elastic tissue with some collagen fibres remaining in different directions. It forms extensible attachment Ligament connects one bone to another.
II. SUPPORTING CONNECTIVE TISSUE (1) Cartilage: Cartilage is solid semirigid and flexible connective tissue. A single cartilaginous cell is called chondrocytes (or) also known as chondroblast cells scattered in the matrix. Matrix of cartilage is known as chondrin. Chondrin provide rigidity to the chondrocytes. Cartilaginous tissues are large bluntly angular cells. Chondrocytes usually occurs in cluster of two or three cells in small spaces scattered in the chondrin. Covering of cartilage is known as Perichondrium. Types of cartilage : Cartilage is categorized in to 4 major parts 1. Hyaline cartilage (Primitive cartilage) 2. Elastic cartilage (occurs after formation of bones) 3. White fibrous cartilage or white fibro cartilage (strongest cartilage) 4. Calcified cartilage (due to deposition of calcium phosphate) (i) Hyaline cartilage : These are glass like cartilage where matrix is partly white or bluish. Chemical exchange between the chondroblast takes place by diffusion through the matrix Occurance: In early Embryo (1 to 5 months) cartilage of larynx (voice box) sternum part of ribs, nasal septum is made up of hyaline cartilage.
Tissue : The living fabric
(ii) Elastic cartilage : It is yellow in colour, opaque and highly elastic. These have more matrix and perichondrium. Occurance : Ear pinna, Tip of nose, Eustachian tube, Epiglottis
- 50 (iii) White fibro cartilage These are the strongest cartilage, perichondrium is absent. Collagen fibres are more, matrix is firm, opaque and highly elastic due to the presence of fibrous cells. Occurance : In the inter vertebral disc. In the pubic symphysis of the pelvic girdle.
Tissue : The living fabric (iv) Calcified cartilage : It is a modified hyaline cartilage due to deposition of Hydroxy appetite. Due to presence of calcium salts elasticity is reduced. Occurance : In the terminal region of long bones. Skull of frog. In the pectoral girdle of frog. BONE Bone is a solid, rigid and strong Connective tissue. Tissue of bone is known as Osseus tissue made up of Osteocytes cells. Covering of bones is called Periosteum. Study of bones is known as osteology and the matrix of the bone is known as ossein. Osteocytes are also known as osteoblast The matrix of bones is heavily deposited with appetite salt of Ca and phosphorous and chiefly a protein called ossein. The bones has centrally a protein called ossein. The bones has centrally placed soft part called bone marrow. Flat irregular spaces occur in the solid matrix called Lacuna Each lacuna has a flat bone cell which has a irregular shape and a long cytoplasmic process. This processes extend minute canals called These canaliculi radiate from lacuna the innermost soft layer of the bones is bone marrow which is of two types
- 51 1 Red bone marrow. 2. Yellow bone marrow. 1. Red bone marrow is specialized for synthesis of RBC and granular white corpusles Formation of Blood is known as Haemopoiesis.Red bone marrow occurs through out the skeletal of the embryonic stage (or) Foetal stage with development of the age Red bone marrow is restricted to humor, Femur, top Vertebra etc. Cranial bones under go gelatinization 2. Yellow Bone marrow has more fatty acids or fatty tissue. They can only undergo hemopoiesis during emergencies. Bone forms dense outer layers of longitudinal column like structure called the * Haversian system. These are connected to each other . In each Haversian system there are several concentric layers called Lamellae in longitudinal central canal . These canal carries blood vessel and nerves., Osteoblast produces phosphatase enzyme in a developing bone cell. Bone are of two types :(1) Spongy bone. (2) Compact bone.
Tissue : The living fabric
BONE 1. Bone has matrix of inflexible material 2. Bone is a hard rigid and solid connective 3. Osteocyte have protoplasmic processes 4. Bones are richly vascularised inside the bone marrow cavity III. Fluid Connective Tissue Blood :
CARTILAGE Cartilage has flexible material known as called ossein. chondrin. Cartilage is soft semirigid and flexible tissue. connective tissue. Chondroblast do not form protoplasmic processes. Cartilage does not have rich blood supply.
Blood is a fluid connective tissue. Blood cells are known as Corpuscles. Blood always exists from the pre occuring blood cells Blood lacks fibres.- 52 It is heavier than water PH in between 7.3 to 7.4 It is more viscous than water The matrix of the blood is plasma Blood constitutes 2 main components plasma and corpuscles. Composition of Blood
Tissue : The living fabric
lood
Plasma
Blood corpuscles Formed elements of blood
Erythrocytes (RBCs)
Leucocytes (WBC’s)
Thrombocytes (Blood platelets)
Granulocytes
Agranulocytes
Eosinophils
Basophils
Neutrophils
Monocytes
Lymphocytes
Plasma Plasma is a viscous aqueous solution which is slightly alkaline. It contains many organic and inorganic substances and it has about 92 % of water and 8% of solid salts (or) solutes The solute includes glucose, Aminoacid, Fatty acids, Vitamins, Enzymes, Harmones, Antibodies, oxygen, urea, uric acid & creatinine etc. Out of the 8% solid content, 7% is the organic component and 1% inorganic content. Plasma contains 3 major classes of plasma proteins with in its 7% content :(i) Albumin (4.4 %) (ii) Globulin (2.3 %) (iii) Fibrinogen (0.3 %) Albumin is also known as serum albumin. Globulin is responsible for formation of Antibodies. Fibrinogen whose content is very low helps in blood clotting. Blood plasma retains water due to presence of Albumin and Globulin by their osmotic effects. Whenever excessive amount of plasma protein is filtered out of the blood it leads to swelling (or) oedema Albumin and globulin transports various substances such as thyroxin, ferric ions, Fe3+ etc. Globulins have a category called Immunoglobulins which basically act as antibody. These antibodies inactivate micro-organisms and other toxins. Plasma maintains the blood pH by neutralizing strong acid and bases which is dissolve as inorganic constituents Hence plasma acts as acid base buffers Functions of Plasma 1. Plasma helps in transportation of various chemicals, Harmones , ions etc. 2. Plasma provides body immunities through immunoglobulins.
Tissue : The living fabric 3. It helps in retention of fluid in the blood 4. It helps in maintenance of blood pH 5. It helps in uniform distribution of heat all over the body. 6. It conducts heat to skin for dissipation. Blood Corpuscles Blood cells are known as corpuscles It forms 40% - 45% of the whole blood Blood corpuscles are of 3 types (i) RBC (ii) WBC RBC (Red blood corpuscles) or [Erythrocytes] RBC are present in all the vertebrates .They are nucleated except in mammals.The shape and size of erythrocytes vary in different class of animals. In humans these are circular, biconcave and non nucleated. Human RBC measures 7 – 8 m. Whenever human erythrocytes mature, it is devoid of all the organelles including nucleus, mitochondria, etc. It is only constituent of a cytoplasm and plasma lemma surrounding is. The entire volume of cell is filled with oxygen adhering pigment called Haemoglobin. Haemoglobin is scattered through out the cell and appears to be red hence the cell is known as RBC. [Hemoglobin is a conjugate protein. The main protein is called globin and the complex protein with the ferrous (Fe+) complex is called heam. The haemoglobin pigment capacity to bind 4 molecules of oxygen to its 4 Ferrous ions Hence it forms oxyhemoglobin. When oxygen pressure is low oxygen dissociates from the Haemoglobin and CO2 replaces it which is called deoxyhaemoglobin. Hence, Hemoglobin carries oxygen and CO2. Carbondioxide is mainly carried by plasma and the RBC Haemoglobin is a respiratory pigment which is attached by coordination bonding to the O2. WBC (White Blood corpuscles-Leukocytes) (leuko -white) These are non-haemoglobin containing cells comparatively larger than the RBC and appear to be colourless. They can perform ameboid movements Their main function is to defend the body.. If the number of WBCs increase abnormally it leads to Leukemia [Blood cancer] But if the number declines it leads to leukopenia WBCs are of two types (a) Granulocytes [ with cytoplasmic granules] (b) Agranulocytes [ without granules in the cytoplasm (or) with a very low % of granules] (a) Granulocytes : Granules are 68%- 54 Granulocytes are further categorized into 3 types (i) Acidophils (Eosinophils) (ii) Basophilis (iii) Neutrophils (i) Acidophils (or) Eosinophils They have bilobed nucleus. They can be stained by acidic dyes. They show hypersensitivity of the body. (ii) Basophils These are minimum in the WBCs. Nucleus is less distinct. They represent most cells. They secretes Histamine, Heparin, and serotonin, (iii) Neutrophils These does not retain any of the dyes (neither acidic nor basic)
Tissue : The living fabric They are more in no in WBC. There nucleus is multilobed Neutrophils are phagocytic (feeder) in nature Its number always increases during pus formation (or) bacterial infection. (b) Agranulocytes Granules are 32% if present Granules are either absent or in very low percentage Agranulocytes are produced in the lymph glands like spleen, thymus etc. Agranulocytes are divided into 2 parts Lymphocytes, Monocytes LYMPHOCYTES 1. These are the smallest WBCs. 2. Nucleus is central 3. Life span is of 3 days 4. It produces chemical called Antibodies PLASMA 1. Plasma is a viscous solution containing organic and inorganic substances 2. Plasma can coagulate due to presence of fibrinogen. 3. Plasma contains normal no. of RBCs and platelets. BLOOD 1. Blood consists of erythrocytes and platelets plasma, leukocyte MONOCYTES These are the largest WBCs. Nucleus is horse shoe shaped. Life span is of 28 days They are phagocytic (engulfing) in nature. SERUM Serum is the blood plasma without. fibrinogen protein Serum can not coagulate due to absence of Fibrinogen. It has less no of RBCs and platelets. LYMPH It consists of plasma and leukocyte. . Lymph appears to leukocytes. be transparent due to
2. Blood appears to be red due to haemoglobin 3. Glucose concentration is less in blood 4. Blood carries several materials in the body 5. The amount of CO2 and other metabolic waste are normal in the blood 6. The percentage of ions (Ca2+ and Phosphorous) can be more in the blood with the dissolve metabolised. Thrombocytes (or) Platelets
Glucose concentration is higher in lymph Lymph transfers material from the blood to the body cell. The metabolic waste are much more in. the lymph. The percentage of ions (Ca2+ phosphorous and other protein) can be normal in the lymph
Platelets are also called thrombocytes They are non nucleated, rounded, oval, biconvex, disc likes cells whose number is 3 lacks/mm3 of blood. They bud (form) out from cytoplasm of megakaryocyte of the bone marrow. They are responsible for coagulation of the blood and they have life span of 5 to 6 days
Tissue : The living fabric when blood vessel injured they clump at the injured part and release certain factors also known as coagulating factors They promote coagulation and hence helps in preventing the blood loss. FUNCTIONS OF BLOOD 1. Blood transports many substances from one part of the body to the other part. Blood helps in transport of various chemicals, hormones, ions, food materials (from intestine to the various body parts), and respiratory gases (i.e., O2 from lungs to various tissues and CO2 from various tissue to lung.) 2. Blood helps in uniform distribution of heat all over the body. 3. The fluid of blood (plasma) helps in retention of water in the blood. 4. Blood helps in transport of excretory substance (urea ) from tissues to the excretory organs. 5. Blood maintains the body temperature by distribution of heat. 6. Blood helps in maintaining water balance in the body by exchange of water between circulating flood and tissue fluid. 7. Blood helps in maintenance of pH of the body because it has lot of inorganic substance or ions dissolve in plasma which neutralize acid (or) base. 8. Blood (RBCs of blood) capture the oxygen and carbondioxide by haemoglobin and hence, helps in respiration. 9. White blood corpuscles are defensive in function. It provide immunity to the body and secrete various antibodies to kill foreign microorganism. 10. Blood contains various anticoagulant substances like heparin, antithrombin etc. These chemicals does not allow to coagulate the blood. That is, It prevents internal bleeding. 11. The platelets of blood prevent excessive loss of blood by clotting it during injuries. MUSCULAR TISSUE These are developed from the mesoderm of the embryo. Muscular tissues are responsible for locomotion of the organisms and due to specialized property of contractibility i.e. they can shortened themselves and return to the original relaxed state. The cell contracts in a debinate direction. There are certain organized proteins responsible for contraction (or) relaxation, which are present in the cytoplasm of a muscle cells. The cells are usually called muscle fibres because they are thin and elongated. Humans muscle cells remain attach to the skeletal parts where as in certain animals these remain in the hollow visceral organs, blood vessels etc. The muscles are classified into three types (a) Striated (or) striped (or) voluntary muscles (b) Unstriated (or) Unstriped (or) involuntary muscles (c) Cardiac muscles Striated Muscular Tissue - 56 Striated muscles have transverse strip which show alternate bands of light and dark. Most of the Striated muscles are attached to the bones by tendons and they are also known as skeletal muscles. Striated muscles can be controlled by our will hence, they are also known as Voluntary muscles
Tissue : The living fabric Voluntary muscles are fibres of long unbranched cylindrical cells. They are approximately 40 mm long and 20m thin. It consist of various bonds called A-Bond, I - Band, Z -Band. Muscle fibres have a plasma membrane covering it known as sarcolemma and the fluid present inside the cell is sarcoplasm Sarcoplasm contains thin, long unbranched cross striations or cylindrical structures called myofibrils. These are arranged in the axis of muscle fibres. Striated muscles have sarcomere which has a distance between two Z line.
1. A - band (Anisotropic band or dark Band ) A - band is made up of myosin filament. Myosin filaments are thick filament. Myosin is a protein which has high rate of contractility. 2. I - Band ( Isotropic Band or Light Band) These bands have Actin filament which is made up of Actin protein. These are very thin filaments. These filaments are more in number and these are non-contractile filaments, (These are relaxing filaments i.e. they don’t contract) 3. Z- line (Krause line) They provides a very thin krause membrane [ these represent contractile unit] 4. H - band (or) H - zone (M - line) These are middle zone in the dark band, These are also known as Helles - lines (or) micellar lines When a muscle contracts, large amount of energy is needed which is produced by oxidation of Glucose in the muscle fibres. A muscles cell bears many elongated flat - nuclei and large amount of scattered mitochondria and Glycogen granules. A muscle fibre is rich in protein and during muscular contraction actin filament slide over myosin. This process is carried consequently by Acto - myosin. During Aerobic respiration, normal muscle contraction takes place and druing anaerobic respiration, oxygen supply is very less and contraction is very fast.
UNSTRIATED MUSCLE These are also known as smooth muscles cells. They do not have cross striation [ parallel arrangement of muscle fibre]. Functionally they are of 2 types
Tissue : The living fabric 1. Unit smooth muscles 2. Multi unit smooth muscles.
- 57 1. Unit Smooth Muscles They are composed of muscle fibres, joint together and all the muscle fibres contract together in a single unit. Unit smooth muscles may contract automatically and rhythmically. These occurs in the organs like hollow visceral in the walls like urinary bladder and gastric intestinal tract(Alimentary canal ) 2. Multiunit Smooth Muscle They are composed of more independent muscle fibres which are not closely arranged Hence, individual fibres contract as separate unit. for e.g they occur in hair roots, These are also present in large walls of blood vessels etc. smooth muscles cells are shorter than the Striated muscles. Number of nucleus, mitochondria and glycogen granules are lesser in numbers. Sarcoplasmic reticulum is less extensive and the protein filaments are not regularly arranged in to striations CARDIAC MUSCLE Cardiac muscles possess automatic rhythm and generate its own wave of excitation. Excitation passes directly from one cardiac fibre to another This is totally under involuntary control. Cardiac muscles have cross striations but they are very faint (light). Cardiac cells are short cylindrical cells joined end to end in a row. These cells have abundant cytoplasm rich in myofribrils known as sarcoplasts They have numerous mitochondria and glycogen granules. A cardiac muscle has very fine dark and light bands in a regular alternate arrangement Cardiac muscle have Sarcomeres and they are frequently branched to the neighbouring cells. Cardiac muscle fibres are arranged in Zig - Zag manner and a junction between them is known as intercalated disc ( the portion from where branching occurs) Cardiac muscles are present in the walls of heart . Cardiac muscles are enriched with red muscle fibre.
Tissue : The living fabric
NERVOUS TISSUE Nervous tissue is Ecodermal in Origin. Minimum power of regeneration is found in Nervous tissues (some time also consider power of regeneration is absent in Nervous tissue. ) Stimulation and conduction of impulses are represented by it. Show irritability Cell division is absent after maturity. Unit of Nervous tissue is Neuron (Nerve Cell).
I. Neuron or Sensory cell. Neuron is unit of nervous tissue or nervous system made up of 2 main parts (a) main body – cyton or perikaryon or soma (b) Long process – Axon or nerve fibre. Cyton Forms central Nervous system or Ganglia It consists of Granular cytoplasm (= Neuroplasm), large Nucleus , mitochondria, Ribosomes, fat globules, Nissil’s granules (Nissil bodies) and Neurofibrils. Small processes arises from cyton. These are known as dendrons and small branching of Dendron known as Dendrites. To serve high energy needs for impulse conduction Neurons have many mitochondria. Axon
Tissue : The living fabric Also known as Axis or Axis Cylinder or Neuraxis May form Nerve fibre The part of cyton where axon arises is called Axon hillock. Axon ends with small branches on muscle fibres or other neurons. Terminal part of axon is known as Telodendria which terminates in the form of end bulb called Buttons or Button terminates or knobs. Axon terminals inter connect with dendrite terminals and forms synapses.
- 59 II Nerve fibres Nerve fibre is an axon together with its enveloping sheaths. In peripheral Nervous system (Nerves) Nerve fibre is surrounded by (a) Outer most sheath - Myelin sheath (b) Middle sheath – Sheath of Schwann cell or Neurolemma (c) Inner most sheath – Endoneural sheath Endoneural sheath is made up of connective tissue having Neuroglial cells, also known as Sheath of Henle or key Retzious. The Myelin sheath appears as a tube around the axon At regular intervals (of about 1 mm in Humans ), the neurilemma is constricted and the myelin sheath is interrupted, forming the so called Nodes of Ranvier The segments between successive Nodes are called Internodes. The myelin sheath consists merely of the plasma membrane of over lying Schwann cells or (Oligodendrocytes) wrapped around the axon several times in a spiral fashion On the basis of structure Nerve fibres are of two types. 1. Myelinated Nerve fibres [medullated Nerve fibre] 2. Non – Myelinated Nerve fibres [ Non – medullated Nerve fibre ] Eg : - Certain axons of sympathetic Nervous system do not have a myelin sheath Each Internodal segment of axon and its myelin sheath is the product of a single schwann cell (oligodendrocyte) whose flattened nucleus is visible on external surface of the sheath Myelin sheath is lipoprotein but mainly lipoid in nature Nerve A nerve is a bundle of nerve fibres A single nerve fibre is surrounded by endoneurium Group of Nerve fibres are surrounded by perineurium
Tissue : The living fabric Whole Nerve is covered by a sheath of connective tissue known as Epineurium. Most nerves (Cranial and Spinal) possesses only myelinated fibres, but some (Sympathetic) possess both types of fibres. Sensory Nerve fibres – It bring the impulse towards the central Nervous system. Motor Nerve fibres – It carries the impulses away from central Nervous System. The numerous fibres of a nerve are aggregated into several small bundles Called fasciculi.
MORPHOLOGICAL TYPES OF NEURON
(i) Unipolar neurons : In this type of neuron only one axon, often with dendrites or collateral processes, takes its origin from the cell body. (ii) Pseudounipolar neurons : In this type of neuron, there may be single process arising from the cell body and then dividing into an axon and a dendrite. (iii) Bipolar neurons : The neurons in which two processes take their origin from the cell body, one on either side of the cell body, are known as bipolar neurons. (iv) Multipolar neurons : Such type of neurons have a large number of cell processes, at least one of which is an axon.
- 60 III. Neuroglia (Glial cell ) These are supporting cells which form a packing around the Neurons. This tissue divided into three kinds on the basis of their size, shape and functions. (a) Astrocytes – are found around the Blood vessels and appear to serve as regulator of the ionic environment of Neurons. (b) Oligodendroglial cells – form insulatory covering on the nerve fibres (c) Microglial cells – form reticulo – endothelial system.
Tissue : The living fabric
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