Muscular Tissue PDF - Dubai Medical College for Girls

1 Updated 01/11/2024 MUSCULAR TISSUE ILOs: by the end of the session the students will be able to: 1- Differentiate the 3types of muscles under the microscope 2- Correlate structure with function of intercalated disc 3- Identify the triad tubular system There...

1 Updated 01/11/2024 MUSCULAR TISSUE ILOs: by the end of the session the students will be able to: 1- Differentiate the 3types of muscles under the microscope 2- Correlate structure with function of intercalated disc 3- Identify the triad tubular system There are three types of muscles: 1. Smooth 2. Skeletal 3. Cardiac General Characteristics of Muscles: ❖ The structural and functional unit is muscle fiber or muscle cell. ❖ The muscle cell is an elongated cell. ❖ The cell membrane is called sarcolemma. ❖ The cytoplasm is called sarcoplasm. ❖ The sarcoplasm contains both cell organelles and cell inclusions. ❖ Sarcoplasm is rich in fat, glycogen, pigments (myoglobin and lipofuscin), mitochondria, SER, and myofibrils. ❖ The muscle fibers have striations (skeletal and cardiac muscles) but, no striations in smooth muscles (plain muscles). ❖ The SER is known as sarcoplasmic reticulum. Skeletal Muscles Sites: Skeletal muscles are attached to the skeleton. Skeletal muscles are voluntary muscles except those in the upper third of esophagus, and some muscles of the pharynx. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  2 Updated 01/11/2024 The connective Tissue around Muscles: The C.T. around the whole muscle is called the epimysium. The perimysium is the C.T. around the muscle bundle. Each muscle fiber is surrounded by C.T. endomysium. This connective tissue has B.V, nerves, and lymph vessels. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  3 Updated 01/11/2024 https://www.pinterest.com/pin/141933825743000298/ Characteristics of Skeletal Muscles: Skeletal muscle fiber is a single cell that varies in length from 1 mm up to 40 cm. The muscle cell is surrounded with a basal lamina that has satellite cells. These satellite cells are responsible for regeneration of skeletal muscle. They are spindle shaped cells scattered in the basal lamina. The skeletal muscle fibers do not branch except in the face and tongue. Skeletal muscle fiber is a multinucleated cell. The nuclei are oval, flat, and peripherally situated. The sarcoplasm is strong acidophilic and granular. It is rich in glycogen and myoglobin granules. The sarcoplasm contains many mitochondria, Sarcoplasmic Reticulum and specific organelles known as Myofibrils. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  4 Updated 01/11/2024 https://www.physio-pedia.com/Sarcomere DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  5 Updated 01/11/2024 Types of Skeletal Muscle Fibers: 1. Red Fibers have large amounts of myoglobin, mitochondria, and cytochrome. They have small diameters. They can sustain contraction for long time without fatigue. 2. White Fibers: have small amounts of myoglobin and few mitochondria. They have wide diameters. Their contractions are quick, but they become easily fatigued. 3. Intermediate Fibers: have intermediate characters between red and white fibers. Development of Skeletal Muscles: In the embryo muscle fibers develop from myoblasts. In adults muscle fibers develop from satellite cells. Changes at the Musculo-Tendonous (myotendinous) junction: 1. The C.T. of the muscle (epimysium, perimysium, endomysium) and the sarcolemmae are firmly attached together and become continuous with the C.T. of the tendon. 2. The muscle fibers stop abruptly at the junction of the muscle with its tendon. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  6 Updated 01/11/2024 THE MYOFIBRILS OF SKELETAL MUSCLES Myofibrils are the contractile threads arranged longitudinally in the sarcoplasm giving longitudinal striation. The transverse striations in the muscle fibers are due to the presence of alternating dark and light bands on each myofibril. All dark bands of myofibrils are present beside each other and all light bands are also found beside each other. These arrangements of dark and light bands give the muscle fiber transverse striations. The dark bands are called A- bands. The light bands are called I-Bands. Each dark band is further subdivided by a pale area in its center called H-Disc. Bisecting the H-band is the M-line, M line is a region where lateral connections are between adjacent thick filaments. The major protein of M-line is creatine kinase. Phosphate + ADP → ATP This ATP is necessary for muscle contraction. Each light band is subdivided by a darkly stained zone present at its center called Z-line. Actin filaments anchor perpendicularly on the Z-line, and exhibit opposite polarity on each side of the line. The protein alpha-actinine, a major component of the Z-line. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  7 Updated 01/11/2024 The Sarcomere: The area of the myofibril enclosed between two adjacent Z-lines is called Sarcomere. The sarcomeres are the functional contractile units of muscle fiber. Each Sarcomere includes the whole dark band and the two halves of the two l- bands on both sides. The sarcomeres of each muscle fiber contract and relax as one unit. Myofibrils are formed of Myofilaments. The Myofilaments There are of 2 types: thin and thick myofilaments. 1-Thin Filaments: They extend from the Z line till the middle of the dark band. They terminate just before the middle of the dark band; therefore, the middle of the dark band appears light and is called H-zone. 2- Thick Filaments: They extend in dark bands only. One end of the thick filament is free, and the thin filament has only one free end and the other end is attached to the Z-line. N.B. The dark band, therefore, appears darker because it contains the two types of filaments (thick and thin filaments). The light band appears light because it contains one type of filament (thin filaments.). The H-Zone that is present in the center of the dark band is lighter because it has only one type of filament (thick myosin filaments). Thin myofilaments are formed of actin troponin, and tropomyosin. Thick filaments are formed of myosin. Electron Microscopic Structure of Sarcolemma Sarcolemma plays an important role in conducting the wave of excitation to the myofibrils through the presence of three tubules (Triad tubular system). DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  8 Updated 01/11/2024 The Triad Tubular System Includes: One Transverse T. Tubule Surrounded by Two Sarcoplasmic Tubules: 1. The T-Tubule is a transverse tubule is an invigilation of sarcolemma. Each two T-tubules encircle a sarcomere like a collar. The cavity of each T-tubule is continuous with the exterior. 2. Two sarcoplasmic Tubules are modified longitudinal parts of the sarcoplasmic reticulum. Myoneural Junction (Motor End Plate) Myelinated motor nerves branch out within the perimysium, where each nerve gives several terminal twigs. At the site of innervations, the motor nerve twig loses its myelin sheath and forms a dilated termination (axon terminal) that sits within a groove on the muscle fiber surface. At this site, Schwann cells continue to cover sarcolemma. Within the axon terminal, there are numerous mitochondria and synaptic vesicles that contain the neurotransmitter (acetylcholine). Between the axon and muscle fiber is a space (synaptic cleft). Inside the synaptic cleft, an amorphous basal lamina matrix is found. At myoneural junction, the sarcolemma of the muscle fiber is thrown into numerous deep folds (junctional folds). In the sarcoplasm below the junctional folds, there are several nuclei, numerous mitochondria, ribosomes, and glycogen granules. This area of sarcoplasm is known as the sole plate. On the surface of junctional folds of the post synaptic membrane, there are receptors for acetylcholine. A single nerve fiber (axon) can innervate one muscle fiber, or it might branch and innervate up to 160 or even more muscle fibers. The multiple DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  9 Updated 01/11/2024 innervations of many muscle fibers by a single nerve fiber called (motor unit). Clinical application Myasthenia Gravis It is an autoimmune disorder characterized by progressive muscle weakness caused by reduction in the number of functionally active acetylcholine receptors on the sarcolemma (post synaptic membrane) at myo-neural junctions as the circulating antibodies bind to acetylcholine receptors. Thus, inhibition of normal nerve-muscle communication. The body attempts to correct the condition, the segment of the membrane with affected receptors is internalized, and digested by lysosomes, and replaced by a new segment with unoccupied receptors. These receptors, however, are again made unresponsive to acetylcholine by the same antibodies and the disease has a progressive course. Myasthenia gravis is treated with medication (?) and or plasmapheresis. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  10 Updated 01/11/2024 Smooth Muscles Characteristics of smooth (plain) or involuntary muscles: * Smooth muscles are pale acidophilic. * They are arranged singly in the dermis of skin or in layers as in the wall of the internal viscera. * They are spindle – shaped (fusiform) cells. * Each muscle fiber is surrounded by a basal lamina & a network of reticular fibers. * The cytoplasm is rich in glycogen. * The nucleus is single, central (found in the widest portion), and rod- shaped or oval. *The juxta-nuclear region contains a small Golgi complex, mitochondria, and sarcoplasmic reticulum. * Pinocytic vesicles are frequent near the cell surface. * The peripheral cytoplasm appears homogeneous as the myofibrils appear only at high magnification. * Myofilaments (actin and myosin) are found. Actin is formed of (actin and tropomyosin and calmodulin). Calmodulin protein replaced troponin of skeletal muscle. * The myofibrils are arranged longitudinally and obliquely. * Desmin is an intermediate filament in all smooth muscles. * Vimentin is an intermediate filament present in vascular smooth muscles. * T- tubules are not present in smooth muscles instead there are caveolae on the surface. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  11 Updated 01/11/2024 *All smooth muscles originate from the mesoderm except the muscles of the iris are ectodermal in origin. *The number and size of smooth muscle fibers may increase during life as in pregnant uterus and in certain arteries. * Regeneration of smooth muscles takes place from pericytes. * All smooth muscles are involuntary except the ciliary muscles of the eye and special muscles in the urinary bladder. * Two types of dense bodies are present in smooth muscles; One is membrane associated the other is cytoplasmic. * These dense bodies contain alpha actinine protein, so they resemble the Z- line in skeletal muscle cells. * Thin & intermediate filaments are inserted into dense bodies. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  12 Updated 01/11/2024 https://ar.inspiredpencil.com/pictures-2023/smooth-muscle-cell Contracted smooth muscle cells appeared thick, short and deformed. There are two types of smooth muscles regards innervation: Visceral smooth muscles: present in large sheets. These cells have an abundant gap junction in between as they have a relatively poor nerve supply. These muscles function in syncytial fashion. Multiunit smooth muscles: each muscle fiber has its own innervation so rich innervations found as those of the iris. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  13 Updated 01/11/2024 Sites of Smooth Muscles 1. Digestive system: Muscles in the wall of the lower third of wall of esophagus, stomach, intestine, and gall bladder. 2. Respiratory system: Wall of trachea, bronchi, and bronchioles. 3. Urinary system: Wall of ureter, urinary bladder, and urethra. 4. Male genital system: Epididymis, vas deferens, and prostate. 5. Female genital system: Fallopian tube, and uterus. 6. All the media (middle part) of blood and lymph vessels. Cardiac Muscles Are striated branched muscles found in the heart. The muscle fiber is multicellular. The cells have intercalated discs in between. These discs are H and Ag stained. The sarcoplasm is acidophilic and pale. The nuclei might be one or two in number. The nuclei are oval, central, and vesicular. DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License  14 Updated 01/11/2024 Intercalated discs have desmosomes, adherence, and gap junctions. Clinical Relevance: Psoriasis ▪ Myasthenia Gravis Summaries and Key Points: stratified squamous o Different types of muscles o Different types of skeletal muscles o Different types of smooth muscles References and Additional Resources: Basic Histology by Jane Quire Latest Edition Color Atlas of Histology by Lesie P Gartner Latest Edition NAME: Nadia Mahmoud DESIGNATION: prof. of Histology DEPARTMENT: biomedical sciences DUBAI MEDICAL COLLEGE FOR GIRLS (DMCG), 2023. ©2023 by DMCG. This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License