Motivational Corner: + There’s no elevator to success, you have to take the stairs. Objectives: By the end of this lecture you should be able to: MUSCULAR TISSUE - Identify and describe the histological structure of the three types of muscle cells and list the differences between them. Extra notes Important notes in red Remember: + Types of muscles LM = Light Microscope EM = Electron Microscope Made of elongated muscle cells (fibers). New Vocabularies in this lecture: ▪Epimysium ▪Perimysium ▪Endomysium Striated Striated Non-striated ▪Contractile threads ▪Sarco-lemma Involuntary ▪Sarco-plasm Voluntary Involuntary ▪Sarco-plasmic Reticulum (SR) ▪Sarcomere ▪Intercalated discs LM pictures: + Skeletal muscle ▪ Cylindrical in shape. ▪ Non-branched. ▪ Covered by a clear cell membrane, the Sarcolemma. ▪ Multinucleated: nuclei are multiple and are peripherally located (close to the REMEMBER: sarcolemma). Bone and cartilage ▪ Cytoplasm (sarcoplasm) is acidophilic and shows clear transverse striations. have Basophilic cytoplasm We have 3 connective tissues that covers the muscle cell, from inside (Endomysium) covers the muscle fibers then the muscle fibers becomes a group to form bundles that are covered by (perimysium) then those bundles are covered by (Epimysium) Mysium = Flesh Epimysium Perimysium Endomysium Epi = Over Peri = Surrounding C.T septa that C.T that C.T that covers separates the Septa = separates plural of septum i.e the whole parallel bundles individual muscle partition to separate muscle of skeletal muscle 2 or more fibers. fibers. compartment from each other. Can not divide + There’s a video in the Regeneration of summary slide that Skeletal muscle Limited regeneration by satellite cells explains the satellite cells (stem cells on the muscle cell’ cells check it, it’s so s surface). helpful. Skeletal Muscle Fibers (EM picture) Sarcoplasm contains: ▪Parallel myofibrils.* ▪Numerous mitochondria arranged in rows between Because you’re smart you know that skeletal muscle needs so the myofibrils. much energy that’s why it have so many mitochondria :) ▪ Well developed smooth endoplasmic reticulum* Smooth ER is abundant because it secretes glycogen (Sarcoplasmic reticulum) “SR”. + calcium ▪Myoglobin pigment. [carry & store O2] - Myofibrils = fibers in the muscle cells -Myofilaments = actin + myosin ▪Glycogen. [store food] (Group of myofilaments gives me myofibrils) - Arrangement of actin + myosin is what gives us striation + Skeletal Muscle fibers (EM picture) • - Contractile threads (organelles), arranged DArk = A band longitudinally in the sarcoplasm. LIght = I band - Each myofibril shows alternating dark (A) and light bands (I). - The A band shows a pale area in the middle (H band) which is divided by a dark line (M line). You know H&M shop? :) - The (I) band shows a dark line in the middle (Z line). - The sarcomere is the segment between 2 successive Z lines. It is the contractile unit of a myofibril. - The myofibrils are formed of myofilaments (thick myosin and thin actin) - The (A) band is formed of myosin myofilaments mainly and the terminal ends of actin myofilaments. - The (I) band is formed of actin myofilaments. Didn’t get it? Don’t worry! Check this Video ➢ Found in the myocardium. ➢ Striated and involuntary. + Cardiac muscle ➢ No regenerative capacity L.M Picture E.M Picture ➢ Cylindrical in shape. ➢ Few myofibrils. ➢ Intermediate in diameter between skeletal ➢ Numerous mitochondria. and smooth muscle fibers. ➢ Less abundant SR. (Smooth ER) ➢ Branched and anastomose. ➢ Glycogen & myoglobin. (Source of energy) ➢ Covered by a thin sarcolemma. ➢ Intercalated discs: are formed of the two Remember: ➢ Mononucleated. Nuclei are oval and central. cell membranes of 2 successive cardiac Cardiac muscle ➢ Sarcoplasm is acidophilic and shows non- muscle cells, connected together by is covered by clear striations (fewer myofibrils). junctional complexes (desmosomes and gap Thin sarcolemma but Skeletal ➢ Divided into short segments (cells) by the junctions). muscle is intercalated discs. covered by thick sarcolemma. Skeletal muscle is not branched but cardiac muscle is branched because we need every part of the heart to contract at the same time. + Smooth muscle E.M. Picture L.M. Picture Features Sarcoplasm contains mitochondria Fusiform in shape and sarcoplasmic reticulum Present in walls of blood Small diameter vessels and viscera (digestive, urinary, genital.... etc). All involuntary muscles (Cardiac + smooth) have Myosin & actin filaments are Non-branched Gap junctions to allow irregularly arranged (that’s why no impulses to pass through (striations could be observed a regulated gate Thin sarcolemma between cells. (check the video in the previous slide) Cells are connected together by Mononucleated Nuclei are oval & Non-striated and involuntary gap junctions for cell central in position communication Sarcoplasm is non-striated and acidophilic Smooth muscle cells regeneration: - Can divide. - Regenerate from pericytes. → active regenerative response Summary: + SMOOTH CARDIAC SKELETAL Amazing video that Site Viscera, e.g. stomach Myocardium of the heart Muscle attached to simplify regeneration of skeleton muscles cells Shape Fusiform Cylindrical Cylindrical Interesting extra note Dr. Smallest Medium-sized Largest Diameter Raeesa mentioned in the lecture: Branching Non-branched Branched Non-branched If you have a patient that is suffering from hypertension and we took a chest x-ray, if we found Striations Absent Not clear Clear the heart has hypertrophied it means that he’s been suffering from hypertension for a while, but Absent Present Absent Intercalated discs if the heart appeared normal then hypertension has just started. Nuclei One central nucleus One central nucleus Numerous and peripheral NOTE: During cardiac hypertrophy the number of cardiac muscle cells Action Involuntary Involuntary Voluntary is not increased; instead, they become longer and larger in diameter. Active No Limited Regeneration + MCQ’s Q1: Which one of these features appears in the L.M Q5: Which of the following C.T. separates each of the skeletal muscle? individual skeletal muscle fibres: A. Multinucleated: Nuclei are peripherally located A. Epimysium. B. Mononucleated: Nuclei are central located B. Endomysium. C. Multinucleated: Nuclei are central located C. Perimysium. D. Mononucleated: Nuclei are peripherally located D. Sarcoplasm. Q2: The contractile unit of myofibril ? Q6: Cytoplasm (sarcoplasm) of skeletal muscles fibres is basophilic: A. Sarcoplasmic reticulum B. Sarcolemma A. True. C. Sarcomere B. False. D. Sarcoplasm Q7: Intercalated discs is present in which of the following type of muscle fibres. Q3: What is the name of the dark line in the middle of The ( I ) band ? A. Cardiac muscle. Q8: D Q8: A. M line B. Smooth muscle. Q7: A Q7: B. H line C. Skeletal muscle. Q6: B Q6: C. E line Q5: B Q5: D. Z line Q8: Which one of the following is a common feature Q4: B Q4: in both smooth and cardiac muscles? Q3: D Q3: Q4: The (A) band is contains only myosin Q2: C Q2: A. Steriation. myofilaments. Q1: A Q1: B. Fusiform cells. A. True C. Multinucleated. B. False D. Gap junctions. + Credit Done by: Team leaders: - Adnan Alkhaldi - Areeb AlOgaiel - Mohammed Amarshoud - Hazim Bajri - Abdulkarim Alharbi - Khalid Alghsoon - Anas Ali - Abdullad Alshathry Edited by: - Areeb AlOgaiel Thanks for checking our work, Good luck. -Team histology. For any questions or suggestions: [email protected].