Lecture 1 The Muscular Tissue PDF

PROF Dr Noha A Makhlouf The MUSCULAR TISSUE Lecture 1: Histology of muscular By the end of the lecture the student will be able to : tissue. Classify the muscular tissue according to structure & function. Desc...

PROF Dr Noha A Makhlouf The MUSCULAR TISSUE Lecture 1: Histology of muscular By the end of the lecture the student will be able to : tissue. Classify the muscular tissue according to structure & function. Describe the organization of skeletal muscle and its surrounding connective tissue. Describe the types and characters of skeletal muscle fibers. Describe the LM & EM structure of skeletal muscle fibers and the correlated function. Define the sarcomere. Describe the ultrastructure of sarcomere and different filaments and the bands. Identify regulation of sarcoplasmic contraction and its deficiency. Correlate the disturbed structure to different clinical conditions (e.g. Duchenne’s Muscular Dystrophy) Describe regeneration in skeletal muscle, muscular atrophy & hypertrophy in different situations. Describe the LM & EM structure of cardiac muscle fibers and the correlated function. Identify the contractile properties of cardiac myocytes. Discriminate sarcoplasmic reticulum organization in different types of muscles. Describe smooth muscle structure. State the mechanism of contraction of smooth muscle and its regulation. Compare between different types of muscles(skeletal, cardiac and smooth). Compare between regeneration, atrophy & hypertrophy in the three types of muscle fibers. Classification 1. According to morphology: A. Striated B. Non striated 2. According to function: A. Voluntary B. Involuntry TYPES OF MUSCLE 1.Skeletal muscle: striated &voluntary 2.Cardiac muscle: striated & involuntary 3.Smooth muscle: non striated & involuntary Terms: Sarco Myo mysium  Skeletal muscle Muscle responsible for voluntary movement. Sites: Muscle attached to skeleton Face muscles. Eye muscle. Tongue muscle. The diaphragm (involuntary).  Connective tissue of skeletal muscle 1) Epimysium: dense CT covers the whole muscle. 2) Perimysium: dense CT surrounding each muscle bundle (fascicles). 3) Endomysium: loose CT surrounds individual muscle fibers. Function: it carries blood vessels & lymphatic & nerves to muscle fibers. C.T also firmly attach the muscle bundles together. Skeletal Muscle ▪ Shape and size :The muscle cell (fiber) is a contractile cell called muscle fiber (myocyte). ▪ Fibers are long cylindrical (1-40mm length) and appear polygonal in cross section. ▪ Fibers don’t branch (except in tongue and face) ▪ Structure: ▪ 1- L/M: ▪ Cell membrane (sarcolemma): is distinct ▪ Nuclei: multiple, oval and peripheral in position. ▪ Cytoplasm (sarcoplasm): acidophilic, shows clear transverse striation (alternating dark and light bands). ▪ 2-polarized microscope: ▪ The dark band is called anisotropic or A band ▪ The light band is called isotropic or I band 3-E/M of skeletal muscle A-Membranous organelles: 1-well developed SER named sarcoplasmic reticulum 2. Rows of mitochondria in-between myofibrils 3. Numerous golgi apparatus. 4. Few RER. 5. Inclusions:-myoglobin & glycogen.  3-Electron microscope of skeletal muscle B-Non membranous organelles: 1-well developed parallel longitudinally arranged myofibrils composed of myofilaments (thick and thin filaments) 2. Few ribosomes. C-Inclusions:-myoglobin & glycogen.  Sarcomere  Inclusions ❑ Glycogen acts as a source of energy for muscle contraction ❑ Myoglobin:- It is Oxygen binding protein. It is functionally & chemically related to HB It is red to brown in color according to its concentration in muscle fibers:- 1) Red fibers 2) White fibers  1) Red fibers (type 1) 1) White fibers ( type 2) ❖ Small in diameter ❖ Larger ❖ Large amount of ❖ Less myoglobin myoglobin ❖ More glycogen (pale) ❖ Many mitochondria. ❖ Few mitochondria ❖ Rich in oxidative ❖ Poor in oxidative enzymes. enzymes. Types of sk. ❖ Gets energy from aerobic ❖ Gets energy from M. oxidative glycolysis. phosphorylation of FAs. ❖ Slow continuous ❖ Fast (sprinting), and in contraction over time fingers(playing music & (long distance running) computer games) and muscles of posture of the back. ❖ Easily fatigued ❖ Not easily fatigued  Skeletal muscle fibers contain myofibrils that lie in the sarcoplasm (cytoplasm ) parallel to the long axis of the muscle fibers. Myofibrils consist of series of sarcomeres that consist of thin & thick filaments. Myofibrils  The arrangement of myofibrils beside each other shows transverse striations. Each dark band of one myofibril is present beside the dark band of the adjacent myofibril and so on. These arrangements of dark and light bands give the muscle fiber the appearance of transverse striations. The transverse striations in the muscle fiber are due to presence of alternating dark and light bands on each myofibril.. Myofibrils Sarcomere Thick filaments occupy the central portion of the sarcomere. Thin filaments attach to the z line and run parallel to & between thick filaments but not reaching the center of A band. I band is composed of thin filaments only. A bands are formed of thick filaments & thin filaments between them. H band is formed of thick filaments only. M line is a dark line in the middle of the H zone  Sarcomere Definition: It is the basic unit of contraction of striated muscle, It is the distance between 2 successive Z line. By EM: 1-Dark bands (A bands)in the middle of the sarcomere & are composed of thick filaments & thin filaments between them. In the center of A band a paler region, H zone, is seen in relaxed muscle 2-Light bands (I bands): are composed of thin filaments only. Darker transverse line, the Z line, bisects each I band. 3-H bands: are composed of thick filaments only. The sarcomere consists of : dark band in the middle and Half of light band (I band) on either side. Z lines.(α actinin)  Item Light band (I band) Dark band (A band) L/M Pale acidophilic Dark acidophilic E/M Light with central dark Z dark with lighter H zone line and middle dark M line. Molecular Only actin Both actin and myosin structure  Desmin a. Arrangement of myofibrils results in a characteristic banding (alternating dark & light bands. b. Intermediate filament called desmin; joins Z disks of adjacent myofibrils together. Medical application Desmin-related myopathy (DRM) The absence of desmin results in disorganized myofilaments and skeletal muscle fibers. The symptoms of the disease begin as progressive weakness in the muscles of the legs, followed by the rest of the body. DRM can affect cardiac muscles also (fatal). Medical application Duchenne muscular dystrophy (DMD) Dystrophin is a protein that binds actin & link it with the sarcolemma of skeletal muscle fibers then to extracellular matrix. Duchenne muscular dystrophy: a defect in dystrophin can lead to atrophy of muscle fibers.  Sarcomere (thin & thick filaments) nice to know Consist of 3 types of proteins: actin , troponin, tropomyosin. Actin is formed of (f actin) 2 strands of globular G-actin twisted in double helix. Tropomyosin are filaments in the grooves of actin. Troponin It is present in skeletal & cardiac muscle only. Thick filaments consist of myosin (has a tail and two heads). The heads are active sites The transverse tubular system T-tubule Definition: finger like invagination of the sarcolemma that surrounds each myofibril. These invaginations constitute the transverse T tubule system. -The sarcolemma sends this transverse(T-tubules) invagination into sarcoplasm at A-I junction Function: It conducts the impulse from outer to deeper parts of skeletal muscle.  Sarcoplasmic Reticulum It is SER Consists of longitudinal network and transverse parts. The transverse part is called terminal cisternae. Each t tubule lies between 2 terminal cisternae of the sarcoplasmic reticulum to form a triad. There are 2 triads in each sarcomere which are present in the junction between A and I bands (A-I junction). Function:- regulation of muscle contraction by releasing or sequestering Calcium. these units serve to couple excitation of muscle cells to their contraction (excitation contraction coupling.  Contraction of the muscle ✔ when nerve impulse arrives, the wave of depolarization sweeps along sarcolemma into T- tubules ✔ Depolarization of T- tubules releases Ca from sER + energy from ATP in mitochondria lead to interaction of actin & myosin pushing the 2 z lines inward shortening the distance between them & muscle contraction. During muscle contraction: H zone disappears as it contains now both actin & myosin. I band decreases in length while A band remains the same. The sarcomere & whole myofibril are shortened. Growth & Growth:- 1.In length{by satellite cells} regeneration 2.In width{by synthysis of new proteins by ribosomes} of skeletal Regeneration:- muscle By activity of satellite cells. Satellite cells After injury the satellite cells become activated, proliferating and fusing to form new skeletal muscle fibers Effect of exercise on muscle During prolonged inactivity: muscle shrink in mass (disuse atrophy) Exercise (strength training: muscle contraction against resistance, e.g weight lifting) increases the muscle size (hypertrophy) without increase in number of muscle fibers. Medical application Anabolic steroid use is used by athletes to increase their muscle mass with serious side effects. The presence of anabolic steroids is detectable in the body fluids for 6 months after the last dose was taken.  Cardiac muscle Contract spontaneously & display rhythmic beat. Shape and size: 1-Fibers are formed of individual short cylinderical cells connected together by cell junction to form long fibers. These junctions are called Intercalated discs 2-Fibers branch & anastomose forming network. 3-fibers are intermediate in diameter between skeletal & smooth m.  Cardiac muscle L/M: Nucleus: mono or binucleated, oval and central. Cytoplasm: acidophilic and shows less distinct striation than that in skeletal muscle. Thick and thin filaments arranged in poorly defined myofibrils.  EM 1. Mitochondria are more abundant than in skeletal muscle. 2. Sarcoplasmic Reticulum:- SR is poorly defined and contributes to the formation of diads, each of which consists of one T tubule and one profile of SR at the level of Z- line. 3-T tubules are larger than those in skeletal muscle associated with sarcoplasmic reticulum at the Z discs not at A–I junctions as in skeletal muscle. 4. Contain glycogen granules, especially at either pole of the nucleus, myoglobin.and lipochrome pigment(increases with the advance of age. Lippincot pp: 159  Intercalated discs :a step-like junction forming end to-end attachments between adjacent cardiac muscle cells. It consists of transverse & lateral portions. a. The transverse portion: 1-fasciae adherents: act as anchoring sites for actin filaments 2-Desmosomes (macula adherentes): bind muscle cells together and prevent their pulling apart under constant contractile activity. b. The lateral portion : large gap junctions, which facilitate ionic continuity between cells and aid in coordinating contraction; thus, cardiac muscle behaves as a functional syncytium. Regeneration in cardiac muscle. Cardiac muscle: do not regenerate because they have NO satellite cells. Injuries to cardiac muscle are repaired by the formation of fibrous connective (scar) tissue by fibroblasts.  Medical application Glycogen pathway abnormalities: muscle weakness due to muscle glycogen accumulation. Example is Pompe disease, which causes muscle hypotonia from lysosomal glucosidase deficiency (lysosomal enzyme). Glycogen accumulation leads to skeletal muscle & heart problems.  Smooth muscle Smooth muscle cells are nonstriated & involuntary. The muscle fiber having broad central part and tapering ends. Sites:- 1.Wall of blood Vs. 2.Viscera. 3. Erector pili muscle of the skin.  General appearance Shape and size: They are small, non branching spindle (FUSIFORM)shaped cells They have the smallest diameter. They have variable length according to the site. They range in length from 20 μm in small blood vessels to 500 μm in the uterus of pregnant women. They are arranged in layers {circular,longitudinal or oblique} Smooth muscle L/M Nucleus:- single, oval & central. Cytoplasm:- homogenous & acidophilic with no striations. Actin & myosin are present but are arranged irregularly No striation.  E/M 1-Small darkly stained Dense bodies (formed of α actinin corresponding to Z line of striated muscle) along internal surface of plasmalemma and in the sarcoplasm. 2-Sarcolemma shows caveoli (invaginations): these function like T tubules in conducting contraction impulses. 3-T Tubules are not present in smooth muscle 4-No sarcomere 5-SR is poorly defined.  The intermediate filaments insert into dense bodies forming lattice like arrangement. The intermediate filaments and actin are inserted into dense bodies. Muscle fibers are connected by gap junction that permit rapid passage of an electrical impulse from one cell to another. There is no troponin. Instead there is calmodulin. T.S. smooth muscles L.S. smooth muscle Regeneration in smooth muscle Smooth muscle can divide and regenerate.  Smooth Cardiac Skeletal Item Involuntary Involuntary Voluntary Action Wall of blood vessels and Myocardium of heart and Muscles attached to skeleton, tongue, Site viscera proximal aorta pharynx Non-striated striated striated Appearance Distinct Indistinct Distinct Structure sarcolemma Single, oval and central One or two, oval and central Numerous, oval and peripheral Nuclei Irregular arrangement No less Less in amount, branching Numerous, regular distinct striation Myofibrils and sarcomere distinct striation striation Absent (replaced by caveolae) Diad at Z- line Triad at A-I junction T tubules Absent present Absent Intercalated discs From mitosis can’t occur From satellite cells Regeneration  Resources Integrated Systems Lippincott illustrated review,p.121-123 Kaplan medical - Anatomy- muscle pp: 35-40 BRS (board review series) joints p 120 Thank you