Muscle Tissue PDF

The State University of Medicine and Pharmacy Muscle tissue Department of histology, cytology and embryology  Types of movement in nature and in the human body ❖- by movement of cilia and flagella ❖- by contraction of cells of the body Muscle ce...

The State University of Medicine and Pharmacy Muscle tissue Department of histology, cytology and embryology  Types of movement in nature and in the human body ❖- by movement of cilia and flagella ❖- by contraction of cells of the body Muscle cells satisfy requirement of the body in movement. ❑Excitable ❑Contractile ❑Extensible ❑Elastic  Muscle is classified according to the appearance of the contractile cells. Striated muscle, in which the cells exhibit cross- striations at the light microscope level, and Smooth muscle, in which the cells do not exhibit cross striations. Striated muscle tissue is further subclassified on the basis of its location: Skeletal sriated muscle is attached to bone and is responsible for movement of the axial and appendicular skeleton and for maintenance of body position and posture. In addition, skeletal muscles of the eye (extraocular muscles) provide precise eye movement. Visceral striated muscle is morphologically identical to skeletal muscle but is restricted to the soft tissues, namely, the tongue, pharynx, lumbar part of the diaphragm, and upper part of the esophagus. These muscles play essential roles in speech, breathing, and swallowing. Cardiac muscle is a type of striated muscle found in the wall of the heart and in the base of the large veins that empty into the heart. Types of muscle tissues  Muscle Distribution: Skeletal – striated muscles mostly associated with the skeleton  Muscle Distribution: Cardiac – striated muscles associated with the heart large artery of lung  Muscle Distribution: Smooth – fusiform cells associated with the viscera, respiratory tract, blood vessels, uterus, etc. Smooth muscle Ureter Ductus deferens Striated muscles  SKELETAL MUSCLE is innervated by the somatic nervous system – voluntary!! consists of very long tubular structures ( called muscle fibres). contain many nuclei (up to several hundred ) placed beneath the plasma membrane (sarcolemma) Striated Muscle A I Striated Muscle (Skeletal) Repeating A and I bands alone each cell’s length creates repeating sarcomeres A I A I A I Three cells with sarcome res each SKELETAL MUSCLE Stimulation of Muscle Cells  Skeletal muscles (C) are stimulated by nerve impulses carried by axons (A) of motor neurons. Axon forms synapse – motor end plate (B). The excitatory transmitter is acetylcholine. Invaginations of the sarcolemma form the T-tubule system which "leads" the excitation into the muscle fiber. Close to the border between A- and I-bands of the myofibrils T-tubules are in close apposition with cisternae of sarcoplasmatic reticulum. This association is called a triad.  Innervation of Skeletal Muscle Motor end-plate: Synaptic cleft Acetylcholine and receptor Junctional Folds Junctional folds are cell membrane modifications of skeletal muscle cells to increase surface area of synapse Innervation of Muscle Calcium Regulation The transverse tubule (T tubule) is a cell membrane modification to transmit the action potential deep within the cell to stimulate local scarcoplasmic reticulum to release Ca++ T tubule = invagination of the cell membrane Innervation of Muscle  Sensory Innervation of Muscle Muscle Fiber / Cell Muscle Spindle  Regeneration. Satellite cells Satellite cells are small cells which are closely apposed to muscle fibers within the basal lamina which surrounds the muscle fiber. Satellite cells are believed to represent persistent myoblasts. They may regenerate muscle fibers in case of damage.  Red and White Red muscle fibers are comparatively thin and contain large amounts of myoglobin and mitochondria. Red fibers contain an isoform of myosin with low ATPase activity, i.e. the speed with which myosin is able to use up ATP. Contraction is therefore slow. Red muscles are used when sustained production of force is necessary, e.g. in the control of posture. White muscle cells, which are predominantly found in the white muscles, are thicker and contain less myoglobin. ATPase activity of the myosin isoform in white fibres is high, and contraction is fast.  CARDIAC MUSCLE Location: the heart Function: involuntary, rhythmic contraction Unit – cardiomyocyte (cell)  Cardiac muscle Light Microscope Picture. Electronic Microscope Picture. 1) Cylindrical 1) Few myofibrils. 2) Intermediate in diameter 2) Numerous mitochondria. between skeletal and smooth 3) Less abundant SR. muscle fibers. 4) Glycogen (Food source) & 1) Branch and anastomose myoglobin ( oxygen source). 2) Covered by a thin 5) Intercalated discs: are formed sarcolemma. of the two cell membranes of 2 3) Mononucleated. The Nuclei successive cardiac muscle are oval and central. cells, connected together by 4) Sarcoplasm is acidophilic and junctional complexes shows non-clear striations (desmosomes and gap (fewer myofibrils). junctions). 5) Divided into short segments (cells) by the intercalated discs. Skeletal muscle is not branched but cardiac muscle is branched because we need every part of the heart to contract at the same time  CARDIAC MUSCLE cardiac muscle cells are cylindrical, connected end-by- end, and form “functional fiber”, which often branches at acute angles.  CARDIAC MUSCLE They are connected by special junction - intercalated discs – that consist of gap junctions and desmosomes.  Cardiac muscle cells: 3 types: Contractile, Conducting, Secretory. Regeneration - intracellular  Excitation in cardiac muscle A special system of modified cardiac muscle cells – conducting myocytes – they form conducting system - Purkinje fibers.  Excitation in cardiac muscle Modified nodal muscle cells, which are called P-cells (pacemaker or pale- staining), generate rhythm of the heart contraction The rhythm can be modified by the autonomic nervous system, which accelerates (sympathetic) or decelerates (parasympathetic) heart rate. SMOOTH MUSCLE Smooth Muscle Anatomy  Origin of smooth muscle 1. Smooth muscle cells arise from mesenchymal cells. 2. These cells differentiate first into mitotically active cells, myoblasts, which contain a few myofilaments. 3. Myoblasts differentiate into mature smooth muscle cells. Very good regenerates!  Locations: walls of visceral hollow organs (stomach, uterus, ureter, blood vessels, eye) Functions: involuntary movement -- changes of lumen of hollow organs, movement of its contens , i.e.: - churning of food - peristalsis, - movement of urine from the kidney to the bladder, - parturition, - blood pressure, - accomodation and adaptation of the eye (The innervation -- by autonomic nervous system)  Unit – myocyte (cell) SMOOTH Cells are spindle- shaped. MUSCLE Individual cells are organized in sheaths In hollow organs they form layers: - longitudinal, - circular, - oblique. Contraction is usually slow and may take minutes to develop.  Smooth Muscle Contraction: also Ca+ dependent, but mechanism is different than striated muscle 1. Ca2+ ions released from caveloae/SER and complex with calmodulin 2. Ca2+-calmodulin activates myosin light chain kinase 3. MLCK phosphorylates myosin light chain 4. Myosin unfolds & binds actin; ATP-dependent contraction cycle ensues. 5. Contraction continues as long as myosin is phosphorylated. 6. “Latch” state: myosin head attached to actin dephosphorylated causing decrease in ATPase activity –myosin head unable to detach from actin (similar to “rigor mortis” in skeletal muscle). 7. Smooth muscle cells often electrically coupled via gap junctions Triggered by: Voltage-gated Ca+ channels activated by depolarization Mechanical stimuli Neural stimulation Ligand-gated Ca+ channels  Mechanics of Smooth Muscle Contraction Dense bodies are analogous to Z lines (plaques into which actin filaments insert) Myosin heads oriented in “side polar” arrangement Contraction pulls dense bodies together Contraction is slow and sustained Smooth Muscle (vascular) Relaxed Contracted