Muscular Tissue PDF

Muscular Tissue MUSCULAR TISSUE It is formed of Striated muscles Skeletal Striated, voluntary Cardiac Striated, involuntary Non striated muscles Smooth muscles Non-striated, involuntary Types of muscle fibers SkeletalMuscle They are cylindrical in shape, multinucleated with transverse striations. Nu...

Muscular Tissue MUSCULAR TISSUE It is formed of Striated muscles Skeletal Striated, voluntary Cardiac Striated, involuntary Non striated muscles Smooth muscles Non-striated, involuntary Types of muscle fibers SkeletalMuscle They are cylindrical in shape, multinucleated with transverse striations. Nuclei are elongated and peripheral under the sarcolemma. In the transverse section, The cut section are polygonal and rounded. L.M.: It consists of parallel skeletal muscle fibers arranged in bundles (fascicles) separated by a loose connective tissue (perimysium). The whole muscle is enveloped in a dense connective tissue (epimysium) continuous with the tendon. Individual muscle fibers are sheathed by a thin connective tissue called (endomysium) in which blood vessels and nerve fibers run. Skeletal muscles LM of Skeletal Muscle Fibers -Are cylindrical parallel fibers. -Covered by a plasma membrane (sarcolemma). -Are multinucleated fibers: have multiple cigar- shaped peripheral nuclei. -Their cytoplasm (sarcoplasm) is acidophilic &shows transverse striations. Structure of the muscle fiber EM of Skeletal Muscle Fibers -The muscle fiber is mostly occupied by longitudinal fibrils (myofibrils). Between the fibrils the scanty sarcoplasm contains mitochondria localized around myofibrils in the region of light bands. The Golgi is present in the perinuclear sarcoplasm while SER forms an elaborate membrane system around myofibrils. The sarcoplasm contains glycogen granules and lipid droplets which serve as energy sources. A pigment known as myoglobin Each myofibril shows alternate dark& light bands. The myofibril is divided into repeating segments which are separated by dark lines called z-lines. The segment between two successive z-lines is called the sarcomere and is 2-3 um in length Sarcomere Contents of the sarcomere: There are two types of filaments in the sarcomere: A- Thick filaments formed of myosin present in the center of the sarcomere. constitute the dark or Aband. B- Thin filaments formed of actin extending from the zline on both sides for a distance of 1 um forming the I-band and extend into the A-band C-There is an area in the center of the Aband which is not reached by thin filaments and called Hband. D-At exactly the center of thick filaments, a series of projections connect the thick filaments together in a transverse direction, forming a thin dark line in the middle of the Hband and called M-line Sarcoplasmic reticulum The sarcoplasmic membrane system: Each myofibril is surrounded by an elaborate system of SER called sarcoplasmic reticulum which is closely related to the fibril. Cardiac Muscle Cardiac muscle fibers compose the main bulk of the wall of the heart. They are striated involuntary fibers. LM: cardiac fibers are striated cylindrical branching fibers, each cardiac muscle cell possesses only one or two central nuclei. Adjacent cardiac cells are associated with each other by dark irregular line (intercalated disc). EM: The myofibril of cardiac muscle is almost similar to that mentioned with regards to skeletal fibers except for some peculiarities. - Cadiac Muscle sarcoplasmic reticulum is less abundant and run the whole length of the sarcomeres no fenestrated cisternae at the H-band. Transverse tubules run at the level of the z-line. the terminal cisternae are not regularly developed and only two tubes at a time (diads) can be seen in cross sections. Intercalated Discs Are junctional complexes between successive cardiac cells. - There are three main junctional specializations within the disc: 1-zonula adherents 2- Desmosomes. 3-gap junction is - Smooth muscles Smooth Muscle Fibers LM: Are spindle-shaped, broad in the middle and tapering at the two ends. The nucleus is spiral in shape and is present in the center of the wide portion of the fibers EM of Smooth Muscle Fibers -The organelles are mainly located in a small area on both sides of the nucleus. -There are mitochondria, Golgi, RER and free ribosomes. The remainder of the sarcoplasm is occupied by filaments. -The sarcolemma is invaginated to form little caves or caveolae which get in contact with the widely distributed SER cisternae localized beneath the membrane. Smooth muscle (Atlas of Histology with Functional and Clinical Correlations, 1E (2010) Smooth muscle (Wheater ’s Functional Histology)