Module 4: Muscle Tissue PDF

MODULE 4: MUSCLE TISSUE Mary Judith S. Rebosa, MD, FPPS Faculty, Biology Department Our Lady of Fatima University UNIT EXPECTED OUTCOMES Describe the general characteristics and functions of the smooth, skeletal, and cardiac muscle tissues Explain the mechanism of muscle c...

MODULE 4: MUSCLE TISSUE Mary Judith S. Rebosa, MD, FPPS Faculty, Biology Department Our Lady of Fatima University UNIT EXPECTED OUTCOMES Describe the general characteristics and functions of the smooth, skeletal, and cardiac muscle tissues Explain the mechanism of muscle contraction in smooth, skeletal, and cardiac muscle tissues Analyze selected histological photomicrographs/pictures of muscle tissues GENERAL CHARACTERISTICS OF MUSCLE TISSUE Primary tissue of motion because of its fundamental property of contraction Derived from mesoderm Unit of structure is elongated in shape Muscle cells or fibers are grouped usually into bundles GENERAL CHARACTERISTICS OF MUSCLE TISSUE Cells and fibers are bound together by areolar connective tissue Sarcoplasm appears fibrillar due to myofibrils Requires a rich network of blood capillaries Acidophilic or pinkish when stained  SKELETAL MUSCLE Striated, voluntary, and attached to bones Consists of cylindrical non- branching cells with plenty of flattened Oval nuclei pushed to the periphery of the cell Arranged in bundles or fascicles  SKELETAL MUSCLE Sarcoplasm is acidic and contains myofibrils and organelles Contains inclusions such as lipid droplets and glycogen granules Contains dissolved myoglobin responsible for the brownish color of the muscle Sarcomere is the structural and functional unit of the skeletal muscle Region between 2 Z lines CONNECTIVE TISSUE SHEATHS OF SKELETAL MUSCLE ENDOMYSIUM Surrounds each muscle fiber PERIMYSIUM Surrounds groups of muscle fibers (each fascicle) EPIMYSIUM Surrounds whole muscles (groups of fascicles)  SKELETAL MUSCLE SARCOLEMMA Covering membrane SARCOPLASM Occupied by parallel columns of myofibrils for muscle contraction STRIATIONS Due to alternating light and dark bands of myofibrils SARCOMERE Structural unit of skeletal muscles SARCOPLASMIC RETICULUM Endoplasmic reticulum  MYOFIBRILS Roughly 80 of cellular volume Contractile elements of the muscle cell Arranged parallel to the long axis of the cell Consist of repeating units called sarcomeres Contractile unit Region between 2 Z lines Collection of myofilaments  MYOFIBRILS A bands (Birefringence in polarized light) Dark bands (anisotropic) I bands (do not alter polarized light) Light bands (isotropic) Thin filaments only H zone (Heller band) Middle of A band Z disc (Zwischenscheiben) Perpendicular protein plate in the middle of the I band M line proteins (Mittelscheibe) Middle of H zone Help hold thick filaments in place Sarcomere 2 Z lines  MYOFILAMENTS MYOFILAMENTS Comprise the sarcomere Parallel to the long axis of the myofibril THICK FILAMENTS Occupy the middle zone of a sarcomere Span the region of the A-band THIN FILAMENTS Occupy the peripheral zones of a sarcomere More numerous but shorter Attached to each side of the Z lines PROTEINS IN MYOFILAMENTS THICK FILAMENTS Myosin THIN FILAMENTS F-actin (composed of G-actin subunits) Tropomyosin Troponin  MYOSIN Makes up 60% of total proteins 6 polypeptide chains 2 Heavy chains 4 Light chains 2 heads and 1 tail  F-ACTIN Formed by polymerization of two strands of G-actin molecules which are coiled around each other Possesses binding sites for myosin Anchored to the Z-line by alpha-actinin and desmin Troponin and Tropomyosin Arranged along both sides of the actin filaments Regulation of contraction  TRANSVERSE TUBULES AND SARCOPLASMIC RETICULUM Contains loose network of flattened tubules Surrounds the myofibrils (actin and myosin) Transverse Tubules Invaginations of sarcolemma at the junction of A & I bands 2 T-tubules surround each sarcomere Terminal Cisternae Expanded sarcoplasmic reticulum at both sides of T-tubules Triad One T-tubule + 2 terminal cisternae  MOTOR ENDPLATE/MYONEURAL JUNCTION/NEUROMUSCULAR JUNCTION Neuromuscular Junction Connection between an axon terminal and a muscle fiber where stimulation of the muscle cell to contract occurs Consists of the plasma membrane of the motor neuron axon terminal, synaptic cleft, and the motor endplate  MOTOR UNIT Somatic motor neuron together with muscle fibers it supplies  THE SLIDING FILAMENT THEORY OF MUSCLE CONTRACTION Each muscle cell or fiber contains myosin and actin filaments Sliding of filaments initiated by an influx of calcium ions into the sarcoplasm Actin filaments slide past between the thick filaments of the A-bands Myosin filaments form crossbridges with the actin filaments Contraction occurs Acetylcholine is removed by acetylcholinesterase Sarcoplasmic reticulum recaptures calcium Active sites are covered by the troponin-tropomyosin complex Relaxation occurs  TYPES OF SKELETAL MUSCLE FIBERS RED MUSCLE FIBERS (Slow-Twitch) Smaller with richer blood supply Sarcoplasm has more mitochondria, glycogen granules, and myoglobin Found in long muscles of the back and postural muscles of the neck and leg  TYPES OF SKELETAL MUSCLE FIBERS WHITE MUSCLE FIBERS (Fast-Twitch) Contract at a faster rate More forceful contraction Fatigue faster Muscles used for running (gastrocnemius)  TYPES OF SKELETAL MUSCLE FIBERS INTERMEDIATE MUSCLE FIBERS Have morphological and physiological characteristics that are in between red and white muscle fibers  PROPRIOCEPTIVE ORGANS IN SKELETAL MUSCLES NEUROMUSCULAR SPINDLE Muscle Spindle Stretch receptor within the body of a muscle that primarily detects changes in the length of a muscle Encapsulated fusiform structure that is between 1-6mm length PROPRIOCEPTIVE ORGANS IN SKELETAL MUSCLES NEUROMUSCULAR SPINDLE Parallel to muscle fibers Larger concentration in muscles involving complex movements Important for maintaining posture Respond to stretch by initiating reflexive contraction (Stretch Reflex) E.g. Patellar Tendon Stretch PROPRIOCEPTIVE ORGANS IN SKELETAL MUSCLES GOLGI TENDON ORGAN Senses changes in muscle tension generated by muscle contraction Golgi Tendon Reflex protects the muscle from excessively heavy loads by causing the muscle to relax CARDIAC MUSCLE Cylindrical, branching cells Mono- or binucleated Pale-staining centrally located nuclei More abundant sarcoplasm More numerous and larger mitochondria Also exhibit cross-striations  CARDIAC MUSCLE Striated, involuntary, found in the heart Muscle fibers arranged in bundles or fascicles Sarcomeres laid end-to-end Sarcomeres contain thick and thin filaments like skeletal muscle T-tubules surround the Z-lines  CARDIAC MUSCLE Sarcoplasmic reticulum is not as well-developed as compared to skeletal muscle Intercalated Discs Specialized junctional complexes which attach the terminal branches of cardiac muscle cells end-to-end Dark, transverse lines that occur at irregular intervals  CARDIAC MUSCLE Purkinje Fibers Modified cardiac cells specialized to initiate and conduct the electrical impulse that controls cardiac contraction  CARDIAC MUSCLE Purkinje Fibers Modified cardiac cells specialized to initiate and conduct the electrical impulse that controls cardiac contraction  CARDIAC MUSCLE FIBERS MYOFIBRILS Consist of sarcomeres laid end- to-end Sarcomeres contain thick and thin filaments Cross-striations are not as prominent as those of skeletal muscle cells T-TUBULES Surround the Z-lines Bigger lumen Only one cisternae is associated with a T-tubules (DYADS)  INTERCALATED DISC Allow instantaneous spread of contractile stimuli from one cell to another Regions Transverse portion Contains two forms of junctional complexes Fascia adherens: broad intercellular junctions Terminal Z-lines of the cell Desmosome Lateral portion Gap Junction: exchange of ions between adjacent cells  CARDIAC MUSCLE CONTRACTION Same events as skeletal muscle cells Calcium Comes from the sarcoplasmic reticulum and from outside the cells AUTONOMIC NERVOUS SYSTEM Efferent Fibers from the Motor Neurons Regulate the rate and strength of cardiac muscle contraction  SMOOTH MUSCLE Non-striated, involuntary, and found at the walls of hollow visceral organs Spindle-shaped, non-branching cells with single nucleus at the center Consists of thick and thin filaments which do not form sarcomeres Myofibrils do not run exactly longitudinally or parallel to each other Poorly developed sarcoplasmic reticulum No T-tubules  SMOOTH MUSCLE MYOFILAMENTS Thick Filaments Consist of myosin (less in number) Scattered all over the sarcoplasm Thin Filaments Mostly actin Anchored on dense bodies that contain alpha-actinin correspond to the Z-disks of the myofibrils of skeletal muscles Dense Bodies Anchored on a network of intermediate filaments made up of desmin  ORGANIZATION OF SMOOTH MUSCLE Organized to form bundles or fascicles separated by connective tissue Cells may occur singly or in disorganized cluster ENDOMYSIUM Wraps individual cells Made up of reticular fibers DESMOSOMES AND GAP JUNCTIONS Attach sarcolemmas of adjacent cells Cells are arranged parallel to each other with the thick part of one cell lying on the thin parts of neighboring cells SMOOTH MUSCLE  SMOOTH MUSCLE CONTRACTION Contraction caused by interaction of myosin and actin molecules Shortening occurs in all directions Calcium regulates contraction Calcium comes from the extracellular substance and sarcoplasmic reticulum  SMOOTH MUSCLE CONTRACTION Contraction does not need neural stimulation Controlled by autonomic nervous system Neurotransmitters from axon terminals are released into the intercellular space Neurotransmitters reach receptors on the surface of smooth muscle cells by diffusion and propagated to the other cells by gap junctions THANK YOU!