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WHERE AM I? Online Anatomy Module 1 INTRO & TERMS CELL EPITHELIUM CONNECTIVE TISSUE MUSCLE NERVOUS SYSTEM AXIAL SKELETON APPENDICULAR SKELETON MUSCLES EMBRYOLOGY MUSCLE see Marieb pp. 82-84, 153-166 MUSCLE CELL’S ROLE Muscle cell contracts along an axis to furnish force applied to what it is attached to MUSCLE CELL = MUSCLE FIBER Muscle cells are often called muscle fibers. Note the distinction with connective tissue cells, which construct extracellular fibers such as collagen. Muscle cells are also called ‘myocytes’, e.g., cardiomyocyte MUSCLE ACTIONS Muscle cells work together as ‘muscles’ (abs. etc) or layers of heart or tubes, for a purpose Visceral Somatic skeletal muscle rotation around joint* squeezing/ * constriction * how the force is applied lumen MUSCLE CONTRACTION: Requirements Force Generated Applied usefully Controlled Energized Sustained Varied for conditions MUSCLE CONTRACTION: Requirements GENERATED by interactions between actin & myosin Applied usefully connective tissues to tendons; visceral & cardiac muscle contract in a circle CONTROLLED voluntary & involuntary: nervous; & nervous + diffuse chemical control ENERGIZED blood supply; mitochondria ; ATP; glycogen - stored form of glucose SUSTAINED multiple muscle units; prolonged contraction (smooth muscle) VARIED FOR CONDITIONS sub-types of muscle The diverse requirements demand 3 three separate kinds of muscle MUSCLE CONTRACTION: Requirements GENERATED by interactions between actin & myosin ACTIN & MYOSIN FILAMENTS IN MUSCLE Z line/disc thin ACTIN filament thick MYOSIN filament In muscle, for strong shortening (contractile) force the actin filaments are stabilized and interdigitated with thicker myosin filaments, which pull them in deeper SKELETAL MYOFIBER IN LONGITUDINAL EM VIEW I band Z line/disc thin ACTIN filament A band I band H zone with M line thick MYOSIN filament Banding pattern - I & A bands, Z lines, H zones, M lines The regular arrangement of the filaments & their attachments yields a visible banding pattern across the fiber BANDING-PATTERN CHANGES IN CONTRACTION A band I band Z line 1 M line but no H zone I band myosin Sarcomere shortens 3 A band unchanged 2 I band shortens 4 H zone disappears actin SKELETAL MYOFIBER: Generating contraction Z line/disc thin ACTIN filament H zone with M line thick MYOSIN filament Tails of heavy (H) myosin bundle together to make the myosin filament ACTIN filament attached globular F actin molecules H & L myosin heads hinge step-wise along actin filament Actin-myosin interaction to generate myosin’s pull on actin filament Myosin head / Motor domain Parts of Motor domain Actin-binding site Regulatory domain interacts with tropomyosin under control of Ca 2+--switched troponin Thick filament - Rods of H myosin Catalytic domain Actin filament myosin rods held stationary 2 Actin filament ATP-catalysing site 1 Regulatory domain does the lever work, aided by the flexible start of the rod pulled MUSCLE CONTRACTION: Requirements Applied usefully connective tissues to tendons; SKELETAL MUSCLE striated/cross-banded myofiber sarcolemma capillary TENDON endomysium CT Myofiber in cross-section myofibrils SKELETAL MUSCLE: Connective Tissue Organization MYOCYTE PERIMYSIUM creates FASCICLE/ bundle endomysium EPIMYSIUM SKELETAL MUSCLE striated/cross-banded myofiber sarcolemma capillary TENDON endomysium CT Myofiber in cross-section myofibrils Myofiber in cross-section myofibrils Each myofibril consists of bundled myofilaments thick MYOSIN thin ACTIN But, at regular intervals along the relaxed fiber, only thin or only thick filaments are found. Why? PERIPHERAL MYOFIBRIL IN LONGITUDINAL EM VIEW I band A band I band Z line/disc thin ACTIN filament thick MYOSIN filament Hits thick & thin Hit only thin MUSCLE CONTRACTION: Requirements CONTROLLED voluntary & involuntary: nervous; & nervous + diffuse chemical control SKELETAL MUSCLE: INNERVATION Axons/nerve fibers to motor end-plates to cause contraction striated/cross-banded myofiber TENDON MOTOR END-PLATE or NEUROMUSCULAR/MYONEURAL JUNCTION AXON SCHWANN CELL AXOLEMMA SARCOLEMMA SYNAPTIC VESICLES mitochondrion synaptic cleft secondary/ junctional folds of POST-SYNAPTIC MEMBRANE SKELETAL MUSCLE FIBER/MYOCYTE MOTOR END-PLATE: LOCATION OF ‘TRANSMISSION’ MOLECULES SARCOLEMMA voltage-gated ion channels AXOLEMMA voltage-gated ion channels Acetyl Choline/ACh SYNAPTIC VESICLES synaptic cleft Cholinesterase PRE-SYNAPTIC MEMBRANE Ca2+ channels Ligand-gated ion channels ACh receptors POST-SYNAPTIC MEMBRANE SKELETAL MUSCLE FIBER/MYOCYTE SKELETAL MYOFIBER: Initiating contraction T/transverse tubule A-I junction Feet Terminal cisterna of SR sarcolemma Sarcoplasmic reticulum wraps around myofibril and releases Calcium ion, when stimulated via T-tubule & feet } Z line motor end-plate Triad = Ttubule + two terminal cisternae Motor end-plate - Sarcolemma AP - T-tubule AP - Feet - SR - Ca 2+ release MUSCLE CONTRACTION: Requirements CONTROLLED voluntary & involuntary: nervous; & nervous + diffuse chemical control ENERGIZED blood supply; mitochondria ; ATP; glycogen - stored form of glucose AROUND EACH MYOFIBRIL, meaning between myofibrils Glycogen granules energize Sarcoplasmic reticulum control Myofilaments generate force Mitochondria energize MYOFIBRIL THREE MAIN TYPES OF MUSCLE SMOOTH small but prolongable force; diverse types, uses, & controls; controlled partly by autonomic/involuntary nervous system, partly by chemicals released from nearby cells, and by cell-to-cell connections CARDIAC strong rhythmic contractions; controlled by own cell-to-cell connections; pace determined by autonomic innervation to a little of the cardiac muscle SKELETAL most forceful kind, but contracts only in response to voluntary/somatic nervous system activity; applies its force via well-organized connective tissue; strength of contraction needs high internal organization within the muscle cell/fiber THREE MAIN TYPES OF MUSCLE I SMOOTH small but prolongable force; diverse types, uses, & controls; controlled partly by autonomic/ involuntary nervous system, partly by chemicals released from nearby cells, and by cell-to-cell connections THREE MAIN TYPES OF MUSCLE II CARDIAC strong rhythmic contractions; controlled by own cell-to-cell connections; pace determined by autonomic innervation to a little of the cardiac muscle THREE MAIN TYPES OF MUSCLE III SKELETAL most forceful kind; but contracts only in response to voluntary/somatic nervous system activity; applies its force via well-organized connective tissue; strength of contraction needs high internal organization within the muscle cell/fiber THREE MAIN TYPES OF MUSCLE IV Muscle cells are often called muscle fibers. Note the distinction with connective tissue cells, which construct extracellular fibers such as collagen. Muscle cells are also called ‘myocytes’, e.g., cardiomyocyte THREE MAIN TYPES OF MUSCLE: Sub-types SMOOTH skin, cardiovascular, airway, uterine, other reproductive, urinary, gastrointestinal (GI) CARDIAC atrial, ventricular, nodal, Purkinje SKELETAL type I - slow, type IIa - fast oxidative, type IIb - fast glycolytic SKELETAL MYOFIBER: Needs determining structure Generation Force generation Stabilization Force application Control of contraction Energize CARDIAC MUSCLE INTERCALATED DISK striated/cross-banded CARDIOMYOCYTES Reticular fiber Capillary central NUCLEUS Sarcolemma & external lamina branching muscle fibers INTERCALATED DISC - electro-mechanical union ID is a strong myocyte-myocyte attachment + electrical connections Fascia adherens strength Maculae adherens strength Gap junction transmits contraction PURKINJE FIBER ventricle } Endocardium Subendocardium Large, pale cell specialized for conduction, not contraction Myofilaments Glycogen SMOOTH MUSCLE SMOOTH MUSCLE CELL has same contractile & control *machinery as skeletal myocyte, but less organized Reticular fiber Autonomic nerve axon Gap junction/Nexus Myocyte plasmalemma + glycoprotein External lamina * There is the important difference that smooth muscle uses Myosin Lightchain Kinase (MLCK) to phosphorylate the regulatory myson light chain as the main means to provoke the actomyosin ATPase to start contraction SMOOTH MUSCLE SMOOTH MUSCLE CELL has same contractile & control machinery* as skeletal myocyte, but less organized Filaments attach to DENSE BODIES serving the role of Z-lines CAVEOLAE for stimuluscontraction coupling serve role of T-tubule & SR system SMOOTH MUSCLE * There is the important difference that smooth muscle uses Myosin Lightchain Kinase (MLCK) to phosphorylate the regulatory myosin light chain as the main means to provoke the actomyosin ATPase to start contraction CAVEOLA Caveolae are plasma membrane invaginations found in most cell types of all four tissues. They are conspicuous in endothelial cells & smooth muscle. Membrane molecules: Caveolin - characteristic integral membrane protein Plasmalemma Cholesterol (lots) Molecules related to Transcytosis Endocytosis or Signal transduction SMOOTH MUSCLE View with H & E staining - solid pink mass (stained sarcoplasm) crosssection long.section Unseen are reticular and nerve fibers, plasmalemmas & external laminae Trichrome stains distinguish smooth muscle cells from collagen fibers SKELETAL MYOFIBER: Needs determining structure Generation Force generation Stabilization Force application Control of contraction Energize MYOFIBER: Stabilization* & Force Application materials Sarcolemma External lamina Nebulin* a-actinin* Z line Dystrophin Integrin M line* Titin* (“elastic”) Desmin* intermediate filaments SKELETAL MUSCLE: SENSORY INNERVATION striated/cross-banded myofiber TENDON Golgi tendon receptor Muscle spindle Sensory axon & spindle receptor The fine control of contraction in individual myofibers requires abundant sensory feedback on how the muscle as a whole is performing CARDIAC MUSCLE INTERCALATED DISK striated/cross-banded CARDIOMYOCYTES Reticular fiber Capillary central NUCLEUS Sarcolemma & external lamina branching muscle fibers CARDIAC PATHOLOGY Enlarged, but altered and weakened muscle of Ventricular hypertrophy Reticular fiber More & thicker fibers of Fibrosis Capillary Bad gap junctions Arrythmia altered connexin Blocked vessels damaged heart muscle (Cardiac infarct) WHERE AM I? Online Anatomy Module 1 ORIENTATION You are at the End CELL EPITHELIUM Caution how you exit. BACK on your CONNECTIVE TISSUE browser is needed MUSCLE Unfortunately there is NERVOUS SYSTEM no way that you can directly reach other AXIAL SKELETON topics listed here by APPENDICULAR SKELETON clicking on them. You get there by going back MUSCLES to the Paramedical Anatomy menu EMBRYOLOGY
