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Chapter 10 Muscle Tissue and Organization 1 Muscles • Skeletal muscles are voluntary muscles because they can be moved voluntarily • Heart and digestive muscles contract on their own Muscles • Functions: – Body movement – Maintenance of posture – Temperature regulation (especially shivering when you are cold) – Storage and movement of materials • control of openings (sphincters) to gastrointestinal and urinary tracts – Support • abdominal cavity • floor of pelvic cavity Table 10.1a • Muscles made up of fascicles – groups of muscle cells Muscle Fascicle Copyright © McGraw-Hill Education. Permission required for reproduction or display. Table 10.1a • Muscle cells are called muscle fibers • Muscle fibers contain protein strands called myofibrils Muscle Myofibril Muscle fiber Fascicle Copyright © McGraw-Hill Education. Permission required for reproduction or display. Table 10.1a • Myofibrils made up of proteins called myofilaments Thin filament Thick filament Actin molecules Heads of myosin molecules Myofibril Muscle fiber Fascicle Copyright © McGraw-Hill Education. Permission required for reproduction or display. Fig. 10.1 Tendon Deep fascia Skeletal muscle • Tendons attach muscles to bones • Deep fascia covers muscle – – – – – – dense irregular connective tissue separates individual muscles binds muscles with similar function helps distribute nerves and blood vessels fills spaces between muscles sits deep to superficial fascia (aka subcutaneous layer) Fig. 10.1 • Epimysium surrounds whole muscle (deep to deep fascia) Tendon Deep fascia Skeletal muscle (a) Muscle Epimysium Fig. 10.1 • Perimysium surrounds each fascicle – dense irregular connective tissue – contains neurovascular bundles Tendon Deep fascia Skeletal muscle Epimysium Perimysium Perimysium Nuclei Muscle fiber Fascicle Vein NerveArtery (a) Muscle (b) Fascicle Fig. 10.1 • Endomysium surrounds each muscle fiber – areolar connective tissue – insulates each fiber from electrical charge of other fibers (each can contract individually) – contains reticular fibers that bind neighboring muscle fibers together Fascicle Muscle fiber Endomysium (a) Muscle Copyright © McGraw-Hill Education. Permission required for reproduction or display. Endomysium Table 10.1c Myofibril Sarcoplasm Sarcolemma (plasma membrane) Satellite cell Muscle fiber Striations Nuclei (c) Muscle fiber Fig. 10.4 • Muscle fibers derive from myoblasts in embryo • Multiple myoblasts fuse into single cell with multiple nuclei • Satellite cells are myoblasts that didn’t fuse – assist in repair if muscle injured Myoblasts Satellite cell Satellite cell Myoblasts fuse to form a skeletal muscle fiber Muscle fiber Fig. 10.3 • Plasma membrane of muscle cell = sarcolemma (sarco = flesh) • Cytoplasm = sarcoplasm • Sarcoplasmic reticulum stores calcium ions needed for muscle contraction – Parts of SR extend deeper across cell, called transverse tubules Sarcolemma Sarcoplasm Mitochondria Myofibrils Myofilaments Transverse (T) Sarcoplasmic reticulum tubule Terminal cisternae Nucleus Table 10.1d • Muscles move when myofilaments “walk” past each other • Myofibril shortens, contracting muscles • Muscles don’t “push”; They always pull Sarcomere Myofibril Myofilaments Thin filament Thick filament Actin molecules Heads of myosin molecules Copyright © McGraw-Hill Education. Permission required for reproduction or display. Muscle fiber Fig. 10.6 Sarcomeres I band A band Z disc H zone I band Myofibril • Sections of fibers create striations (stripes) in muscle tissue Z disc Myofilaments M line Sarcomere Transverse sectional plane (a) Sarcomere Z disc Thick filament Z disc Thin filament Thin filament Connectin M line M line Thick filaments and accessory proteins H zone I band A band I band (c) (b) Sarcomere TEM 400x Z disc M line Z disc H zone I band (d) A band I band A band H zone I band Thick filaments Thick filaments Thin filaments Thin filaments Connectin Z disc Thin filaments Connectin and accessory proteins Copyright © McGraw-Hill Education. Permission required for reproduction or display. Fig. 10.7 Thin filament • As muscles contract, striations change size M line Connectin Z disc Z disc H zone Z disc H zone H zone Thick filament Z disc I band M line Z disc I band A band I band Sarcomere M line I band A band Sarcomere A band I band Sarcomere (a) Relaxed muscle Sarcomere, I band, and H zone at a relaxed length. M line Z disc Z disc H zone Z disc I band H zone A band M line Z disc I band I band A band M line A band I band Sarcomere Sarcomere Z disc H zone I band Sarcomere (b) Partially contracted muscle Thick and thin filaments start to slide past one another. The sarcomere, I band, and H zone are narrower and shorter. M line Z disc Z disc M line A band Z disc Z disc Z disc M line A band A band Sarcomere Sarcomere (c) Fully contracted muscle The H zone and I band disappear, and the sarcomere is at its shortest length. Remember the lengths of the thick and thin filaments do not change. a-c: © Dr. H.E. Huxley Sarcomere Fig. 10.10 • Motor unit is a motor neuron and all the muscle fibers it controls • One motor unit controls some fibers in a muscle • Smaller motor units provide finer control (ex. eye muscles) Spinal cord Motor neuron 1 Motor neuron 2 Neuromuscular junctions Muscle fibers innervated by motor neuron 1 Fig. 10.10 • all-or-none principle means fibers contract completely or not at all – Force exerted depends on number of motor units activated Spinal cord Motor neuron 1 Motor neuron 2 Neuromuscular junctions Muscle fibers innervated by motor neuron 1 Fig. 10.8 Neuromuscular junction Axon of a motor neuron Synaptic knob Skeletal muscle fiber LM 500x Fig. 10.8 Neuromuscular junction Axon of a motor neuron Path of nerve impulse Synaptic knob Synaptic knob Skeletal muscle fiber Endomysium Sarcolemma Synaptic cleft Acetylcholine (ACh) ACh receptor Acetylcholinesterase (AChE) Synaptic knob Motor end plate Synaptic vesicles Sarcolemma Sarcoplasm Fig. 10.2 Muscle attachment • At end of muscle, connective tissue layers merge to form tendon – attaches muscle to bone, skin, or another muscle Tendon • thin, flattened sheet of tendon is called aponeurosis Copyright © McGraw-Hill Education. Permission required for reproduction or display. Fig. 10.2 Muscle attachment Origin • Less mobile point of attachment of muscle is origin Relaxed • More mobile point of muscle attachment is insertion • Insertion usually moves Tendon toward origin • In limbs, origin is proximal to insertion Contracted muscle Movement of insertion of muscle Insertion Copyright © McGraw-Hill Education. Permission required for reproduction or display. Actions of Skeletal Muscles • Agonist is a muscle that contracts to produce a particular movement • Antagonist is a muscle whose actions oppose agonist – ex. agonist extends; antagonist flexes • Synergist assists the agonist – stabilizes point of origin or contributes to tension at point of insertion – ex. biceps brachii and brachialis muscles Naming of Skeletal Muscles • Muscle action – Some names reflect function or movement of muscle -flexor -extensor -pronator • Specific body region – anterior, posterior – superficialis or externus are visible from body surface – profundus or internus are deeper or more internal Naming of Skeletal Muscles • Muscle attachment – Named for origin, insertion, or prominent attachment – first part of name indicates origin and second part indicates insertion – ex. sternocleidomastoid originates on sternum and clavicle and inserts on mastoid • Orientation of muscle fibers – rectus = straight – oblique = oblique angle to longitudinal axis of body Naming of Skeletal Muscles • Shape and size – – – – – – deltoid = shaped like a triangle (delta, Δ) orbicularis = shaped like a circle (orbit) trapezius = shaped like a trapezoid brevis = short longus or longissimus = long teres = long and round Naming of Skeletal Muscles • Shape and size – magnus = large, big – major = bigger – maximus = biggest – minor = small – minimus = smallest Naming of Skeletal Muscles • Heads/tendons of origin – biceps = two tendons of origin – triceps = three tendons of origin – quadriceps = four tendons of origin • ex. quadriceps femoris = thigh muscle with four heads/tendons of origin Fig. 10.15 Cardiac muscle • Striated; bands visible under microscope • One nucleus per cell • Autorhythmic: individual cells can generate contractions by themselves Cardiac muscle cell (cardiocyte) Intercalated disc Endomysium Z discs Centrally located nucleus Intercalated discs I band Endomysium A band Gap junctions Desmosomes Mitochondrion (a) Sarcolemma Nucleus (b) Copyright © McGraw-Hill Education. Permission required for reproduction or display. Cardiac muscle cell Cardiac Muscle Intercalated discs Fig. 10.16 Smooth muscle • Not striated; each cell tapered at each end • Contractions slow, resistant to fatigue • Present in gut, blood vessel walls, etc.; under involuntary control
