18_Muscular+System+and+Muscle+Tissue.pptx

Muscle Tissue and Organization Chapter 9, Human Anatomy (LibreTexts) "Muscular System" by Termininja is licensed under CC BY-SA 3.0 Introduction to Muscle Tissue • Characterized by properties that allow movement • Excitable: ability to respond to a stimulus • Contractile: ability to shorten and g...

Muscle Tissue and Organization Chapter 9, Human Anatomy (LibreTexts) "Muscular System" by Termininja is licensed under CC BY-SA 3.0 Introduction to Muscle Tissue • Characterized by properties that allow movement • Excitable: ability to respond to a stimulus • Contractile: ability to shorten and generate a pulling force • Elasticity: ability to return to resting length after shortening or lengthening • Extensibility: ability to be stretched beyond resting length • Can be voluntary (skeletal) or involuntary (cardiac or smooth) • Three types according to structure and function • Skeletal • Cardiac • Smooth Skeletal Muscle Tissue • Allows for locomotion, facial expressions, posture, and other voluntary movements of the body • Attached to bones of skeleton • Voluntary • Cells are called muscle fibers and are long and cylindrical • Muscle fibers are striated (has stripes) and multinucleated (each cell has multiple nuclei) Skeletal Muscle Tissue Histology "Skeletal Smooth Cardiac" by OpenStax is licensed under CC BY 3.0 Functions of Skeletal Muscle • Voluntary movements of the body • Maintenance of posture • Regulation of materials entering/exiting body i.e. sphincters • Protection and support of internal organs • Thermoregulation: production of heat Cardiac Muscle Tissue • Allows heart to pump • Found in the contractile walls of the heart • Involuntary and autorhythmic • Cells are called cardiomyocytes and are Yshaped and short • Cardiomyocytes are attached together by intercalated discs that form gap junctions to allow passage of electrical signals • Cardiomyocytes are striated and are single nucleated "Cardiac Muscle" by OpenStax is licensed under CC BY 3.0 Cardiac Muscle Tissue Histology "Cardiac muscle histology 400x" by Alexander G. Cheroske is licensed under CC BY-SA 4.0 Smooth Muscle Tissue • Allows internal organs to move • Found in: • Contractile component of the digestive, urinary, and reproductive systems as well as the airways and arteries • Eyes – changes shape of iris and lens • Skin – causes hair to stand up • Involuntary • Cells are called myocytes and are fusiform (tapered at ends and wide in the middle) • Myocytes do not have visible striations Smooth Muscle Tissue Histology "Muscle Tissue: Smooth" by Fayette A Reynolds M.S. from Berkshire Community College Bioscience Image Libraryis in the Public Domain, CC0 Muscle Tissue II Muscle Tissue Type Striations Nucleus Regulation Skeletal Yes Multinucleate Voluntary d Cardiac Yes One or Two nuclei Involuntary Smooth No One nucleus Involuntary Microscopic Anatomy of Skeletal Muscles • Muscle fibers are the cells of skeletal muscles and are long and cylindrical in shape. • Muscle fibers are multinucleated because they form by the fusion of myoblasts during embryonic development which contribute to the number of nuclei. • Myoblasts that do not fuse remain in the adult skeletal muscle tissue as satellite cells: if the skeletal muscle is injured, some satellite cells will fuse and help regeneration. Muscle Fibers • Muscle fibers contain: • Sarcolemma = plasma membrane • Sarcoplasm = cytoplasm • Sarcoplasmic reticulum: internal membrane complex to store calcium • Transverse tubules (Ttubules): deep depressions of sarcolemma to carry electrical impulses. • Myofibrils: myofilaments made of proteins that can move "The Triad" by Whitney Menefee is licensed under CC BY 4.0 / A derivative from the original work Sarcomere • Within the sarcoplasm are myofibrils which are cylindrical structures that run the length of the cell. • Myofibrils have the ability to shorten, resulting in contraction of the muscle fiber. • Contain myofilaments which are strands of proteins. Two types: • Thin filaments made of actin • Thick filaments made of myosin • Myofibrils are divided into repeated sections called sarcomeres which are the structural and functional units. The arrangement pattern of the myofilaments is what causes the striated appearance of skeletal muscle. Organization of a Sarcomere • A sarcomere contains overlapping thick and thin filaments • The boundaries of a sarcomere are delimited by Z disc which is the anchoring place for thin filaments. One sarcomere spans from one Z disc to the next Z disc. • In the middle of the sarcomere there is the M line which is the anchoring place for thick filaments. • Thin and thick filaments overlap to some degree. • The I band around the Z disc contains only thin filaments. • The H band around the M line contains only thick filaments. • The A band contains both thin and thick filaments. • Mnemonic: “Mike Has An Invisible Zoo” The Sarcomere (Image) "Muscle Fibers" by Openstax is licensed under CC BY 4.0 Myofilaments "Thick and Thin Filaments" by Openstax is licensed under CC BY 4.0 Neuromuscular Junction (NMJ) and Motor Unit • Neuromuscular junction (NMJ): Site where a somatic motor neuron’s axon terminal meets the muscle fiber • Every skeletal muscle fiber in every skeletal muscle is innervated by a motor neuron at the NMJ • A motor unit is a single motor neuron and the muscle fibers it controls. A motor unit contains only some of the muscle fibers in an entire muscle. Size of motor units (how many fibers per motor neuron) determines the force and the specificity of the movement. • All-or-none principle: When a motor unit is stimulated, all muscle fibers within it contract. "Motor Endplate and Innervation" by Openstax is licensed under CC BY 4.0 Neuromuscular Junction "Motor End Plate - Labeled" by Whitney Menefee is licensed under CC BY-SA 4.0 / A derivative from the original work Structure of a Neuromuscular Junction (NMJ) - 1 • Components of neuromuscular junction: • Synaptic knob: Expanded tip of neuron axon • Synaptic vesicles: Membrane sacs in synaptic knob, filled with the neurotransmitter acetylcholine (ACh) • Synaptic cleft: Narrow space separating synaptic knob and motor end plate "Motor Endplate and Innervation" by Openstax is licensed under CC BY 4.0 Structure of a Neuromuscular Junction (NMJ) - 2 • Components of neuromuscular junction (continued): • Motor end plate: Region of sarcolemma with many folds (increased surface area) under the synaptic knob • ACh receptors: Proteins that bind Ach on the motor end plate "Motor Endplate and Innervation" by Openstax is licensed under CC BY 4.0 The Sliding Filament Model of Muscle Contraction 1. A motor neuron carries an electrical signal to the neuromuscular junction (NMJ) of the skeletal muscle that needs to move. 2. The axon terminal releases a neurotransmitter (acetylcholine) that binds to the motor end plate of the NMJ. 3. This causes the calcium in the sarcoplasmic reticulum to be released in the cytoplasm. 4. The calcium and the ATP present in the muscle fiber activate the thick filaments anchored to the M line, which start pulling on the thin filaments. 5. The thin filaments are pulled closer to the M line, overlapping the thick filaments even more. 6. The Z discs come closer together making the sarcomere shorter. 7. The entire muscle fiber, and consequently the skeletal muscle, shortens (contracts). Contraction of a Muscle Fiber "Contraction" by Openstax is licensed under CC BY 4.0 Changes to the Sarcomere during Contraction • The Z discs come closer together. • The I and H bands shorten while the A band stays the same. • The length of the myofilaments never change, only their reciprocal overlap. "Sliding Filament Model of Muscle Contraction" by Openstax is licensed under CC BY 4.0 Gross Anatomy of Skeletal Muscle • Two layers called fascia: a superficial fascia separates the skeletal muscle from the skin: a deep fascia separates or joins together individual muscles. • Three layers of connective tissue compartmentalize skeletal muscle • Epimysium: Surrounds entire muscle; separates muscle from other tissues and organs in the area. • Perimysium: Surrounds individual bundles of muscle fibers called fascicles and contains blood vessels and nerves. • Endomysium: Surrounds individual muscle fibers (the cells of skeletal muscle) to provide electrical insulation. Skeletal Muscle Arrangement (Image) "The Three Connective Tissue Layers" by Openstax is licensed under CC BY 4.0 Skeletal Muscle Attachments • A tendon is a dense regular connective tissue that attaches a muscle to bone, skin, or another muscle. Sometimes tendons form a thin, flattened sheet, called an aponeurosis. • Muscle contraction usually causes one bone to move while the other bone remains fixed. • The less moveable attachment is often called the origin; the more moveable attachment is often called the insertion • Muscles that move the axial skeleton have a superior attachment and an inferior attachment • Muscles that move the appendicular skeleton have a proximal attachment and a distal attachment. Muscle Tone and Contraction Types • Muscle tone refers to the constant tension in a resting muscle • Two types of muscle contraction: • Isometric contraction: Length is constant; tension is changing (static strength). Examples: climbing, gymnastic, yoga, carrying object in front of you, pushing on a wall • Isotonic contraction: Tension is constant; length is changing. Examples: walking, running, weight lifting, push-ups, biceps curls, etc. Actions of Skeletal Muscles • Several muscles may be involved in an action. • Agonist (or Prime Mover) – principal muscle involved in action • Example: The triceps brachii is the agonist for forearm extension • Synergist – assists the agonist • Antagonist – has the opposite action of the agonist • Example: The biceps brachii is the antagonist for forearm extension; it is antagonistic to the triceps brachii • If the agonist produces extension, the antagonist produces flexion. Prime Movers and Synergists "Biceps Muscle" by Openstax is licensed under CC BY 4.0