Biology 232 Lecture Outline: Muscle & Muscle Tissue PDF
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This document outlines muscle types, including skeletal, cardiac, and smooth muscles. It describes their functional characteristics, such as excitability, contractility, extensibility, and elasticity, and details muscle functions like producing movement, maintaining posture, stabilizing joints, and generating heat. The document also delves into the microscopic anatomy of skeletal muscle fibers, including sarcolemma and sarcoplasm, myofibrils, sarcomeres, myofilaments (thick and thin), and the interactions between them.
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Biology 232 Lecture Outline. Chapter 9: Muscle and Muscle Tissue. Part 1: Muscle Structure and Function. I. Muscle types - Muscle terminology uses several, similar root words - Myo, mys, and sacro all refer to muscle - E.g. myofilaments, epimysium, sarcolemma - Three types di...
Biology 232 Lecture Outline. Chapter 9: Muscle and Muscle Tissue. Part 1: Muscle Structure and Function. I. Muscle types - Muscle terminology uses several, similar root words - Myo, mys, and sacro all refer to muscle - E.g. myofilaments, epimysium, sarcolemma - Three types differ in structure, location, function, and means of activation A. Skeletal muscle tissue - Has a banding pattern called striations - Found in skeletal muscles attached to the skeleton - Is controlled voluntarily - Is extremely adaptable (can exert a variable amount of force) B. Cardiac muscle tissue - Is striated like skeletal muscle - Occurs only in the heart - Involuntary neural controls allow the heart to respond to changes in bodily needs C. Smooth muscle tissue - Has no striations - Is found in the walls of hollow organs - Is controlled by involuntary neural and hormonal mechanisms II\. Functional characteristics of muscle A. Excitability (irritability) - The ability to receive and respond to stimuli B. Contractility - The ability to shorten forcibly C. Extensibility - The ability to be stretched or extended D. Elasticity - The ability to recoil and resume the original resting length III\. Muscle functions A. Producing movement - Muscle produces movement of the body or of materials within the body B. Maintaining posture - Keep the body upright against the force of gravity C. Stabilizing joints - Muscle tone and tension reinforces joints D. Generating heat - Muscle activity generates heat; important in maintaining body temperature IV\. Skeletal muscle A. Microscopic anatomy of a skeletal muscle fiber (muscle cell) 1. Sarcolemma and sarcoplasm - Each muscle cell is called a muscle fiber - Sarcolemma -- the cell membrane surrounding the muscle fiber - Sarcoplasm -- the cytoplasm of a large muscle cell which contains large amounts of the following: - Glycogen -- stored glucose - Myoglobin -- binds and stores oxygen 2. Myofibrils - Are densely packed, rodlike contractile elements - Are bundles of myofilaments - The arrangement of myofilaments and myofibrils creates a repeating series of dark and light bands (striations) in a muscle fiber a. Sarcomeres and myofilaments - Sarcomeres - Are the smallest contractile unit of a muscle - Are also the region of a myofibril between two successive Z discs - Are composed of myofilaments or contractile proteins - Myofilaments - Are contractile protein filaments of two types -- thick and thin 1. Thick (myosin) filaments and thin (actin) filaments - Composed of myosin, extend the entire length of an A band of a sarcomere 2. A bands, I bands, H zone, M line and Z disc (sarcomere) - Composed mainly of actin, extend across the I band and partway into the A band - Within a sarcomere are the following regions or structures: - A band -- dark band where thick filaments are found - I band -- light band between the ends of thick filaments - H zone -- lighter area in the A band where thick and thin filaments do not overlap - M line -- dark line in the H zone due to the presence of the protein myomesin (connects adjacent thick filaments) - Z disc -- coin shaped sheet of protein that anchors the thin filaments and connects myofibrils to one another b\. Molecular composition of myofilaments 1\. Thick filaments (myosin cross bridges) - Are composed of the protein myosin - Each myosin molecule has a rodlike tail and two globular heads - Tails -- two interwoven polypeptide chains - Heads -- two smaller polypeptide chains that form cross bridges 3. Thin filaments (actin, tropomyosin and troponin) - Chiefly composed of the protein actin - Each actin molecule is a helical polymer of globular subunits called G actin - These subunits contain the active sites to which myosin heads attach during contraction - Tropomyosin and troponin are regulatory subunits bound to actin 4. Elastic filaments (titin) - Composed of the protein titin - Extend from the Z disc to the thick filament - Run within the thick filament and attach to the M line - Functions: - Holf the thick filaments in place - Help the cell to recoil back to shape when stretched 3\. Sarcoplasmic reticulum and T tubules a\. Sarcoplasmic reticulum (terminal cisternae) - An elaborate, smooth endoplasmic reticulum that surrounds each myofibril - Paired terminal cisternae from perpendicular cross channels - Functions in the regulation of intracellular calcium levels b. T tubules - Elongated tubes that penetrate into the cell's interior at each A band -- I band junction - T tubules are continuous with the sarcolemma - T tubules associate with terminal cisternae to form triads - T tubules conduct impulses that signal for the release of Ca2+ from adjacent terminal cisternae c. Triads - T tubules and terminal cisternae form triads that conduct signals for muscle contraction - T tubule proteins act as voltage sensors - SR foot proteins are receptors that regulate Ca2+ release from the SR cisternae
