Chapter 1 Structure and Function of Exercising Muscle Types of Muscles 1Smooth · Involuntary muscle; Cardiac nervous system control – Located in walls of blood vessels and throughout internal organs, digestion, urinary, birth canal. 2Cardiac · Involuntary muscle; autonomic nervous and endocrine systems control – Located only in the heart. 3Skeletal · Voluntary muscle; controlled consciously by the somatic nervous system. – More than 600 different skeletal muscles Muscle Structure · Epimysium: outer connective tissue covering, surrounds the entire muscle · Fasciculi: Small bundles of fibers wrapped in a connective tissue sheath. The connective sheath is called the Perimysium. · Endomysium: sheath of connective tissue that covers each muscle fiber (muscle cell)_ Muscle Fiber · Plasmalemma: membrane that surrounds each muscle Fiber. - Transports Metabolites from capillaries into the muscle fiber – Assists with the transmission of an action potential. – Helps maintain acid-base balance. . Sarcolemma: plasmalemma + basement membrane. Fuses with the tendon` at the end of the muscle fiber. · Sarcoplasm: Inside the plasmalemma, a cytoplasm, a gelatin-like substance that fills the spaces between Myofibrils.
- Contains dissolved proteins minerals, glycogen, fats. - Contains glycogen and myoglobin (binds 02) Mitochondria Site of energy production · Transverse Tubules (t-tubules): - Extensions of the sarcolemma - Interconnected, Pass through the muscle fiber to help deliver nerve impulses to myofibrils ` · Sarcoplasmic Reticulum (SR): – Storage and release of Ca+ Myofibril: contractile elements of the muscle fiber - hundreds to thousands in each muscle - straited appearance - dark region: A-band, light: I - band Sarcomere The Functional Unit of the Myofibril The sarcomere contains the contractual elements between each pair of Z disks – I band (light zone) - A band (dark zone) - H zone (in the middle of the A-band) – M line in the middle of the H zone – Z disk: in the center of the I- band . I Band: contains only thin filaments (actin) . A Band: contains both thick filaments (myosin) and thin filaments (actin) · H zone: contains only thick filaments (myosin) . M line: serves as an attachment site for thick filaments, assists in stabilizing the sarcomere . Z disk: at each end of the sarcomere, point of attachment for thin filaments, stability Thick filaments: Myosin · Made up of 2 twisted strands, each strand has a globular head (myosin head)
Each thick filament contains many heads which form cross-bridge to interact with the thin filaments. Thin Filaments · Composed of Actin, Tropomyosin and Troponin · Extend from Z-disk towards center of sarcomere. . Located between the thick filaments. · Equally spaced out · Tropomyosin: protein that twists around the actin · Troponin: protein that attaches to both actin and tropomyosin · Ca+ binds to troponin, troponin then pulls tropomyosin off the active site. Allows for contraction of the myofibril when myosin head binds to the active site. Alpha Motor Neurons . Alpha motor neuron innervates many muscle fibers, collectively called the motor Unit . The action potential arrives