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Biology 322 Human Anatomy I Histology of Muscle Muscle Tissue: 3 Types: Skeletal Muscle Cardiac Muscle Smooth Muscle Skeletal Muscle Very long Myocytes Unbranched Nuclei Striations Cardiac Muscle Smooth Muscle Shorter Branched Short Unbranched Spindle-shaped Hundreds per cell Peripheral One or two per cell Central One per cell Central Yes Yes No Muscle: Special Terminology: Prefixes = Cell = Plasma membrane = Endoplasmic reticulum = Cytoskeletal Filaments = Skeletal Muscle: Always voluntary. Each myocyte connected to and controlled by an axon from a motor neuron. Because of high metabolism, myocytes must be very close to capillaries. Myocytes are all oriented parallel to long axis of muscle which is Parallel to direction which muscle pulls when it contracts & lengthens when it relaxes Prominent Organelles in Myocytes: - Sarcolemma - Nuclei - Myofibrils (highly organized bundles of myofilaments - Transverse tubules (inward extensions of sarcolemma) - Sarcoplasmic reticulum - Mitochondria Keep in mind: Even though not prominent, all other organelles also present (vesicles, ribosomes, lysosomes, Golgi apparatus, etc. Myocyte (muscle cell) Myofibril Thick & thin myofilaments Thick and thin myofilaments forming part of a myofibril Skeletal Muscle Anatomy: Each myocyte surrounded by, and firmly attached to, layer of loose connective tissue called Skeletal Muscle Anatomy: Myocytes grouped together into bundles called each fascicle surrounded by, and firmly attached to, layer of dense irregular connective tissue called Skeletal Muscle Anatomy: Entire muscle surrounded by, and firmly attached to, layer of dense irregular connective tissue called Skeletal Muscle Anatomy: All three layers of connective tissue blend together at each end of muscle. Thus force transmitted from: Myocytes Endomysium Perimysium Epimysium Tendon, bone, etc. Skeletal myocytes = VOLUNTARY Can only contract when stimulated by motor neuron Myoneural junction or Neuromuscular junction One motor neuron + All myocytes it innervates = Skeletal Muscle: 1. Myocytes and muscles always pull (exert force by contraction), they never push. They usually, although not always, pull on bone through a tendon. 2. If a sarcomere shortens, it always does so completely "All-or-none" 3. All of the sarcomeres in the entire myocyte shorten at the same time. "All-or-none" But: 4. All of the myocytes in a muscle don't always contract at the same time. No "all-or-none" Skeletal Muscle: The total force produced by a myocyte is equal to the sum of the forces produced by individual sarcomeres. Thus: More sarcomeres = more force The total force produced by a muscle is equal to the sum of the forces produced by individual sarcomeres. Thus: More myocytes = more force