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Unformatted text preview: Midterm 2 Lecture 15 Muscle Physiology Muscle Comprises largest group of tissues in body o Produce force; different control mechanisms o Similar contractile mechanisms; different morphologies Three types of muscle o Skeletal muscle (40-50% of body mass) Make up muscular system- voluntary o Smooth muscle (5-10% of body mass) Appears throughout the body systems as components of hollow organs and tubes involuntary; ANS control o Cardiac muscle Found only in the heart; involuntary; ANS control Classified in two different ways o Striated or unstriated o Voluntary or involuntary Categorization of Muscle Striated muscle: skeletal and cardiac Unstriated muscle: smooth Voluntary muscle: skeletal Involuntary muscle: cardiac and smooth Muscle Controlled muscle contraction allows o Purposeful movement of the whole body or parts of the body o Manipulation of external objects by reaching out and such o Propulsion of contents through various hollow internal organs (small intestines) o Emptying of contents of certain organs to external environment (bladder) Muscle contraction A 1-2 second action potential can cause a muscle twitch of about 100 seconds Structure of Skeletal Muscle Muscle consists a number of muscle fibers lying parallel to one another and held together by connective tissue Single skeletal muscle cell is known as a muscle fiber o Multinucleated o Larger, elongated, and cylindrically shaped o Fibers usually extend entire length of muscle (from tendon to tendon) Myofibrils o Inside the cell body are myofibrils o Contractile elements of muscle fiber o Regular arrangement of thick and thin filaments Thick filaments myosin (protein) Thin filaments actin (protein) Sarcomere o Functional unit of skeletal muscle o Found between two Z lines (connects thin filaments of two adjoining sarcomeres) o Shortening the sarcomere produces force Muscle > muscle fiber bundles > each bundle contains several muscle cells > one muscle cell contains many myofibrils Each myofibril is composed of many segments of Dark A bands and Light I bands Myosin Component of thick filament Protein molecule consisting of two identical subunits shaped somewhat like a golf club o Tail ends are intertwined around each other o Globular heads project out at one end Tails oriented toward center of filament and globular heads protrude outward at regular intervals o Heads form cross bridges aka bonds between thick and thin filaments o Two important sites An actin-binding site: myosin binds to the actin A myosin ATPase (ATP-splitting) site: where the energy source derived for the force The myosin are laid out in an hexagonal order; the heads pointing towards the Z line Actin Primary structural component of thin filaments Spherical in shape Thin filament also has two other proteins o Tropomyosin and troponin Each actin molecule has special binding site for attachment with myosin cross bridge...
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This note was uploaded on 11/02/2010 for the course GEL GEL 107 taught by Professor Jishin during the Winter '09 term at UC Davis.
- Winter '09