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  • Muscle is one of the primary tissue types.

  • Skeletal muscle perform six major functions.

  • Skeletal muscle produces skeletal movement by

  • contracting and pulling on the bones of the skeleton.

  • Skeletal muscles maintain posture and body position by

  • maintaining tension, thereby allowing you to hold your head

  • while sitting and reading a book or balancing your body

  • when you walk or stand.

  • Skeletal muscles support soft tissues, such as abdominal

  • muscles and pelvic floor muscles, supporting the organs

  • of the abdominal-pelvic cavity.

  • Skeletal muscles guard entrances and exits by

  • surrounding the openings of the

  • digestive and urinary tracts.

  • Skeletal muscles maintain body temperature by releasing heat

  • when they are working.

  • And finally, skeletal muscles can store nutrient reserves

  • because the protein in muscles can be broken down into amino

  • acids, which can then be used to produce energy.

  • Each muscle is composed of muscle cells

  • called muscle fibers.

  • These muscle fibers are contained in

  • bundles called fascicles.

  • Muscles have connective tissue that's associated with the

  • entire muscle, with the fascicle or muscle bundle, and

  • with the individual muscle fiber.

  • Epimysium is a dense layer of collagen fibers that surrounds

  • the entire muscle.

  • It separates the muscle from nearby tissues and organs.

  • The perimysium divides the skeletal muscle into a series

  • of compartments.

  • Each compartment contains a muscle fascicle.

  • The perimysium contains blood vessels and nerves.

  • Within each fascicle, the endomysium is more delicate

  • and surrounds each individual muscle fiber.

  • The endomysium contains capillary blood vessels, nerve

  • fibers, and myosatellite cells, which are stem cells,

  • that help to repair damaged muscle tissue.

  • The collagen fibers of the epimysium, the perimysium and

  • the endomysium come together to form either a bundle, known

  • as the tendon, or a broad sheet, called an aponeurosis.

  • Tendons and aponeuroses usually attach skeletal

  • muscles to bones.

  • Skeletal muscle cells or fibers are very different from

  • the typical cells we've seen so far.

  • One obvious difference is that these skeletal muscle fibers

  • are much larger than other cells.

  • A muscle fiber from the thigh muscle could have a length up

  • to 12 inches.

  • A second difference is that skeletal muscle contains

  • hundreds of nuclei just internal to the cell membrane.

  • These nuclei are needed to produce enzymes and structural

  • proteins that are required for normal muscle contractions.

  • The cell membrane of a muscle fiber is known as the

  • sarcolemma and the cytoplasm is known as the sarcoplasm.

  • Inside each muscle fiber are hundreds to thousands of

  • structures called myofibrils.

  • These structures are cylindrical in shape.

  • They can actively shorten in shape and are responsible for

  • skeletal muscle fiber contraction.

  • Myofibrils consist of protein filaments called myofilaments.

  • These myofilaments are either thin filaments composed

  • primarily of actin or thick filaments composed

  • primarily of myosin.

  • The Myofibrils are anchored to each end of the muscle fiber,

  • which is connected to its tendon.

  • As a result, when the myofibrils contract, the

  • entire cell shortens and pulls on the tendon.

  • Transverse tubules or T-tubules are narrow tubes

  • that are continuous with the sarcolemma and extend deep

  • into the sarcoplasm.

  • They are filled with extra cellular fluid and form

  • passageways through the muscle fiber, like a network of

  • tunnels through a mountain.

  • Electrical impulses called action potentials travel along

  • the T-tubules into the cell interior.

  • These action potentials trigger muscle fiber

  • contraction.

  • Branches of the T-tubules surround each myofibril.

  • The sarcoplasmic reticulum is similar to the smooth

  • endoplasmic reticulum of other cells.

  • The sarcoplasmic reticulum fits over each individual

  • myofibril like a lacy shirt sleeve.

  • Where a T-tubule encircles the myofibril, the sarcoplasmic

  • tubule expands, and these chambers are

  • called terminal cisternae.

  • The terminal cisternae contains stored calcium.

  • And sometimes the concentration of calcium

  • inside the cisternae is a thousand times higher than the

  • levels inside the sarcoplasm.

  • The thick and thin filaments of the myofibril are organized

  • into repeating functional units called sarcomeres.

  • Sarcomeres are the smallest functional units

  • of the muscle fiber.

  • Interactions between the thick and thin filaments of

  • sarcomeres are responsible for muscle contraction.

  • One myofibril consists of approximately 10,000

  • sarcomeres end to end.

  • A sarcomere contains thick filaments, thin filaments,

  • proteins that stabilize the positions of the thick and

  • thin filaments, and proteins that regulate the interactions

  • between the thick and thin filaments.

  • The thick and thin filaments are different in size,

  • density, and distribution.

  • These differences account for the banded

  • appearance of each myofibril.

  • The thick filaments are at the center of each sarcomere.

  • Proteins of the M-line connect the central portion of each

  • thick filament to neighboring thick filaments.

  • M stands for middle.

  • The thin filaments are located between the thick filaments in

  • an area called the zone of overlap.

  • A single thin filament contains two rows of 300 to

  • 400 individual globular molecules.

  • Each of these molecules contains an active site that

  • can bind to myosin.

  • Under resting conditions, a complex called the

  • tropomyosin-troponin molecule covers the active sites and

  • prevents the binding of myosin to the active site.

  • Tropomyosin is a double-stranded, rope-like

  • structure that covers the active sites

  • on the actin molecules.

  • Troponin is a molecule that locks the tropomyosin molecule

  • to the actin molecule, thereby preventing the exposure of the

  • actin molecule's active site.

  • A thick filament contains about 300 myosin molecules.

  • The myosin molecules are twisted around each other.

  • Each myosin molecule has a long tail and a head which

  • projects outward toward the nearest thin filament.

  • When the myosin heads interact with thin filaments during a

  • contraction, they are known as cross-bridges.

  • The connection between the head and the tail of the

  • myosin acts as a hinge that lets the head pivot.

  • When they head pivots, it swings toward the M-line or

  • the center of the sarcomere.

  • All the myosin molecules are arranged with their tails

  • pointing towards the M-line.

  • When the myosin head forms a cross-bridge with the actin

  • molecule's active site and the head pivots, causing the thin

  • filaments to slide toward the center of each sarcomere, this

  • is known as the sliding filament theory.

  • During a contraction, sliding occurs in every sarcomere

  • along the myofibril.

  • As a result, the myofibril gets shorter.

  • When myofibrils get shorter, so does the muscle fiber.

Muscle is one of the primary tissue types.

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第10章 肌肉組織 mp4 (Ch 10 Muscle Tissue mp4)

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    Cheng-Hong Liu 發佈於 2021 年 01 月 14 日
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