Chapter 9 Flashcards
Consist of hundreds to thousands of muscle cells, plus connective tissue wrappings, blood vessels, & nerve fibers
Covered externally by epimysium
Muscle (organ)
Discrete bundle of muscle cells, segregated from rest of muscle by a connective tissue sheath
Surrounded by perimysium
Fascicle (a portion of the muscle)
Elongated multinucleate cell; has a striated appearance
Surrounded by epimysium
Muscle Fiber
Rodlike contractile elements that occupy most of muscle cell volume. Composed of sarcomeres arranged end to end, appear banded, and bands of adjacent myofibrils are aligned
Myofibril
Contractile unit, composed of myofilaments made up of contractile proteins
Sarcomere
Lateral Thin filaments; extend across the I band and partway into the A band. Z disc anchors thin filaments.
Actin protein
Thick filaments; extend the entire length of the A band. Connected in middle of Sarcomere at the M line
Myosin protein
Epimysium of muscle is fused to periosteum of a bone or perichondrium of cartilage
Direct (fleshy) attachment
Muscles ct wrappings extend beyond the muscle either as a tendon or aponeurosis
Indirect attachment
Cytoplasm of muscle cell, contains unusually large amounts of glycosomes and myoglobin
Sarcoplasm
Red pigment that stored oxygen; similar to hemoglobin; pigment that transports oxygen in blood
Myoglobin
Muscle cell contains 3 specialized structures
Myofibrils, sarcoplasmic Reticulum (SR), T Tubules
_______ bands & ________ bands are nearly perfectly aligned, giving the cell its striated look
Dark A; light I
Each dark A band has a lighter region in its midsection called?
H zone
Each H zone is bisected vertically by a dark line called?
Formed by molecules of myomesin protein
M line
Each light I band has a midline interruption, darker area called?
Z disc (Z line)
Region of a myofibril between 2 successive Z discs
Sarcomere
Muscle equivalents of the actin-containing micro filaments and myosin motor proteins
Myofilaments (filaments)
What consists of 6 polypeptide chains: 2 heavy & 4 light?
A myosin molecule
Heavy chains twist together to form _______ tail; each heavy chain ends in a ______ _____ attached to the tail via a flexible hinge
Myosin’s rodlike; globular head
What contains about 300 myosin molecules, tails forming the central part of the filament, & their heads face outward at the end of each molecule?
Thick filament
What has kidney-shaped polypeptide subunits (globular actin or G actin), has a myosin-binding site (active site), & G actin subunits polymerize into long actin filaments called filamentous or F actin? Also contains tropomyosin and troponin
Thin filaments
Rod-like protein, spirals about actin core & helps stiff in & stabilize it. Blocks myosin-bind sites on actin so that myosin heads on thick filaments cannot bind to thin filaments
Tropomyosin
Globular protein w/ 3 polypeptide subunits
1. Attaches troponin to actin
2. Binds tropomyosin & helps position it on actin
3. Binds calcium ions
Troponin
Elastic filament; extends from a disc to thick filament & then runs within thick filament to attach to M line; holds thick filaments in place, maintaining organization of A band & helps muscle cells spring back into shape after stretching
Does not resist stretching in ordinary range of extensions, but stiffens as it uncoils, helping muscle resist excessive stretching, which might pull sarcomeres apart
Titin protein
Structural proteins; links thin filaments to integral proteins of sarcolemma
Dystrophin
Skeletal muscle fibers contain 2 sets of intercellular tubules that help regulate muscle contraction
Pg 288
- Sarcoplasmic reticulum
- T Tubules
What regulates intracellular levels of ionic calcium, stores calcium & releases it on demand when the muscle fiber is stimulated to contract?
Pg 288
Sarcoplasmic Reticulum (SR)
Form larger, perpendicular cross channels at A band- I band junctions & always occur in pairs
Pg 288
Terminal Cisterns (“end sacs”)
Tremendously increase the muscle fiber’s surface area
Pg 288
T Tubules
At each A band- I band junction, the sarcolemma of the muscle cell protrudes deep into the cell interior, forming elongated tube
Pg 288
T Tubule
3 membranous structures:
Terminal cistern, T Tubule, & terminal cistern
Triads
Each T Tubule runs between the paired terminal cisterns of the SR forming what?
Triads
Circles each Sarcomere
T Tubules
