Title: CH 10 Anatomy Flashcards | Quizlet
Headings: CH 10 Anatomy
CH 10 Anatomy
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Terms in this set (104)

Content: Transverse tubules (aka T-tubules)
-deep invaginations of the sarcolemma that extend into the sarcoplasm of skeletal muscle fibers as a network of narrow membranous tubules
-muscle impulses generated when a nerve impulse reaches the sarcolemma travel rapidly along the sarcolemma and then spread internally along the membranes of the T-tubule network
-the passage of this impulse helps stimulate and coordinate muscle contractions
Sarcoplasmic reticulum (SR)
-another internal membrane complex in the skeletal muscle fiber
-similar to the smooth endoplasmic reticulum of other cells
-stores calcium ions needed to initiate muscle contraction
-some parts of the SR run parallel to the muscle fiber, whereas other parts appear as blind sacs perpendicular to the fiber's length
Terminal cisternae
-expanded ends of the sarcoplasmic reticulum that are in contact with the transverse tubules
-site of calcium ion release to promote muscle contraction contact with the transverse tubules
Together, the two terminal cisternae and the centrally placed T-tubule formed a...
triad
Myofibrils
-hundreds to thousands of long, cylindrical structures in the sarcoplasm of a skeletal muscle fiber
-during contraction, the myofibrils shorten as their component proteins change position
-because myofibrils are attached to the ends of the muscle fiber, the shortening of the myofibrils during a contraction causes the fiber to shorten. Myofilaments
-myofibrils consist of bundles of short myofilaments
-whereas a single myofibril runs the length of the muscle fiber, it takes many successive groupings of myofilaments to run the entire length of a myofibril
Thin filaments
-they are primarily composed of two strands of the protein actin twisted around each other to form a helical shape
-in each helical strand of actin, many small, spherical molecules are connected to form a long filament resembling a string of beads
-each spherical molecule is called G (globular) actin, and each filament composed of a strand of G-actin molecules is called F actin. Two regulatory proteins, tropomyosin and troponin are part of the thin filaments
Tropomyosin
-a short, thin, twisted filament that covers small sections of the actin strands
Troponin
Three functions
structurally, it (1) attaches to actin to anchor itself in place, and (2) attaches to tropomyosin to hold it in place over the surface of the actin
(3) functionally, troponin provides a binding site for calcium ions
Thick filaments
-are assembled from bundles of the protein myosin
-thick filaments are positioned at the center of the sarcomere
Myosin
-a thick filament that consists of two strands; each strand has a free, globular head and an attached, elongated tail. -are oriented on either end of the thick filament so that the long tails point toward the center of the filament and the heads point toward the edges of the filament and project outward toward the surrounding thin filaments
-during a contraction, myosin heads form crossbridges by binding thick filaments to actin in the thin filaments. Different types of striations (bands)
-A bands
-I bands
A bands
-dark bands that contain the entire thick filament
I bands
-light bands that contain thin filaments but no thick filaments
-in addition to thin filaments, there are also titin
Titin
-protein filaments
-play a role in muscle elasticity, control of thick filament assembly, and passive stiffness generated in the muscle
H zone (aka H band)
-a light, central region in the A band
-it is lighter shaded because only thick filaments are present—that is, there are no thin filaments overlapping the thick filaments in the H zone in a relaxed muscle fiber
-at maximal contraction, the thin filaments are pulled into this zone, and the H zone disappears
M line
-a thin transverse protein meshwork structure in the center of the H zone of a relaxed fiber
-serves as an attachment site for the thick filaments and keeps the thick filaments aligned during contraction and relaxation
Z disc (aka Z line)
-a thin transverse protein structure in the center of the I band that serves as an attachment site for thin filament ends. -although the Z disc is circular, when viewed "head-on," only the edge of the circle is visible, so it sometimes looks like a line. Connectins
-Z disc proteins that anchor and interconnect the thin filament ends at either end of a sarcomere
Sarcomere
-the functional contractile unit of a skeletal muscle fiber
-defined as the distance from one Z disc to the next adjacent Z disc. -each sarcomere shortens as the muscle fiber contracts
Tension
-tension is exerted on the portion of the skeleton where the muscle is attached
-the thick and thin protein filaments in sarcomeres interact to cause muscle contraction
-the mechanism for contraction is explained by the sliding filament theory. Sliding filament theory
-when a muscle contracts, thick and thin filaments slide past each other, and the sarcomere shortens
-the following changes occur within a sarcomere during a contraction: