Chapter 6: Contraction of Skeletal Muscle Flashcards
Percent composition of the body that is skeletal muscle
40%
Percent composition of the body that is smooth and cardiac muscle
10%
The diameter of skeletal muscle fibers
10-80 micrometers
Except for about 2% of the muscle fibers, each fiber is usually innervated by only one nerve ending, located near the _________ of the fiber.
A. Middle
B. Tendinous End
C. Muscle Spindle
A. Middle
The thin membrane enclosing a Skeletal Muscle Fiber
Sarcolemma
What makes up the outer coat of the sarcolemma?
Thin layer of Polysaccharide material that contains numerous thin collagen fibrils
At each end of the muscle fiber, the polysaccharide layer of the sarcolemma fuses with a _________ fiber.
tendon fiber
The tendon fibers, in turn, collect into bundles to form the muscle tendons that then connect the muscles to the bones.
Each myofibril is composed of about how many adjacent myosin and actin filaments?
1500 myosin (thick filaments) 3000 actin (thin filaments)
What causes the alternating light and dark bands of the myofibrils?
interdigitation of the myosin and actin filaments
The light bands contain only actin filaments and are called:
I bands because they are isotropic to polarized light
The dark bands contain myosin filaments, as well as the ends of the actin filaments, where they overlap the myosin, and are called:
A bands because they are anisotropic to polarized light.
These are the projections from the sides of the myosin filaments:
cross-bridges
Which parts of the myofibrils interact to cause contraction
It is the interaction between these cross-bridges
and the actin filaments that causes contraction
The ends of the actin filaments are attached to a ______ from which these filaments extend in both directions to interdigitate with the myosin filaments
Z disk
At which length of the sarcomere is the muscle capable of generating its greatest force of contraction?
2 micrometers
The length of the sarcomere is about 2 micrometers. At this length, the actin filaments completely overlap the myosin filaments, and the tips of the actin filaments are just beginning to overlap one another. As discussed later, at this length, the muscle is capable of generating its greatest force of contraction.
This part of the myofibril is composed of filamentous proteins different from the actin and myosin filaments, passes crosswise across the myofibril and also crosswise from myofibril to myofibril, attaching the myofibrils to one another all the way across the muscle fiber.
Z disk
The portion of the myofibril (or of the whole muscle fiber) that lies between two successive Z disks is called a:
sarcomere
What is the length of the sarcomere when the muscle is contracted
2 micrometers
Which filamentous molecules keep the myofilaments in place?
Titin Filamentous Molecules Keep the Myosin and Actin Filaments in Place
This protein forms the filamentous molecules that maintain the side-by-side relationship between myosin and actin filaments
Titin
Each titin molecule has a molecular weight of about ________, which makes it one of the largest protein molecules in the body.
3 million
These springy molecules act as a framework that holds the myosin and actin filaments in place so that the contractile machinery of the sarcomeres will work
Titin
To which portion of the sarcomere does the elastic end of titin attach to?
Z disk
To which portions of the sarcomere do the ends of the titin molecule attach to?
Myosin thick filament Z disk (elastic end)