Ch 39: Motor Mechanisms and Behavior Flashcards
Muscle cell contraction relies on the interaction between protein structures called thin and thick filaments. The major component of thin filaments is the globular protein actin. In thin filaments, two strands of polymerized actin are coiled around one another; similar actin structures called microfilaments function in cell motility.
The thick filaments are staggered arrays of myosin molecules. Muscle contraction is the result of filament movement powered by chemical energy; muscle extension occurs only passively.
Do muscle cells have one nuclei each or multiple nuclei?
multiple
The myofibrils in muscle fibers are made up of repeating sections called sarcomeres, which are the basic contractile units of skeletal muscle. The borders of the sarcomeres line up in adjacent myofibrils, forming a pattern of light and dark bands (striations) visible with a microscope. For this reason, skeletal muscle is also sometimes called striated muscle.
Starting out, the myosin head is bound to ATP, and is in its low-energy configuration.
The myosin head hydrolyzes ATP to ADP and P (inorganic phosphate) and is in its high-energy configuration.
The myosin head binds to actin, forming a cross-bridge with the thin filament.
The cross-bridge couples the release of ADP and phosphate to a power stroke that slide the thin filament along the myosin and returns the myosin head to a low-energy state.
Binding of a new molecule of ATP releases the myosin head from actin, and a new cycle begins.
The contraction of skeletal muscles is based on
a. ) actin filaments coiling up to become shorter
b. ) myosin filaments coiling up to become shorter
c. ) actin cross-bridges binding to myosin and transitioning from a high-energy to a low-energy state
d. ) myosin cross-bridges binding to actin and transitioning from a high-energy to a low-energy state
d.)
filaments do not get shorter, so it can’t be a or b.
myosin is thick, actin is thin
Muscles have multiple innervations. Each innervation stimulates a different set of muscle fibers.
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The muscles of a recently deceased human can remain in a contracted state, termed rigor mortis, for several hours due to the lack of….
….ATP needed to break actin-myosin bonds.
Which of the following statements correctly describe(s) the relationship between Ca2+ concentration in the cytosol and the response in the sarcomere?
a. ) Decreasing Ca2+ concentration promotes interactions between actin and myosin.
b. ) Increasing Ca2+ concentration causes troponin and tropomyosin to bind to actin.
c. ) Decreasing Ca2+ concentration causes dissociation of Ca2+ from troponin.
d. ) Increasing Ca2+ concentration causes movement of tropomyosin, exposing myosin-binding sites on actin.
e. ) Increasing Ca2+ concentration causes troponin to bind to tropomyosin.
c. ) Decreasing Ca2+ concentration causes dissociation of Ca2+ from troponin.
d. ) Increasing Ca2+ concentration causes movement of tropomyosin, exposing myosin-binding sites on actin.
Which of the following statements correctly describes why a series of closely spaced action potentials causes a sustained contraction rather than a series of closely spaced twitches?
Ca2+ ions are released quickly from troponin, keeping the Ca2+ concentration in the cytosol high between closely spaced action potentials.
When a series of action potentials is closely spaced, there is not sufficient time for Ca2+ uptake into the sarcoplasmic reticulum between action potentials, and Ca2+ remains bound to troponin throughout the series.
Release of Ca2+ from the sarcoplasmic reticulum through channels is slow compared to the uptake of Ca2+ into the SR via ATP-dependent pumps, resulting in Ca2+ slowly trickling into the sarcomeres between closely spaced action potentials.
Fewer Ca2+ ions are released from the sarcoplasmic reticulum as a result of several closely spaced action potentials than as a result of a single action potential.
When a series of action potentials is closely spaced, there is not sufficient time for Ca2+ uptake into the sarcoplasmic reticulum between action potentials, and Ca2+ remains bound to troponin throughout the series.
An unlearned behavior directly linked to a stimulus that is carried to completion once initiated and is essentially unchangeable is _________.
a fixed action pattern
