Which of the following is the first step in the sliding mechanism of muscle contraction?
A) A carbohydrate molecule is broken down to produce energy.
B) Thin filaments are pulled toward the center of the sarcomere.
C) The cross-bridges detach and return to their original positions.
D) The myosin heads of the thick filaments bind to active sites on the thin filaments.
E) Myosin heads pivot toward the M line when cross-bridge binding occurs.
D) The myosin heads of the thick filaments bind to active sites on the thin filaments.
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The role of inhibin in male reproduction is to
A) decrease the production of testosterone. B) keep testosterone levels high inside the seminiferous tubule. C) stimulate the testes to descend. D) stimulate spermiogenesis. E) provide negative feedback regulation of FSH and GnRH secretion.
After shedding the zona pellucida, the outermost cells of the blastocyst differentiate to form the __________
Fill in the blank with the correct word.
________ enable the immune system to launch a faster, stronger response to a previously encountered antigen.
A) Plasma cells B) Memory cells C) Helper T cells D) NK cells E) Pathogenic cells
The flexor reflex
A) prevents a muscle from overstretching. B) prevents a muscle from generating damaging tension. C) moves a limb away from a painful stimulus. D) usually depends on cranial neurons. E) is an example of a monosynaptic reflex.