Which of the following is not a role of calcium in the body?

A. Muscular system: Does not undergo a dramatic transition at birth.
B. Integumentary system: Adapts, but not as critically as the respiratory or circulatory systems.
C. Respiratory system: At birth, the newborn must shift from obtaining oxygen via the placenta to breathing air-a major physiological change.
D. Circulatory system: Also undergoes important changes (closure of fetal shunts), but the respiratory transition is more immediately life-sustaining.
E. Nervous system: Immature but does not require immediate postnatal adjustment for survival in the way the lungs do.

A. It is an autonomic reflex mediated predominantly by parasympathetic nerve fibers: Erection is primarily driven by parasympathetic stimulation (S2–S4), which causes vasodilation of penile arteries and engorgement of erectile tissue.
B. It is an autonomic reflex mediated predominantly by sympathetic nerve fibers: Sympathetic fibers are involved in ejaculation and detumescence, not erection initiation.
C. It is a somatic reflex mediated predominantly by parasympathetic nerve fibers: Erection is not mediated by somatic (voluntary) control.
D. It is a somatic reflex mediated predominantly by sympathetic nerve fibers: Both components are incorrect—erection is not somatic and not sympathetic.
E. It is an exclusively voluntary action mediated by the cerebral cortex: Erection can be influenced by psychological stimuli, but the physiological mechanism is autonomic, not voluntary.