Final answer:
The correct answer is option d. The sacral (pelvic) level of the spinal cord must be intact for sexual response in both males and females, involving pelvic splanchnic nerves and the pudendal nerve necessary for the autonomic and somatic processes of sexual function.
Step-by-step explanation:
The sexual response in both males and females requires an intact sacral spinal cord level. The sacral region of the spinal cord, which includes the nerves designated as S1 to S5, is responsible for the innervation of the pelvic organs. Sexual function involves the autonomic nervous system, which includes both sympathetic and parasympathetic nerve fibers, as well as somatic fibers that are essential for the integrity of sexual function.
Although the sympathetic nervous system has origins in the thoracic and lumbar regions (thoracolumbar system), the specific innervation for sexual response primarily involves the sacral region, making option D (Sacral (pelvic) level) the correct answer. This is because the pelvic splanchnic nerves, which arise from the S2 to S4 levels, and the pudendal nerve, arising from the S2 to S4 levels as well, are critical in providing the parasympathetic stimulation required for engorgement and secretion, as well as the somatic control needed for muscle contraction associated with orgasm.