B

Preganglionic sympathetic fibers arising chiefly from the lower thoracic (T8–T12) and first lumbar (L1) spinal segments pass through the sympathetic chain without synapsing and reach the adrenal medulla via the thoracic splanchnic nerves, providing its principal nerve supply and triggering catecholamine secretion [Kesse, 1988, PMID 3198482]. The other statements are incorrect: catecholamine release is strongly dependent on this innervation, the cortex receives vasomotor fibers rather than none, and the medulla is the most densely innervated part of the gland.