Final answer:
Sweat glands are exclusively innervated by the sympathetic ANS, where postganglionic fibers release acetylcholine to stimulate sweating.
Step-by-step explanation:
Among the structures that are innervated solely by the sympathetic autonomic nervous system (ANS), the sweat glands are a unique example. Unlike most other organs in the body which receive inputs from both the sympathetic and parasympathetic systems as part of their dual innervation, sweat glands are exclusively controlled by the sympathetic nervous system. These postganglionic sympathetic fibers that innervate sweat glands release acetylcholine (ACh) onto muscarinic receptors, which is atypical for the sympathetic system where norepinephrine is usually released, and this neurotransmitter then induces the production and secretion of sweat.