Complex sentence: However, when sympathetic postganglionic neurons innervate sweat glands they secrete acetylcholine and hence are termed sympathetic "cholinergic" neurons, the only sympathetic postganglionic neurons known to secrete acetylcholine instead of norepinephrine.
Split into simpler sentences: However, when sympathetic postganglionic neurons innervate sweat glands they secrete acetylcholine and hence are termed sympathetic "cholinergic" neurons. The only sympathetic postganglionic neurons known to secrete acetylcholine instead of norepinephrine.