Final answer:
The statement is false because the parasympathetic nervous system does not innervate the skin, and its postganglionic fibers are not found within spinal nerves but are close to their target organs.
Step-by-step explanation:
The statement regarding parasympathetic postganglionic fibers and skin innervation is false. The parasympathetic nervous system does not innervate the skin; rather, it mainly targets internal organs to promote rest and digest functions. Additionally, no parasympathetic postganglionic fibers are found in the spinal nerves, as these fibers are typically located near their target organs. It's also important to note that the sympathetic nervous system, not the parasympathetic, has some influence on the skin through innervation of sweat glands which secrete sweat in response to acetylcholine (ACh), despite sweat glands not receiving parasympathetic innervation.
In summary, the statement is false because the parasympathetic nervous system does not innervate structures of the skin, and this is consistent with the fact that the parasympathetic postganglionic fibers are not found within spinal nerves. Instead, these fibers are located close to or within the target effector organs they regulate, which do not include the skin.