Final answer:
The parasympathetic and sympathetic nerves are part of the autonomic nervous system and have an antagonistic but complementary relationship, maintaining bodily homeostasis by controlling opposing 'rest and digest' and 'fight or flight' responses respectively.
Step-by-step explanation:
Relationship Between Parasympathetic and Sympathetic Nerves
The relationship between the parasympathetic and sympathetic nerves can be described as antagonistic but complementary. These two divisions of the autonomic nervous system work in tandem to maintain the body's homeostasis. The sympathetic nervous system prepares the body for stress-induced, fight-or-flight activities, increasing heart rate and blood pressure, and diverting blood flow away from the digestive system. In contrast, the parasympathetic nervous system promotes the rest and digest state, reducing heart rate and blood pressure while stimulating digestive processes after the stress has subsided. Both systems help regulate the organs to ensure optimal functioning of the body.
Parasympathetic preganglionic neurons, which release acetylcholine, have their cell bodies in the brainstem and sacral spinal cord. These neurons usually activate postganglionic neurons located near the target organs, which also release acetylcholine, or sometimes nitric oxide, to exert their calming effects. Sympathetic preganglionic neurons originate in the spinal cord and target postganglionic neurons within sympathetic ganglia to activate the body's stress responses.