Postganglionic parasympathetic fibers are a type of nerve fibers belonging to the parasympathetic nervous system that carry signals from the autonomic ganglia to the target organs or tissues.
The parasympathetic nervous system is one of the two divisions of the autonomic nervous system, alongside the sympathetic nervous system. Its main function is to promote the body's "rest and digest" response, which involves calming and conserving energy. Postganglionic parasympathetic fibers are an essential part of this system as they transmit signals from the parasympathetic ganglia, located close to the target organ or tissue, to the final destination.
These fibers are responsible for delivering the parasympathetic signals, primarily mediated by the neurotransmitter acetylcholine, to various body structures, including smooth muscles, cardiac muscles, and glands. They have a long, thin, and unmyelinated structure, enabling them to conduct nerve impulses at a relatively slow pace, allowing for precise and localized control of the target organs.
Activation of postganglionic parasympathetic fibers results in a range of physiological responses, such as increased glandular secretions, contractions of smooth muscles in the gastrointestinal tract, increased digestive activity, slowed heart rate, and constriction of the pupil. These actions help maintain homeostasis by enhancing digestion, reducing heart rate, and conserving energy during times of rest and relaxation.
In summary, postganglionic parasympathetic fibers are specific nerve fibers that transmit signals from the parasympathetic ganglia to target organs or tissues, contributing to the parasympathetic division's effect on the body's resting and restorative functions.
