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Parasympathetic nervous system

Structure and Pathways: – Parasympathetic nerves are autonomic branches of the peripheral nervous system. – Parasympathetic nerve supply arises from cranial nerves, the vagus nerve, […]

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Structure and Pathways:
– Parasympathetic nerves are autonomic branches of the peripheral nervous system.
– Parasympathetic nerve supply arises from cranial nerves, the vagus nerve, and pelvic splanchnic nerves.
– Parasympathetic ganglia are located close to target organs for synapsing.
– Efferent parasympathetic signals are carried by a system of two neurons.
– Parasympathetic nerves synapse at ganglia close to target organs.
– Presynaptic parasympathetic neurons have long axons that extend to ganglia close to target organs.

Functions and Activities:
– Parasympathetic system stimulates rest-and-digest activities.
– Activities include sexual arousal, salivation, lacrimation, urination, digestion, and defecation.
– Parasympathetic action complements the fight-or-flight response of the sympathetic nervous system.
– It is known for craniosacral outflow compared to the sympathetic system’s thoracolumbar outflow.
– Regulates activities during rest and after eating.

Nerve Innervation:
– Cranial nerves like the oculomotor, facial, and glossopharyngeal control parasympathetic functions.
– Trigeminal nerve innervates nasal mucosa glands.
– Chorda tympani and lesser petrosal nerve are parasympathetic branches of the facial nerve.
– Vagus nerve originates in the dorsal nucleus and supplies various organs.
– Pelvic splanchnic nerves innervate pelvic viscera and control urinary bladder, anus, and other organs.

Physiological Effects:
– Heart rate is controlled by the parasympathetic system.
– Vagus nerve modulates heart rate via the sinoatrial node.
– Parasympathetic system influences heart rate variability.
– Regulates sexual function in males and females.
– Acetylcholine is the primary neurotransmitter involved in parasympathetic function.

Clinical Significance and Receptors:
– Parasympathetic system promotes day-to-day living functions.
– Enhances food digestion and absorption while decreasing respiration and heart rate.
– Clinical implications include dry eye diseases and heart rate variability.
– Acetylcholine, muscarinic, and nicotinic receptors play key roles in parasympathetic function.

Parasympathetic nervous system (Wikipedia)

The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

Parasympathetic nervous system
Autonomic nervous system innervation, showing the parasympathetic (craniosacral) systems in blue.
Latinpars parasympathica divisionis autonomici systematis
Anatomical terminology

The autonomic nervous system is responsible for regulating the body's unconscious actions. The parasympathetic system is responsible for stimulation of "rest-and-digest" or "feed-and-breed" activities that occur when the body is at rest, especially after eating, including sexual arousal, salivation, lacrimation (tears), urination, digestion, and defecation. Its action is described as being complementary to that of the sympathetic nervous system, which is responsible for stimulating activities associated with the fight-or-flight response.

Nerve fibres of the parasympathetic nervous system arise from the central nervous system. Specific nerves include several cranial nerves, specifically the oculomotor nerve, facial nerve, glossopharyngeal nerve, and vagus nerve. Three spinal nerves in the sacrum (S2–4), commonly referred to as the pelvic splanchnic nerves, also act as parasympathetic nerves.

Owing to its location, the parasympathetic system is commonly referred to as having "craniosacral outflow", which stands in contrast to the sympathetic nervous system, which is said to have "thoracolumbar outflow".

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