What are the differences between the sympathetic and parasympathetic nervous systems?

May 23, 2023 Source: Cainiu Health

Dr. Yang Jun

Introduction

The differences between the sympathetic and parasympathetic nervous systems generally include different origins, distributions, and functions. Specifically: the sympathetic nerves originate from the thoracic and lumbar segments of the spinal cord, forming chain-like structures (sympathetic trunks) along the spine, with ganglia located in areas such as internal organs and blood vessel walls. In contrast, the parasympathetic nerve fibers arise from the cranial region, form the pelvic nerves, and extend to the genital organs.

Differences between the sympathetic and parasympathetic nervous systems generally include differences in origin, distribution, and function. A detailed analysis is as follows:

1. Different origins

The sympathetic nerves originate from the thoracic and lumbar segments of the spinal cord, forming chain-like structures (ganglia) along the spine, which are distributed in internal organs, blood vessel walls, and other areas. Parasympathetic nerve fibers arise from the cranial region, form pelvic nerves, and extend to the genital organs.

2. Different distributions

Sympathetic nerves are distributed in the neck, internal organs, and blood vessels, whereas parasympathetic nerves primarily innervate cranial organs and have ganglia located adjacent to or within the target organs.

3. Different functions

The sympathetic nervous system regulates vasoconstriction and increases heart rate, helping maintain physiological demands during states of stress or arousal. The parasympathetic nervous system typically becomes active during rest, promoting gastrointestinal motility, slowing heart rate, and reducing unnecessary energy expenditure.

In addition, differences also include locations of peripheral ganglia, effects on various organs, and central control regions. If abnormal symptoms such as headache, hypotension, or tinnitus occur in daily life, it is recommended to seek medical attention at a hospital as early as possible.

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Is pupil dilation controlled by the sympathetic or parasympathetic nervous system?

Under normal circumstances, pupil dilation is caused by sympathetic nerve excitation. When light intensity is high, the parasympathetic nervous system becomes activated to contract the sphincter muscle and constrict the pupils, thereby protecting the retina from excessive stimulation. Conversely, in dim lighting conditions, the sympathetic nervous system becomes activated, causing the dilator muscle to enlarge the pupils, allowing better focus and clearer vision.

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Reasons for increased blood glucose due to sympathetic nervous system activation

The reason for elevated blood glucose due to sympathetic nervous system activation may be related to emotional stress, which stimulates the sympathetic nervous system and increases secretion of adrenal hormones. In addition, intense physical exercise can activate the sympathetic nervous system, leading to increased production of norepinephrine and adrenal hormones, thereby raising blood glucose levels. Acute cerebrovascular disease can also cause sympathetic nervous system activation and heightened basal metabolism, resulting in elevated blood glucose.