The autonomic nervous system (ANS) is a crucial component of the peripheral nervous system responsible for regulating involuntary bodily functions. It consists of two main branches: the sympathetic nervous system and the parasympathetic nervous system. These two systems have complementary roles and work in harmony to maintain homeostasis in the body. Here’s a detailed note on the structure and functions of each system:
1. Sympathetic Nervous System (SNS):
Structure:
The sympathetic nervous system comprises a chain of ganglia (clusters of nerve cell bodies) that runs alongside the spinal cord.
It originates from the thoracic and lumbar regions of the spinal cord, and the preganglionic neurons are relatively short.
Preganglionic fibers are myelinated, while postganglionic fibers are unmyelinated.
Functions:
People often call the SNS the “fight or flight” system because it prepares the body for action in response to stress or danger.
– Functions of the sympathetic system include:
– Increasing heart rate and the force of heart contractions to deliver more blood to vital organs.
– Dilating the airways to enhance oxygen intake.
– Redirecting blood flow away from non-essential organs (e.g., digestive system) to the muscles, heart, and brain.
– Mobilizing energy reserves by stimulating the release of glucose and fatty acids into the bloodstream.
– Dilating pupils to enhance vision.
– Inhibiting non-essential functions like digestion and reproduction.
2. Parasympathetic Nervous System (PNS):
Structure:
The parasympathetic nervous system has a more localized organization compared to the SNS.
It originates from the cranial nerves and the sacral region of the spinal cord.
Preganglionic fibers are relatively long, and ganglia are situated close to or within target organs.
Preganglionic and postganglionic fibers are both myelinated.
Functions:
The PNS is often called the “rest and digest” system, as it promotes relaxation and recovery.
Functions of the parasympathetic system include:
slowing heart rate and reducing blood pressure
constricting airways to decrease oxygen intake.
Increasing digestive processes, such as salivation and intestinal activity.
promoting energy storage and conservation.
stimulating the pupils to constrict for closer vision.
Enhancing reproductive functions.
Balance and Homeostasis:
The sympathetic and parasympathetic systems operate in a dynamic balance to maintain homeostasis in the body.
This balance ensures that the body can rapidly respond to stress or danger (sympathetic) and return to a resting state when the threat is removed (parasympathetic).
