How the sympathetic and parasympathetic nervous system affects organs. The organs to discuss are the heart, eyes, gastrointestinal system.
Questions
First up, let’s look at the human nervous system. The nervous system is split up into the central nervous system and the peripheral nervous system. The central nervous system includes the brain and spinal cord, while the peripheral nervous system is split up into the somatic and autonomic nervous systems.
The somatic nervous system is involved in the movement of our skeletal muscles. The autonomic nervous system – which as the name suggests is involved in a number of typically automatic, regulatory functions – is then further split up into the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS).
These two systems are activated in times of arousal or recovery. Put simply, SNS activation leads to a “fight or flight” response, and PNS activation leads to a “rest and digest” response.
The fight or flight response involves the SNS changing activity in the body to help prepare for a perceived threat, and includes: inhibition of the digestive and immune systems, increases in pupil size and heart rate, expansion of the lungs, and the release of epinephrine/norepinephrine. These processes are meant to optimize functions in the body when it’s under attack – you won’t benefit from digesting food, but you’ll likely need more oxygen from the lungs.
To facilitate the rest and digest response, the PNS alters a number of functions in the body to help it recover. These functions are largely mirror opposites of SNS activation, and include: stimulation of the digestive and immune systems, decreases in pupil size and heart rate, and contraction of the lungs. These processes optimize functions in the body at rest, and allow it to focus on maintenance.