Index
Control involuntary acts and functions.
To understand the parasympathetic nervous system, you first have to know what the autonomic nervous system (ANS) is and what is the relationship and how it works with the sympathetic nervous system.
What is the autonomic nervous system?
The autonomic nervous system regulates visceral functions , such as the heart, stomach, and intestines (internal organs). The ANS is part of the peripheral nervous system and also has control over some muscles within the body.
The functions of the ANS are involuntary and reflexive, for example, the beat of the heart, the expansion or contraction of blood vessels etc., so we are rarely aware of it. The parasympathetic and sympathetic nervous systems, along with the enteric nervous system make up the ANS.
The parasympathetic nervous system (PNS) controls homeostasis and the body at rest and is responsible for the body’s “rest and digest” function. Instead, the sympathetic nervous system (SNS) controls the body’s responses to a perceived threat and is responsible for the “fight or flight” response.
The SNP and SNS are part of the autonomic nervous system that is responsible for the involuntary functions of the human body.
What is the parasympathetic nervous system?
It originates from the spinal cord and cord and controls homeostasis or maintenance of body systems. The general response of the body is counterbalanced; restores the body to a state of calm.
The effects they have on the organs are as follows:
- Iris: constriction of the pupil.
- Salivary glands: increased production of saliva.
- Oro-nasal mucosa: increased mucosa production.
- Heart: bradycardia (decreased heart rate).
- Lung: bronchoconstriction (contraction of the bronchial muscle).
- Stomach: increases peristalsis and secretions.
- Small intestine: increases mobility and secretions.
- Large intestine: increases its mobility.
- Liver: no significant change.
- Pancreas: stimulates the gallbladder.
- Kidney: increased urine production.
- Adrenal gland: no significant change.
- Bladder: urinary meatus that relaxes and walls that contract.
- Musculoskeletal system: relaxation of the muscles.
What is the sympathetic nervous system?
The sympathetic nervous system, also part of the autonomic nervous system, originates from the spinal cord; specifically in the thoracic and lumbar regions. It controls the body’s “fight or flight” responses, or how the body reacts to perceived danger.
The effects it has on the organs are as follows:
- Iris: dilation of the pupil.
- Salivary glands: decreased saliva production.
- Oro-nasal mucosa: reduction of mucosa production.
- Heart: tachycardia (increased heart rate).
- Lung: bronchodilation (dilation of the bronchial muscle).
- Stomach: decreases peristalsis and secretions.
- Small intestine: reduces mobility and secretions.
- Large intestine: reduces its mobility.
- Liver: increases the conversion of glycogen into glucose and increases the levels of sugar present in the blood.
- Pancreas: stimulates the release of glucose from the liver.
- Kidney: reduced urine production.
- Adrenal glands: adrenaline and norepinephrine secretion.
- Bladder: urinary meatus that relaxes and walls that contract.
- Musculoskeletal system: contraction of muscles.
Sympathetic vs. parasympathetic
With sympathetic nervous responses, the body speeds up, tenses up, and becomes more alert. Functions that are not essential for survival are shut down.
The following are the specific reactions of the sympathetic nervous system:
- Increased speed and constriction of the heart.
- Dilation of bronchial tubes in the lungs and pupils in the eyes.
- Contraction of the muscles.
- Release of adrenaline from the adrenal gland.
- Converting glycogen to glucose to provide energy to the muscles.
- Closure of non-critical processes for survival.
- Decreased saliva production: the stomach does not move for digestion, nor does it release digestive secretions.
- Decrease in urinary production.
- Sphincter contraction.
The parasympathetic nervous system counterbalances the sympathetic nervous system. Restores the body to a calm state.
The specific answers are:
- Decrease in heart rate.
- Constriction of the bronchi in the lungs and the pupils in the eyes.
- Relaxation of the muscles.
- Saliva production: the stomach moves and increases secretions for digestion.
- Increase in urinary production.
- Sphincter relaxation.
How does the parasympathetic nervous system work?
This system is slower and moves along longer tracks. Preganglionic fibers from the cord or spinal cord project ganglia close to the target organ. They create a synapse, which ultimately creates the desired response.
The sympathetic nervous system is a faster system as it moves along very short neurons. When the system is activated, it activates the adrenal medulla to release hormones and chemical receptors into the bloodstream.
The target’s glands and muscles are activated. Once the perceived danger is gone, the parasympathetic nervous system takes over to counteract the effects of the sympathetic nervous system responses.
