What is parasympathetic nervous system ? Its functions?

© 2021 Google

 

              What is the Parasympathetic System and its function? 

Keywords: Craniosacral outflow| hypothalamus controls| limbic system| third |seventh|nineth| tenth cranial nerve|

Edinger Westphal nucleus|Superior|inferior salivary nucleus| pterygopalatine ganglion| esophageal plexus|gastric plexus|

 

The autonomic nervous system is also known as the vegetative nervous system. It has two divisions: sympathetic and parasympathetic.

1.     The sympathetic system arises from all thoracic spinal segments to the first two lumbar spinal segments, and sometimes from the third lumbar spinal segment are also involved. Therefore this is also known as thoracolumbar outflow.

2.     The parasympathetic system arises from the brain and sacral spinal segments, S2, S3, and S4. Therefore this is known as craniosacral outflow.

Sympathetic and parasympathetic systems usually act opposite to each other.

Table of Contents:

 

Sr. no	contents
1.	Types of Autonomic nervous  system  Sympathetic system Parasympathetic system
2.	Parasympathetic system
3.	Neurotransmitter    Acetylcholine    Adrenalin    Noradrenaline
4.	The hypothalamic controls The limbic system control
5.	Effects of the parasympathetic system on the heart On blood vessels On metabolism On digestive system Respiratory system Genitourinary system Nervous system On skin On temperature regulation
6.	Fig 1 and2

 

 

 

                                    The hypothalamic  control

 The hypothalamuscontrols the sympathetic and parasympathetic systems.

 The posterolateral nucleus of the hypothalamus controls sympathetic activity and anteromedial parasympathetic activity.

 The posterolateral nucleus stimulates sympathetic activity, and the anteromedial nucleus stimulates parasympathetic activity.

 Multiple areas of the CNS influence the action of the anteromedial and posterolateral nucleus of the hypothalamus via the limbic system.

 

The limbic system is associated with the auditory cortex, visual cortex, parietal lobe, and prefrontal lobe. In addition, the limbic system affects the activity of the sympathetic and parasympathetic systems.

 The parietal lobe is concerned with memory, and the prefrontal cortex with the thinking process. Therefore, higher centers will control the activity of the limbic system and hypothalamic centers.

.

  After interpretation of different pieces of information coming to the limbic system, higher centers regulate the hypothalamus and, therefore, sympathetic and parasympathetic activity.

 The sympathetic system is also known as the fight and flight or catabolic system, while the parasympathetic system is known as the ‘rest and digest’ or ‘anabolic system.’

 

                                      Cranial outflow

Parasympathetic nerves arise from the brain stem –Midbrain, Pons, and Medulla -as well as from the sacral spinal segments of the spinal cord; therefore, it is also known as cranial sacral outflow.

 The third cranial nerve - Oculomotor  

 The seventh cranial nerve- Facial

The ninth cranial –Glossopharyngeal, and

 The tenth cranial nerve- Vagus,

They are the nerves through which the cranial parasympathetic nerve emerges from the brain and is distributed to the peripheral structures.

The third cranial nerve

The third cranial nerve is the oculomotor nerve which contains somatic motor and parasympathetic nerves. The somatic motor fibers arise from the third nerve nucleus present in the midbrain. It supplies some of the extrinsic muscles of the eye. The parasympathetic motor fibers arise from the Edinger Westphal nucleus of the midbrain and supply the smooth muscles of the pupil and ciliary body of the eye.

The seventh cranial nerve

The somatic motor fibers of the seventh supply the muscles of facial expression and the muscles of the scalp. Its nucleus is situated in the pons. The sensory and parasympathetic fibers of the facial nerve are together known as the nerve of Wrisberg. The parasympathetic fibers from the superior salivary nucleus supply the submandibular and sublingual salivary glands. The sensory fibers bring test sensation from the anterior two-thirds of the tongue to the brain. The sensory fibers of somatic sensation of the 7 th nerve ends at the ‘nucleus of tractus solitarius,’ and from that, the final order neurons terminate on the superior salivary nucleus.

The ninth cranial nerve

The ninth cranial nerve is the glossopharyngeal, which contains parasympathetic fibers arising from its nucleus in the inferior salivary nucleus. Its somatic motor fibers are ‘special visceral motor fibers’ arising from nucleus ambiguus ‘in the medulla, which supply the stylopharyngeus muscle.

Sensory fibers of the glossopharyngeal nerve end at

1. Those fibers with bringing test sensation end at the ‘nucleus of tractus solitarius ‘

2. Those fibers bringing general information ends at the spinal nucleus of the Trigeminal nerve, and

3. Those fibers bring baroreceptor information from the carotid sinus end at the ‘dorsal motor nucleus of the vagus.’

                             The 10th cranial nerve

The 10th cranial nerve is the vagus. It is the essential cranial nerve and contains the parasympathetic, somatic motor, and sensory fibers. The parasympathetic motor fibers arise from the dorsal motor nucleus of the vagus situated on the floor of the fourth ventricle in the medulla. The fibers supply the thoracic viscera- heart and lungs,

and viscera of the upper abdomen. The sensory fibers bringing information from these viscera end in various parts of the brainstem. The somatic efferents arise from the nucleus ambiguus and supply some laryngeal and pharyngeal muscles.

 The parasympathetic stimulation causes increased activity of gastrointestinal glands, stimulates glands to increase secretion, and causes increased motility resulting in increased movements of the GIT.

Parasympathetic nucleus

 1. Edinger westphal nucleus (3rd nerve ) is situated in the midbrain.

 2. Superior salivatory nucleus(7 th nerve) is situated in the lower part of the pons

 3. Inferior salivatory nucleus (ninth nerve )is situated in the upper part of the medulla, and

 4. Dorsal nucleus of the vagus (tenth nerve ) is situated in the medulla.

These nerves contain the parasympathetic system fibers along with somatic fibers.

                             Outflow from the sacral segment

 From the lateral horn of the second, third, and fourth spinal segments of the sacral part of the spinal cord, the parasympathetic fibers emerge to form ‘Pelvic splanchnic nerves’  one on either side. It is also known as ‘nervous erigens’(Nervous erigentis pl.).

                                                Ganglions

They are preganglionic fibers and relay in their ganglion, called the ciliary (3^rd ), submaxillary(7^th), and otic(9^th) ganglion. Ganglions for the vagus are situated close to their target organs. The preganglionic parasympathetic fibers are myelinated and long, while the postganglionic fibers are short and unmyelinated.

                             Nerve distribution of cranial outflow

The parasympathetic nuclei ‘Edinger Westphal nucleus’ of the third cranial nerve supplies the intrinsic muscles of the eye through the ciliary ganglion, an intramural ganglion. It supplies the ciliary muscle and the sphincter pupillae.

1. When ciliary muscle contracts, the suspensory ligaments relax, the lens becomes globular, and near vision accommodation.

2. The other muscle is the sphincter pupilli. When this contracts, the pupil constricts, the condition is known as meiosis.

 The parasympathetic nuclei of the 7th cranial nerve are ‘Superior salivatory nucleus. The preganglionic parasympathetic fibers  ‘synapse 

1.    The pterygopalatine ganglion and its postganglionic fibers supply lacrimal, nasal, and palatine glands. It causes increased secretion from these glands.

2.    In the submandibular ganglion, and the postganglionic fibers supply the submandibular and sublingual salivary glands. It increases secretions of the glands-watery, enzyme-rich saliva.

The parasympathetic nucleus of the 9th cranial nerve is ‘Inferior salivatory nucleus. The preganglionic fibers synapse in the otic ganglion, and the postganglionic fibers supply the parotid gland. It increases secretions of the glands-watery, enzyme-rich saliva.

The parasympathetic of the 10th cranial nerve ‘Dorsal nucleus of the vagus’ supplies different body organs by nerve plexuses. Their ganglions are very close to the organ.

The esophageal plexus supplies the esophagus and increases its peristalsis.

The gastric plexus supplies the stomach with anterior and posterior gastric nerves, increasing its peristalsis, secretion, and absorption.

 The small intestine, large intestine up to two-thirds of the transverse colon, pancreas, liver, and gallbladder. The parasympathetic of the 10th cranial nerve supply the smooth muscles and exocrine glands.

The celiac plexus supplies the duodenum, jejunum, ileum, caecum, ascending colon, and two-third of the transverse colon. The postganglionic parasympathetic fibers increase motility, secretion, and absorption in these organs.

It increases urine formation and motility of the ureter.

 The cardiac plexus:  The parasympathetic fibers are present in the atrium and cause contraction of the atrium, in AV node delay the conduction. The parasympathetic stimulation causes bradycardia and a fall of cardiac output and blood pressure. Parasympathetic fibers are not present in the ventricle.

The pulmonary plexus: Parasympathetic fibers in the lungs supply bronchial muscles, bronchial glands, and bronchial arteries. The parasympathetic stimulation causes bronchial constriction, increases mucus secretion, and reduces bronchial blood supply.

The hepatic plexus: Parasympathetic fibers from the right vagus form the hepatic plexus. In the liver, it increases glycogenesis, contraction of the gall bladder, and relaxation of the sphincter of Oddi. In addition, it releases insulin from beta cells of the ‘islet of Langerhans’ of the pancreas.

Cranial outflow

The sacral spinal segments S2,3,4  join to make ‘pelvic splanchnic nerve.

The postganglionic parasympathetic fibers supply one-third of the transverse colon, descending colon, sigmoid colon, and rectum and increase motility, secretion, and absorption.

These fibers relax the internal anal sphincter. (The external anal sphincter is under voluntary control.)

The bladder contracts, and the internal urethral sphincter relaxes.        (The external urethral sphincter is under somatic control).

It causes erection in males and clitoris engorgement in females due to blood vessels dilations and increased blood flow.

 

Sacral outflow

We have seen that the organs receive both sympathetic and parasympathetic nerves. Both are present, and the resultant of the opposing effects determines the state of activity of a particular organ at a specific time.

 

Hashtags: craniosacral outflow|Edinger Westphal nucleus|

 esophageal plexus|gastric plexus|

Internal links:  https://blog.totalphysiology.com/2021/08/hypothalamus-html

https://blog.totalphysiology.com/2021/08/hypothalamus-connections-and-functions.html

https://blog.totalphysiology.com/2021/11/what-is-autonomic-nervous-system-what.html

External link: http://en.m.wikipedia.org/wiki