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Autonomic Nervous System

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Sympathetic and Parasympathetic Nervous System

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The autonomic nervous system (ANS), previously known as the vegetative nervous system, is a branch of the peripheral nervous system which controls the role of internal organs by supplying smooth muscle and glands. The autonomic nervous system is responsible for controlling that regulates bodily functions including respiratory rate, urination, heart rate, digestion, pupillary response, and sexual arousal in a mostly unconscious manner. The primary control mechanism for the fight-or-flight response is this system.


Integrated reflexes from the brainstem to the spinal cord as well as organs control the autonomic nervous system. Management of respiration, cardiac regulation (the cardiac control centre), vasomotor movement (the vasomotor centre), visceral nervous system and reflex acts like sneezing, chewing, coughing, and vomiting are all autonomic functions. The autonomic subsystems, as well as the peripheral nervous system, are both related to these regions, which are further subdivided into some other areas. The hypothalamus, which is located a little above the brainstem and receives autonomic regulatory feedback from the limbic system, serves as an integrator for autonomic functions.

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Structure:

The sympathetic and parasympathetic nervous system are two parts of the autonomic nervous system. The sympathetic division of the spinal cord occurs from the thoracic and lumbar regions of the spinal cord, ending around L2-3. The parasympathetic division seems to have a craniosacral “outflow,” which means the neurons start at the cranial nerves (primarily, the oculomotor nerve, glossopharyngeal nerve, facial nerve, and vagus nerve) as well as the sacral (S2-S4) spinal cord.


Sympathetic Nervous System Division:

From T1 to L2/3, the sympathetic nervous system is made up of cells containing bodies within a lateral grey column. The preganglionic neurons are "GVE" (general visceral efferent) neurons with these cell bodies. Preganglionic neurons could synapse with their postganglionic neurons in a variety of places:

  • The sympathetic chain's paravertebral ganglia

  1. cervical ganglia (3)

  2. rostral lumbar ganglia (2 or 3) and thoracic ganglia (12)

  3. sacral ganglia and caudal lumbar ganglia

  • Prevertebral ganglia(celiac ganglion, superior mesenteric ganglion, aorticorenal ganglion, inferior mesenteric ganglion).

  • The adrenal medulla's chromaffin cells (this can be stated as one of the exceptions to the two-neuron pathway rule: the synapse is straight efferent onto the target cell bodies).

Parasympathetic Nervous System Division:

The parasympathetic nervous system is made up of cells including bodies in the brainstem (namely, Cranial Nerves III, VII, IX, X) or perhaps the sacral spinal cord (namely, S2, S3, S4). Preganglionic neurons synapse with postganglionic neurons throughout the following areas:

  • Ciliary (Cranial nerve III), Otic (Cranial nerve IX), Pterygopalatine (Cranial nerve VII), and Submandibular (Cranial nerve VII) parasympathetic ganglia of the head (Cranial nerve IX).

  • Within and close the wall of Sacral nerves (S2, S3, S4) or Vagus (Cranial nerve X) innervated organ.

Such ganglia give rise to postganglionic neurons, which then innervate target organs. Here are some examples:

  • The parasympathetic meaning splanchnic (visceral) nerves are postganglionic.

  • The vagus nerve, which runs via the thorax as well as abdominal regions, innervates the liver, heart, lungs, and stomach, among several other organs.

Sensory Neurons:

The sensory arm has been made up of primary visceral sensory neurons located in the PNS (peripheral nervous system), in the petrosal, geniculate, and nodose ganglia, which are attached to cranial nerves VII, IX, and X, respectively. The quantities of oxygen, carbon dioxide, and sugar in the blood, as well as arterial pressure and also the chemical composition of the stomach and gut contents, are all monitored by all these sensory neurons.


They often transmit the sense of taste and smell, which, just like the majority of ANS functions, is a significant indication. The carotid body, a small set of chemosensors located at the carotid artery's bifurcation and innervated by the petrosal (IXth) ganglion, can detect blood oxygen and carbon dioxide immediately.


Motor Neurons:

The autonomic nervous system's motor neurons are located in the "autonomic ganglia." The parasympathetic branch's ganglia are near to the target organ, while the sympathetic branch's ganglia are near to the spinal cord.


The sympathetic ganglia are divided into two groups: prevertebral and pre-aortic. Preganglionic neurons throughout the central nervous system regulate the behaviour of autonomic ganglionic neurons. Preganglionic sympathetic neurons are found in the thorax and upper lumbar layers of the spinal cord. The medulla oblongata, where they create the dorsal motor nucleus of the vagus nerve; visceral motor nuclei; the salivatory nuclei; the nucleus ambiguous, and the sacral region of the spinal cord are all home to preganglionic parasympathetic neurons.


Autonomic Nervous System Function:

In most cases, the sympathetic and parasympathetic divisions work in contrast to one another. However, rather than being antagonistic, this opposition seems complementary with nature. The sympathetic division can be thought of as the accelerator and also the parasympathetic division brake.


The sympathetic system is used for acts that require rapid reactions. The parasympathetic division is responsible for acts that do not necessitate an immediate response. The sympathetic nervous system is known as the "fight or flight" system, whereas the parasympathetic nervous system is known as the or "feed and breed" or "rest and digest" system.


Sympathetic Nervous System Function:

Below mentioned are some of the sympathetic nervous system function-

  • Vasoconstriction redirects the flow of the blood away from the gastrointestinal (GI) tract and the skin.

  • The blood supply to the skeletal muscles and lungs is improved (by as much as 1200 per cent in skeletal muscles).

  • The circulating epinephrine dilates the bronchioles of the lungs, allowing for better and greater alveolar oxygen exchange.

  • Improves heart rate and cardiac cell contractility (myocytes), creating a way for increased blood flow towards skeletal muscles.

  • Allows enough light to penetrate the eye and improves far vision by dilating pupils and relaxing the ciliary muscle around the lens.

  • Vasodilation of the heart's coronary arteries is given.

  • All of the intestinal sphincters, as well as the urinary sphincter, are constricted.

Parasympathetic Nervous System Function:

Below mentioned are some of the Parasympathetic nervous system function-

  • Blood vessels heading to the GI tract are dilated, increasing the flow of the blood.

  • Whenever the requirement for oxygen tends to decrease, the bronchiolar diameter is constricted.

  • The heart is regulated by parasympathetic control(myocardium) through dedicated cardiac branches of the vagus as well as thoracic spinal accessory nerves.

  • The pupil contracts and the ciliary muscles contract, allowing for easier accommodation and better vision.

  • Salivary gland secretion is stimulated, and peristalsis is accelerated, facilitating food digestion thereby, consequently, nutrient absorption.

Caffeine Effects

Caffeine is indeed a bioactive ingredient used in tea, coffee, and sodas, among other drinks. Caffeine causes an increase in blood pressure and sympathetic nerve outflow throughout the short term. Caffeine intake regularly can reduce physiological short-term effects. In regular caffeine users, caffeinated espresso enhances parasympathetic behaviour; nevertheless, decaffeinated espresso reduces parasympathetic activity. Certain bioactive ingredients within decaffeinated espresso could potentially lead to the suppression of parasympathetic activity in caffeine addicts.


Caffeine has been shown to increase workability in people who are doing strenuous tasks. Caffeine caused a higher maximum heart rate during a strenuous task with one study as contrasted to a placebo. Caffeine's capacity to enhance sympathetic nerve outflow is most eager to judge for this phenomenon. Moreover, when caffeine became ingested prior to exercise, recovery following vigorous exercise was observed to be slower. Caffeine's ability to suppress parasympathetic behaviour in non-habitual users is reflected in this result. As the body tries to preserve homeostasis, the caffeine-stimulated rise in nerve activity is likely to elicit certain physiological effects.

FAQ (Frequently Asked Questions)

Q1. What are the Three Types of Nervous Systems?

Ans. The brain and spinal cord make up the central nervous system, while the Somatic and Autonomic nervous systems make up the peripheral nervous system.

Q2. What are the Effects of Emotions on the Autonomic Nervous System?

Ans. In response to emotional cues, the autonomic nervous system, in collaboration with the hypothalamus, breathing, blood pressure, controls heartbeat, and arousal. The sympathetic nervous system, once stimulated, the body prepares for emergency measures by regulating the endocrine system's glands.