The nervous system is a huge and complex anatomical system with many nerves. It is the one which regulates the whole of our body. In this article we will discuss only about the divisons in autonomic nervous system.
But we will see few details leading to sympathetic vs parasympathetic System
The nervous system can be broadly divided as the
- The Central Nervous System {has the brain and spinal cord}
- The Peripheral Nervous System {has nerves from brain and spinal cord)
This peripheral nervous system is again categorized as the
- The visceral nervous system (somatic and sensory nervous system)
- The autonomic nervous system
This autonomic nervous system is divided as
- Sympathetic nervous system
- Parasympathetic nervous system.
The Autonomic Nervous System is so called because, it is not under our ‘voluntary control.’
It is always active in regulating the body physiology. It controls the action of the organs at the subconscious level.
Autonomic Nervous System shares a relationship with the somatic nervous system and has functional links with it.
It also has a great relationship with the Endocrine System.
The examples are.
a) Cortisol is a catecholamine hormone secreted from Adrenal Cortex, and from sympathetic nerve endings.
b) The adrenal Medulla is itself a modified sympathetic ganglion. Hormones secreted from Adrenal Medulla is actually secreted from sympathetic nerve endings.
c) Thyroxine or the T4 hormone, secreted from the Thyroid gland increases the number of beta-adrenergic receptors in the heart.
Sympathetic Vs Parasympathetic Nervous System
| Feature | Sympathetic Nervous System | Parasympathetic Nervous System |
|---|---|---|
| Also called as | Thoraco-lumbar outflow as its nerves emerges from the thoracic and lumbar regions of the vertebral column. | Cranio-sacral outflow as its nerves emerges from the cranium and sacral vertebrae. |
| The nerves origin | Nerves emerge from a level of T1 to 3rd or 4th lumber, i.e., L3 or L4. | The parasympathetic parts of the cranial nerve include the 3rd nerve, i.e., Occulomotor 7th nerve, i.e., Facial, the 9th nerve, i.e., Glossopharyngeal and the 10th nerve (Vagus nerve). The sacral counterpart of the parasympathetic nervous system has the root value of S2 to S4. |
| Preganglionic nerve fiber | The preganglionic nerve efferents come out through the efferent root of the spinal segment. It then passes through the white rami, and it communicates the white rami, which connects the ventral root to the paravertebral sympathetic chain. In this point or region, most of the neural ends of preganglionic fiber send and relay with postganglionic neurons. | The preganglionic nerve efferents come out through the lateral horn of the spinal cord, the preganglionic nerve fiber arises, traveling long up to the target organ where there is a ganglion, there they terminate. |
| Neurotransmitters | Two or more types of neurotransmitters are seen in the Sympathetic Nervous System. Acetylcholine: The preganglionic nerve fibers that originate from the spinal cord and ends up in the sympathetic ganglion secrete acetylcholine inside the ganglion. This acetylcholine acts on nicotinic receptors. Noradrenaline: The postganglionic nerve fibers originate from the sympathetic ganglion and end up in viscera secrets noradrenaline inside the viscera. This secreted noradrenaline acts on adrenergic receptors, | The neurotransmitter of the parasympathetic nervous system is only acetylcholine. |
| Receptor types | Receptors in the Sympathetic nervous system include adrenergic receptors, which are 5 in numbers- α1, α2, β1, β2, and β3. | Muscarinic receptors or simply M receptors are of 5 types as M1 – present in the brain M2 – present in the heart M3 – present in the stomach M4 – present in the pancreas M5 – located in smooth muscles. |
| Postganglionic nerve fiber | Postganglionic fiber is the supplier of the sympathetic system. It is the fiber which connects the sympathetic ganglion with different visceral organs. There are two other possibilities – either they may return to the spinal cord through gray rami communicantes, or they may spread along spinal nerves to supply to autonomic effectors like sweat glands or vascular smooth muscles. | The preganglionic nerve fibers originate from inside the brain and the spinal cord, and here, they are longer unlike that of sympathetic nervous a system where the postganglionic nerve fiber was longer. The postganglionic nerve fibers are very short; originate from the Parasympathetic ganglia situated very close to the target organ. |
| Effect on the Eyes | Through α receptors, they constrict the soft tissue dilator- pupillae, which results in dilation of pupils of the eye. | They tend to constrict the pupil, stimulating the tissue constrictor- papillae. |
| Effect on salivary glands | Saliva secretion is minimized | Saliva secretion is profuse and enhanced |
| Effect on the gut of digestive system | Through α receptors, they decrease peristaltic movements by decreasing motility and tone of stomach and intestine. | They increase the peristalsis of the gut as well as increase gastric emptying. |
| Effect on skin | Through α receptors, facilitates adrenergic sweating, by contraction of pilomotor muscles, which causes sweating in hands and palms. | No effect |
| On heart | Β1 receptors are exclusively present in the heart and kidneys. So stimulating them to increase heart rate. Through β1 receptors, It exerts positive chronotropic, dromotropic, ionotropic and bathmotropic effects on the heart. | Effects on the heart include all opposite to that of the sympathetic nervous system. It has negative ionotropic, chronotropic, bathmotropic effects. All these effects are carried by the vagus nerve. |
| Effect on fats and lipids in the body | Through β3 receptors, being exclusively present in adipose tissue, initiate the lipolysis. | Parasympathetic nervous the system has no such effects. |
| On sex organs | Male: Ejaculation and vasoconstriction | Male: Erection |
| Effects on muscles and glands | It causes vasodilation of skeletal muscles and liver. It causes dilation of bronchial smooth muscles. This property is used in inhalers, giving β2 agonists. | They increase gland secretion, e.g., of gastric, pancreatic, etc. |
| Protection response | The sympathetic nervous system is the actual seat of the triple F response. The 3 Fs stand for Fright Fight Flight. It prepares the body to tackle dangerous situations. | The parasympathetic nervous system has no such effects. |
