Sympathetic and parasympathetic nervous system: differences and characteristics

The sympathetic and parasympathetic nervous systems promote the organism’s interaction with the world through neurons.

The entire nervous system is a complex network of structures and processes. whose main mission is to control and regulate the functioning of our organs and systems, and coordinate their respective relationships. Likewise, it is responsible for mediating the organism’s relations with the external environment, processing the electrical and chemical signals it receives from the sense organs.

At a “simple” level of operation, The nervous system is responsible for regulating the internal environment of every organism, controlling their autonomic and endocrine responses. Meanwhile, at a more complex level, it is responsible for communicating the organism with the external environment in which it operates, through sensory and motor functions (Merino and Noriega, 2011).

The nervous system, then, is organized to recognize disturbances, alterations or changes that occur in the internal and external environment of the organism. You are also equipped to predict, evaluate and interpret information and respondconsequently, through changes in the muscles or glands.

This system is divided into two large subsystems:

Central nervous system (CNS) composed of the brain and spinal cord.Peripheral nervous system (PNS)which is the nervous part that is located outside the brain and spine, and is made up of two parts: the somatic nervous system and the autonomic nervous system (also called neurovegetative).

The autonomic nervous system: sympathetic and parasympathetic

The autonomic nervous system (ANS) operates without conscious and voluntary control. Blood pressure regulation, gastrointestinal responses to food, urinary bladder contraction, eye focusing, and thermoregulation are just a few of the many homeostatic functions regulated by this system (McCorry, 2007).

The ANS plays an important role in the interaction of the organism with the environment, regulating organic processes in order to adjust their operation to the demands of the environment. Because we live in environments that are continually changing from one state to another, it is necessary to have this type of systems that allow us to maintain a state of internal balance or homeostasis (Del Abril, et al., 2009).

sympathetic nervous system

The sympathetic nervous system (SNS) is a part of the autonomic nervous system that prepares the body for action in stressful momentsraising the metabolic rate and involving a large part of the body’s resources to cope with the situation (Feldman, 2014).

This system is what triggers “fight or flight” responses to threatening situations that warrant an immediate response. Some of the main effects caused by its activation are the following:

Increases heart rate.Increases blood pressure by constricting blood vessels.Increases blood glucose.Decreases peristaltic movements.Dilates pupils to improve vision.Relaxes bronchi to increase air flow to the lungs.Decreases secretion of saliva.Contraction of the pilomotor muscles (goosebumps).Increases sweating.Provokes the secretion of adrenaline.

Increased metabolism

parasympathetic nervous system

The parasympathetic nervous system (PNS) is opposite to the SNS. Both exclude each other, but they promote balance in the body. A state of constant excitement or activation such as those caused by the SNS would not be adaptive for any organism, therefore, it is necessary for another system to counteract it when appropriate.

From the above it follows that the PNS is that part of the autonomic nervous system that calms the body after a stressful situation in which the sympathetic nervous system participated; It is the means to conserve energy resources (Feldman, 2014). Some of the main effects caused by its activation are:

Decreases heart rate. Decreases blood pressure. Increases peristaltic movements. Constricts the pupils. Constricts the bronchi. Increases salivation. Relaxes the pilomotor muscles. Decreases sweating.

Clitoral swelling and penile erection.

Allows the release of digestive enzymes and insulin.

Differences between the sympathetic and parasympathetic nervous system

The previous approach has allowed us to observe some differences between the sympathetic and parasympathetic nervous systems. Next, we will analyze some more differential points:

The parasympathetic system stimulates activities that occur under normal conditions to ensure long-term well-being (e.g. digestion), while the activation of the sympathetic is used to deal with short-term emergencies (Redolar et al., 2010). Sympathetic nerves stimulate, organize and mobilize energy resources in emergency situations; while the parasympathetic nerves act by conserving energy (Pinel, 2007).Sympathetic changes indicate psychological activation, while parasympathetic changes indicate psychological rest (Pinel, 2007). The sympathetic nervous system originates in the thoracic and lumbar regions of the spine (T1-L2), while the parasympathetic nervous system originates in the brain stem (cranial nerves III, VII, IX and while the latter are at a short distance from or in the target organs and do not form any chains. The postganglionic axons of the SNS are relatively long and myelinated, while for the PNS they are short and unmyelinated. The neurotransmitter released by the postganglionic neurons on the target organs of the SNS it is adrenaline, while for the PNS it is acetylcholine. The sympathetic nervous system inhibits the activity of the stomach, while the parasympathetic stimulates it. The parasympathetic nervous system contracts the bladder; the sympathetic relaxes it. The PNS is a system for the conservation and recovery of energy, and its influence predominates in conditions of rest. For its part, the sympathetic is related to processes that require energy expenditure. The parasympathetic activates the immune system, while the sympathetic suppresses it. The sympathetic decreases the secretion of enzymes such as insulin, while the parasympathetic increases it.

The sympathetic and parasympathetic nervous systems are antagonistic. Besides, Thanks to their coexistence we are able to have a balanced organism capable of adapting to very different circumstances.. In this way, our nervous system is capable of putting our body in very different states: letting us relax for a while reading or quickly crossing a zebra crossing because a car is coming very fast. The wonderful thing about the existence of the two systems is the product of both.

These systems work involuntarily, that is, the body has no voluntary influence on their activation. Finally, both systems are totally necessary for survival and adaptation to the various circumstances we face in our daily lives.

You might be interested…