Parasympathetic vs Sympathetic Nervous System

Your nervous system is composed of two physically separate but functionally connected networks of nervous tissue, the central nervous system (brain and spinal cord) and the peripheral nervous system. Both networks perceive and respond to internal and external stimuli to preserve homeostasis (balance). The peripheral nervous system is further divided into the autonomic and somatic systems somatic systems. This article will focus on the autonomic system and its subdivisions. The autonomic system consists of neurons and nerve fibres that convey messages (impulses) from the central nervous system to the heart, internal organs with smooth muscles, and glands. It controls internal organ functions that happen subconsciously, like digestion, breathing, and heartbeat.

It’s made up of the following:

The neurons and nerve fibres of the parasympathetic nervous system come from the brainstem and sacral part (tail) of the spinal cord. You’ll know that this system is in place when you feel relaxed and resting. It’s responsible for physiologic activities like constriction of the pupils, slowing the heart rate, relaxation of blood vessels, and activation of the digestive and urinary systems. The parasympathetic nervous system is the housekeeper of your body because it maintains the regular functioning of your organs when you’re not in stressful situations.

The neurons and nerve fibres of the sympathetic nervous system come from the thoracic (chest) and lumbar (lower back) regions of the spinal cord. It responds to stress and is primarily responsible for increasing your heart rate and blood pressure. It also gives you a sense of excitement that you may experience because of the increase in epinephrine in your system. When your body is under stress, the sympathetic nervous system acts like a triple zero emergency responder in Australia (or 111 in New Zealand).

This recently added subdivision of the autonomic nervous system is composed of two groups of neurons, all located within the walls of the gastrointestinal system. This is unlike the two other subdivisions wherein the neurons are located in the central nervous system. The ENS is self-contained and functions via local reflex activity (like a loop). It’s not entirely a loner since it also receives occasional input and gives feedback to the PNS and SNS. The function of the ENS is predominantly centred on the motility and contractility of the gastrointestinal tract. This article will focus more on the SNS and PNS subdivisions of the autonomic nervous system.

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HOW TWO SEEMINGLY OPPOSING SYSTEMS (PNS AND SNS) BECAME FRIENDS AND WORK TOGETHER

Under typical everyday conditions, the SNS and PNS are continually active, and their basal rates of activity are known as sympathetic tone and parasympathetic tone. The value of this tone is that it permits a single system to both increase and decrease the activity of a stimulated organ.

1. For example, sympathetic tone regularly keeps almost all tiny arteries in the body constricted to aFor example, the sympathetic tone regularly keeps almost all tiny arteries in the body constricted to about one-half their maximum diameter. An increase in tone will narrow these arteries and a decrease will do the opposite. This is essential to properly distribute blood flow and increase the supply of oxygen to tissues. An example of the parasympathetic tone is its background stimulation on the digestive tract, keeping food and liquids moving along towards your rear end. If you remove or decrease the parasympathetic tone, it will result in atony (lack of tone) and lead to constipation.

Your body can perform vigorous muscle activity in several ways when vast portions of the SNS discharge or are stimulated simultaneously. This is primarily the purpose of the sympathetic nervous system, to give extra activation to the body in stressful conditions. This response is called the sympathetic stress response.

1. The SNS is particularly strongly stimulated in many emotional states. For example, in the state of fear, which is manifested to a great extent by activating the amygdala (the fear centre of the brain), signals are transmitted down through the brainstem and into the spinal cord to cause a massive sympathetic discharge of electrical signals and hormones.

1. During this phase, one crucial thing to mention is your SNS's stimulation of the adrenal glands. This causes the adrenal glands to release catecholamines, particularly epinephrine and norepinephrine. The addition of these two hormones ensures that your body is more capable of responding to the imminent threat, whether it’s physical danger, mental threat, or both. The chain of reactions results in numerous physiological responses from multiple tissues and organs in your body. This is termed an alarm reaction or more frequently known as the fight-or-flight reaction. The person may decide to run because of the fear or face it. Whichever the person chooses, the alarm reaction makes the person’s subsequent responses and activities vigorous. Take for example, the following diagram:

Your sympathetic alarm reaction or fight-or-flight response (full emergency responder mode) includes the following:

1. Your heart rate, respiratory rate, and blood pressure increase to give your body the oxygen and energy it needs to respond rapidly.
2. Blood flow to your brain, heart, and skeletal muscles all increase. Are you ready to fight the snake or make a run for it? At the same time, blood flow to your gastrointestinal tract, skin, and kidneys decreases. Also, your blood increases its clotting factors just in case you may have suffered an injury leading to blood loss. You may have a flushed face and pale areas on your body. It’s proof that blood is diverted to vital organs.
3. Metabolismthroughout your body increases to provide more glucose as an immediate energy source.
4. Your mental sharpness and activity increase.

5. You have increased muscle strength and sometimes tremble. Shaking or trembling is an expected response when primed for a sympathetic alarm reaction. You may also have goosebumps (or goose-pimples) and sweating.

6. Your pupils dilate to allow more light to come in for better vision.

After fleeing the snake (we hope you did), your body’s response dies down after about 30 minutes to 1 hour. After that, the SNS fades into the background, and we’re back to a baseline parasympathetic tone. The scenario above would be similar to watching a scary movie, going into a haunted house, or giving a big presentation at work. The difference is that you may not reach a fight-or-flight reaction, just a sympathetic stress response. Just remember that we all respond to stimuli differently and to varying degrees. Rage is another emotion that can reach a sympathetic alarm reaction level.

IT’S TRUE. OPPOSITES ATTRACT EACH OTHER

It’s pretty apparent what would happen to our body if we didn’t have an intact autonomic nervous system. It plays an essential role in regulating your body’s automatic processes, lots of them. This system includes the sympathetic nervous system, which prepares the body to adapt to stress and cope with dangers or threats. On the other hand, the parasympathetic nervous system helps the body return to its normal or resting state after the stress response. They may have opposing functions, but they need each other to operate better. More research is being done on these nervous system divisions because it can help us understand the mechanisms underlying our body’s response to stress and disease.