[Biology Class Notes] on Difference between Sympathetic and Parasympathetic Nervous System Pdf [2024]

To know the difference between sympathetic and parasympathetic nervous systems, let’s first look at their definitions.

What is a Sympathetic Nervous System?

It is the division of the autonomic nervous system which prepares the body for stressful situations and is located near the lumbar and thoracic regions in the spinal cord. A small amount of sympathetic nervous system activity can regulate vital body functions by stimulating the body’s fight or flight response. It responds as a physiological reaction by perceiving a threat or attack to survival. A few examples are regulating the rate of respiration, heart rate and pupillary responses.

What is a Parasympathetic Nervous System?

It is one of the divisions of the autonomic nervous system also known as the rest and digest system. It conserves energy when the body is relaxed, feeding or resting. Situated between the spinal cord and the medulla, it slows the heart rate, increases gland and intestinal activity in the gastrointestinal tract. Parasympathetic nervous system activities are essential for the overall functioning of the body as restoring the body’s nervous system is important to further function at the optimal level.

The Autonomic Nervous System

Often abbreviated as ANS, the Autonomic Nervous System is the part of our nervous system that supplies nerve endings in the blood vessels, intestines, heart, smooth muscles and glands. It is responsible to govern the involuntary functioning of all these body systems without a person’s conscious effort. When ANS doesn’t function properly, disorders may arise leading to affected body parts or processes, which are often progressive. However, some of the autonomic nervous system disorders can be reversed.

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What is Sympathetic and Parasympathetic?

As defined above, the two main divisions of Autonomic Nervous System (ANS) are:

Sympathetic ANS
Parasympathetic ANS

Functions of the Autonomic Nervous System

The functions of the autonomic nervous system in the body processes can be listed as follows-

Blood pressure
Body temperature
Heart and breathing rates
Digestion
Metabolism and body weight
Keeping a balance of water and electrolytes like Na (Sodium) and Ca (Calcium)
Production of body fluids such as saliva, tears, and sweat
Defecation
Urination
Sexual response

How does the Autonomic Nervous System work?

When the ANS receives information about the external environment and the body, it responds by stimulating varied body processes, through the sympathetic nervous system, or can also inhibit the body systems through the parasympathetic nervous system. There are two nerve cells in an autonomic nerve pathway, one cell is situated in the brain stem region or spinal cord connected by nerve fibers to the rest of the cells. It is located as a cluster of nerve cells called autonomic ganglia from where the nerve fibers connect with internal organs.

Most of the ganglia for sympathetic division are situated just outside the spinal cord on both sides of it, whereas for parasympathetic ANS, these are located nearby organs where they are connected. Mostly, organs are controlled primarily by one of them, either sympathetic ANS or the parasympathetic ANS. In a few cases, the two nervous systems have opposite effects on the same organ. The sympathetic nervous system function is opposite to that of parasympathetic nervous system function. One of the best examples is increased blood pressure due to sympathetic division and decreased blood pressure due to the parasympathetic division. However, when both work in coordination, it is ensured to have a balanced situation according to different situations.

Difference between Sympathetic and Parasympathetic ANS

Let’s discuss the Differences between the Sympathetic and Parasympathetic Nervous System in a Tabular Form-

Characteristic	Sympathetic ANS	Parasympathetic ANS
Response	It is involved in the fight or flight response of the body.	It is involved in maintaining homeostasis and allows rest and digest response.
Major Function	It prepares the body for any potential stress or danger.	It aims to bring the body towards calmness and relaxation.
Neuron Pathways	It has shorter neuron pathways resulting in a faster response time.	It has longer neuron pathways and therefore a slower response time.
Heart Rate and Muscles	It increases heart rate and makes the muscles tense up.	It reduces heart rate and relaxes muscle cells.
Pupil	It makes the pupil dilate to let in more light.	Here, it makes the pupil contract.
Saliva Secretion	It inhibits saliva secretion.	It increases saliva secretion and therefore digestion also increases.
Fight and Flight Situation	In this state, adrenaline is released by the adrenal glands and more glycogen can be converted to glucose.	It doesn’t have a fi ght or flight state.

Acetylcholine

Acetylcholine is a neurotransmitter that works for both the central nervous system and the peripheral nervous system. Acetylcholine activates muscles in the peripheral nervous system and it also acts as an important neurotransmitter in the autonomic nervous system. Acetylcholine and its neurons form the cholinergic system in the central nervous system.

Acetylcholine is secreted at all pre and post ganglionic parasympathetic neurons, some postganglionic sympathetic fibers, all preganglionic sympathetic neurons, and in the pseudo motor neurons to sweat glands.

Acetylcholine produces a wide variety of effects in the central nervous system. It acts as a neuromodulator for arousal, plasticity, and reward. It also helps in the enhancement of sensory perceptions when we wake up.

Conclusion

Both the sympathetic and parasympathetic nervous systems comprise the autonomic nervous system. In response to a perceived threat, the sympathetic nervous system activates the fight or flight response, while the parasympathetic nervous system restores the body to a state of calm.