Parasympathetic Nervous System: Videos & Practice Problems

The parasympathetic nervous system, often referred to as the craniosacral division, promotes rest and digest functions, conserving energy through decreased heart rate and bronchiole constriction. It enhances gastrointestinal activity, facilitating digestion via increased peristalsis and secretion. Urination is encouraged through bladder muscle contraction and sphincter relaxation. Additionally, pupil constriction optimizes near vision. The vagus nerve, crucial for parasympathetic innervation, synapses close to target organs, ensuring efficient communication between preganglionic and postganglionic fibers, which are long and short, respectively.

Function of the Parasympathetic Nervous System

The parasympathetic nervous system plays a crucial role in promoting the body's rest and digest functions, focusing on restoration and energy conservation. This system is essential for maintaining homeostasis and facilitating various physiological processes that occur when the body is in a relaxed state.

One of the primary effects of the parasympathetic system is a decrease in heart rate, which helps conserve energy. Additionally, it causes constriction of the bronchioles in the lungs, further supporting energy efficiency. In the gastrointestinal tract, the parasympathetic system enhances digestive processes by increasing movement and secretion while relaxing sphincters, thereby facilitating the passage of food through the digestive system.

In the bladder, the parasympathetic response leads to the contraction of smooth muscle and relaxation of the sphincter, promoting urination. This is particularly important as the body prioritizes digestion and waste elimination during restful states, contrasting with the fight or flight response where such functions are suppressed.

Another notable effect is the constriction of the pupils, which optimizes near vision. This adjustment allows individuals to focus on nearby objects without the need to scan for potential threats, reflecting the calm state induced by the parasympathetic system.

Overall, the parasympathetic nervous system is vital for facilitating relaxation, digestion, and energy conservation, ensuring that the body can effectively recover and maintain balance.

Parasympathetic Nervous System Example 1

The autonomic nervous system is divided into two main branches: the sympathetic and parasympathetic divisions, each responsible for different physiological responses in the body. Understanding these responses is crucial for grasping how our body reacts to various situations.

Firstly, the parasympathetic division is often referred to as the "rest and digest" system. It increases activity in the gastrointestinal tract, promoting digestion and nutrient absorption. This is a key function of the parasympathetic response, which can be denoted as 'P'.

In contrast, the sympathetic division prepares the body for "fight or flight" situations. For instance, vasodilation in skeletal muscles occurs under sympathetic influence, allowing increased blood flow to these areas. This response enhances oxygen and glucose delivery, essential for physical exertion.

Another sympathetic response is pupil dilation, which allows more light to enter the eyes, improving vision in low-light conditions. This evolutionary adaptation helps individuals better detect potential threats in their environment.

On the other hand, the parasympathetic division is responsible for constricting bronchioles. This action reduces airflow, as the body does not require excessive oxygen intake during restful states. The sympathetic division, conversely, dilates bronchioles to facilitate increased oxygen intake during stress or physical activity.

Additionally, a decrease in heart rate is a hallmark of the parasympathetic response, reflecting a state of calm and relaxation. This is essential for maintaining homeostasis and supporting digestion.

In summary, the autonomic effects can be categorized as follows: increased gastrointestinal activity and decreased heart rate are parasympathetic responses, while vasodilation in skeletal muscles, pupil dilation, and bronchiole dilation are sympathetic responses. Understanding these distinctions is vital for comprehending how our body manages stress and relaxation.

Structure of the Parasympathetic Nervous System

The parasympathetic nervous system is a crucial component of the autonomic nervous system, often referred to as the craniosacral division due to its origins from the brainstem and sacral spinal cord. A key player in this system is the vagus nerve, also known as cranial nerve X, which is responsible for approximately 90% of parasympathetic innervation, making it a vital nerve for regulating various bodily functions.

In this division, many preganglionic fibers synapse within the target organs themselves, rather than in ganglia located further away. These synapses occur in structures known as terminal ganglia, which are situated very close to the effector organs. This proximity allows for more direct communication between the preganglionic and postganglionic fibers, enhancing the efficiency of the parasympathetic response.

Preganglionic fibers in the parasympathetic system are notably long, extending from the brainstem or sacral region to the target organs, while the postganglionic fibers are relatively short. This anatomical arrangement is illustrated by the long purple fibers representing preganglionic fibers and the short green fibers representing postganglionic fibers. The synaptic connections can occur either within the target organs or at the terminal ganglia, which serve a similar function to collateral ganglia but are much closer to the organs they innervate.

Overall, the structure of the parasympathetic nervous system facilitates its role in promoting rest and digest functions, highlighting the importance of its components in maintaining homeostasis within the body.

Parasympathetic Nervous System Example 2

In the context of spinal cord injuries, particularly those affecting the sacral nerves, it is essential to understand the role these nerves play in bodily functions. The sacral nerves, originating from the sacrum at the base of the spinal cord, are responsible for innervating several critical organs, including the genitals, bladder, and parts of the large intestine. When these nerves are damaged, as in the case of Gordon after his car accident, functions related to the urinary bladder are likely to be significantly impacted. This is because the bladder's control is primarily governed by the sacral nerves, which are part of the parasympathetic nervous system. In contrast, functions such as saliva production and blood pressure regulation are controlled by cranial nerves, also part of the parasympathetic division, but not directly related to the sacral nerves. Additionally, adrenaline production is associated with the sympathetic division of the nervous system, which operates independently of the parasympathetic functions managed by the sacral nerves.Thus, the most affected bodily function following damage to the sacral nerves would be the urinary bladder function, highlighting the critical role these nerves play in lower body organ control.

In the parasympathetic nervous system, preganglionic fibers are ________ and postganglionic fibers are __________.

• A. Short; long.
• B. Short; short.
• C. Long; short.
• D. Long; long.

Answer: (C)

Here’s what students ask on this topic:

What are the main functions of the parasympathetic nervous system?

The parasympathetic nervous system primarily promotes rest and digest functions, conserving energy. Key functions include decreasing heart rate and constricting bronchioles to conserve energy. It enhances gastrointestinal activity by increasing peristalsis and secretion, facilitating digestion. In the bladder, it promotes urination through smooth muscle contraction and sphincter relaxation. Additionally, it constricts the pupil to optimize near vision, allowing for better focus on close objects. These actions collectively help maintain homeostasis and energy conservation during restful states.

How does the parasympathetic nervous system affect the gastrointestinal tract?

The parasympathetic nervous system significantly enhances gastrointestinal activity. It increases peristalsis, which is the movement of the digestive tract that propels food forward. It also boosts the secretion of digestive enzymes and fluids, aiding in the breakdown and absorption of nutrients. Additionally, the relaxation of sphincters in the gastrointestinal tract allows for the smooth passage of food and waste. These actions collectively facilitate efficient digestion and nutrient absorption, promoting overall digestive health.

What role does the vagus nerve play in the parasympathetic nervous system?

The vagus nerve, also known as cranial nerve 10, is crucial in the parasympathetic nervous system. It provides approximately 90% of parasympathetic innervation to various organs, including the heart, lungs, and digestive tract. The vagus nerve helps decrease heart rate, constrict bronchioles, and enhance gastrointestinal activity. It also plays a role in promoting urination and pupil constriction. By innervating these organs, the vagus nerve ensures efficient communication and coordination of parasympathetic functions, maintaining homeostasis and energy conservation.

What is the structure of the parasympathetic nervous system?

The parasympathetic nervous system, also known as the craniosacral division, consists of fibers arising from the brainstem and sacral spinal cord. Preganglionic fibers are long and extend to target organs, where they synapse with postganglionic fibers in terminal ganglia located very close to or within the target organs. The vagus nerve is a major component, providing extensive parasympathetic innervation. This structure allows for efficient and localized control of parasympathetic functions, promoting rest and digest activities in the body.

How does the parasympathetic nervous system promote urination?

The parasympathetic nervous system promotes urination by causing the contraction of the smooth muscle in the bladder wall and the relaxation of the internal urethral sphincter. This combination of actions facilitates the expulsion of urine from the bladder. During restful states, the parasympathetic system ensures that urination can occur efficiently, as opposed to during fight or flight situations where urination is not a priority. This helps maintain fluid balance and waste elimination in the body.