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Overview of the Parasympathetic Nervous System

The Parasympathetic Nervous System (PSNS) is essential for the 'rest and digest' state, regulating bodily functions such as digestion, urination, and sexual arousal. It consists of preganglionic and postganglionic neurons, with the vagus nerve playing a significant role in innervating various organs. Acetylcholine is the primary neurotransmitter, acting on muscarinic and nicotinic receptors to maintain homeostasis.

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1

Divisions of autonomic nervous system

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Three divisions: sympathetic, parasympathetic, enteric

2

PSNS vs SNS functions

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PSNS: rest and digest. SNS: fight or flight.

3

PSNS primary activities

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Sexual arousal, salivation, lacrimation, urination, digestion, defecation

4

The ______ nervous system connects the central nervous system to the organs it controls using two types of neurons.

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parasympathetic

5

Preganglionic neurons of the parasympathetic nervous system originate from the brainstem nuclei linked to cranial nerves ______, ______, ______, and ______, as well as sacral spinal cord segments ______ to ______.

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III VII IX X S2 S4

6

The ______ nerve, also known as cranial nerve ______, plays a crucial role in the parasympathetic system by innervating thoracic and abdominal organs.

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vagus X

7

Arising from the sacral spinal cord, the ______ ______ nerves target the lower abdominal and pelvic organs.

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pelvic splanchnic

8

Cranial nerve III function in PSNS

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Constricts pupil, accommodates lens for near vision.

9

Cranial nerve VII function in PSNS

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Stimulates salivary and lacrimal glands.

10

Cranial nerve IX function in PSNS

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Activates parotid salivary gland.

11

Emerging from the ______ ______, the vagus nerve reaches various internal organs, carrying fibers that manage essential bodily functions.

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medulla oblongata

12

The fibers transmitted by the vagus nerve are of the ______ type, which help in regulating heartbeat, respiration, and digestion.

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parasympathetic

13

Due to its extensive influence on major organs, the vagus nerve is a critical component of the ______ ______ system.

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parasympathetic nervous

14

Origin of pelvic splanchnic nerves

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Arise from sacral spinal segments S2 to S4.

15

Functions of pelvic splanchnic nerves

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Control urinary bladder, large intestine, reproductive organs; enable peristalsis, micturition, defecation.

16

The ______ nervous system transmits sensory data from internal organs to the brain and spinal cord.

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parasympathetic

17

General visceral afferent fibers may relay feelings of ______ or discomfort, often felt as referred pain when an organ is in distress.

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fullness

18

The PSNS can lower the ______ by releasing acetylcholine at the sinoatrial node via the vagus nerve.

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heart rate

19

A primary role of the PSNS is to help the body achieve a ______ state by controlling the heart rate.

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restful

20

PSNS role in male sexual function

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Induces vasodilation in penile arteries to achieve erection.

21

PSNS role in female sexual function

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Facilitates vaginal lubrication and oocyte movement in fallopian tubes.

22

Acetylcholine targets two receptor types: ______ and ______ cholinergic receptors.

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muscarinic nicotinic

23

______ receptors are categorized into five subtypes, labeled ______ to ______, and are located in the heart, smooth muscles, and glands.

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Muscarinic M1 M5

24

______ receptors are split into two types: one found at the neuromuscular junction and the other in the autonomic ______.

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Nicotinic ganglia

25

When ______ binds to its receptors, it triggers a variety of ______ responses in the body.

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acetylcholine parasympathetic

26

Sympathetic division function

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Primes body for action - increases heart rate, dilates airways, releases energy stores.

27

Parasympathetic division role

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Conserves energy - slows heart rate, stimulates digestion, promotes relaxation.

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Overview of the Parasympathetic Nervous System

The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic and enteric systems. The PSNS is primarily responsible for the body's "rest and digest" activities that occur when the body is relaxed, such as after eating. It promotes functions including sexual arousal, salivation, lacrimation, urination, digestion, and defecation. The PSNS works in concert with the sympathetic nervous system, which mediates the "fight or flight" responses. The PSNS's preganglionic neurons originate in the brainstem and the sacral spinal cord, projecting to ganglia close to or within the target organs.
Detailed anatomical model of sagittally sectioned human brain with cranial nerves and brainstem, blurred blue background.

Structural Components of the Parasympathetic Nervous System

The parasympathetic nervous system consists of preganglionic and postganglionic neurons that connect the central nervous system to the organs they innervate. The preganglionic neurons arise from the brainstem nuclei associated with cranial nerves III, VII, IX, and X, and from the sacral spinal cord segments S2 to S4. The vagus nerve (cranial nerve X) is a key component, providing parasympathetic innervation to many thoracic and abdominal organs without synapsing in the head. The pelvic splanchnic nerves arise from the sacral spinal cord and innervate the lower abdominal and pelvic organs. The PSNS's two-neuron chain, consisting of a preganglionic neuron synapsing at a ganglion with a postganglionic neuron, allows for precise control over organ function.

Cranial Nerves and Their Parasympathetic Functions

The parasympathetic functions of the cranial nerves include the oculomotor nerve (III), which constricts the pupil and accommodates the lens for near vision; the facial nerve (VII), which stimulates salivary and lacrimal glands; and the glossopharyngeal nerve (IX), which activates the parotid salivary gland. These nerves originate from specific brainstem nuclei and project to parasympathetic ganglia where they synapse before reaching their target organs, modulating activities that are essential for daily living.

The Vagus Nerve and Its Extensive Influence

The vagus nerve (cranial nerve X) has a broad influence on the body, innervating the heart, lungs, and most of the digestive tract. It originates from the medulla oblongata and extends to the viscera, transmitting parasympathetic fibers that regulate critical functions such as heart rate, breathing, and digestive processes. The vagus nerve's ability to directly affect such a wide range of organs underscores its importance in the parasympathetic nervous system.

Pelvic Splanchnic Nerves and Their Role in Visceral Functions

The pelvic splanchnic nerves, which originate from the sacral spinal segments S2 to S4, innervate the organs of the lower abdomen and pelvis. They contribute to the control of the urinary bladder, large intestine, and reproductive organs, facilitating essential functions like peristalsis, micturition, and defecation. The PSNS's modulation of these visceral activities is vital for the maintenance of internal homeostasis.

Sensory and Vascular Effects of the Parasympathetic Nervous System

The parasympathetic nervous system includes sensory pathways that carry information from the viscera to the central nervous system. These general visceral afferent fibers can convey sensations such as fullness or discomfort, which may be perceived as referred pain during organ distress. Additionally, the PSNS has a significant impact on heart rate through the vagus nerve, which can decrease the heart rate by releasing acetylcholine at the sinoatrial node, thereby influencing ionic currents and calcium levels in cardiac cells. This regulation of heart rate is a key function of the PSNS in promoting a restful state for the body.

Parasympathetic Nervous System's Role in Sexual Activity

The parasympathetic nervous system plays a crucial role in sexual function for both sexes. In males, it is involved in achieving an erection by inducing vasodilation in the penile arteries, while in females, it contributes to vaginal lubrication and the movement of the oocyte through the fallopian tubes. The PSNS and sympathetic nervous system work in tandem during sexual activity to orchestrate a series of physiological responses that facilitate reproduction.

Neurotransmitters and Receptors of the Parasympathetic Nervous System

Acetylcholine is the primary neurotransmitter used by the parasympathetic nervous system. It acts on two types of receptors: muscarinic and nicotinic cholinergic receptors. Muscarinic receptors, of which there are five subtypes (M1-M5), are found in various locations including the heart, smooth muscles, and glands, and have diverse functions. Nicotinic receptors are divided into muscle-type, found at the neuromuscular junction, and neuronal-type, which are present in the autonomic ganglia. The binding of acetylcholine to these receptors elicits the wide array of parasympathetic responses in the body.

Complementary Actions of the Sympathetic and Parasympathetic Nervous Systems

The sympathetic and parasympathetic nervous systems often act in a complementary manner to maintain physiological equilibrium. The sympathetic division primes the body for action, while the parasympathetic division conserves energy and facilitates recovery processes such as digestion and relaxation. This dynamic balance is crucial for the body's homeostasis and its ability to adapt to changing environmental conditions.