Systems Biology
The parasympathetic nervous system is the “rest and digest” division of the autonomic nervous system which acts automatically and promotes energy conservation, counterbalancing the “fight or flight” actions of the sympathetic division. It is also known as the craniosacral division due to its nerve fibers stemming from the cranial and sacral regions of the spinal cord. The parasympathetic nervous system innervates all glands except for the sweat glands and almost every organ in the body, primarily through the vagus nerve (cranial nerve X).
Preganglionic neurons in the parasympathetic nervous system are relatively long, while postganglionic neurons are generally shorter. Both pre and postganglionic neurons release acetylcholine, which binds to nicotinic receptors at the ganglia and muscarinic receptors at the target organs. The system induces actions like increasing digestion and salivation, decreasing airflow through the lungs, constricting the pupils, and lowering heart rate to promote energy conservation and the body’s long-term needs, counterbalancing the sympathetic nervous system.
Lesson Outline
<ul> <li>Introduction to the parasympathetic nervous system (PNS)</li> <ul> <li>Rest and digest division of NS</li> <li>Part of the autonomic nervous system</li> <li>Counterbalances the sympathetic nervous system</li> </ul> <li>Nerves and organization</li> <ul> <li>Craniosacral division</li> <ul> <li>Cranial nerves III, VII, IX, and X</li> <li>Sacral nerves II through IV</li> </ul> <li>Vagus nerve (Cranial nerve X)</li> <ul> <li>Innervates most thoracic and abdominal organs</li> </ul> </ul> <li>Roles in the body</li> <ul> <li>Innervates all glands except sweat glands</li> <li>Innervates most organs</li> <li>Two-neuron relay system</li> <ul> <li>Preganglionic neurons (long) and postganglionic neurons (short)</li> </ul> </ul> <li>Neurotransmitters</li> <ul> <li>Both pre- and postganglionic neurons are cholinergic</li> <li>Acetylcholine binds to muscarinic and nicotinic receptors</li> </ul> <li>Specific parasympathetic effects</li> <ul> <li>Pupillary constriction</li> <li>Increased digestion and salivation</li> <li>Decreased airflow through the lungs (bronchoconstriction)</li> <li>Lowered heart rate</li> </ul> </ul>
Don't stop here!
Get access to 71 more Systems Biology lessons & 8 more full MCAT courses with one subscription!
FAQs
The parasympathetic nervous system is one of the two main branches of the autonomic nervous system, with the other being the sympathetic nervous system. Its primary role is to maintain homeostasis by conserving and restoring energy in the body. It promotes relaxation, digestion, and energy conservation by slowing the heart rate, constricting the pupils, and increasing digestive and metabolic activities. The parasympathetic nervous system counteracts the 'fight or flight' response initiated by the sympathetic nervous system.
The vagus nerve, also known as cranial nerve X, plays a crucial role in the parasympathetic nervous system as it provides innervation to various organs in the thoracic and abdominal cavities. It contributes to a wide range of functions, such as regulating the heart rate, controlling smooth muscle contractions in the gastrointestinal tract, and promoting the secretion of digestive enzymes. Approximately 75% of all parasympathetic fibers in the body are part of the vagus nerve, making it a vital component of the parasympathetic nervous system.
Acetylcholine is the primary neurotransmitter involved in the parasympathetic nervous system. It is released by both preganglionic and postganglionic neurons. Muscarinic receptors and nicotinic receptors are two major types of acetylcholine receptors found throughout the body. In the parasympathetic nervous system, acetylcholine acts on nicotinic receptors located on postganglionic neurons within the autonomic ganglia, and on muscarinic receptors located on the target organs. The activation of these receptors leads to various physiological responses that promote relaxation, digestion, and energy conservation in the body.
The parasympathetic and sympathetic nervous systems are the two main branches of the autonomic nervous system, and they have opposing effects on the body. The parasympathetic nervous system is responsible for conserving and restoring energy in the body by promoting relaxation, digestion, and energy conservation. In contrast, the sympathetic nervous system prepares the body for action, initiating the 'fight or flight' response, by increasing heart rate, dilating the pupils, and diverting blood flow to the muscles. Additionally, the parasympathetic nervous system is associated with the craniosacral division, while the sympathetic nervous system is associated with the thoracolumbar division.
