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Ch. 22 The Respiratory System
Hoehn - Marieb Human Anatomy & Physiology, 12th edition
Hoehn, Haynes, Abbott12th EditionMarieb Human Anatomy & PhysiologyISBN: 9780138242732Not the one you use?Change textbook
Chapter 22, Problem 1

Cutting the phrenic nerves will result in:
a. Air entering the pleural cavity
b. Paralysis of the diaphragm
c. Stimulation of the diaphragmatic reflex
d. Paralysis of the epiglottis

Verified step by step guidance
1
Step 1: Understand the role of the phrenic nerves. The phrenic nerves originate from the cervical spinal cord (C3-C5) and are responsible for motor innervation to the diaphragm, which is the primary muscle involved in breathing.
Step 2: Analyze the consequences of cutting the phrenic nerves. If the phrenic nerves are severed, the diaphragm will lose its motor innervation, leading to paralysis of the diaphragm. This would impair the ability to contract and relax the diaphragm, which is essential for normal breathing.
Step 3: Evaluate the options provided in the question. Option (a) refers to air entering the pleural cavity, which is associated with pneumothorax and not directly related to cutting the phrenic nerves. Option (c) mentions stimulation of the diaphragmatic reflex, which would not occur if the nerves are cut. Option (d) refers to paralysis of the epiglottis, which is unrelated to the phrenic nerves as the epiglottis is controlled by other nerves.
Step 4: Focus on option (b), which states 'Paralysis of the diaphragm.' This aligns with the physiological consequence of cutting the phrenic nerves, as the diaphragm would no longer receive motor signals.
Step 5: Conclude that cutting the phrenic nerves results in paralysis of the diaphragm, as this is the most accurate and relevant outcome based on the anatomy and physiology of the phrenic nerves.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Phrenic Nerve Function

The phrenic nerves are crucial for diaphragm function, as they provide motor innervation to the diaphragm muscle. When these nerves are intact, they stimulate the diaphragm to contract, facilitating inhalation. Damage or cutting of the phrenic nerves disrupts this process, leading to respiratory complications.
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Diaphragm Anatomy and Physiology

The diaphragm is a dome-shaped muscle that separates the thoracic cavity from the abdominal cavity and plays a key role in breathing. Its contraction lowers the diaphragm, increasing thoracic volume and allowing air to flow into the lungs. Paralysis of the diaphragm, due to phrenic nerve damage, results in impaired breathing and reduced lung capacity.
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Respiratory Reflexes

Respiratory reflexes involve automatic responses that regulate breathing patterns, including the diaphragmatic reflex. This reflex can be stimulated by various factors, such as changes in carbon dioxide levels. However, if the phrenic nerves are cut, the reflex mechanisms that depend on diaphragm movement are compromised, leading to ineffective respiratory responses.
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