Textbook Question
Which eye muscle passes through the trochlea and turns the eye inferiorly and laterally?
a. Lateral rectus muscle
b. Inferior rectus muscle
c. Inferior oblique muscle
d. Superior oblique muscle
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10. Muscles
Origin and Insertion
Problem L2.2
Textbook Question
Explain how the diaphragm muscle is able to increase the size of the thoracic cavity even though it doesn't insert into a bone.
Verified step by step guidance1
Understand the anatomy of the diaphragm: The diaphragm is a dome-shaped sheet of skeletal muscle that separates the thoracic cavity from the abdominal cavity. It is unique because it does not insert into a bone but attaches to structures such as the central tendon, the lower ribs, the sternum, and the lumbar vertebrae.
Learn the mechanism of contraction: When the diaphragm contracts, its muscle fibers shorten, causing the dome-shaped structure to flatten and move downward. This movement increases the vertical dimension of the thoracic cavity.
Explore the role of the central tendon: The diaphragm's central tendon is a strong, fibrous structure that serves as the insertion point for the muscle fibers. When the diaphragm contracts, the central tendon is pulled downward, facilitating the expansion of the thoracic cavity.
Understand the pressure changes: As the diaphragm moves downward, it reduces the pressure in the thoracic cavity relative to the atmospheric pressure. This creates a vacuum effect, allowing air to flow into the lungs during inhalation.
Connect the movement to respiration: The diaphragm's ability to increase the size of the thoracic cavity is essential for breathing. By expanding the thoracic cavity, the diaphragm enables the lungs to fill with air, supporting the process of gas exchange necessary for oxygen delivery and carbon dioxide removal.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Diaphragm Anatomy
The diaphragm is a dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. It is primarily composed of skeletal muscle fibers and is innervated by the phrenic nerve. Although it does not insert into a bone, it is anchored to the lower ribs, sternum, and lumbar vertebrae, allowing it to function effectively during respiration.
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Mechanics of Breathing
Breathing involves the expansion and contraction of the thoracic cavity, which is essential for inhalation and exhalation. When the diaphragm contracts, it flattens and moves downward, increasing the volume of the thoracic cavity. This decrease in pressure allows air to flow into the lungs, demonstrating how muscle contraction can influence cavity size without direct bony attachment.
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Pressure Gradient in Respiration
The principle of pressure gradient is crucial in respiration, as air moves from areas of higher pressure to lower pressure. When the diaphragm contracts and the thoracic cavity expands, the pressure inside the cavity decreases relative to atmospheric pressure. This pressure difference is what drives air into the lungs, illustrating the diaphragm's role in respiratory mechanics despite its lack of bony insertion.
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