BIOL 221 Lecture Notes - Lecture 7: External Intercostal Muscles, Internal Intercostal Muscles, Phrenic Nerve
3 Mar 2020
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Document Summary
Muscles of inspiration include the diaphragm served by the phrenic nerve (arising from the 3rd to 5th cervical spinal cord segments) and the external intercostal muscles served by thoracic spinal nerves. The diaphragm pulls down on the central tendon and increases the size of the thoracic cavity dorsoventrally. The external intercostal muscles pull the ribs upwards and slightly outwards; they increase the size of the thoracic cavity from front to back. Muscles of forced expiration include the internal intercostal muscles and abdominal wall muscles all of which are served by thoracic spinal nerves. The internal intercostal muscles pull down on the ribs to decrease the size of the thoracic cavity from front to back. When the abdominal muscles contract, they push the diaphragm upwards thus decreasing the size of the thoracic cavity dorsoventrally. The lungs are served by both the pulmonary and bronchial circulations.
