IGCSE Biology glossary
Intercostal muscle
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Definition
Muscles found between the ribs that work together with the diaphragm to ventilate the lungs. External intercostal muscles contract during inhalation, pulling the ribs up and out. Internal intercostal muscles contract during forced exhalation, pulling the ribs down and in.
What to include in an exam answer
For IGCSE, focus on external intercostal muscles contracting to raise the ribs during inhalation. In ventilation questions, describe both the diaphragm and intercostal muscles together for full marks.
Example in context
Describe the changes in the thorax during inhalation (3 marks): External intercostal muscles contract, pulling the ribs up and out. The diaphragm contracts and flattens. These actions increase the volume of the thoracic cavity, decreasing pressure, so air flows into the lungs.
Related syllabus topic
Gas exchange in humans