Application:
• External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of antagonistic
muscle action
Inspiration (inhaling) and expiration (exhaling) are controlled by two sets of antagonistic muscle groups
- Antagonistic means working oppositely – when the inspiratory muscles contract, the expiratory muscles relax (and vice versa)
Inspiration
The muscles responsible for inspiration are the diaphragm and external intercostals (plus some accessory muscles)
- Diaphragm muscles contract, causing the diaphragm to flatten and increase the volume of the thoracic cavity
- External intercostals contract, pulling ribs upwards and outwards (expanding chest)
- Additional muscle groups may help pull the ribs up and out (e.g. sternocleidomastoid and pectoralis minor)
Expiration
The muscles responsible for expiration are the abdominal muscles and internal intercostals (plus some accessory muscles)
- Diaphragm muscles relax, causing the diaphragm to curve upwards and reduce the volume of the thoracic cavity
- Internal intercostal muscles contract, pulling ribs inwards and downwards (reducing breadth of chest)
- Abdominal muscles contract and push the diaphragm upwards during forced exhalation
- Additional muscle groups may help pull the ribs downwards (e.g. quadratas lumborum)
Respiratory Muscles
⇒ Click on the diagram to show / hide accessory muscles