Muscles of respiration

Major inspiratory muscles

• Diaphragm
• External intercostal muscles

Accessory muscles of inspiration (forceful inspiration only)

• Sternocleidomastoid
• Scalenus
• Pectoral

Muscles of active expiration (active expiration only)

• Abdominal muscles
• Internal intercostal muscles

Lung capacities and volumes

Volumes

Tidal volume (TV)

• Volume that enters and leaves with each breath, from a normal quiet inspiration to a normal quiet expiration

Inspiratory reserve volume (IRV)

• The amount of air that can be forcibly inhaled after a normal tidal volume
• Relies on muscle strength, lung compliance (elastic recoil) and a normal starting point (end of tidal volume)

Expiratory reserve volume (ERV)