Respiratory Muscles: Diaphragm and Intercostals in Breathing

Diaphragm (Primary Inspiratory Muscle)

• Dome-shaped; separates thorax/abdomen.
• Contraction → flattens → ↑ thoracic volume → ↓ intrapulmonary pressure → air inflow.
• Relaxation → passive exhalation (elastic recoil).

Intercostal Muscles

• External intercostals: Elevate ribs → ↑ anteroposterior/lateral diameter (inspiration).
• Internal intercostals: Depress ribs (forced expiration).
• Innermost intercostals: Assist internal.

Accessory Muscles

Scalenes, SCM, pectoralis minor (inspiration); abdominals, internal intercostals (forced expiration).

Diaphragm contributes ~75% of tidal volume at rest.