Muscles of Respiration, G1.21, Anatomy, Thorax, Thoracic Wall

Quiet Breathing:

1. Inspiration
1. Diaphragm
2. Tonic contraction of the external intercostals and intracondral portion of the internal intercostals to resist negative pressure
2. Expiration
1. Passive or elastic recoil
2. Tonic contraction of muscles of the anteriolateral abdominal walls to antagonise the diaphragm

Active (Forced).

1. Inspiration
1. Diaphragm
2. Tonic contraction of the external intercostals and intracondral portion of the internal intercostals to resist negative pressure
3. Sternocleidomastoid, Descending (superior ) Trapezius, Pectoralis Minor and Scalenes
4. Subcostales, Levatores Costarum and Serratus Posterior Superior to Elevate Ribs  
2. Expiration
1. Passive or elastic recoil
2. Tonic contraction of muscles of the anteriolateral abdominal walls to antagonise the diaphragm
3. Rectus abdominis, External and Internal Obliques, and Transverse Abdominis
4. Internal Intercostals and Serratus Posterior to depress ribs