Canonical Question
Resp Mechanics – Insp/Exp
Master answer
Primary groups of Muscles
| INNERVATION | FUNCTION | |
|---|---|---|
| DIAPHRAGM | ||
| Sheet of skeletal muscle Domed Inserts into lower ribs | Phrenic nerves C3, C4, C5 | Flattens on inspiration – Abdominal contents moved inferiorly → Vertical dimension of thorax increased – Ribs lift and move outwards → Circumference of thorax increased Moves up and down 1cm in tidal breathing can move 10cm in forced inspiration and expiration |
| EXTERNAL INTERCOSTAL MUSCLES | ||
| Insert into superior and inferior borders of ribs Slope inferiorly and outwardly* | Intercostal nerves Anterior rami of thoracic spinal nerves (T1 to T11) | Move the ribs superiorly and outward, increasing circumference of thorax |
| INTERNAL INTERCOSTAL MUSCLES | ||
| Insert into superior and inferior borders of ribs Slope superiorly and inwardly* | Intercostal nerves Anterior rami of thoracic spinal nerves (T1 to T11) | Move the ribs inferiorly and inward, increasing circumference of thorax Not required in quiet breathing, as expiration is passive |
*NSFW:
External Intercostal muscles: ‘hands in pockets’
Internal Intercostal muscles: ‘hands on tits’
Accessory muscles
Accesory inspiratory muscles
(not used in quiet breathing within tidal volume)
- Scalene muscles
- Elevate first two ribs
- Sternomastoids
- Raise the sternum
Accessory expiratory muscles
(not used in quiet breathing within tidal volume)
- Abdominal wall muscles
- Rectus abdominus
- Internal obliques
- External obliques
- Transversus abdominus
- Reduce abdominal cavity volume → Increase abdominal pressure → Diaphragm moves up → lungs decrease in volume
Mooney 2016
Exam appearances
| Exam | Exact wording | Relationship | Success |
|---|---|---|---|
| 2010B Q14 | List the muscles involved in Firation and briefly describe their function. | historical_member | — |