Transcript Mechanics of Breathing (1)

Overview
- Focus on thorax, breathing, and biomechanics.
- Importance of understanding the mechanics of air flow during breathing.
- Expansion of the chest and abdomen allows air to flow inwards; it does not expand due to the air flowing in.
- Reference to Boyle's Law indicates the relationship between pressure and volume in breathing.

Function
- The diaphragm is the most crucial muscle for respiration.
- Decreases pressure in the thoracic cavity to facilitate air inflow.
Anatomy
- Attachments:
  - xiphoid process of sternum
  - inferior six ribs
  - lumbar vertebrae (L1-L3)
  - fibrous pericardium of the heart
- Innervated by the phrenic nerve originating from cervical nerves C3, 4, and 5.
- Peripheral muscles consist of radial fibers converging on a central tendon, which acts as a tough insertion point.
Openings in the Diaphragm
- Three main openings and one large gap for movement of structures between the thoracic and abdominal cavities.

Inspiration
- Diaphragm contracts, moving downwards, increasing thoracic volume.
- External intercostal muscles elevate the rib cage, creating a bucket handle motion.
- The rib movement in costovertebral joints facilitates the pump handle motion, causing an increase in thorax dimensions.
Expiration
- Generally a passive process during quiet breathing, relying mainly on the diaphragm and intercostal muscles.
- In active breathing conditions (exercise, pathology), accessory muscles are recruited.

Used during High Demand Activities
- Inspiration:
  - Sternocleidomastoid
  - Scalenes
  - Pectoralis major and minor
  - Serratus anterior (inferior fibers)
  - Latissimus dorsi
  - Serratus posterior superior
  - Iliocostalis cervicis
- Expiration:
  - All abdominal muscles contract to assist.
  - Additional muscles include the lowest fibers of iliocostalis, longissimus, serratus posterior inferior, and quadratus lumborum.