Part 4: Breathing Mechanics — How the Body Powers Every Breath

In the earlier parts, we explored the structure of the pulmonary system and the anatomy of the airways and lungs. In this section, we focus on how breathing actually happens — the muscles, movements, and pressure changes that allow air to enter and leave the lungs.

1. The Diaphragm: The Primary Breathing Muscle

The diaphragm is a dome-shaped muscle located below the lungs and above the abdomen.

• During inhalation, the diaphragm contracts and flattens, increasing chest volume and drawing air into the lungs.

• During exhalation, it relaxes and rises, allowing air to escape.

Weakness or paralysis of the diaphragm significantly impairs breathing efficiency.

2. Intercostal Muscles and Chest Wall Movement

Between the ribs lie the intercostal muscles, which assist breathing by expanding and stabilizing the rib cage.

• External intercostals lift the ribs during inhalation.

• Internal intercostals assist forced exhalation.

  
  

Restricted chest wall movement — due to obesity, injury, or spinal disorders — limits lung expansion and reduces oxygen intake.

3. Negative Pressure Ventilation

Human breathing relies on negative pressure ventilation.

As the chest cavity expands, pressure inside the lungs drops below atmospheric pressure, pulling air inward.When the chest relaxes, pressure rises, pushing air outward.

This pressure-based system explains why injuries like chest trauma or pneumothorax disrupt normal breathing.

4. Resting vs. Forced Breathing

At rest, breathing is mostly passive and energy-efficient. During exercise, illness, or stress, the accessory muscles in the neck and shoulders help meet the increased oxygen demand.

5. Neural Control of Breathing

Breathing is regulated automatically by respiratory centers in the brainstem.

• These centers respond to rising carbon dioxide levels

• They adjust breathing rate and depth without conscious effort

  
  

Neurological injuries or sedative drugs can suppress this control, leading to dangerous breathing irregularities.

Key Takeaway

Breathing is a finely coordinated mechanical process powered by muscles, pressure changes, and neural control. When any component fails — muscle weakness, chest restriction, or nerve disruption — breathing efficiency declines.