Breathing Mechanics and Muscles

Overview

This lecture explores the mechanics of breathing, focusing on the diaphragm’s movement and its interaction with the intercostal muscles.

The diaphragm is the primary muscle for breathing, contracting and flattening during inhalation.
Upon inhalation, it moves downward toward the abdominal cavity; during exhalation, it relaxes into a dome shape.
The dome of the diaphragm is asymmetrical due to the liver pushing the right side higher than the left.
The diaphragm can shift position by up to 6 cm, depending on stress and individual anatomy.
There are three openings in the diaphragm for the aorta, esophagus, and inferior vena cava.
Contracting diaphragm typically thickens from 1 to 2 cm.

Intercostal muscles are located between the ribs and assist the diaphragm in breathing.
External intercostal muscles contract during inhalation, lifting and expanding the rib cage.
Internal intercostal muscles contract during forced exhalation, depressing the ribs and aiding air expulsion.
You can physically feel intercostal muscle movement by touching the spaces between your ribs while breathing.

The diaphragm and intercostal muscles increase activity during heightened oxygen demand (exercise, stress).
During rest, these muscles reduce activity to conserve energy.
This dynamic action maintains an optimal balance between oxygen supply and demand.

Diaphragm — main respiratory muscle separating chest from abdominal cavity; contracts and flattens to aid inhalation.
Dome of Diaphragm — curved top part of diaphragm, higher on right side due to the liver.
Intercostal Muscles — muscles between the ribs aiding in rib movement for breathing.
External Intercostal Muscles — outer layer, lifts ribs during inhalation.
Internal Intercostal Muscles — inner layer, depresses ribs during forced exhalation.