How do the external and internal intercostal muscles, diaphragm, and abdominal muscles work in antagonistic pairs to control ventilation?

Sourav PanNovember 8, 2024

Answered

The process of ventilation involves the coordinated actions of various muscles that work in antagonistic pairs to control the inhalation and exhalation of air. The primary muscles involved in this process are the diaphragm, external intercostal muscles, internal intercostal muscles, and abdominal muscles. Here’s how these muscles function in opposition to facilitate effective breathing:

Inspiration (Inhalation)

1. Diaphragm

• Function: The diaphragm is the main muscle responsible for inspiration. When it contracts, it flattens and moves downward, increasing the volume of the thoracic cavity.
• Effect: This increase in volume lowers the pressure within the thoracic cavity (intrapulmonary pressure), allowing air to flow into the lungs from the atmosphere.

2. External Intercostal Muscles

• Function: These muscles are located between the ribs and contract during inhalation to elevate the rib cage.
• Effect: By pulling the ribs upward and outward, they further expand the thoracic cavity, contributing to a decrease in pressure that facilitates air intake.

3. Antagonistic Action During Inspiration

• During inspiration, the diaphragm and external intercostal muscles contract simultaneously while their antagonistic counterparts (internal intercostals and abdominal muscles) relax. This coordinated contraction allows for maximum expansion of the thoracic cavity and efficient airflow into the lungs.

Expiration (Exhalation)

1. Relaxation of Diaphragm and External Intercostals

• Function: During normal expiration, the diaphragm relaxes and returns to its dome shape, while the external intercostal muscles also relax.
• Effect: This relaxation decreases the volume of the thoracic cavity, leading to an increase in intrapulmonary pressure, which forces air out of the lungs.

2. Internal Intercostal Muscles

• Function: These muscles become active during forced expiration. They contract to pull the ribs downward and inward.
• Effect: This action further reduces thoracic volume, increasing pressure in the lungs and expelling air more forcefully.

3. Abdominal Muscles

• Function: The abdominal muscles assist in forced expiration by contracting to push up against the diaphragm.
• Effect: This contraction helps to expel air from the lungs more rapidly by decreasing thoracic volume even further.

4. Antagonistic Action During Expiration

• In expiration, particularly during forced breathing, internal intercostal and abdominal muscles contract while their antagonistic partners (external intercostals and diaphragm) relax. This opposition is crucial for controlling airflow out of the lungs efficiently.

Summary of Antagonistic Muscle Pairs