Question

Expiration involves (a) Relaxation of diaphragm and intercostals muscles (b) Contraction of diaphragm and intercostals muscles (c) Contraction of diaphragm muscles (d) Contraction of intercostals muscles

Short answer

The correct answer is (a) Relaxation of diaphragm and intercostals muscles.

Step-by-step solution

Understanding the muscles and processes

Firstly, it's important to understand what diaphragm and intercostals muscles are and their roles. The diaphragm is a large, dome-shaped muscle located at the base of the lungs. Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. Respiration includes two processes: inspiration (breathing in) and expiration (breathing out). These processes involve these muscles contracting or relaxing.

Identifying the muscles' action during expiration

Contrary to inspiration where diaphragm and intercostal muscles contract to expand the chest cavity, expiration involves the relaxation of these muscles. When these muscles relax, the chest cavity decreases, forcing air out of the lungs.

Choosing the correct answer

From the explanation, it's clear that during expiration, the diaphragm and intercostal muscles relax. So the correct answer is (a) Relaxation of diaphragm and intercostals muscles.

Key concepts

Diaphragm

The diaphragm is a crucial muscle for breathing, located at the bottom of the ribcage, just underneath the lungs.

Shaped like a dome, it acts like a partition between the chest cavity and the abdominal cavity, playing a central role in the process of respiration. When you inhale, the diaphragm contracts, pulling downward to create more space in the chest cavity, enabling the lungs to expand. This action helps draw air into the lungs. During exhalation, however, the diaphragm does quite the opposite.

It relaxes and returns to its original dome shape, which reduces the space in the chest cavity. This pushes air out of the lungs as the pressure inside the chest cavity increases. This relaxing movement is essential for the passive, automatic part of breathing known as expiration. Thus, the diaphragm is central to controlling the air pressure inside your lungs, ensuring that each breath flows smoothly.

Intercostal Muscles

Located between the ribs, intercostal muscles are key players in supporting the breathing function of the respiratory system. There are two main types of intercostal muscles: the external and the internal intercostal muscles.

During inhalation, the external intercostal muscles contract, lifting the ribs upward and outward. This action enlarges the chest cavity, similar to the diaphragm's movement. On the other hand, during expiration, the process is reversed. The external intercostals relax, and the internal intercostals may slightly contract to help bring the ribs back into place, reducing the space in the chest.

The relaxation of both the diaphragm and intercostal muscles during expiration decreases the volume of the thoracic cavity, creating pressure that forces air out of the lungs. This harmonious interaction ensures that breathing is efficient and effective.

Expiration

Expiration is the process of breathing out, and it's just as vital as inhaling to keep the body functioning.

Unlike inhalation, which is powered by the contraction of muscles like the diaphragm and external intercostals, expiration primarily relies on muscle relaxation. When these muscles relax, the diaphragm moves back to its dome shape, and the rib cage falls back down due to the relaxation of the intercostal muscles.

This process is normally passive and takes less effort because the elastic nature of the lungs and chest wall helps expel air out naturally. However, during increased physical activity, expiration can become active, where the internal intercostals and abdominal muscles might actively contract to push air out of the lungs more forcefully.

• Passive process: Muscle relaxation and elastic recoil
• Active process: Engaged during intense activity

Understanding expiration is fundamental to recognizing how breath is managed efficiently, ensuring oxygen intake and carbon dioxide expulsion during both rest and physical exertion.