In this article “Role of Respiratory Muscles and Thoracic Cage” we will discuss the respiration process in detail. Read this article to know how humans breathe. This article includes:


The respiratory system is a vital part of our bodies, allowing us to breathe and get the oxygen we need to survive. It’s like our body’s “breathing machine” that keeps us alive and healthy. Two essential players in this system are the respiratory muscles and the thoracic cage. In this article, we will explore their significance and importance.

Overview of the Respiratory System

The respiratory system helps us breathe. When we breathe in, we take air into our body through our nose or mouth. The air goes down a tube called the windpipe and reaches our lungs. Inside the lungs, the oxygen from the air goes into our blood, which helps our body work properly. At the same time, the waste gas called carbon dioxide is taken out from our blood and then we breathe it out.


Importance of Respiratory Muscles and the Thoracic Cage

To breathe, our body uses two important things: respiratory muscles and the thoracic cage.

  • Respiratory Muscles: These muscles help us breathe in and out. When we breathe in, the diaphragm (a big muscle under our lungs) moves down, making space for the lungs to expand. At the same time, muscles between our ribs lift the ribcage, allowing even more room for the lungs to fill with air. When we breathe out, these muscles relax, and the diaphragm moves back up, pushing the air out of our lungs.
  • Thoracic Cage: The thoracic cage is made up of our ribs and breastbone. It protects our lungs and other organs while still letting them move when we breathe.

In the next section, we will discuss the role of respiratory muscles.

Role of Respiratory Muscles

Breathing, also known as respiration, is a fundamental process that ensures our body receives the necessary oxygen and expels carbon dioxide. The respiratory system relies on a group of muscles to facilitate this essential exchange of gases. In this section, we will explore the significant contributions of the → diaphragm, intercostal muscles, and accessory respiratory muscles, shedding light on their crucial roles in breathing, lung volume regulation, and activation during respiratory distress.

Role of the Diaphragm

The diaphragm is a significant muscle located under our lungs. It plays a crucial role in the process of breathing. Let’s discuss its role in detail:


1. Contraction and Relaxation

  • When we breathe in, the diaphragm contracts and moves downward.
  • This creates more space in the chest, allowing the lungs to expand.
  • We take in the air during this inhalation process.
  • When we breathe out, the diaphragm relaxes and moves back up.
  • This reduces the space in the chest, causing the lungs to compress.
  • We release air from our body during this exhalation process.

2. Influence on Lung Volume

  • The diaphragm’s contraction and relaxation directly influence our lung volume.
  • Contraction expands the lungs, enabling inhalation.
  • Relaxation compresses the lungs, facilitating exhalation.

Role of Intercostal Muscles

The intercostal muscles are a group of muscles located between the ribs. They are organized into three layers: the external intercostal muscles, internal intercostal muscles, and innermost intercostal muscles. These muscles work in harmony to promote various respiratory actions. Let’s discuss its function and contribution to rib movement.

Intercostal Muscles

Function of Intercostal Muscles During Breathing

During breathing, the intercostal muscles play two primary roles – inspiration (inhaling) and expiration (exhaling). Let’s discuss it in detail:


1. Inspiration (Inhaling): When we take a deep breath, certain muscles (diaphragm and external intercostal muscles) make our chest bigger. This creates space inside our lungs, and air from the atmosphere rushes in to fill them up.

2. Expiration (Exhaling): When we breathe out normally, it happens naturally without much effort. Our lungs and chest wall have elastic properties, so they go back to their normal resting position, and the air is pushed out. In more forceful exhaling, like when we exercise, additional muscles (internal intercostal muscles) help push the air out by making the chest cavity smaller.

Contribution to Rib Movement

The intercostal muscles significantly contribute to the movement of the ribs during breathing, allowing for efficient ventilation of the lungs.

1. External Intercostal Muscles

As mentioned earlier, the external intercostal muscles are active during inspiration. When they contract, they elevate the ribs and cause the ribcage to expand laterally. This movement not only increases the anterior-posterior diameter of the chest but also raises the sternum, contributing to overall lung expansion.

2. Internal Intercostal Muscles

The internal intercostal muscles are primarily involved in forced expiration. During this phase, they contract to depress the ribs and decrease the thoracic cavity’s volume, helping to expel air from the lungs.

Role of Accessory Respiratory Muscles

Accessory respiratory muscles are extra muscles that assist the main ones in breathing. They include muscles like the sternocleidomastoid, scalene muscles, pectoralis major, and abdominal muscles. Let’s discuss its importance and what does its effect on respiratory distress in detail:

1. Importance of breathing support: When we need to breathe more or if the main breathing muscles are weak, the accessory muscles come to the rescue. They help us breathe better by increasing the amount of air we take in and release with each breath.

2. Activation during respiratory distress: During respiratory distress, like in asthma attacks or pneumonia, the main breathing muscles may struggle. In these situations, the accessory muscles kick in to help us inhale and exhale effectively. They work together to keep our oxygen levels up and prevent the buildup of harmful carbon dioxide.

In the next part, we will discuss The Thoracic Cage Anatomy and structure and its role in respiratory mechanics.

Thoracic Cage

The thoracic cage, also known as the rib cage or chest, is a crucial anatomical structure that plays a vital role in protecting the organs within the thoracic cavity and facilitating the process of respiration. Composed of bones, cartilage, and muscles, the thoracic cage is an intricate framework that provides support and flexibility to the chest region.


Anatomy and Structure of Thoracic Cage

The thoracic cage is formed by the ribs and sternum (breastbone) and protects the lungs and other organs. Let’s discuss it in detail:

  1. Ribs: The thoracic cage consists of twelve pairs of ribs that attach posteriorly to the vertebral column. The first seven pairs are known as “true ribs” because they directly connect to the sternum via costal cartilage. The next three pairs are “false ribs,” with their cartilages indirectly connecting to the sternum. The final two pairs are “floating ribs,” which lack sternal attachments and only connect to the vertebral column.
  1. Sternum: The sternum, commonly referred to as the breastbone, is a flat, elongated bone located in the center of the chest. It connects to the ribs through costal cartilage and completes the front part of the thoracic cage. The sternum serves as an essential anchor for various muscles involved in respiration.
  1. Thoracic Vertebrae: The thoracic vertebrae form the posterior part of the thoracic cage, providing structural support and articulation points for the ribs. These vertebrae play a crucial role in maintaining the overall stability of the thoracic cage.
  2. Intercostal Muscles: Between the ribs lie the intercostal muscles, divided into external and internal layers. The external intercostals aid in the elevation of the ribcage during inhalation, while the internal intercostals assist in its depression during exhalation.

Role in Respiratory Mechanics

The thoracic cage plays a significant role in the process of respiration, allowing for the expansion and contraction of the lungs during breathing.

When we inhale

  1. The diaphragm contracts and moves downward.
  2. The thoracic cage expands, creating more space in the chest.
  3. The ribs move upward and outward, further expanding the thoracic cage. 
  4. The intercostal muscles lift and spread the ribs.

When we exhale

  1. The diaphragm relaxes.
  2. The thoracic cage returns to its original position.
  3. Air is pushed out of the lungs.

In the next section, we will discuss the Clinical Assessment of Respiratory Muscles and the Thoracic Cage.

Clinical Assessment of Respiratory Muscles and the Thoracic Cage.

Evaluation Techniques

When doctors assess the respiratory muscles and thoracic cage, they use different methods to understand how well a person breathes. These techniques may include:

  1. Physical Examination: The doctor examines the chest and muscles to look for any abnormalities or signs of respiratory issues.
  2. Breathing Tests: These tests measure how much air a person can breathe in and out and how well the respiratory muscles work.
  3. Imaging Studies: X-rays or other imaging techniques can provide detailed pictures of the chest and help identify any problems.
  4. Lung Function Tests: These tests check how efficiently the lungs and respiratory muscles are working.

Importance in Respiratory Disease Management

Assessing the respiratory muscles and the thoracic cage is crucial in managing respiratory diseases because:

  1. Diagnosis: It helps doctors identify the specific respiratory problem a person is facing.
  2. Treatment Planning: Knowing the strength and function of the respiratory muscles helps doctors design appropriate treatment plans.
  3. Monitoring Progress: Regular assessments help track improvements or changes in the respiratory condition.
  4. Predicting Outcomes: Evaluation provides valuable information about the potential course of respiratory disease and helps in predicting outcomes.


In conclusion, the respiratory system is essential for our survival, allowing us to breathe and get the oxygen our bodies need. The respiratory muscles and thoracic cage play crucial roles in this process.

The respiratory muscles, including the diaphragm and intercostal muscles, help us breathe in and out. The diaphragm contracts and relaxes, influencing lung volume and allowing us to inhale and exhale. The intercostal muscles lift the ribcage during inhalation and assist in forced exhalation.

The thoracic cage, formed by ribs and sternum, protects our organs and supports the chest region. It expands and contracts during breathing, facilitating lung movement.

Assessing the respiratory muscles and the thoracic cage is vital in managing respiratory diseases. Through various techniques like physical examinations, breathing tests, and imaging studies, doctors can diagnose problems, plan treatments, and monitor progress.

Further Reading

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