accessory muscles of respiration

4 min read 19-03-2025

Meta Description: Dive deep into the accessory muscles of respiration! Learn their roles in breathing, when they become active, and the implications of their overuse. This comprehensive guide explains how these muscles support normal breathing and what happens during respiratory distress. Understand the anatomy and function of muscles like the sternocleidomastoid, scalenes, and pectoralis minor, and explore conditions like COPD and pneumonia where their involvement is crucial. Expand your knowledge of respiratory physiology today!

Introduction: Beyond the Basics of Breathing

We all know breathing is essential for life. But the seemingly simple act of respiration involves a complex interplay of muscles. While the diaphragm and intercostal muscles are the primary players, a group of muscles called accessory muscles of respiration jump in to assist during times of increased respiratory demand. Understanding these accessory muscles is key to comprehending respiratory health and various respiratory conditions. This article will explore their roles, when they become active, and the implications of their overuse.

The Primary Muscles of Respiration: A Quick Review

Before delving into the accessory muscles, let's briefly review the primary muscles responsible for quiet, normal breathing:

Diaphragm: This dome-shaped muscle forms the floor of the chest cavity. Its contraction flattens it, increasing the volume of the chest and drawing air into the lungs (inspiration). Relaxation allows the diaphragm to return to its dome shape, decreasing chest volume and expelling air (expiration).
Intercostal Muscles: These muscles lie between the ribs. The external intercostals assist in inspiration by raising the rib cage, while the internal intercostals aid in forced expiration by depressing the rib cage.

When Accessory Muscles Step In: Increased Respiratory Demand

During activities like exercise, or when dealing with respiratory illnesses, the body needs more air. This is where the accessory muscles of respiration come into play. They augment the action of the primary respiratory muscles, increasing the efficiency of breathing. However, relying heavily on these muscles often indicates respiratory distress.

Key Accessory Muscles of Inspiration:

These muscles help increase the volume of the chest cavity during inspiration:

Sternocleidomastoid Muscles

Location: Located in the neck, running from the sternum and clavicle to the mastoid process of the temporal bone.
Action: Contraction elevates the sternum and rib cage, increasing chest volume. You can feel these muscles working when you take a deep breath and hold it.
Clinical Significance: Prominent use suggests respiratory distress.

Scalene Muscles (Anterior, Middle, and Posterior)

Location: Situated in the neck, these muscles run from the cervical vertebrae to the first and second ribs.
Action: Elevate the first two ribs, expanding the upper chest cavity.
Clinical Significance: Their activation during normal breathing may indicate underlying respiratory issues.

Pectoralis Minor Muscles

Location: Found on the upper chest wall, underneath the pectoralis major.
Action: Elevates the ribs, increasing the anteroposterior diameter of the chest.
Clinical Significance: Overuse can indicate significant respiratory compromise.

Trapezius Muscles

Location: Large muscles covering the upper back and neck.
Action: Assist in elevating the rib cage, particularly in forced inspiration.
Clinical Significance: Their engagement in breathing is a strong indicator of severe respiratory difficulty.

Accessory Muscles of Expiration:

While inspiration often requires more assistance, certain muscles aid in forceful expiration:

Abdominal Muscles (Rectus Abdominis, External Obliques, Internal Obliques, Transversus Abdominis)

Location: Form the abdominal wall.
Action: Contraction of these muscles forces the diaphragm upwards, decreasing the volume of the chest cavity and pushing air out of the lungs.
Clinical Significance: Their increased use during expiration can signal respiratory distress or underlying lung disease.

Internal Intercostal Muscles (Reinforced Expiration)

Location: Between the ribs.
Action: These muscles depress the ribs, reducing chest volume and aiding in expiration. They're more active during forceful exhalation.

Clinical Significance of Accessory Muscle Use

The recruitment of accessory muscles is not inherently abnormal. However, their consistent use during normal breathing suggests underlying respiratory compromise. Conditions that often lead to increased reliance on accessory muscles include:

Chronic Obstructive Pulmonary Disease (COPD): COPD, encompassing emphysema and chronic bronchitis, makes it difficult to exhale. Patients often use their accessory muscles to force air out of their lungs.
Pneumonia: This lung infection can fill the alveoli with fluid, making it harder to breathe. Patients may rely on accessory muscles to compensate.
Asthma: Airway constriction makes breathing difficult, and the use of accessory muscles is a common sign of an asthma attack.
Pneumothorax: A collapsed lung necessitates the use of accessory muscles to aid in breathing.
Pleural Effusion: Fluid buildup around the lungs restricts lung expansion, leading to accessory muscle use.

How to Identify Accessory Muscle Use

Observing a patient's breathing pattern can reveal reliance on accessory muscles. Look for:

Neck muscle retraction: Sternocleidomastoid and scalene muscle use is visible as neck muscle contraction.
Elevated shoulders: Trapezius muscle involvement lifts the shoulders during inspiration.
Use of abdominal muscles: Abdominal muscle contraction during exhalation often accompanies respiratory distress.
Nasal flaring: Widening of the nostrils indicates increased respiratory effort.
Retractions: Indrawing of the skin between the ribs or above the clavicles during inspiration.

Conclusion: Accessory Muscles – Indicators of Respiratory Health

The accessory muscles of respiration play a crucial role in supporting breathing during increased demand. While their temporary use is normal, consistent reliance suggests underlying respiratory issues. Understanding their function and recognizing their activation is vital for healthcare professionals in diagnosing and managing respiratory conditions. If you notice persistent reliance on accessory muscles for breathing, consult a healthcare professional for proper evaluation and treatment.