Intercostal muscles

Intercostal Muscles

Diagram of the intercostal muscles

The intercostal muscles are a group of muscles located between the ribs that play a crucial role in the mechanical aspect of breathing. These muscles are primarily involved in the expansion and contraction of the thoracic cavity, facilitating the process of respiration.

Anatomy

The intercostal muscles are divided into three distinct layers:

External Intercostal Muscles

The external intercostal muscles are the outermost layer of the intercostal muscles. They originate from the lower border of one rib and insert into the upper border of the rib below. These muscles are oriented obliquely downward and forward, resembling the direction of putting hands in pockets. During inspiration, they contract to elevate the ribs, increasing the volume of the thoracic cavity.

Internal Intercostal Muscles

The internal intercostal muscles lie just beneath the external intercostals. They run perpendicular to the external intercostals, originating from the inner surface of a rib and inserting into the upper border of the rib below. These muscles are primarily involved in expiration, as they depress the ribs and decrease the volume of the thoracic cavity.

Innermost Intercostal Muscles

The innermost intercostal muscles are the deepest layer and are similar in orientation to the internal intercostals. They are separated from the internal intercostals by the intercostal nerves and blood vessels. These muscles assist in the function of the internal intercostals.

Function

The primary function of the intercostal muscles is to aid in the process of breathing by altering the dimensions of the thoracic cavity. During inspiration, the external intercostal muscles contract, elevating the ribs and expanding the chest cavity. This action decreases the pressure within the thoracic cavity, allowing air to flow into the lungs. During expiration, the internal intercostal muscles contract, pulling the ribs downward and inward, which increases the pressure in the thoracic cavity and forces air out of the lungs.

Nerve Supply

The intercostal muscles are innervated by the intercostal nerves, which are the anterior rami of the thoracic spinal nerves. These nerves provide the necessary motor and sensory innervation to the muscles and the overlying skin.

Clinical Significance

The intercostal muscles can be involved in various clinical conditions, such as intercostal muscle strain, which can occur due to excessive physical activity or trauma. Additionally, these muscles may be affected in conditions that impair respiratory function, such as chronic obstructive pulmonary disease (COPD).

Related Pages

• Respiratory system
• Thoracic cavity
• Rib cage
• Diaphragm (anatomy)