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Intercostal muscles
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The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are divided into three groups, going from superficial to deep:
- External intercostal muscles
- Internal intercostal muscles
- Innermost intercostal muscles
All three groups of muscles support the rib cage. Moreover, they are all accessory respiratory muscles that participate in the process of forced breathing. Specifically, the external intercostals facilitate forced inspiration, while the internal and innermost intercostals aid forced expiration.
| Definition | Three sets of rib muscles that occupy the 11 intercostal spaces |
| Function | Mechanical support to the thoracic cage, accessory respiratory muscles |
This article will introduce you to the anatomy and function of the intercostal muscles.
- External intercostal muscles
- Internal intercostal muscles
- Innermost intercostal muscles
- Clinical aspects
- Sources
External intercostal muscles
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The external intercostals are the most superficial intercostal muscles. They originate from the inferior border of one rib, course inferomedially and insert to the superior border of the immediate rib below.
They are innervated by the anterior rami of spinal nerves T1-T11, i.e. the intercostal nerves of the corresponding intercostal space. The blood supply to the external intercostals comes from the anterior and posterior intercostal arteries. The function of the external intercostal muscles is to elevate the ribs during forced inspiration.
Learn everything about the external intercostal muscles in this comprehensive article on their anatomy.
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Internal intercostal muscles
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The internal intercostals form the middle layer of the intercostal musculature. They originate from the costal groove of one rib, course inferolaterally and insert to the superior border of the immediate rib below.
They are innervated in the same way as the external intercostals, by the intercostal nerves. Their blood supply comes from the anterior and posterior intercostal arteries, as well as from the costocervical trunk, internal thoracic and musculophrenic arteries. The function of the internal intercostal muscles is to depress the ribs during forced expiration.
The detailed anatomy of the internal intercostal muscles is waiting for you here.
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Innermost intercostal muscles
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The innermost intercostals are the deepest intercostal muscles. They originate from the costal groove of one rib, posteriorly to the origin of the internal intercostals. They course inferomedially, in the same fashion as the internal intercostals, and insert to the superior border of the immediate rib below.
The vascularization and innervation of the innermost intercostals follows the same pattern as for the internal intercostals;
- The blood supply comes from the anterior and posterior intercostal arteries, costocervical trunk, internal thoracic and musculophrenic arteries
- The innervation comes from the intercostal nerves
The function of the innermost intercostals is to assist in the depression of ribs during forced expiration.
Learn the detailed anatomy and function of the innermost intercostals here.
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Clinical aspects
Deficient intercostal muscles (e.g. caused by neuromuscular diseases) may not provide an appropriate tension of the intercostal spaces anymore leading to internal and external movements of the chest wall during thoracic pressure changes. Consequently this will lead to respiratory insufficiency. The lesion of a single intercostal nerve (e.g. after trauma or surgical procedures) causes a “strip-like” paresthesia. However in this case motor impairments are absent.
Test your knowledge on the main muscles of the thoracic wall with this quiz.
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