Dominic Stone
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three layers: the external intercostals, the internal intercostals, and the innermost intercostals. All three groups of muscles support the rib cage and are involved in the mechanical aspect of breathing by helping to expand and shrink the size of the chest cavity.
| Characteristics | Values |
|---|---|
| Location | Between the ribs |
| Number of layers | 3 |
| External intercostals | outermost layer |
| Internal intercostals | intermediate layer |
| Innermost intercostals | deepest layer |
| Function | Support the rib cage, aid in forced breathing |
| Number of external intercostal muscles | 11 on each side |
| Number of internal intercostal muscles | 11 pairs |
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What You'll Learn
Intercostal muscles are divided into three layers
The intercostal muscles are intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three layers, namely the external intercostals, the internal intercostals, and the innermost intercostals.
The external intercostals are the outermost layer of the three and lie directly under the skin. They originate from the lower border of the rib above and insert into the upper border of the rib below. These muscles expand the chest wall during inhalation. They are the most superficial intercostal muscles and are innervated by the anterior rami of spinal nerves T1-T11.
The internal intercostals form the middle layer of the intercostal musculature. They originate from the costal groove of one rib, course inferolaterally, and insert into the superior border of the rib below. They are innervated by the intercostal nerves, just like the external intercostals. The function of the internal intercostals is to depress the ribs during forced expiration, aiding in the process of breathing.
The innermost intercostals are the deepest layer of the intercostal muscles. They cross more than one intercostal space and assist the internal and external intercostals in their functions. All three groups of muscles support the rib cage and participate in the process of forced breathing.
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They occupy 11 intercostal spaces
The intercostal muscles are intrinsic rib cage muscles that occupy 11 intercostal spaces. They are divided into three groups: external, internal, and innermost. These muscles support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing.
The external intercostals are the most superficial intercostal muscles. They originate from the inferior border of one rib and insert into the superior border of the rib below. They facilitate forced inspiration and are responsible for the elevation of the ribs, expanding the chest cavity.
The internal intercostals form the middle layer of the intercostal musculature. They originate from the costal groove of one rib and insert into the superior border of the rib below. They aid in forced expiration by depressing the ribs and decreasing the thoracic volume.
The innermost intercostals are the deepest intercostal muscles. They have a similar direction of muscle fibres to the internal intercostals and are responsible for further decreasing the thoracic volume during forced expiration.
All three groups of intercostal muscles work together to support the respiratory process by changing the volume of the thoracic cavity during breathing.
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They aid in forced breathing
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups, from superficial to deep: external, internal, and innermost. All three groups of muscles support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing.
The external intercostal muscles are the outermost layer and lie directly under the skin. They originate from the lower border of the rib above and insert into the upper border of the rib below. They expand the chest wall during inhalation and facilitate forced inspiration.
The internal intercostal muscles form the middle layer of the intercostal musculature. They originate from the costal groove of the rib above and insert into the upper border of the rib below. They are responsible for depressing the ribs during forced expiration.
The innermost intercostal muscles are the deepest layer of intercostal muscles. They cross more than one intercostal space and assist the internal and external intercostals in their function. They aid in forced expiration along with the internal intercostal muscles.
Together, the three layers of intercostal muscles work to support the rib cage and facilitate forced breathing. They help to expand and shrink the size of the chest cavity, allowing for the mechanical aspect of breathing.
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External intercostals facilitate inhalation
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are divided into three groups: external, internal, and innermost intercostals. The external intercostals are the outermost layer of intercostal muscles, lying directly under the skin. They originate from the lower border of one rib and insert into the upper border of the rib below.
The external intercostals facilitate inhalation by lifting and expanding the rib cage. When the external intercostals contract, they expand the chest wall, allowing the lungs to fill with air. This is known as forced inspiration or forced breathing. During this process, the rib cage recoils elastically from a state of complete or near-complete expansion. The external intercostals remain active until receptors within these muscles indicate that the lungs have been fully filled. This is detected by stretch receptors, which signal for the external intercostals to shut off once the lungs have reached a critical volume.
The internal and innermost intercostals serve a different function, aiding forced expiration. When the external intercostals shut off, it signals the internal intercostals to contract, which allows for active exhalation. The internal intercostals produce a lowering of the ribs and a reduction in the anterior-posterior dimension, pushing air out of the lungs.
The diaphragm, located at the base of the rib cage, is another major muscle group that promotes inhalation. During inspiration, the diaphragm contracts and moves in an inferior direction, increasing the vertical diameter of the thoracic cavity and producing lung expansion.
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Internal and innermost intercostals aid exhalation
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups: the external intercostals, the internal intercostals, and the innermost intercostals. While the external intercostals facilitate inhalation, the internal and innermost intercostals aid exhalation.
The internal intercostals form the middle layer of the intercostal musculature. They originate from the costal groove of a rib, course inferolaterally, and insert into the superior border of the rib below. Their function is to depress the ribs during forced exhalation. The internal intercostals have the opposite function of the external intercostals, which lift the ribs and expand the rib cage during inhalation. When the internal intercostals contract, they produce the lowering of the ribs and a reduction in the anterior-posterior dimension of the rib cage.
The innermost intercostals are the deepest intercostal muscles. They originate from the costal groove of a rib, posteriorly to the origin of the internal intercostals, and insert into the superior border of the rib below. The innermost intercostals assist the internal intercostals in depressing the ribs during forced exhalation. They are important for normal speech and singing, as they are the muscles that propel air out through the mouth and nose.
The timing of respiratory muscle activity during the inhalation-exhalation cycle of speech has been studied. After inhalation, the external intercostals remain active until receptors indicate that the lungs are full. Then, the elastic recoil process begins, and the lung volume decreases. Once the lung volume reaches a critical value, the external intercostals shut off, signalling the internal intercostals to contract and allow for active exhalation.
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Frequently asked questions
Intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups: external, internal, and innermost.
The external intercostal muscles aid in quiet and forced inhalation. They are responsible for the elevation of the ribs and help expand the chest cavity.
The internal intercostal muscles aid in forced expiration. They are responsible for depressing the ribs and bending them inward, thus decreasing the chest cavity.
The innermost intercostal muscles are deep layers of the internal intercostal muscles. They have similar functions, aiding in forced expiration.
The internal and external intercostal muscles are primarily involved in expiration and inspiration, respectively. They work in opposite phases of respiratory activity but have a similar distribution of innervating motoneurons.
