Victor Forge
The intercostal muscles are a group of muscles that aid in the process of respiration by contributing to inhalation and exhalation. They are attached between the ribs and help manipulate the width of the rib cage. There are three types of intercostal muscles: external, internal, and innermost intercostal muscles. The external intercostal muscles are the most important in respiration, as they lift the rib cage and assist in inhalation. The internal intercostal muscles, on the other hand, pull the rib cage down and aid in exhalation. While breathing is typically an involuntary action, there are instances where we need to voluntarily control our breathing, such as when we speak, sing, or exercise. This raises the question of whether the voluntary control of breathing overrides or interacts with the involuntary neural signals that originate in the brainstem.
| Characteristics | Values |
|---|---|
| Control | Breathing is usually controlled involuntarily, but there are instances where it needs to be controlled voluntarily, such as when speaking, singing, or exercising. |
| Neural Pathways | The breathing muscles are controlled automatically from the brainstem during normal breathing but can also be controlled voluntarily from the motor cortex. |
| Function | The intercostal muscles aid in inhalation and exhalation by manipulating the width of the rib cage and contributing to the expansion and contraction of the thoracic cavity. |
| Types | There are three types of intercostal muscles: external, internal, and innermost. |
| Attachment | The intercostal muscles are attached between the ribs. |
| Innervation | The external intercostal muscles are innervated by intercostal nerves originating in the thoracic segments of the spinal cord. |
| Blood Supply | The intercostal muscles receive blood supply from anterior and posterior intercostal arteries, internal thoracic arteries, and musculophrenic arteries. |
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What You'll Learn
The external intercostal muscles aid inhalation
The external intercostal muscles are one of the most important groups of respiratory muscles. They aid inhalation by lifting and expanding the rib cage, which increases the volume of the thoracic cavity and draws air into the lungs.
The external intercostal muscles originate on the inferior surfaces of the proximal parts of the ribs and insert on the superior and distal parts of the next lower rib. These muscles are innervated by intercostal nerves that originate in the thoracic segments of the spinal cord. When these muscles contract, they raise the rib cage upward and outward, increasing the volume of the thoracic cavity and reducing pressure within the lungs, which causes air to move into the lungs.
The diaphragm is the main inspiratory muscle and is responsible for most of the work during quiet breathing. However, the external intercostal muscles play a crucial role in respiration, especially during times of increased respiratory effort, such as during exercise or when playing a musical instrument. During these activities, the accessory muscles of respiration, including the sternocleidomastoid and scalenes, are also recruited to assist in elevating the rib cage.
The timing of respiratory muscle activity during the inhalation-exhalation cycle can vary depending on the activity. For example, in singing, professional singers regulate the amount of air they inhale and the speed of inhalation depending on the length and loudness of the phrase they are about to sing. The external intercostals remain active during inhalation until receptors within these muscles indicate that the lungs have been fully filled.
While breathing is typically controlled involuntarily by the brainstem, it can also be controlled voluntarily by the motor cortex during activities such as speaking, singing, and swimming. The interaction between these two neural drives to the breathing muscles is still not fully understood, and it is possible that the voluntary control signals from the cortex override or replace the involuntary signals from the brainstem.
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The internal intercostal muscles aid exhalation
The intercostal muscles are the muscles that reside in the rib cage and facilitate breathing. There are three types of intercostal muscles: external intercostal muscles, internal intercostal muscles, and innermost intercostal muscles. The external intercostal muscles are the most superficial of the three types and are responsible for inhalation. The internal intercostal muscles aid exhalation by pulling down on the rib cage and pushing air out of the lungs. The innermost intercostal muscles assist the function of the external and internal intercostal muscles.
The internal intercostal muscles are essential for normal speech and singing as they propel air out through the mouth and nose. The greater the pressure of the escaping air, the louder one's voice. During vocalization, there is a short period of inhalation followed by a longer period of exhalation. This is in contrast to silence, where inhalation and exhalation occur at a relatively even rate.
The internal intercostal muscles also play a role in forceful expiration, along with other muscles such as the intercostalis intimi, subcostals, and abdominal muscles. These muscles work together to depress the ribs and sternum, facilitating exhalation.
The respiratory system includes the lungs and associated muscle groups. Two major muscle groups promote inhalation: the diaphragm, which lies at the base of the rib cage, and the external intercostals, which lift and expand the rib cage. The internal intercostals, on the other hand, aid in exhalation by producing the opposite effect of the external intercostals. They lower the ribs and reduce the anterior-posterior dimension of the rib cage, pushing air out of the lungs.
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Intercostal muscles are attached between the ribs
Intercostal muscles are the muscles attached between the ribs. They allow the rib cage to expand and contract, facilitating the process of breathing. These muscles can be voluntarily contracted, and they play a crucial role in singing and speaking. Intercostal muscles consist of three layers: external, internal, and innermost. The external intercostal muscles are the outermost layer, lying directly under the skin. They originate from the lower border of the rib above and insert into the upper border of the rib below, contributing to the expansion of the thoracic cavity and aiding inhalation.
The internal intercostal muscles, on the other hand, originate from the costal groove near the inferior border of the rib above and connect to the upper border of the rib below. These muscles help in collapsing the lungs during exhalation. The innermost intercostal muscles cross more than one intercostal space and assist the internal and external intercostals in their respective functions. Intercostal muscles can be strained or torn due to various reasons, including overexertion, direct trauma, twisting, or repetitive movements.
Intercostal muscle strain can cause pain in the rib cage or upper back and affect breathing patterns, resulting in shallow and short breaths. The pain may worsen with coughing, sneezing, or deep breathing. In some cases, intercostal muscle strain may lead to muscle tension and stiffness, making movement difficult. Treatment for intercostal muscle strain may include physical therapy, safe stretching exercises, and electrical nerve stimulation. It is important to seek medical attention if the pain is severe, persists for several days, or interferes with daily activities.
Additionally, intercostal muscles play a significant role in singing and speaking. The internal intercostal muscles are crucial for propelling air out through the mouth and nose, making them essential for normal speech and singing. Singers, especially professionals, regulate the amount of air inhaled and the speed of inhalation depending on the duration and volume of the phrase they are about to sing. Therefore, intercostal muscles are not only important for breathing but also for vocal expression in singing and speech.
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The diaphragm is the main inspiratory muscle
The diaphragm is the primary muscle responsible for inhalation. Located below the lungs, it is a large, dome-shaped muscle that contracts and moves in an inferior direction, increasing the vertical diameter of the thoracic cavity and expanding the lungs, which causes air to be drawn into them. During exhalation, the diaphragm relaxes and returns to its dome-like shape, forcing air out of the lungs.
The diaphragm is also involved in the process of pulmonary ventilation, along with a variety of other muscles. The diaphragm lies at the base of the rib cage and separates the thoracic cavity from the abdominal cavity. During inspiration, the diaphragm contracts and pulls the lower surfaces of the lungs downwards, while the muscles of inspiration, mainly the external intercostals, elevate the rib cage. The intrathoracic volume increases as the abdominal organs are pushed downwards.
The external intercostal muscles originate on the inferior surfaces of the proximal parts of the ribs and insert on the superior and distal parts of the next lower rib. These muscles are innervated by intercostal nerves originating in the thoracic segments of the spinal cord. Contraction of the external intercostals raises the rib cage upward and outward, contributing to the expansion of the thoracic cavity and reduction of pressure within the lungs, causing air to move into the lungs.
The internal intercostals have the opposite effect, aiding in expiration. They pull down on the rib cage and push air out of the lungs. The internal intercostals are the most important respiratory muscles for normal speech and singing, as they propel air out through the mouth and nose.
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Voluntary breathing is controlled by the motor cortex
Voluntary breathing is under conscious control and is mediated by the motor cortex in the cerebrum. The motor cortex receives input from the limbic system and the hypothalamus. While the mechanisms involved are not fully understood, it is thought that signals are sent from the motor cortex to the spinal cord, which are then passed on to the respiratory muscles.
The neural basis for the corticomotor control of respiratory muscles was first investigated during neurosurgery. Electrical stimulation of the cortical surface induced a twitch of the diaphragm, indicating the representation of respiratory muscles within the primary motor cortex. Further studies using transcranial magnetic stimulation of the brain have identified a fast-conducting pathway from the motor cortex to the diaphragm. Each hemisphere of the diaphragm is represented predominantly in the contralateral motor cortex.
The motor network controlling voluntary breathing is also important for mediating other spontaneous breathing behaviours, including exercise, speech, and the response to loaded breathing. Observations from transcranial magnetic stimulation suggest a direct functionally distinct corticospinal pathway in humans. The behavioural control of breathing is mediated by the respiratory centres in the medulla and by bulbospinal motoneurons.
The respiratory muscles are also called the 'breathing pump muscles'. They form a complex arrangement in the form of semi-rigid bellows around the lungs. All muscles attached to the human rib cage have the potential to cause a breathing action. Muscles that expand the thoracic cavity are called inspiratory muscles, as they help in inhalation. Those that compress the thoracic cavity are called expiratory muscles, which induce exhalation.
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Frequently asked questions
Intercostal muscles are generally controlled involuntarily, but there are instances where we need to voluntarily control how fast and/or deep we breathe.
Intercostal muscles are one of the most important groups of respiratory muscles. They are attached between the ribs and help manipulate the width of the rib cage.
There are three types of intercostal muscles: external intercostal muscles, internal intercostal muscles, and innermost intercostal muscles.
External intercostal muscles are the most important in respiration. They lift the rib cage, aiding in inhalation.
Internal intercostal muscles pull down on the rib cage and push air out of the lungs. They are the most important respiratory muscles for normal speech and singing.
