Logan Steele
The muscles of respiration, also known as the 'breathing pump muscles', are the muscles that enable inhalation and exhalation by facilitating the expansion and contraction of the thoracic cavity. The diaphragm is the major muscle responsible for breathing, and it is innervated by phrenic motor neurons found in the cervical spinal cord (C3-C5 in humans). The intercostal muscles are another important group of respiratory muscles, with the external intercostals innervated by the thoracic spinal nerves and playing a key role in inhalation. These muscles work together to ensure normal respiration, and their function is closely tied to the mechanics of the chest wall.
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What You'll Learn
The diaphragm is innervated by phrenic motor neurons
The diaphragm is a double-domed musculotendinous sheet, located at the inferior-most aspect of the rib cage. It serves two main functions: separating the thoracic cavity from the abdominal cavity, and undergoing contraction and relaxation, altering the volume of the thoracic cavity and the lungs, producing inspiration and expiration.
The diaphragm is innervated by the phrenic nerve, which is among the most important nerves in the body due to its role in respiration. The phrenic nerve provides the primary motor supply to the diaphragm, the major respiratory muscle. It passes motor information to the diaphragm and receives sensory information from it. The phrenic nerve is the sole motor supply to each hemidiaphragm, and it also provides sensory supply to the diaphragm (except the most peripheral diaphragm, which is supplied by intercostal nerves).
There are two phrenic nerves, a left and a right one, and each one performs the same job. The left phrenic nerve controls the left side of the diaphragm, and the right nerve controls the right side. The phrenic nerve moves the diaphragm by sending signals that make it expand and contract when breathing, allowing the lungs to inhale and exhale air.
Phrenic nerve palsy, or paralysis, can be caused by lesions anywhere along the course of the phrenic nerve, as it travels from the neck to pierce the diaphragm adjacent to the pericardium. This nerve damage can cause a paralyzed diaphragm, resulting in shortness of breath and problems sleeping.
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Intercostal muscles are innervated by thoracic spinal nerves
The intercostal muscles are a group of muscles between the ribs that are essential for respiration. They are attached to the ribs and manipulate the width of the rib cage, aiding in inhalation and exhalation. The intercostal muscles are divided into three layers: the external intercostals, the parasternal internal intercostals, and the interosseus internal intercostals. The external intercostals are the most crucial for respiration, as they help elevate the ribs and expand the rib cage, facilitating inhalation. The parasternal internal intercostals also have inspiratory actions, while the interosseus internal intercostals are responsible for exhalation.
The intercostal muscles, along with other respiratory muscles, are innervated by spinal nerves. Specifically, the intercostal muscles are innervated by the thoracic spinal nerves. This innervation is vital for the coordination of chest expansion and diaphragm movement during respiration. The thoracic spinal nerves provide the necessary electrical impulses for the contraction and relaxation of the intercostal muscles, enabling them to function in synergy with other respiratory muscles.
The diaphragm, a thin, dome-shaped muscle located at the inferior-most aspect of the rib cage, is another critical respiratory muscle. It separates the thoracic cavity from the abdominal cavity and plays a significant role in inhalation and exhalation. During inhalation, the diaphragm contracts, moving its centre downward and its edges upward, which expands the thoracic cavity and draws air into the lungs. When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out during exhalation.
The diaphragm is innervated by phrenic motor neurons that lie in the cervical spinal cord, specifically at the C3-C5 levels in humans. This innervation is crucial for the diaphragm's function, and any interruption can lead to diaphragmatic paralysis. Spinal cord injuries above C3 can paralyse the diaphragm, requiring ventilatory support for the individual. Injuries between C3 and C5 can result in partial denervation, compromising the diaphragm's ability to facilitate inspiration.
The accessory muscles of respiration also play a supporting role in breathing. These muscles are recruited during exercise or when there is a dysfunction in the respiratory system. They assist in elevating the rib cage and manipulating its width. Examples of accessory muscles include the sternocleidomastoid, scalenes, serratus anterior, pectoralis major, and pectoralis minor. These muscles are innervated by various spinal nerves, depending on their location and function.
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Rectus abdominis is innervated by lower thoracic nerves
The rectus abdominis muscle, also known as the "abdominal muscle" or "abs", is a pair of segmented skeletal muscles found on the ventral aspect of a person's abdomen. It is the largest muscle of the abdominal wall and is often referred to as the "six-pack" muscle. The rectus abdominis is innervated by the thoraco-abdominal nerves, which are continuations of the T7-T11 intercostal nerves. These nerves pierce the anterior layer of the rectus sheath, passing between the transversus abdominis and internal oblique muscle layers before piercing the sheath of the rectus abdominis muscle.
The diaphragm is a double-domed sheet of skeletal muscle located at the inferior-most aspect of the rib cage, separating the thoracic cavity from the abdominal cavity. It is innervated by the phrenic nerve (C3-C5) and sensory supply is provided by the phrenic nerve to the central tendon and the lower 6 or 7 intercostal nerves to the peripheral parts.
The muscles of respiration, also known as the "breathing pump muscles", form a complex arrangement around the lungs. The primary inspiratory muscles are the diaphragm and external intercostals, which help in inhalation by expanding the thoracic cavity. The accessory inspiratory muscles include the sternocleidomastoid, scalenus anterior, medius, and posterior, among others. The accessory expiratory muscles include the abdominal muscles, such as the rectus abdominis, external oblique, internal oblique, and transversus abdominis.
The rectus abdominis muscle plays a crucial role in abdominal function and is involved in movements such as flexing the trunk anteriorly and compressing the abdominal viscera, increasing intra-abdominal pressure. It is supplied by a number of vessels, predominantly the inferior and superior epigastric arteries, along with contributions from the lower intercostal arteries, subcostal, and deep circumflex artery.
The muscle extends from the rib cage to the pubic bone and is separated at the midline by a band of dense connective tissue called the linea alba. In individuals with low body fat, the rectus abdominis muscle is visible beneath the skin, forming the well-known "six-pack" appearance.
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Exhalation requires little muscle contraction
The diaphragm is the main inspiratory muscle. During inspiration, it 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. The diaphragm is innervated by the phrenic nerve (C3-C5).
During expiration, the diaphragm and external intercostal muscles relax, causing the thorax and lungs to recoil. This relaxation results in an increase in air pressure within the lungs, which causes air to be forced out. Therefore, exhalation requires little muscle contraction.
The muscles of inspiration elevate the ribs and sternum, and the muscles of expiration depress them. The inspiratory muscles are also called the breathing pump muscles, and 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.
During forced exhalation, the abdominal muscles and internal intercostals may be involved in forcing air out of the lungs. The abdominal muscles contract, raising abdominal pressure, and pushing a relaxed diaphragm against the lungs, causing air to be pushed out. The abdominal muscles are the most important muscles involved in exhalation during vigorous exercise.
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Diaphragmatic paralysis is caused by nervous supply interruption
The diaphragm is a dome-shaped muscle that separates the abdominal and thoracic cavities. It is innervated by the phrenic nerve, which starts in the neck and runs down through the chest to reach the diaphragm. The phrenic nerve is responsible for contracting and expanding the diaphragm, allowing the lungs to move during breathing.
Diaphragmatic paralysis occurs when the diaphragm becomes weak or paralysed, affecting its ability to contract and relax properly. This condition can be unilateral or bilateral, but unilateral paralysis is more common and often asymptomatic. It can result from muscular issues in the diaphragm or, more commonly, from a loss of innervation due to an interruption in the nervous supply to the diaphragm.
There are several causes of diaphragmatic paralysis due to nervous supply interruption. These include birth defects, diseases of the nervous system such as amyotrophic lateral sclerosis (ALS) or multiple sclerosis, injury to the cervical spinal cord, phrenic nerve damage during surgery, compression by a tumour, myopathies such as myasthenia gravis, and neuropathies such as diabetic neuropathy. In some cases, the cause of diaphragmatic paralysis remains unknown.
The symptoms of diaphragmatic paralysis depend on whether it is unilateral or bilateral. Unilateral paralysis may cause dyspnea, or difficulty breathing, especially during exertion or when lying down. Bilateral paralysis is more likely to cause noticeable symptoms, such as difficulty breathing at rest and during activity, orthopnoea, and fatigue.
The treatment options for diaphragmatic paralysis depend on the severity of the condition. Non-surgical options, such as medications and nerve blocks, may be recommended initially. In more severe cases, surgical treatment or diaphragmatic pacing may be considered if breathing is significantly impacted.
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Frequently asked questions
The muscles of respiration are also known as the 'breathing pump muscles'. They form a complex arrangement around the lungs and help with inhalation and exhalation by aiding in the expansion and contraction of the thoracic cavity.
The diaphragm is the major muscle responsible for breathing. The intercostal muscles are also one of the most important groups of respiratory muscles.
The diaphragm is a dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, moving its centre downwards and its edges upwards. This compresses the abdominal cavity, raises the ribs and expands the thoracic cavity, drawing air into the lungs. During exhalation, the diaphragm relaxes, and the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs. The external intercostal muscles work synergistically with the diaphragm during inspiration.
The diaphragm is innervated by phrenic motor neurons that lie in the cervical spinal cord (C3–C5 in humans).
