Muscles of respiration
Encyclopedia
The various muscles of respiration aid in both inspiration
and expiration
, which require changes in the pressure within the thoracic cavity
. The respiratory muscles work to achieve this by changing the dimensions of the thoracic cavity.
The principal muscles are the diaphragm
, the external intercostal and the interchondral part of the internal intercostal muscles. Both the external intercostal muscles and the intercondral elevate the ribs, thus increasing the width of the thoracic cavity, while the diaphragm contracts to increase the vertical dimensions of the thoracic cavity, and also aids in the elevation of the lower ribs.
Accessory muscles are typically only used when the body needs to process energy quickly (e.g. during heavy exercise, during the stress response, or during an asthma attack). The accessory muscles of inspiration can also become engaged in everyday breathing when a breathing pattern disorder exists.
. It's responsible for ~75% of the air that enters the lungs during quiet breathing. During inhalation, the diaphragm contracts, thus enlarging the thoracic cavity (the external intercostal muscles
also participate in this enlargement). This reduces intra-thoracic pressure: in other words, enlarging the cavity creates suction that draws air into the lung
s. When the diaphragm relaxes, air is exhaled by elastic recoil of the lung and the tissues lining the thoracic cavity in conjunction with the abdominal muscles which act as an antagonist
paired with the diaphragm's contraction.
It is not responsible for all the breathing related to voice
, a common misconception espoused by many teachers but few great singers. One has more control over the abdominals and intercostals
than the actual diaphragm, which has relatively few proprioceptive nerve endings. By training proper posture and balance in the rest of the body, the diaphragm naturally strengthens and works in concert with surrounding structures rather than in isolation.
The diaphragm is also involved in non-respiratory functions, helping to expel vomit, feces
, and urine
from the body by increasing intra-abdominal pressure, and preventing acid reflux by exerting pressure on the esophagus
as it passes through the esophageal hiatus
.
, the intercostal muscles are one of the most important groups of respiratory muscles. The external intercostals are responsible for ~25% of the air that enters the lungs during quiet breathing. These muscles are attached between each rib and are important in manipulating the width of the thoracic cage. There are three layers of intercostal muscles:
The antero-inferior fibres have the effect of lifting up the ribs during contraction. Anteriorly, the external intercostal muscles do not directly attach to the sternum, but are replaced by the anterior intercostal membrane.
The innermost intercostal muscles are also "back pocket" muscles. The internal and innermost intercostals have the opposite effect of the external intercostals and aid in forced expiration. The internal intercostal is replaced by the posterior intercostal membrane posteriorly.
(anterior, middle and posterior scalene) are typically considered accessory muscles of breathing ., however the following muscles have also been observed contributing to the breathing: serratus anterior, pectoralis major & minor, upper trapezius, latissimus dorsi, erector spinae (thoracic), iliocostalis lumborum, quadratus lumborum, serratus posterior superior and inferior, levatores costarum, transversus thoracis, subclavius (Kendall et al., 2005).
Scalene muscle activation coincides with the diaphragm even at rest in most humans, suggesting it could be considered a primary muscle of respiration
If a breathing pattern disorder exists, the accessory muscles of inspiration may become overused.
. Forced (active)or expiration occurs in such individuals as well as occurring during exercise. The abdominal muscles and the internal and innermost intercostal muscles help expel air.
Inhalation
Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....
and expiration
Exhalation
Exhalation is the movement of air out of the bronchial tubes, through the airways, to the external environment during breathing....
, which require changes in the pressure within the thoracic cavity
Thoracic cavity
The thoracic cavity is the chamber of the human body that is protected by the thoracic wall ....
. The respiratory muscles work to achieve this by changing the dimensions of the thoracic cavity.
The principal muscles are the diaphragm
Thoracic diaphragm
In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...
, the external intercostal and the interchondral part of the internal intercostal muscles. Both the external intercostal muscles and the intercondral elevate the ribs, thus increasing the width of the thoracic cavity, while the diaphragm contracts to increase the vertical dimensions of the thoracic cavity, and also aids in the elevation of the lower ribs.
Accessory muscles are typically only used when the body needs to process energy quickly (e.g. during heavy exercise, during the stress response, or during an asthma attack). The accessory muscles of inspiration can also become engaged in everyday breathing when a breathing pattern disorder exists.
The diaphragm
The diaphragm is crucial for breathing and respirationRespiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
. It's responsible for ~75% of the air that enters the lungs during quiet breathing. During inhalation, the diaphragm contracts, thus enlarging the thoracic cavity (the external intercostal muscles
Intercostal muscle
Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing...
also participate in this enlargement). This reduces intra-thoracic pressure: in other words, enlarging the cavity creates suction that draws air into the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s. When the diaphragm relaxes, air is exhaled by elastic recoil of the lung and the tissues lining the thoracic cavity in conjunction with the abdominal muscles which act as an antagonist
Antagonist (muscle)
Most muscles work in pairs, and when a muscle works it needs to have an agonist and an antagonist, unless the muscle's natural state is opposite to that which is produced by the muscle, example Sphincter ani externus muscle....
paired with the diaphragm's contraction.
It is not responsible for all the breathing related to voice
Voice
Voice may refer to:* Human voice* Voice control or voice activation* Writer's voice* Voice acting* Voice vote* Voice message-In film:* Voice , a 2005 South Korean film* The Voice , a 2010 Turkish horror film directed by Ümit Ünal...
, a common misconception espoused by many teachers but few great singers. One has more control over the abdominals and intercostals
Intercostal muscle
Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing...
than the actual diaphragm, which has relatively few proprioceptive nerve endings. By training proper posture and balance in the rest of the body, the diaphragm naturally strengthens and works in concert with surrounding structures rather than in isolation.
The diaphragm is also involved in non-respiratory functions, helping to expel vomit, feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
, and urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
from the body by increasing intra-abdominal pressure, and preventing acid reflux by exerting pressure on the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
as it passes through the esophageal hiatus
Esophageal hiatus
In human anatomy, the esophageal hiatus is a hole in the diaphragm through which the esophagus passes. It is located in the right crus of the diaphragm.It is located approximately at level of the tenth thoracic vertebra ....
.
The intercostal muscles
Along with the diaphragmThoracic diaphragm
In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...
, the intercostal muscles are one of the most important groups of respiratory muscles. The external intercostals are responsible for ~25% of the air that enters the lungs during quiet breathing. These muscles are attached between each rib and are important in manipulating the width of the thoracic cage. There are three layers of intercostal muscles:
- The external intercostal have fibres that go forward and downward (obliquely downward and forward from rib to rib). These fibres are called the antero-inferior, and are sometimes referred to as the front pocket muscle since the fibres mimic the direction a hand would enter a front pocket. The external intercostals assist in deep inspiration by increasing the anterioposterior diameter of the chest.
- The internal intercostal also have fibres, which go backward and downward (obliquely downward and posteriorly from rib to rib). These are called the postero-superior, or the back pocket muscles. The internal intercostals assist in expiration by pulling the ribcage down.
- The last layer is the innermost intercostals and consists of three separate parts; the subcostal (posteriorly), the innermost intercostal (laterally, which often causes confusion with the innermost intercostal referring to all twenty groups) and the transversus thoracis (anteriorly).
The antero-inferior fibres have the effect of lifting up the ribs during contraction. Anteriorly, the external intercostal muscles do not directly attach to the sternum, but are replaced by the anterior intercostal membrane.
The innermost intercostal muscles are also "back pocket" muscles. The internal and innermost intercostals have the opposite effect of the external intercostals and aid in forced expiration. The internal intercostal is replaced by the posterior intercostal membrane posteriorly.
Accessory muscles of inspiration
There is some controversy as to which muscles may be considered accessory muscles of inspiration (Kendalll, McCreary, Provance, Rodgers, Romani, 2005). The sternocleidomastoid (elevated sternum) and the scalene musclesScalene muscles
The scalene muscles are a group of three pairs of muscles in the lateral neck, namely the scalenus anterior, scalenus medius, and scalenus posterior.They are innervated by the spinal nerves C4-C6....
(anterior, middle and posterior scalene) are typically considered accessory muscles of breathing ., however the following muscles have also been observed contributing to the breathing: serratus anterior, pectoralis major & minor, upper trapezius, latissimus dorsi, erector spinae (thoracic), iliocostalis lumborum, quadratus lumborum, serratus posterior superior and inferior, levatores costarum, transversus thoracis, subclavius (Kendall et al., 2005).
Scalene muscle activation coincides with the diaphragm even at rest in most humans, suggesting it could be considered a primary muscle of respiration
If a breathing pattern disorder exists, the accessory muscles of inspiration may become overused.
Muscles of expiration
During quiet breathing, there is little or no muscle contraction/relaxation involved in expiration. This process is simply driven by the elastic recoil of the lungs in healthy individuals. In certain conditions the elasticity of the lung can be lost, such as in emphysemaEmphysema
Emphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath. In people with emphysema, the tissues necessary to support the physical shape and function of the lungs are destroyed. It is included in a group of diseases called chronic obstructive pulmonary...
. Forced (active)or expiration occurs in such individuals as well as occurring during exercise. The abdominal muscles and the internal and innermost intercostal muscles help expel air.
Further reading
- Kendall, F., McCreary, E., Provance, P., Rodgers, M., Romai, W. (2005). Muscles testing and function with posture and pain (5th ed.). PA, USA: Lippincott Williams & Wilkins.