Logan Steele
The thorax is the anatomical region that houses vital organs such as the heart and lungs. The thoracic wall, which surrounds the thoracic cavity, is made up of five muscles: the external, internal, and innermost intercostal muscles, the subcostalis, and the transversus thoracis. These muscles are responsible for changing the volume of the thoracic cavity during respiration. Other muscles, such as the pectoralis major and minor, attach to the thoracic wall but are primarily involved in movements of the upper limbs. The diaphragm, located below the lungs, is another important muscle in the thorax, separating the contents of the chest from the abdomen and aiding in respiration.
| Characteristics | Values |
|---|---|
| Muscles that make up the thorax wall | External intercostal muscles, internal intercostal muscles, innermost intercostal muscles, subcostalis, and transversus thoracis |
| Number of intercostal muscles in each intercostal space | 11 pairs |
| Superficial layer | External intercostal muscle |
| Intermediate layer | Internal intercostal muscle |
| Deepest layer | Innermost intercostal muscle |
| Muscles that do not make up the thoracic wall but attach to it | Pectoralis major and minor, subclavius, and serratus anterior (anteriorly), primary costarum and serratus posterior superior and inferior (posteriorly) |
| Muscles that provide movements to the arm and shoulder | Muscles of the anterior thorax |
| Muscle that separates the contents of the chest from the abdomen | Diaphragm |
| Muscle that is the primary muscle of inspiration | Diaphragm |
| Muscle that aids in depressing the ribs during forced expiration | Subcostalis |
| Organs in the thorax | Heart, lungs, thymus, trachea, and esophagus |
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What You'll Learn
The diaphragm is a muscle in the thorax
The diaphragm is an upward curved, C-shaped structure of muscle and fibrous tissue. It has two surfaces: the thoracic and abdominal. The thoracic diaphragm is in contact with the serous membranes of the heart and lungs, while the abdominal diaphragm is in contact with the liver, stomach, and spleen. The diaphragm is pierced by many structures, including the oesophagus, aorta, and inferior vena cava.
The diaphragm is composed of two distinct muscle regions: the costal and the crural diaphragm. The costal diaphragm serves as the driver in the work of breathing, while the crural diaphragm acts as an anchor, attaching the muscle to the lower ribs and lumbar vertebrae. The diaphragm is supplied by various arteries, including the subcostal arteries and the five most inferior pairs of intercostal arteries.
The diaphragm is important for respiration, as it changes the volume of the thoracic cavity, allowing air to be drawn into the lungs. It also plays a role in expulsive actions such as coughing, sneezing, vomiting, and defecation. Additionally, the diaphragm provides a passageway for certain structures from the thorax to the abdomen.
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The thorax contains the heart and lungs
The thorax is the chest region of the body between the neck and the abdomen, along with its internal organs and other contents. The thoracic wall is made up of five muscles: the external, internal, and innermost intercostal muscles, the subcostalis, and the transversus thoracis. These muscles are primarily responsible for changing the volume of the thoracic cavity during respiration.
The diaphragm is a dome-shaped muscle that sits just beneath the heart and lungs. It separates the thoracic cavity from the abdominal cavity and requires three openings to act as channels for structures to pass through from the thorax to the abdomen. The diaphragm is considered the primary muscle of respiration, as it can change shape to alter the volume of the thoracic cavity to allow for respiration.
The heart is located in the middle mediastinum within the pericardial sac. It is one of the most important organs in the thorax, receiving direct blood from the coronary circulation and consisting of four chambers: two atria and two ventricles. The heart handles both deoxygenated and oxygenated blood, with several major blood vessels entering and leaving to carry blood to and from the pulmonary and systemic circulations.
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The thoracic wall is made up of five muscles
The thorax houses several vital organs and structures, including the heart, lungs, thymus, trachea, and oesophagus. The thoracic wall encloses the thoracic cavity, which is divided into several compartments, such as the mediastinum and pleural cavities.
The internal intercostal muscles form the intermediate layer, originating from the costal groove of the rib above and inserting into the rib below, perpendicular to the external intercostal muscles. These muscles depress the ribs and reduce thoracic volume during forced expiration. The deepest layer of the thorax wall is made up of the innermost intercostal muscles, which originate from the medial aspect of the costal groove of the rib above and insert onto the internal aspect of the rib below. They are lined internally by the endothoracic fascia.
The subcostalis and transversus thoracis muscles are also part of the thoracic wall. The subcostalis is present in abundance in the lower regions of the posterior thoracic wall, originating from the internal aspect of the lower ribs and inserting onto the second or third rib below. The transversus thoracis originates from the posterior surface of the inferior sternum and costal cartilage of the lower ribs, ascending and attaching to the internal surface of costal cartilages 2 through 6. These muscles aid in depressing the ribs during forced expiration.
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The thorax has accessory muscles of respiration
The thorax is the part of the body between the neck and the abdomen, containing vital organs such as the heart, lungs, and oesophagus. The thoracic wall surrounds the thoracic cavity, which is the anatomical region where viscera like the heart and lungs are found. The thoracic wall is made up of five muscles: the external, internal, and innermost intercostal muscles, the subcostalis, and the transversus thoracis. These muscles are primarily responsible for changing the volume of the thoracic cavity during respiration.
The intercostal muscles occupy the space between the ribs and are organised into three layers. There are 11 pairs of external intercostal muscles that run from the rib above to the rib below. During inspiration, these muscles contract and raise the lateral part of the ribs, increasing the transverse diameter of the thorax. The internal intercostal muscles form the intermediate layer. They originate from the lateral aspect of the costal groove of the rib above and insert into the superior aspect of the rib below, depressing the ribs and reducing the thoracic volume during forced expiration. The deepest layer of the thorax wall is made up of the innermost intercostal muscles, which have a similar structure to the internal intercostals.
In addition to the intercostal muscles, the subcostalis and the transversus thoracis also make up the thoracic wall. The subcostalis is present in abundance in the lower regions of the posterior thoracic wall. The transversus thoracis is located on the internal surface of the thoracic wall and is continuous with the transversus abdominis inferiorly. It acts as a weak depressor of the ribs during expiration.
Other muscles that do not make up the thoracic wall but attach to it are termed accessory muscles of respiration. These include the pectoralis major and minor, subclavius, and serratus anterior (anteriorly), and the primary costarum and serratus posterior superior and inferior (posteriorly). The diaphragm is another muscle in the thorax that serves as the main muscle of inspiration, separating the contents of the chest from those of the abdomen.
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The pectoralis major and minor muscles overlay the thorax
The thorax is a region of the body that contains vital organs and structures, including the heart, lungs, thymus, trachea, and oesophagus. The thoracic wall is made up of several muscles, including the external, internal, and innermost intercostal muscles, the subcostalis, and the transversus thoracis. These muscles are primarily responsible for changing the volume of the thoracic cavity during respiration.
In addition to these muscles, other muscles attach to the thoracic wall, including the pectoralis major and minor, subclavius, and serratus anterior. The pectoralis major is the superior-most and largest muscle of the anterior chest wall. It is a thick, fan-shaped muscle that lies underneath the breast tissue and forms the anterior wall of the axilla. The pectoralis major consists of two heads: the clavicular and the sternocostal, which reference their area of origin. The clavicular head originates from the anterior surface of the medial half of the clavicle, while the sternocostal head originates from the anterior surface of the manubrium and body of the sternum, among other structures.
The pectoralis minor is a superficial muscle located on the anterior aspect of the chest or thoracic wall, deep to the pectoralis major. It arises as three separate heads from the anterior surface of the third, fourth, and fifth ribs near the corresponding costal cartilages. The pectoralis minor muscle is important clinically and as a surgical landmark due to the structures that lie below or deep to the muscle and its tendon. The pectoralis major and minor muscles work together with other muscles in the region to produce various movements of the scapula, and they can also be used as accessory muscles of respiration.
Together, the pectoralis major and minor muscles form the anterior wall of the axilla, along with their associated fascia. The pectoralis minor is also used as a reference point for the three divisions of the axillary artery. The primary nerve supply to the pectoralis minor muscle comes from the medial pectoral nerve, one of the minor branches of the brachial plexus. Thus, the pectoralis major and minor muscles play important roles in the anatomy and function of the thorax.
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Frequently asked questions
The thorax muscle refers to the muscles of the thoracic wall and the diaphragm. The thoracic wall is made up of five muscles: the external, internal, and innermost intercostal muscles, the subcostalis, and the transversus thoracis. The diaphragm is a sheet of skeletal muscle that separates the contents of the chest from the abdomen.
The muscles of the thorax are responsible for changing the volume of the thoracic cavity during respiration. The external intercostal muscles, for example, contract and raise the lateral part of the ribs during inspiration, increasing the transverse diameter of the thorax. The internal intercostal muscles, on the other hand, depress the ribs and reduce thoracic volume during forced expiration.
The accessory muscles of respiration are muscles that do not form the thoracic wall but attach to it and influence its movement. These include the pectoralis major and minor, serratus anterior, and scalene muscles. The primary function of these muscles may be elsewhere, such as in the arms or neck, but they have a secondary action on the thoracic wall.
