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Skeletal muscles, also known as striated muscles, are the most common type of muscle in the human body, comprising 30% to 40% of total body mass. They are attached to the bones and enable a wide range of movements and functions, including breathing. The diaphragm, a dome-shaped muscle below the lungs, is the primary muscle responsible for inhalation. It contracts and moves downward, increasing the length and diameter of the chest cavity, thereby expanding the lungs and facilitating inhalation. In addition to the diaphragm, external intercostal muscles, and other skeletal muscles in the chest and abdomen, also play a role in the inhalation process by elevating the rib cage and creating a vacuum around the lungs, causing air to flow in.
| Characteristics | Values |
|---|---|
| Muscles that cause inhalation | Diaphragm, external intercostals, internal intercostals, innermost intercostals, sternocleidomastoid, scalenus anterior, scalenus medius, scalenus posterior, abdominal muscles |
| Location of skeletal muscles | Between the bones of the skeletal system |
| Composition | Striated, red and white muscle fibres |
| Control | Voluntary and involuntary mechanisms |
| Function | Expand and contract the chest cavity to enable inhalation and exhalation |
| Blood flow | 2 to 4 L⋅kg−1⋅min−1 in humans |
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What You'll Learn
- The diaphragm contracts, moving down and expanding the lungs
- External intercostal muscles lift the ribs, increasing intrathoracic volume
- Sternocleidomastoid muscles elevate the sternum and clavicle, lifting the ribs
- Scalene muscles extend from C3-C6 vertebrae to the first rib, contributing to rib elevation
- The thoracic cage provides the necessary rigidity for organ protection and weight support
The diaphragm contracts, moving down and expanding the lungs
The diaphragm is a thin,
The diaphragm is attached to the sternum, the bottom of the rib cage, and the spine. It separates the chest cavity from the abdominal cavity. When the diaphragm contracts, it pushes the abdominal organs down, creating a vacuum in the chest cavity. This vacuum lowers the pressure in the lungs, causing air to rush in to fill the space.
The diaphragm is composed of skeletal muscle fibres, which are red and white and appear striated or striped. Skeletal muscles are the most common type of muscle in the body, comprising 30-40% of total body mass. They are attached to the bones and allow for a wide range of movements and functions. These muscles consist of flexible fibres that contract (tighten) and relax, enabling bones to move.
During exhalation, the diaphragm relaxes and returns to its dome shape, forcing air out of the lungs. This relaxation reduces the space in the chest cavity, facilitating the expulsion of air. The diaphragm is a vital muscle for respiration, and any weakness or paralysis can lead to breathing difficulties.
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External intercostal muscles lift the ribs, increasing intrathoracic volume
The skeletal muscles are the most common type of muscles in the human body. They are attached to the bones and allow us to perform a wide range of movements and functions. They are also vital for breathing, eating, and moving our bones.
The intercostal muscles are the muscles that are present within the rib cage. They consist of three layers of muscles: external, internal, and innermost. The external intercostal muscles are the outermost layer and are located in the intercostal spaces between the ribs. They originate on the inferior surfaces of the proximal parts of the ribs and insert into the superior and distal parts of the next lower rib.
The primary function of the external intercostal muscles is to lift the ribs and expand the rib cage during inhalation. When these muscles contract, they lift the ribs and rib cage, expanding the anterior–posterior dimensions of the rib cage. This increases the intrathoracic volume and creates a negative pressure in the pleural cavity, causing the lungs to expand as well.
The internal intercostal muscles, on the other hand, have the opposite effect. They contract to lower the ribs and reduce the anterior–posterior dimension of the rib cage during exhalation. The external and internal intercostals work together during breathing, and they are assisted by other muscles such as the sternocleidomastoid and scalene muscles on the neck.
By lifting the ribs, the external intercostal muscles play a crucial role in inhalation by increasing the volume of the thoracic cavity and allowing the lungs to expand. This expansion of the thoracic cavity is essential for pulmonary ventilation and ensures that we can breathe effectively.
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Sternocleidomastoid muscles elevate the sternum and clavicle, lifting the ribs
Skeletal muscles are a vital part of the musculoskeletal system, allowing us to perform a wide range of movements and functions. They are the most common type of muscle in the body, comprising 30% to 40% of our total body mass. These muscles connect to our bones and are composed of flexible muscle fibres that contract, allowing us to move our bones and perform various actions.
The sternocleidomastoid muscles are large, bilateral neck muscles that originate from two locations: the manubrium of the sternum (sternal head) and the medial third of the clavicle (clavicular head). These two heads merge to form a single muscle belly, which inserts on the mastoid process of the temporal bone and the superior nuchal line of the occipital bone.
The sternocleidomastoid muscles play a crucial role in inhalation by elevating the sternum and clavicle, subsequently lifting the ribs. This action expands the thoracic cavity, facilitating inspiration or inhalation. The elevation of the ribs increases the intrathoracic volume, creating a negative pressure in the pleural cavity. As a result, the lungs expand, causing a decrease in intrapulmonary pressure compared to external pressure, drawing air into the lungs.
Additionally, the sternocleidomastoid muscles have other functions, including rotating the head to the opposite side of contraction and flexing the neck. They also contribute to the posture of the neck and the body, with evidence suggesting a connection between the vestibular area and the motoneurons of the sternocleidomastoid.
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Scalene muscles extend from C3-C6 vertebrae to the first rib, contributing to rib elevation
The scalene muscles are a group of three muscles on each side of the neck: the anterior, middle, and posterior. They are named scalene, from the Ancient Greek "skalēnós", meaning "uneven". The scalenus anterior muscle originates from the anterior tubercles of the transverse processes of the vertebrae C3-C6 and attaches to the first rib. The scalenus anterior is the anteriormost of the three scalene muscles. It gives off a single flat tendon that inserts onto the scalene tubercle and superior border of the first rib. The scalene muscles contribute to rib elevation by lifting the first rib.
The scalene muscles are accessory muscles of respiration, elevating the ribs during forced inspiration. They increase the intrathoracic volume, aiding patients with respiratory distress in ventilating their lungs more effectively. However, they are not required for respiration in healthy individuals, and their use is an important clinical sign of respiratory distress.
The scalene muscles also have other functions, such as flexion, lateral flexion, and rotation of the neck. The scalenus anterior can produce flexion of the neck when the costal attachment is fixed and the head is in the anatomical position. When the vertebral attachment is fixed, the scalenus anterior can fix or lift the first rib superiorly. Combined with the contraction of the external intercostal muscles, this action expands the anteroposterior diameter of the thorax.
The scalene muscles receive their nerve supply from the anterior rami of the spinal nerves C4-C6, and their blood supply comes from the ascending cervical branch of the inferior thyroid artery. The scalene hiatus is formed by the passing of the brachial plexus and subclavian artery through the space between the anterior and middle scalene muscles.
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The thoracic cage provides the necessary rigidity for organ protection and weight support
The thoracic cage, or rib cage, is a complex anatomical structure that plays a crucial role in protecting vital organs, enabling movement, and facilitating breathing. It is composed of 12 pairs of ribs, the sternum, and 12 thoracic vertebrae, along with associated costal cartilages and intervertebral discs.
The thoracic cage's rigidity provides stability and support for the weight of the upper limbs and the body as a whole. This rigidity is essential for maintaining posture and balance, especially during physical activities and movements that require weight bearing and stability.
While providing rigidity, the thoracic cage also offers flexibility, allowing for ventilation and pulmonary ventilation. The ribs and their joints provide this flexibility, enabling the expansion and contraction of the thoracic cavity during inhalation and exhalation. The thoracic cage's apertures or openings facilitate the movement of air during breathing, with the superior aperture permitting trachea passage and the inferior aperture covered by the diaphragm.
The thoracic cage's rigidity, combined with its flexibility, ensures the protection of vital organs while allowing for the necessary movements and changes in volume during the breathing process. This dynamic structure adapts to the body's needs, demonstrating the intricate design of the respiratory system.
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Frequently asked questions
Skeletal muscles are the most common type of muscles in your body, comprising 30% to 40% of your total body mass. They are attached to the bones and allow you to perform a wide range of movements and functions.
Skeletal muscles help with breathing by expanding and contracting the chest cavity, allowing air to flow in and out of the lungs.
The diaphragm, a dome-shaped muscle that separates the chest cavity from the abdomen, is the main muscle used for inhalation. The intercostal muscles and neck muscles also assist in the process by helping to move the rib cage.
When the diaphragm contracts, it moves down and increases the length and diameter of the chest cavity, expanding the lungs and causing air to flow in.
Intercostal muscles are the muscles between the ribs that play a role in breathing, especially during physical activity. There are three types: external, internal, and innermost intercostal muscles.
