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The ribs are the bony framework of the thoracic cavity, forming the main structure of the thoracic cage, which protects the organs within it. There are twelve pairs of ribs, and their main function is to aid respiration. Several muscles are attached to the ribs, including the serratus anterior, pectoralis major and minor, and latissimus dorsi. The intercostal muscles are within the rib cage and consist of three layers: external, internal, and innermost. These muscles help to change the thoracic volume during breathing. The quadratus lumborum is a muscle in the lower back that attaches to the spine, rib cage, and pelvis, and it plays a role in stabilizing the pelvis, lumbar spinal joints, and the twelfth rib.
| Characteristics | Values |
|---|---|
| Number of rib pairs | 12 |
| Types of ribs | True, False, Floating |
| Muscle attachments | Serratus Anterior, Pectoralis Major, Pectoralis Minor, Latissimus Dorsi, Scalenus Anterior, Scalenus Posterior, Scalenus Medius, Rectus Abdominis, Serratus Posterior Superior, Serratus Posterior Inferior, Quadratus Lumborum, Intercostals (External, Internal, Innermost), Subcostales, Transversus Thoracis |
| Function of intercostal muscles | Stabilise the position of the ribs during normal respiration, depress the ribs and decrease thoracic volume during forced expiration, expand the chest wall during inhalation, collapse the lung during expiration |
| Intercostal muscle strain symptoms | Chest/upper back pain, shallow short breathing pattern due to pain |
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What You'll Learn
- The quadratus lumborum is a square-shaped muscle that attaches to the twelfth rib
- The serratus anterior muscle attaches to the second rib
- The pectoralis major and minor muscles arise from the superior anterior ribs
- The latissimus dorsi originates from the 9th to 12th ribs
- The internal intercostal muscles help collapse the lung during expiration
The quadratus lumborum is a square-shaped muscle that attaches to the twelfth rib
The human body is a complex structure with many muscles and bones working together to enable movement and stability. One such muscle is the quadratus lumborum, which plays a crucial role in maintaining posture and facilitating various bodily functions.
The quadratus lumborum, often abbreviated as QL, is a square-shaped muscle located in the lower back region of the human body. It is part of the posterior abdominal wall and lies deep inside the abdomen, dorsal to the iliopsoas. The QL is considered a back muscle, although it is technically part of the abdominal wall. This muscle is essential for maintaining posture and stabilizing the lumbar spine and the rib cage.
The QL muscle originates from the iliac crest and the iliolumbar ligament and has attachments to several vertebrae. It connects to the transverse processes of the lumbar vertebrae, from L1 to L5, and it also attaches to the twelfth rib, which is one of the floating ribs that do not articulate with the sternum. The twelfth rib is the lowest rib and is more mobile than the other ribs, making it crucial for stability.
The QL muscle helps to stabilize the pelvis, the lumbar spine, and the twelfth rib. It assists in movements of the spine and the pelvis, and it also plays a role in respiration by fixing the twelfth rib during forced expiration. This muscle is an accessory inspiratory muscle, meaning it supports the diaphragm during inhalation. Additionally, the QL muscle can tilt the pelvis laterally and extend the lumbar spine when contracted bilaterally.
The QL is susceptible to muscle fatigue and pain due to its constant contraction while seated. Conditions such as kyphosis and weak gluteal muscles can contribute to quadratus lumborum pain. It is important to maintain proper posture and strengthen the surrounding muscles to prevent overuse and injury to the quadratus lumborum.
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The serratus anterior muscle attaches to the second rib
The serratus anterior muscle is a fan-shaped muscle located at the lateral wall of the thorax. It is also referred to as the "boxer's muscle" or the "big swing muscle" because it is responsible for the protraction of the scapula, a movement that occurs when throwing a punch. The serratus anterior is innervated by the long thoracic nerve, a branch of the brachial plexus.
The serratus anterior muscle acts to pull the scapula forward around the thorax. When the shoulder girdle is fixed, all three parts of the serratus anterior muscle work together to lift the ribs, assisting with respiration. The muscle is named from the Latin "serrare", meaning "to saw", referring to its shape; and "anterior", meaning "on the front side of the body". The serratus anterior normally originates by nine or ten muscle slips, arising from either the first to eighth ribs, or the first to ninth ribs.
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The pectoralis major and minor muscles arise from the superior anterior ribs
The pectoralis major and minor muscles are two of the five muscles that make up the thoracic cage. 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. Its origin lies on the anterior surface of the medial half of the clavicle, the anterior surface of the sternum, the first 7 costal cartilages, the sternal end of the sixth rib, and the aponeurosis of the external oblique of the anterior abdominal wall. The insertion of the pectoralis major is at the lateral lip of the intertubercular sulcus of the humerus. The pectoralis major has two heads, the clavicular and the sternocostal, which reference their area of origin. The function of the pectoralis major is dependent on which heads of muscles are involved. The clavicular head acts individually to flex the upper limb, while the sternocostal head adducts and medially rotates the upper limb and draws the scapula anteroinferiorly.
The pectoralis minor lies underneath the pectoralis major and almost completely covered by it. It originates from the 3rd to 5th ribs and inserts into the coracoid process of the scapula. The pectoralis minor muscle inferiorly rotates the glenoid cavity when shortened, which could limit the ability of the scapula to fully rotate in the opposite direction. Together with the serratus anterior, the pectoralis minor acts in protraction of the scapula, i.e., moving it laterally and anteriorly against the rib cage. This movement is important in reaching the arm forward. The pectoralis minor also aids in respiration by helping to raise ribs 3-5 during inspiration and expanding the thoracic cavity.
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The latissimus dorsi originates from the 9th to 12th ribs
The latissimus dorsi is a large, flat muscle that covers much of the lower posterior thorax. It is commonly referred to as the
The latissimus dorsi is a climbing muscle that assists in raising the trunk when the arms are fixed overhead. It is important for activities such as rowing, swimming (especially the downstroke), and chopping. The muscle also plays a role in coughing or sneezing, as it compresses the thorax and abdomen during these actions. Additionally, the latissimus dorsi helps to hold the scapula against the thorax during upper limb movements.
The latissimus dorsi is a potential source of muscle for breast reconstruction surgery after mastectomy. It can also be used to correct pectoral hypoplastic defects, such as Poland's syndrome. An absent or hypoplastic latissimus dorsi is one of the associated symptoms of Poland's syndrome.
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The internal intercostal muscles help collapse the lung during expiration
The thoracic cage, or rib cage, is formed by the twelve pairs of ribs in the human body. The main function of the ribs is to aid respiration. The internal intercostal muscles are one of the five muscles that make up the thoracic cage, the others being the external intercostals, innermost intercostals, subcostales, and transversus thoracis.
The internal intercostal muscles lie deep to the external intercostals and extend from the rib above to the one below, but in the opposite direction to the external intercostals. They originate from the lateral edge of the costal groove and insert onto the superior surface of the rib below.
The internal intercostal muscles are involved in respiration, specifically during expiration. During restful breathing, expiration is a passive process and does not require the use of the internal intercostal muscles. However, during forced expiration, the internal intercostal muscles contract and pull the ribs inward and downward, forcing air out of the lungs. This contraction of the internal intercostal muscles has the opposite effect of the external intercostals, resulting in the lowering of the ribs and a reduction in the anterior-posterior dimension of the rib cage. This aids in collapsing the lungs and forcing air out during forced expiration.
In addition to the internal intercostal muscles, other muscles involved in forced expiration include the abdominal muscles, inferior serratus posterior muscles, and the transverse thoracic muscle. These muscles work together to ensure effective expiration during periods of forced or strenuous breathing.
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Frequently asked questions
Intercostal muscles are muscles that present within the rib cage. They consist of three layers of muscles: external, internal, and innermost. They combine to fill the space between the ribs.
The intercostal muscles act to change the thoracic volume during breathing. They help to expand the chest wall during inhalation and collapse the lung during exhalation.
The five muscles that make up the thoracic cage are the intercostals (external, internal, and innermost), subcostales, and transversus thoracis. The serratus posterior superior and inferior, and the quadratus lumborum are also muscles of the spine and rib cage.
The serratus posterior superior and inferior muscles are thin muscles located deep to other muscles. They help to stabilise the rib cage. The serratus posterior inferior also helps to prevent the inferior ribs from being pulled upwards by the diaphragm.
