Dominic Stone
The subcostal muscles are a group of muscles of the thorax that consist of short, individual, skeletal muscles found in the lower half of the posterior thoracic wall. They are inserted onto the second rib that is inferior to their origin sites, which are the ninth to twelfth ribs. The intercostal muscles, on the other hand, are part of the rib cage and link each rib to its neighbours. They work in sets to change the size of the space inside the rib cage, aiding in respiration. There are three types of intercostal muscles: external, internal, and innermost intercostal muscles. The external intercostal muscles contribute to inhalation, while the internal intercostal muscles contribute to exhalation.
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What You'll Learn
- The subcostal muscles are a group of muscles of the thorax
- Subcostal muscles depress the ribs at their costovertebral joints
- The subcostal artery supplies blood to the twelfth rib
- The subcostal nerve innervates the external abdominal oblique
- The first rib is the only rib to articulate with the first thoracic vertebra
The subcostal muscles are a group of muscles of the thorax
The subcostal muscles are part of the five muscles that make up the thoracic wall, along with the three intercostal muscles (external, internal, and innermost) and the transversus thoracis. The intercostal muscles lie in the intercostal spaces between ribs and are organised into three layers. The most superficial layer is the external intercostal muscle, which originates from the inferior aspect of the rib above and inserts onto the superior aspect of the rib below in an inferomedial direction.
The internal intercostal muscles begin posteriorly as the posterior intercostal membrane on the inner aspect of the external intercostal muscles. From approximately the angle of the rib, the internal intercostal muscles run obliquely, upward, and forward from the superior border of the rib and costal cartilage below to the floor of the subcostal groove of the rib and the edge of the costal cartilage above, ending at the sternocostal junctions. The innermost intercostal muscles are the deepest layer of the thorax wall and are similar in structure to the internal intercostals. They originate from the medial aspect of the costal groove of the rib above and insert onto the internal aspect of the rib below.
The subcostal muscles are most developed in the inferior portion of the thoracic wall, with their fibres running in the same direction as the innermost intercostals. They originate from the internal aspect of one of the lower ribs and insert onto the internal aspect of the second or third rib below. The subcostal muscles depress the ribs at their costovertebral joints, stabilising their position during normal respiration and decreasing thoracic volume during forced expiration.
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Subcostal muscles depress the ribs at their costovertebral joints
The subcostal muscles depress the ribs at their costovertebral joints. The ribs are the bony framework of the thoracic cavity, forming the main structure of the thoracic cage, which protects the thoracic organs. The first rib is an exception to the rule that each rib articulates posteriorly with two thoracic vertebrae by the costovertebral joint; the first rib articulates with the first thoracic vertebra only.
The subcostal muscles are a group of muscles of the thorax, consisting of short, individual skeletal muscles that are found in the lower half of the posterior thoracic wall. They originate from the internal surfaces of the seventh to tenth ribs, in the areas that are located adjacent to the angles of these ribs. There can be variations between individuals regarding the origin sites for the subcostal muscles. The fibres of the subcostal muscles travel inferomedially and insert onto the second rib that is inferior to their origin sites, i.e., the ninth to twelfth ribs.
The subcostalis exists in the same layer as the innermost intercostal muscle and is present in abundance in the lower regions of the posterior thoracic wall. They originate from the internal aspect of one of the lower ribs and insert onto the internal aspect of the second or third rib below. The subcostal muscles are involved in depressing the ribs during forced expiration.
The internal intercostal muscles begin posteriorly, as the posterior intercostal membrane on the inner aspect of the external intercostal muscles. From the angle of the rib, these muscles run obliquely, upward, and forward from the superior border of the rib and costal cartilage below to the floor of the subcostal groove of the rib and the edge of the costal cartilage above, ending at the sternocostal junctions. The external intercostal muscles have an inspiratory action on the rib cage, while the internal intercostal muscles are expiratory.
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The subcostal artery supplies blood to the twelfth rib
The human body has twelve pairs of ribs that form the main structure of the thoracic cage, protecting the thoracic organs. The ribs are classified into three groups according to their attachment to the sternum: true, false, and floating ribs. The first seven ribs are true ribs as they directly articulate with the sternum with their costal cartilages. The false ribs are the eighth, ninth, and tenth ribs, which indirectly articulate with the sternum as their costal cartilages connect with the seventh costal cartilage. The floating ribs are the distal two ribs, which do not articulate with the sternum at all.
The subcostal artery is a direct branch of the thoracic aorta, which supplies blood to the twelfth rib. It helps the lower posterior intercostal artery to supply the musculocutaneous structures of the anterolateral abdominal wall at the level of the twelfth rib. The subcostal artery gives off anterior and posterior branches that travel along with the subcostal space below the twelfth rib. It then continues between the internal abdominal oblique and transverse abdominis muscles, terminating close to the rectus abdominis.
The subcostal artery is accompanied by the subcostal nerve, which is the anterior ramus of the twelfth thoracic spinal nerve. It gives off a dorsal branch that travels posteriorly through the transverse processes of adjacent vertebrae. The subcostal artery contributes to the muscular, fascial, and cutaneous supply of the anterior, lateral, and posterior abdominal wall.
The subcostal vein drains the blood of the twelfth rib. The intercostal veins, arteries, and nerves are located in the costal groove of each rib. The intercostal nerves supply the ribs by sensory and motor branches, providing innervation to the skin and musculature of the chest and abdominal walls.
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The subcostal nerve innervates the external abdominal oblique
The subcostal nerve is a branch of the T12 root and travels with the subcostal vessels on the inferior aspect of the T12 rib. It pierces the muscular aponeurosis to travel between the internal oblique and transversus abdominis muscles. The subcostal nerve innervates the skin and subcutaneous tissue of the gluteal region and the lateral side of the thigh. It also supplies the transversus abdominis, rectus abdominis, and pyramidalis, along with some fibres to the peritoneum.
The subcostal nerve also innervates the external abdominal oblique muscle. This muscle is the most superficial lateral muscle of the anterior abdominal wall. The fibres of the external abdominal oblique muscle are oriented inferiorly and anteriorly. The external abdominal oblique muscle is important as it forms the inguinal ligament, which runs from the pubic tubercle to the anterior superior iliac spine. The ligament forms the base of the inguinal canal.
The external abdominal oblique muscle is involved in the flexion and rotation of the vertebral column, which brings about contralateral rotation of the torso. Unilateral contraction of the muscle causes lateral flexion of the vertebral column. It is also important in increasing intra-abdominal pressure.
The subcostal nerve is at risk of damage during autologous bone harvesting from the iliac crest due to its close relation to the anterior superior iliac spine. The subcostal nerve is one of the 11 intercostal nerves, with the ventral rami of the 12th thoracic nerve root. The intercostal nerves supply innervation to the skin and musculature of the chest and abdominal walls.
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The first rib is the only rib to articulate with the first thoracic vertebra
The human rib cage is a complex structure that serves to protect the vital organs of the thorax, such as the heart and lungs, while also facilitating respiration. It is formed by 12 pairs of ribs, numbered from 1 to 12, which articulate with the vertebral column at the back and terminate in cartilage at the front. These ribs have several unique features and functions, with the first rib, in particular, standing out due to its distinct characteristics and attachments.
The first rib, or Rib 1, is structurally unique compared to the other ribs. It is shorter and wider than the rest of the ribs, and it possesses two costal grooves and a single articular facet. This articular facet, or costal facet, allows the first rib to articulate with the first thoracic vertebra, known as T1. This articulation is facilitated by a well-developed superior vertebral notch on the T1 vertebral body, which resembles a cervical vertebra more closely than a typical thoracic vertebra.
The first rib is the only rib that articulates exclusively with the first thoracic vertebra. This is in contrast to the other ribs, which generally articulate with two thoracic vertebrae. For example, the fifth rib articulates with both the fourth and fifth thoracic vertebrae. This pattern continues until the tenth rib, which articulates with the tenth thoracic vertebra.
The reason for this unique articulation of the first rib lies in its anatomical position and function. The first rib is located higher in the thoracic cage and plays a crucial role in supporting the weight of the upper body. By articulating with the first thoracic vertebra, the first rib helps maintain the stability of the thoracic cage and provides a solid foundation for the attachment of the surrounding muscles and ligaments.
Furthermore, the first rib also has a distinct attachment to the sternum, the flat bone located in the centre of the chest. While the true ribs (ribs 1-7) attach directly to the sternum via their costal cartilages, the first rib is an exception. It is classified as a synarthrosis, which means it can articulate with the clavicle through the costoclavicular joint. This unique attachment further highlights the specialised role of the first rib in providing structural integrity to the thoracic region.
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Frequently asked questions
The subcostal muscles arise from the inner surface of one rib near its angle and are inserted into the inner surface of the second or third rib below. They are found in the ninth to twelfth ribs.
Subcostal muscles are a group of muscles of the thorax. They consist of short, individual, skeletal muscles that are found in the lower half of the posterior thoracic wall.
Subcostal muscles are one of the five muscles that make up the thoracic cage, along with the external, internal, innermost intercostals, and transversus thoracis. They act to change the thoracic volume during breathing.
