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The abdominal muscles are strong bands of muscles lining the walls of the abdomen, located between the ribs and the pelvis at the front of the body. They are responsible for holding internal organs in place, supporting the body during movement, and regulating internal abdominal pressure. The abdominal wall is formed of skin, fascia, and muscle, encasing the abdominal cavity and viscera. The abdominal muscles may be divided into anterolateral and posterior components, with the anterolateral muscles including five paired muscles: the external oblique, internal oblique, transversus abdominis, rectus abdominis, and pyramidalis. The abdominal muscles attach to the spine or pelvis, with the rectus abdominis attaching to the xiphoid process of the sternum and the costal cartilage of ribs 5-7, and the pyramidalis attaching to the linea alba.
| Characteristics | Values |
|---|---|
| Number of abdominal muscles | 5 main muscles |
| Function | Hold organs in place, support the trunk, allow movement, protect the spine, stabilise the pelvis, maintain internal abdominal pressure |
| Location | Between the ribs and the pelvis on the front of the body |
| Muscle names | Transversus abdominis, Rectus abdominis, External obliques, Internal obliques, Pyramidalis |
| Attachments | Originate from the inguinal ligament, costal cartilages 7-12, the iliac crest, thoracolumbar fascia, pubic bone, pubic crest, pubic symphysis |
| Insertions | Xiphoid process, linea alba, conjoint tendon, pubic crest |
| Innervation | Thoracoabdominal nerves (T7-T11), subcostal nerve (T12), branches of the lumbar plexus |
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What You'll Learn
- Rectus abdominis: a pair of muscles that run down the middle of the abdomen
- External obliques: the largest of the flat muscles, they sit at the bottom of the stack
- Internal obliques: located just inside the hipbones, they operate in the opposite way to external obliques
- Transversus abdominis: the deepest abdominal muscle, with transversely running fibres
- Pyramidalis: a small, triangular muscle that helps maintain internal pressure in the abdomen
Rectus abdominis: a pair of muscles that run down the middle of the abdomen
The rectus abdominis is a long, flat muscle that extends along the whole length of the front of the abdomen. It is one of five main abdominal muscles and is often referred to as the "abs" muscle. The rectus abdominis is split into two segments by a muscle called the linea alba, which runs vertically down the middle of the muscle, creating the "six-pack" appearance in individuals with low body fat.
The rectus abdominis muscle serves several functions in the body. It helps to hold internal organs in place, providing stability during movement, and assisting with breathing and respiration. It also plays a role in spine flexion, stabilising and controlling the pelvis, and helping with overall core stability. The muscle originates from two points in the pelvis, the pubic crest and pubic symphysis, and extends upward to insert on the costal cartilages of the fifth to seventh ribs and the xiphoid process of the sternum.
The rectus abdominis is enclosed by the rectus sheath, which is composed of connective tissue. The sheath has an anterior and posterior wall for most of its length, formed by the aponeuroses of the external oblique, internal oblique, and transversus abdominis muscles. At a certain point, all the aponeuroses move to the anterior wall, and the rectus abdominis comes into direct contact with the transversalis fascia.
The muscle is innervated by thoraco-abdominal nerves, which are continuations of the T7-T11 intercostal nerves. It receives sensory input from the T7-T12 thoracic nerves. The rectus abdominis can be injured by a direct blow or strain, resulting in a rectus sheath haematoma, which is bleeding into the muscle.
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External obliques: the largest of the flat muscles, they sit at the bottom of the stack
The external obliques are a pair of muscles, one on each side of the rectus abdominis. They are the largest of the flat muscles and sit at the bottom of the stack. The external obliques allow the trunk to twist from side to side, but to the opposite side of whichever external oblique is contracting. For example, the right external oblique contracts to turn the body to the left.
The external obliques originate from the external surfaces of ribs 5-12. The muscle fibres fan out towards the midline and inferior margins of the abdomen. The most posterior fibres course almost vertically, while the remainder passes anteromedially. The external oblique muscle is supplied by the ventral branches of the lower six thoracoabdominal nerves and the subcostal nerve on each side. The uppermost part of the muscle is supplied by the intercostal nerves T7-T11, while the subcostal nerve (T12) innervates the lower part.
The external obliques are involved in several functions, including ipsilateral lateral flexion of the trunk and contralateral rotation of the trunk when contracting unilaterally. Bilateral contraction flexes the trunk anteriorly, increasing intra-abdominal pressure, which is useful in processes such as breathing, singing, and defecation. The external obliques also function to pull the chest downwards and compress the abdominal cavity, increasing intra-abdominal pressure.
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Internal obliques: located just inside the hipbones, they operate in the opposite way to external obliques
The internal obliques are a pair of muscles located just inside the hip bones, on top of the external obliques. They are much thinner and smaller than the external obliques. The internal obliques originate on the inguinal ligament, which is a ligament that runs from the anterior iliac spine to the pubic bone. They also originate on the anterior iliac crest. The abdominal internal oblique muscle lies below the external oblique muscle and just above the transverse abdominal muscle. Its fibres run perpendicular to the external oblique muscle.
The internal obliques function bilaterally with the external obliques to flex the trunk and compress its contents. However, they function unilaterally to laterally flex the trunk and rotate the trunk to the opposite side. For example, the right internal oblique and the left external oblique contract as the torso flexes and rotates to bring the left shoulder towards the right hip. This is known as counter-rotation, where the upper and lower parts move in opposite directions.
The abdominal muscles have many important functions, from holding organs in place to supporting the body during movement. They make up the "core" muscles, along with the back muscles, and help protect the spine and keep the body stable and balanced. The internal obliques, in particular, flank the rectus abdominis and support torsional movement of the trunk.
The rectus abdominis is a pair of muscles that run down either side of the middle of the abdomen from the ribs to the front of the pelvis. They are divided by a muscle called the linea alba. The rectus abdominis holds the internal organs in place and keeps the body stable during movement.
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Transversus abdominis: the deepest abdominal muscle, with transversely running fibres
The transversus abdominis is the deepest abdominal muscle and has transversely running fibres. It is one of the five main abdominal muscles, which together with the back muscles, make up the core muscles. These muscles help protect the spine and keep the body stable and balanced. The transversus abdominis originates from the inguinal ligament, costal cartilages 7-12, the iliac crest and thoracolumbar fascia. It inserts onto the conjoint tendon, xiphoid process, linea alba and the pubic crest.
The transversus abdominis muscle plays an important role in maintaining normal abdominal wall tension and increasing intra-abdominal pressure. It also helps to hold the abdominal organs in place. Weakness in the transversus abdominis or other abdominal muscles increases the risk of abdominal hernias.
The transversus abdominis is a deep abdominal muscle and an important core muscle. Inhibition or inadequate activation of this muscle can contribute to low back pain and lumbar instability.
The abdominal muscles work together to control the movement of the spine, pelvis and rib cage during gait. They also help with breathing, coughing, vomiting, pooping and childbirth.
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Pyramidalis: a small, triangular muscle that helps maintain internal pressure in the abdomen
The abdominal muscles are strong bands of muscles lining the walls of the abdomen. They are located between the ribs and the pelvis at the front of the body. They support the trunk, allow movement, and hold organs in place by regulating internal abdominal pressure.
The pyramidalis is a small, triangular muscle that helps maintain internal pressure in the abdomen. It is a vertical muscle, located at the base of the pubic bone, in front of the rectus abdominis. The rectus abdominis is a pair of muscles that run down either side of the abdomen from the ribs to the pelvis. The pyramidalis attaches to the linea alba, a muscle that divides the rectus abdominis into two segments.
The linea alba is a fibrous strip that, along with the rectus abdominis, gives rise to the 'six-pack' appearance in individuals with well-developed abdominal muscles. The rectus abdominis is responsible for moving the body between the ribcage and the pelvis, and it stabilises the pelvis during walking. It also holds the internal organs in place, keeping the body stable during movement.
The pyramidalis is one of the five main abdominal muscles, along with the rectus abdominis, external obliques, internal obliques, and transversus abdominis. These muscles make up the core muscles, which help protect the spine and keep the body stable and balanced. The external obliques are the largest of the flat muscles and sit at the bottom of the stack. The internal obliques flank the rectus abdominis and operate in the opposite way to the external obliques.
The transversus abdominis is the deepest of the flat muscles, with transversely running fibres. It stabilises the trunk and helps maintain internal abdominal pressure. It is enclosed within the rectus sheath, along with the rectus abdominis and pyramidalis muscles.
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Frequently asked questions
The rectus abdominis is a pair of muscles that run down either side of the abdomen, from the ribs to the pelvis. They are divided by the linea alba, to which the pyramidalis muscle attaches.
The internal and external obliques flank the rectus abdominis. The external obliques are the largest of the flat muscles and sit at the bottom of the stack.
The transversus abdominis is the deepest of the flat muscles. It originates from the inguinal ligament, costal cartilages 7-12, the iliac crest and thoracolumbar fascia.
