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The abdominal wall is a complex structure encasing and protecting the abdominal organs, including the gastrointestinal viscera and the alimentary tract. It is composed of multiple layers, including fascia, muscle, nerves, and vasculature. The innervation of the abdominal muscles is a complex process involving various nerves, including the thoraco-abdominal nerves, the iliohypogastric nerve, and the ilioinguinal nerve. These nerves are responsible for supplying and innervating the rectus abdominis, pyramidalis, transversus abdominis, internal oblique, and external oblique muscles, as well as providing sensation to the skin overlying these muscles. Understanding the anatomy of the abdominal wall and its innervation is crucial for surgical procedures and managing postoperative pain.
| Characteristics | Values |
|---|---|
| Nerves | Thoraco-abdominal nerves, Iliohypogastric nerve, Ilioinguinal nerve |
| Nerve Origins | Anterior divisions of the 7th, 8th, 9th, 10th, and 11th thoracic intercostal nerves, L1 spinal nerve |
| Muscle Innervated | Rectus abdominis, Transversus abdominis, Internal oblique, External oblique, Pyramidalis |
| Muscle Layers | 4 main layers: skin, superficial fascia, muscles and associated fascia, and parietal peritoneum |
| Muscle Function | Compression of abdominal contents, stabilising pelvis during walking, depressing ribs |
| Blood Supply | Superior epigastric artery, Inferior epigastric artery, Musculophrenic artery, Subcostal artery, Posterior intercostal artery, Deep circumflex iliac artery, Superficial circumflex iliac artery |
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What You'll Learn
Thoraco-abdominal nerves
The thoraco-abdominal nerves are the anterior divisions of the seventh, eighth, ninth, tenth, and eleventh thoracic intercostal nerves. They continue anteriorly from the intercostal spaces into the abdominal wall, passing behind the costal cartilages and between the obliquus internus and transversus abdominis muscles. They then perforate the sheath of the rectus abdominis, supplying the muscle and ending as the anterior cutaneous branches of the abdomen. These nerves provide innervation to the skin of the front of the abdomen.
The lower intercostal nerves supply the intercostales and abdominal muscles, with the last three sending branches to the serratus posterior inferior. During their course, they give off lateral cutaneous branches. The T7 to T12 thoraco-abdominal nerves provide segmental innervation to the skin overlying the anterolateral abdominal wall. They also innervate the intercostal, rectus abdominis, pyramidalis, transversus abdominis, internal oblique, and external oblique muscles.
The thoraco-abdominal nerves travel within a neurovascular plane between the transversus abdominis and internal oblique muscles. They pierce the posterior rectus sheath and travel anteriorly through openings in the linea semilunaris. Within the abdominal wall, these nerves travel at an anteroinferior angle. T7 innervates the skin just inferior to the xiphoid process of the sternum, T10 innervates the region of the umbilicus, and T12 innervates the suprapubic skin.
The anterolateral abdominal wall is a layered structure composed of skin, fascia, muscles, extraperitoneal fat, and peritoneum. It extends from the thorax to the pelvis and encloses the abdominal cavity, housing the gastrointestinal viscera. The abdominal wall consists of four main layers: skin, superficial fascia, muscles and associated fascia, and parietal peritoneum. The thoraco-abdominal nerves play a crucial role in innervating the muscles and structures of the abdominal wall, contributing to the movement and stabilization of the torso.
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Iliohypogastric nerve
The iliohypogastric nerve is a nerve that originates from the lumbar plexus and supplies sensation to the skin over the lateral gluteal and hypogastric regions. It also provides motor innervation to the internal oblique muscles and transverse abdominal muscles. The nerve emerges from the upper lateral border of the psoas major muscle and crosses in front of the quadratus lumborum muscle to an area superior to the iliac crest.
The iliohypogastric nerve then pierces the transversus abdominis muscle and continues anteriorly in the abdominal wall between the transversus abdominis and internal oblique muscles. It divides into a lateral cutaneous branch and an anterior cutaneous branch between these muscles. The lateral cutaneous branch pierces the internal and external oblique muscles and supplies the skin of the gluteal region. The size of this branch is inversely proportional to that of the lateral cutaneous branch of the subcostal nerve.
The anterior cutaneous branch, or hypogastric branch, continues onward between the abdominal internal oblique and transverse muscles. It pierces the internal oblique muscle and becomes cutaneous by perforating the aponeurosis of the external oblique muscle, supplying the skin of the hypogastric region. The iliohypogastric nerve gives off anterior and lateral cutaneous branches and supplies branches to the abdominal musculature along its course.
The iliohypogastric nerve is a mixed nerve, providing both motor and sensory innervation to the abdominal muscles. It may be absent in up to 20% of people, with its fibres carried on other nerves such as the ilioinguinal nerve. Damage to the iliohypogastric nerve can occur during surgery or in the third trimester of pregnancy due to rapid abdominal expansion.
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Ilioinguinal nerve
The ilioinguinal nerve is a branch of the thoracolumbar division of the sympathetic nervous system, specifically arising from the lumbar spinal cord and emerging between the psoas major and iliacus muscles. It plays a crucial role in providing sensory innervation to several abdominal muscles and contributing to the overall
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Intercostal nerves
The intercostal nerves are part of the somatic nervous system and arise from the anterior rami of the thoracic spinal nerves from T1 to T11. The first six intercostal nerves give off branches and then end within the corresponding intercostal space just below the corresponding rib. The seventh through eleventh intercostal nerves exit the intercostal spaces and travel into the abdominal wall. These last five intercostal nerves are termed thoraco-abdominal nerves. The intercostal nerves are mixed nerves, carrying motor and sensory fibres. Their main function is to provide segmental supply to the structures of the thoracic wall and abdominal wall.
The intercostal nerves are situated between adjacent ribs and enter the corresponding intercostal space between the posterior (internal) intercostal membrane and the parietal pleura. They then course anteriorly in the costal grooves alongside their corresponding intercostal artery and vein. The majority of intercostal nerves follow a similar pattern from origin to course and branches, but there are some differences.
The intercostal nerves are grouped into typical and atypical intercostal nerves. The typical intercostal nerves include IC3 through IC6, while the atypical intercostal nerves include IC1, IC2, and IC7 through IC11. The reason for this division is that the typical intercostal nerves course solely in their own intercostal spaces, while the atypical spinal nerves go beyond the thoracic wall to supply other regions.
The anterior division of the first thoracic nerve divides into two branches. The larger branch leaves the thorax in front of the neck of the first rib and enters the brachial plexus. The smaller branch, the first intercostal nerve, runs along the first intercostal space and ends on the front of the chest as the first anterior cutaneous branch of the thorax. The anterior rami of the second, third, fourth, fifth, and sixth thoracic nerves enter directly into their corresponding intercostal spaces, passing between the parietal pleura and the posterior intercostal membrane.
The intercostal nerves carry sympathetic innervation to structures such as sweat glands and blood vessels in the thoracic and abdominal walls. They also supply the integument of the front of the thorax and over the mammary gland, forming the anterior cutaneous branches of the thorax. The lateral cutaneous branches are derived from the intercostal nerves and pierce the Intercostales externi and Serratus anterior, dividing into anterior and posterior branches.
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Subcostal nerve
The subcostal nerve is the last and largest of the anterior branches of the thoracic spinal nerves, originating from the anterior or ventral rami of the twelfth thoracic spinal nerve (T12). It shares characteristics with the intercostal nerves, but its course takes it below the ribs, hence the name 'subcostal' (sub- meaning 'below', and costal- meaning 'rib').
The subcostal nerve gives off four types of branches: muscular, cutaneous, communicant, and collateral branches. It is a mixed nerve, carrying both motor and sensory fibres. Its main function is to supply innervation to the skin overlying the abdominal wall, the abdominal muscles, and the parietal peritoneum. The nerve follows the inferior margin of the twelfth rib, running with an artery and a vein in a neurovascular bundle. It passes in front of the quadratus lumborum muscle and pierces the transversus abdominis muscle.
The subcostal nerve then emerges between the transversus abdominis and the internal oblique muscle, travelling between them. It gives off a communicating branch that connects with the iliohypogastric nerve of the lumbar plexus. It also sends a muscular branch to the pyramidalis muscle and the lateral cutaneous branch. The lateral cutaneous branch pierces the internal and external oblique muscles, running towards the gluteal region. After passing over the iliac crest, this branch extends to the greater trochanter of the proximal femur, innervating the skin over the anterior portion of the gluteal region.
The subcostal nerve provides innervation to the abdominal wall muscles, including the pyramidalis, internal oblique, external oblique, and transversus abdominis muscles. It also innervates the rectus abdominis muscle, which is a long, paired muscle found on either side of the midline in the abdominal wall. The lateral cutaneous branch of the subcostal nerve innervates the skin and subcutaneous tissue of the gluteal region and the lateral side of the thigh.
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Frequently asked questions
The abdominal wall consists of four main layers: skin, superficial fascia, muscles and associated fascia, and parietal peritoneum. The nerves that innervate the abdominal muscles include the thoraco-abdominal nerves, the iliohypogastric nerve, and the ilioinguinal nerve.
The thoraco-abdominal nerves are a continuation of the anterior divisions of the seventh, eighth, ninth, tenth, and eleventh thoracic intercostal nerves. They travel within a neurovascular plane between the transversus abdominis and internal oblique muscles before piercing the posterior rectus sheath.
The iliohypogastric nerve gives off a lateral cutaneous branch to supply the skin of the L1 dermatome, which covers the buttocks and ilium. It then pierces the internal and external oblique muscles and gives rise to terminal branches that supply the skin overlying the inferior rectus abdominis muscle. The ilioinguinal nerve travels within the neurovascular plane between the transversus abdominis and internal oblique muscles and pierces the internal oblique muscle at the inguinal canal.
