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The abdominal wall is made up of muscles that enclose the abdominal cavity, which holds the gastrointestinal viscera. The abdominal wall is innervated by several nerves, including the thoracoabdominal nerves, lateral cutaneous nerves, subcostal nerve, iliohypogastric nerve, and ilioinguinal nerve. These nerves originate from the spinal cord and supply the skin and muscles of the anterolateral abdominal wall, providing segmental innervation to the intercostal muscles, rectus abdominis, pyramidalis, transversus abdominis, internal oblique, and external oblique muscles. The lumbar plexus also supplies nerves to the lateral abdominal region, thigh, anterior thigh, and external genitals. The nervous system of the abdomen, lower back, and pelvis contains important nerve conduits that service this region, including the most inferior portion of the spinal cord and major nerves, plexuses, and ganglia that serve the vital organs of the abdominopelvic cavity.
| Characteristics | Values |
|---|---|
| Nerves controlling the anterolateral abdominal wall | Thoracoabdominal, lateral cutaneous, subcostal, iliohypogastric, and ilioinguinal nerves |
| Nerves controlling the abdominal cavity | Thoracic and lumbar spine nerves |
| Nerves controlling the anteromedial abdominal wall | Rectus abdominis muscle |
| Nerves controlling the lateral abdominal region | Lumbar plexus |
| Nerve signals carried to the leg | Sciatic nerve |
| Nerves controlling autonomic processes in the abdomen | Spinal nerves of the lower back |
| Nerves controlling the pelvic organs | Parasympathetic neurons in the spinal cord |
| Nerves controlling the anterolateral abdominal wall muscles | Thoracoabdominal nerves (T7-T11) and subcostal nerve (T12) |
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What You'll Learn
Thoraco-abdominal nerves
The thoraco-abdominal nerves are the anterior divisions of the seventh through eleventh intercostal nerves (T7-T11) and the subcostal nerve (T12). 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 and end as the anterior cutaneous branches of the abdomen, supplying the skin of the front of the abdomen.
The lower intercostal nerves supply the intercostal and abdominal muscles, with the last three sending branches to the serratus posterior inferior. Additionally, around the middle of 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 and 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 before piercing the posterior rectus sheath. They then travel anteriorly through openings in the linea semilunaris to return sensation from the skin overlying the rectus abdominis muscle. The intercostal nerves, which give rise to the thoraco-abdominal nerves, originate from the anterior rami of the thoracic spinal nerves and carry both motor and sensory fibres.
The nervous system of the abdomen, lower back, and pelvis contains important nerve conduits that service this region and the lower limbs. The spinal nerves of the lower back carry neurons of the autonomic nervous system (ANS), which control the vital involuntary processes of the digestive, urinary, endocrine, and reproductive systems. The sympathetic division of the ANS extends from the spinal cord to form nerves that meet at autonomic ganglia in the abdomen, such as the celiac ganglion, which then extend to the organs to control their function.
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Lumbar plexus
The lumbar plexus is a network of nerves (a nerve plexus) in the lumbar region of the body. It is formed by the anterior rami (divisions) of the lumbar spinal nerves L1, L2, L3, and L4, and receives contributions from the thoracic spinal nerve 12. The lumbar plexus supplies nerves to the skin and muscles of the lateral abdominal region, thigh, anterior thigh, and external genitals.
The lumbar plexus is a complex neural network formed by the lower thoracic and lumbar ventral nerve roots. The nerves arising from the lumbar plexus are important for the functioning of the lower extremity function and movement, allowing knee extension, hip flexion, and adduction of the thigh. The origin of the lumbar plexus is within the psoas major muscle, anterior to the lumbar transverse processes.
The iliohypogastric nerve is the first major branch of the lumbar plexus. It runs to the iliac crest, across the quadratus lumborum muscle of the posterior abdominal wall. It then perforates the transversus abdominis and divides into its terminal branches. The ilioinguinal nerve follows a similar anatomical course as the iliohypogastric nerve. After innervating the muscles of the anterior abdominal wall, it passes through the superficial inguinal ring to innervate the skin of the genitalia and middle thigh.
The femoral nerve is the largest nerve that arises from the lumbar plexus. It is created from lumbar spinal nerves L2, L3, and L4. It leaves the plexus and enters the femoral triangle, passing just lateral to the femoral artery. The femoral nerve gives motor innervation to iliopsoas, pectineus, sartorius, and quadriceps femoris, and provides sensory innervation to the anterior thigh, posterior lower leg, and hindfoot.
Damage to the lumbar plexus or nerves proximal and distal to it can result in several pathologies, including LS plexopathy, which can be challenging to diagnose and manage. Symptoms of LS plexopathy include low back and/or leg pain, motor weakness, numbness, paresthesia, and/or sphincter dysfunction.
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Sacral plexus
The sacral plexus is a network of nerve fibres that provides motor and sensory nerves to the skin and muscles of the pelvis and lower limb. It is located on the surface of the posterior pelvic wall, in front of the piriformis muscle and the pelvic fascia. The superior gluteal nerve, for example, leaves the pelvis through the greater sciatic foramen and enters the gluteal region superiorly to the piriformis muscle.
The sacral plexus is formed by the anterior rami (divisions) of the sacral spinal nerves S1, S2, S3, and S4, and receives contributions from the lumbar spinal nerves L4 and L5. These nerves combine to form the lumbosacral trunk, which descends into the pelvis to meet the sacral roots as they emerge from the spinal cord. The anterior rami of the S1-S4 spinal roots divide into several cords, which then combine to form the five major peripheral nerves of the sacral plexus.
The nerves of the sacral plexus have two main destinations. Some leave the pelvis via the greater sciatic foramen and enter the gluteal region, innervating the structures there. Others remain in the pelvis, innervating the pelvic muscles, organs, and perineum. The sciatic nerve, the largest and longest nerve in the human body, carries a major portion of the nerve signals from the sacral plexus into the leg before separating into many smaller branches.
The sacral plexus plays a significant role in sensory innervation for various regions of the lower body. It provides motor innervation to the flexor muscles of the lower limb through its anterior branches, while its posterior branches supply the extensor and abductor muscles. Disorders affecting the nerves of the sacral plexus, known as sacral plexopathies, can be caused by trauma, nerve compression, vascular disease, or infection, and may result in pain, loss of motor control, and sensory deficits.
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Sciatic nerve
The sciatic nerve is the largest and longest nerve in the human body. It originates from the anterior rami of the lower lumbar (L4-L5) and upper sacral spinal nerves (S1, S2, S3). It is derived from the sacral plexus, which supplies nerves to the skin and muscles of the posterior thigh, leg, and foot. The sciatic nerve carries a major portion of the nerve signals from the sacral plexus into the leg before separating into many smaller branches.
The main function of the sciatic nerve is to provide sensory and motor supply to the skin and muscles of the thigh, leg, and foot. It runs between the long head of the biceps femoris muscle and the adductor magnus muscle, and laterally to the semitendinosus and semimembranosus muscles. On its course through the posterior thigh, the sciatic nerve gives off several small motor muscular branches that innervate several muscles of the thigh.
The sciatic nerve then continues its course through the posterior thigh, passing inferior to the piriformis muscle. It exits the pelvis through the greater sciatic foramen, an opening located deep in the buttock, just below the piriformis muscle. The sciatic nerve then courses down and runs below and along the side of the large gluteus maximus muscle in the buttock.
In the leg, the sciatic nerve divides into two main branches: the tibial nerve and the common fibular (peroneal) nerve. The tibial nerve continues the course of the sciatic nerve, descending down through the posterior aspect of the leg to the heel of the foot. The common fibular nerve, on the other hand, courses laterally towards the head of the fibula. It then divides into the superficial fibular nerve and the deep fibular nerve, which supply different compartments of the leg and foot.
Sciatica is a common condition involving pain and other symptoms in the back, butt, and legs. It is often caused by pressure on the sciatic nerve, which can be due to age-related wear and tear on the spine, osteoarthritis, excess weight, insufficient core strength, or other factors. Most cases of sciatica are not serious and can be managed with self-treatment.
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Sympathetic and parasympathetic divisions of the ANS
The abdominal muscles are controlled by a complex network of nerves, including the thoraco-abdominal nerves, which arise from the lower intercostal nerves, and the lumbar plexus, which supplies nerves to the lateral abdominal region. The abdominal muscles are also influenced by the autonomic nervous system (ANS), which comprises the sympathetic and parasympathetic divisions.
The sympathetic division of the ANS emerges from the spinal cord in the thoracic and lumbar regions, extending to form nerves that meet at autonomic ganglia in the abdomen. This division is responsible for the "'fight-or-flight' response, activating processes that help the body respond to stress or danger. It typically functions in situations requiring quick reactions, and its activity can be increased by consuming caffeine.
On the other hand, the parasympathetic division has craniosacral "outflow", with neurons beginning at the cranial nerves and the sacral spinal cord. This division is responsible for the "rest-and-digest" response, promoting relaxation and digestive processes. It functions in actions that do not require immediate reactions. For example, it triggers salivation and increased peristalsis and secretory activity in the digestive tract.
Although the sympathetic and parasympathetic divisions often function in opposition to each other, their relationship is more complementary than antagonistic. The balance between these divisions is crucial for the body's well-being and survival. Together, they effectively control all the organs of the abdomen and pelvis.
The enteric nervous system (ENS), found in the gastrointestinal tract, is sometimes considered a part of the ANS. It consists of around 100 million neurons that regulate digestive functions, monitor the contents of the gastrointestinal tract, and control the movements of smooth muscles and glandular secretions involved in digestion.
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Frequently asked questions
The thoraco-abdominal nerves, lateral cutaneous nerves, subcostal nerves, iliohypogastric nerves, and ilioinguinal nerves are all involved in controlling the abdomen muscles.
The thoraco-abdominal nerves are derived from the T7-T11 spinal nerves and form the inferior intercostal nerves. These nerves run along the internal obliques and transversalis muscles.
Intercostal nerves are situated between the ribs and the internal and innermost intercostal muscle layers. They traverse a long route along the inferior border of the ribs within the costal groove.
The iliohypogastric nerve originates from the superior branch of the ventral ramus of the L1 spinal nerve. It innervates the skin over the buttocks, ileum, and skin overlying the inferior portion of the rectus abdominis muscle. It also sends motor branches to the inferior portions of the transversus abdominis, external oblique, and internal oblique muscles.
