The lumbar nerves originate from the ventral rami of spinal nerves L1 through L4, with a contribution from T12 as well. These nerve roots then come together to form the lumbar plexus.
The Lumbar Plexus
The lumbar plexus is a network of nerve fibers that supplies the lower abdomen, anterior and medial thigh, and medial leg. Its roots are derived from specific spinal nerve segments.
Formation and Location
- The lumbar plexus is formed by the ventral rami of L1, L2, L3, and L4 spinal nerves.
- The first lumbar nerve (L1) also receives a branch from the T12 spinal nerve.
- It is located anterior to the transverse processes of the lumbar vertebrae.
- It sits posterior to the psoas major muscle.
Nerves Arising from the Lumbar Plexus
Several major nerves arise from the lumbar plexus, including:
- Iliohypogastric nerve (T12, L1): Supplies sensation to the skin of the lateral gluteal region and the hypogastric region.
- Ilioinguinal nerve (L1): Supplies sensation to the skin of the upper medial thigh, scrotum (male) or labia majora (female).
- Genitofemoral nerve (L1, L2): Supplies sensation to the skin of the scrotum (male) or labia majora (female) and the skin of the anterior thigh.
- Lateral femoral cutaneous nerve (L2, L3): Supplies sensation to the skin of the lateral thigh.
- Femoral nerve (L2, L3, L4): The largest branch, supplying motor function to the anterior thigh muscles (quadriceps) and sensation to the anterior thigh and medial leg.
- Obturator nerve (L2, L3, L4): Supplies motor function to the medial thigh muscles (adductors) and sensation to the medial thigh.
In summary, the lumbar nerves, specifically the ventral rami of L1-L4 (with a contribution from T12), are the roots that form the lumbar plexus. These nerves then branch to provide motor and sensory innervation to the lower torso and lower extremities.
