The lumbar spinal nerve 1 (L1) is a spinal nerve

Spinal nerve

The term spinal nerve generally refers to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body...

 of the lumbar segment..

It originates from the spinal column from below the lumbar vertebra 1 (L1).

The two terminal branches of this nerve is the iliohypogastric and the ilioinguinal nerve

Ilioinguinal nerve

The ilioinguinal nerve is a branch of the first lumbar nerve . It separates from the first lumbar nerve along with the larger iliohypogastric nerve....

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Muscles

L1 supplies many muscles, either directly or through nerves originating from L1. They may be innervated with L1 as single origin, or be innervated partly by L1 and partly by other spinal nerves. The muscles are:

• quadratus lumborum
  Quadratus lumborum muscle
  The Quadratus lumborum is irregular and quadrilateral in shape, and broader below than above.-Origin and insertion:It arises by aponeurotic fibers from the iliolumbar ligament and the adjacent portion of the iliac crest for about 5 cm., and is inserted into the lower border of the last rib for...
  
   (partly)
• iliopsoas muscle (partly)