S3) Lumbar & Sacral Plexus Flashcards
What is the lumbar plexus?
The lumbar plexus is a network of nerve fibres that supplies the skin and musculature of the lower limb
Where is the lumbar plexus located?
It is located in the lumbar region, within the substance of the psoas major muscle and anterior to the transverse processes of the lumbar vertebrae
Which nerve roots form the lumbar plexus?
- The plexus is formed by the anterior rami (divisions) of the lumbar spinal nerves L1, L2, L3 and L4
- It also receives contributions from the thoracic spinal nerve T12
Identify the 6 peripheral nerves which are formed from the lumbar plexus
Mnemonic: Interestingly, I Get Leftovers On Fridays
Describe the anatomical course and identify the nerve roots of the iliohypogastric nerve of the lumbar plexus
- Course: runs to the iliac crest, across the posterior abdominal wall, then perforates the transversus abdominis
- Roots: T12, L1
Describe the motor and sensory innervations of the iliohypogastric nerve of the lumbar plexus
- Motor: innervates the internal oblique and transversus abdominis
- Sensory: innervates the posterolateral gluteal skin in the pubic region
Describe the anatomical course and identify the nerve roots of the ilioinguinal nerve of the lumbar plexus
- Course: follows iliohypogastric nerve through abdomen then passes through the superficial inguinal ring
- Roots: L1
Describe the motor and sensory innervation of the ilioinguinal nerve of the lumbar plexus
- Motor: innervates the internal oblique and transversus abdominis
- Sensory: innervates the skin on the upper middle thigh
Describe the anatomical course and identify the nerve roots of the genitofemoral nerve of the lumbar plexus
- Course: leaves psoas major muscle and divides into a genital branch, and a femoral branch
- Roots: L1, L2
Describe the motor and sensory innervation of the genitofemoral nerve of the lumbar plexus
- Motor: innervates cremasteric muscle (genital branch)
- Sensory: innervates the skin of anterior scrotum / skin over mons pubis and labia majora (genital branch) and the skin on the upper anterior thigh (femoral branch)
Describe the anatomical course and identify the nerve roots of the lateral cutaneous nerve of the thigh in the lumbar plexus
- Course: enters the thigh at the lateral aspect of the inguinal ligament
- Roots: L2, L3
Describe the motor and sensory innervation of the lateral cutaneous nerve of the thigh in the lumbar plexus
- Motor: no functions
- Sensory: innervates the anterior and lateral thigh to the level of the knee
Describe the anatomical course and identify the nerve roots of the obturator nerve of the lumbar plexus
- Course: descends through psoas major, emerges on its medial border, runs posterolaterally along pelvic wall to obturator foramen, enters thigh through obturator canal and splits into anterior and posterior divisions
- Nerve roots: L2, L3, L4
Describe the motor and sensory innervation of the obturator nerve of the lumbar plexus
- Motor: innervates the obturator externus, pectineus, adductor longus, adductor brevis, adductor magnus, gracilis muscles
- Sensory: innervates the skin over the medial thigh
Describe the anatomical course and identify the nerve roots of the femoral nerve
- Course: descends through psoas major, traverses behind mid-point of inguinal ligament into thigh, passes through femoral triangle, splits into anterior and posterior divisions, terminates with saphenous nerve (cutaneous branch)
- Nerve roots: L2, L3, L4