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
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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
Describe the motor and sensory innervation of the femoral nerve of the lumbar plexus
- Motor: innervates the Illiacus, pectineus, sartorius and quadriceps femorus muscles
- Sensory: innervates the skin on the anterior thigh and the medial leg
Where is the sacral plexus located?
It is located on the surface of the posterior pelvic wall, anterior to the piriformis muscle
Which nerve roots form the sacral plexus?
- The plexus is formed by the anterior rami (divisions) of the sacral spinal nerves S1, S2, S3 and S4
- It also receives contributions from the lumbar spinal nerves L4 and L5
Identify the 5 peripheral nerves which form the sacral plexus
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Describe the anatomical course and identify the nerve roots of the superior gluteal nerve of the sacral plexus
- Course: leaves the pelvis via the greater sciatic foramen, entering the gluteal region superiorly to the piriformis muscle (accompanied by superior gluteal artery and vein)
- Roots: L4, L5, S1
Describe the motor and sensory innervation of the superior gluteal nerve of the sacral plexus
- Motor: innervates the gluteus minimus, gluteus medius and tensor fascia lata muscles
- Sensory: no functions
Describe the anatomical course and identify the nerve roots of the inferior gluteal nerve of the sacral plexus
- Course: leaves the pelvis via the greater sciatic foramen, entering the gluteal region inferiorly to the piriformis muscle (accompanied by inferior gluteal artery and vein)
- Roots: L5, S1, S2
Describe the motor and sensory innervation of the inferior gluteal nerve of the sacral plexus
- Motor: innervates gluteus maximus
- Sensory: no functions
Describe the anatomical course and identify the nerve roots of the sciatic nerve of the sacral plexus
- Course: enters gluteal region via greater sciatic foramen, emerges inferiorly to piriformis, descends inferolaterally, moves posteriorly through gluteal region, enters thigh deep to biceps femoris long head, bifurcates at apex of popliteal fossa
- Nerve roots: L4, L5, S1, S2, S3
Describe the motor innervation of the sciatic nerve of the sacral plexus
- Tibial Portion – innervates muscles in the posterior compartment of the thigh and leg, muscles of the sole of the foot and the hamstring portion of adductor magnus
- Common Fibular Portion – innervates short head of biceps femoris, muscles in the anterior and lateral compartments of the leg
Describe the sensory innervation of the sciatic nerve of the sacral plexus
- Tibial Portion: innervates the skin on the posterolateral and medial surfaces of the foot as well as the sole of the foot
- Common Fibular Portion: innervates the skin on the anterolateral surface of the leg and the dorsal aspect of the foot
Describe the anatomical course and identify the nerve roots of the posterior cutaneous nerve of the thigh in the sacral plexus
- Course: leaves the pelvis via the greater sciatic foramen, enters the gluteal region inferiorly to the piriformis muscle, descends deep to the gluteus maximus and runs down the back of the thigh to the knee
- Roots: S1, S2, S3
Describe the motor and sensory innervation of the sciatic nerve of the posterior cutaneous nerve of the thigh in the sacral plexus
- Motor: no functions
- Sensory: innervates the skin on the posterior surface of the thigh and leg and the skin of the perineum
Describe the anatomical course and identify the nerve roots of the pudendal nerve of the sacral plexus
- Course: leaves the pelvis via the greater sciatic foramen, then re-enters via the lesser sciatic foramen, moving anterosuperiorly along the lateral wall of the ischiorectal fossa
- Roots: S2, S3, S4
Describe the motor and sensory innervation of the pudendal nerve of the sacral plexus
- Motor: innervates the skeletal muscles in the perineum, the external urethral sphincter, the external anal sphincter, levator ani
- Sensory: innervates the penis, clitoris and most of the skin of the perineum
