Gross Anatomy-Lumbosacral Plexes

Question 1

Explain the Lumbar Plexes Nerves

Answer 1

• Consists of VPR from L1-L4;, T12 often contributes
• Formed within psoas major m.
• Each receives postsynaptic sympathetics via gray rami communicantes
• Iliohypogastric and ilioinguinal nn. –
o VPR of L1
o Innervate abdominal wall mm. and L1 dermatome anteriorly (inguinal and pubic regions)
• Lateral femoral cutaneous n. –
o VPR of L2-3
o Enters thigh deep to inguinal l. and medial to ASIS
o Sensory to anterolateral skin of thigh
• Femoral n. –
o Posterior divisions of VPR of L2-4
o Passes deep to inguinal l. and then to anterior thigh
• Innervates hip flexors and knee extensors
• Sensory to anterior and medial thigh and anteromedial leg and foot
• Genitofemoral n. -
o VPR of L1-L2
o Genital branch passes through deep inguinal ring
• Sensory to anterolateral skin of scrotum/labia majora
• Motor to cremaster m.
o Femoral branch passes along external iliac a.
• Sensory innervation over femoral triangle• Obturator n. –

 o Anterior divisions VPR of L2-4
  o Motor to medial thigh mm. sensory to medial thigh above knee **• Lumbosacral trunk** –
  o VPR L4-5
  o Participates with S1-4 in forming sacral plexus

Question 2

Explain the Sacral Plexus of Nerves

Answer 2

• Composed of VPR of S2-S4 and lumbosacral trunk (L4-5)
• All branches except those to pelvic diaphragm leave pelvis via greater sciatic foramen above or below piriformis
• All branches receive gray rami communicans from sympathetic trunk
• Superior gluteal n. –
o Posterior divisions VPR L4-S1
o Enters gluteal region via greater sciatic foramen
o Sensory to hip and motor to gluteus medius, minimus and tensor fascia lata

• Inferior gluteal n. –
o Posterior divisions VPR L5-S2
o Enters gluteal region via greater sciatic foramen
o Sensory to hip and motor to gluteus maximus m.
• **Posterior femoral cutaneous n. ** –
o Anterior and posterior divisions of VPR S1-3
o Sensory to skin of upper medial thigh, inferior buttock, posterior thigh, popliteal fossa, and lateral perineum
**• Sciatic n. ** –
o Anterior and posterior divisions of VPRL4-S3
o Located midway between ischial tuberosity and greater trochanter in gluteal region
o Composed of 2 divisions:
 Tibial division – formed from ventral divisions
 Common fibular division – formed from dorsal divisions
o Sensory to hip, knee, ankle and all foot joints, posterior and anterolateral leg; skin of foot
o Motor to hamstrings, hamstring portion of adductor magnus, all leg and foot mm.
• Pudendal n. –
o Anterior divisions VPR S2-4
o Exits pelvis via greater sciatic foramen below piriformis m. between sacrotuberous and sacrospinous ll.
o Enters perineum via lesser sciatic foramen
o Sensory to perineal skin, penis and clitoris
o Motor to perineal mm., pelvic diaphragm and external anal sphincter

• Nerve to quadratus femoris –
o Anterior divisions of VPR L4-S1
o Enters gluteal region via greater sciatic foramen
o Sensory to hip motor to quadratus femoris and inferior gemellus mm.
• Nerve to obturator internus
o Posterior divisions of VPR L5-S2
o Exits pelvis via greater sciatic foramen
o Enters pelvis via lesser sciatic foramen
o Sensory to hip and motor to superior gemellus and obturator internus mm.