Trunk nerves (intercostal, sympathetic, vagus nerve)
Cauda equina
Cauda equina
- Origin
- Bundle of spinal nerve roots (L2 to Co1) originating from the conus medullaris at the L1-L2 vertebral level
- Insertion
- Descends within the thecal sac (lumbar cistern containing CSF) to exit through their respective lumbosacral intervertebral foramina
- Function
- Provides all motor and sensory innervation to the pelvic floor, perineum, external genitalia, sphincters (bladder/bowel control S2-S4), and lower limbs
- Innervation
- Lumbar and sacral spinal nerves (L2-Co1) including autonomic pelvic splanchnic fibers
- Movement & chain
- Free-floating nerve root bundle within the thecal CSF
- Palpation
- Assessed via anal wink reflex, resting and voluntary anal sphincter tone (DRE), and saddle area sensation
- Clinical
- Cauda equina syndrome (CES; absolute neurosurgical emergency caused by massive central disc herniation or trauma; classic presentation: saddle anesthesia in S3-S5 distribution, acute urinary retention with overflow incontinence, loss of bowel/anal sphincter tone, and lower extremity paraparesis; requires emergency surgical decompression <24-48 hours). Lumbar puncture is safely performed at L3-L4/L4-L5.
- Segmental innervation
- L2-S5 and Co1 spinal segments
- In clinical practice
- Emergency triage of red flag back pain symptoms (saddle numbness, urinary retention, bowel incontinence), urgent lumbar spine MRI ordering, post-void bladder ultrasound scanning
- Region in the model
- Trunk nerves (intercostal, sympathetic, vagus nerve)