10. CN XI/XII

Question 1

CN XI - Name, where it enters/exits skull, components, how to test if damaged, primordium

Answer 1

Spinal Accessory Nerve
Enters from foramen magnum; Exits via JUGULAR CANAL (with CN 9 and 10)

Cranial Root: accessory to CN X in Head/Neck Distribution - considered CN X
Spinal Root: leaves cranial root to neck muscles (SCM/Trapezius), proprioception from cervical spinal nerves, considered all CN XI
Cranial/Spinal Roots share common sheath when in skull

Damaged CN XI: wasting of SCM/trapezius = inability to shrug shoulders (elevate shoulder girdle)

Primordium: somitic mesoderm (near Arch 6)

Question 2

CN XII - Name, where it exits skull, components, testing if damaged, primordium

Answer 2

Hypoglassal Nerve
Exits Hypoglossal Canal (where rootlets converge to nerve)
Components: Somatomotor to tongue muscles:
Intrinsic: don’t attach, but change tongue shape
Genioglossus: to genial tubercle of mandible, keeps tongue from falling back into airway
Hypoglossus: attach to hyoid
Styloglossus: attach to styloid process of mandible

Note: Ansa cervicalis travels within CN12’s nerve sheath to strap muscles of neck due to proximity of postotic somites and cervical plexus somites

Testing: damaged CN12 - genioglossus can’t protrude - tongue deviates to non-working side

Primordium: Post-otic Somites