Neuroanatomy

Question 1

Components of lumbosacral plexus?

Answer 1

• Iliohypogastric - T12/L1 - iliac crest dermatome
• Genitofemoral - L1/L2 - anterior surface of psoas - scrotum, labia majora, femoral triangle
• Lateral femoral cutaneous - L2/L3 - inguinal ligament - anterolateral thigh
• Obturator - L3/L4 - obturator foramen - medial thigh and adductors
• Superior gluteal - L4/L5 - greater sciatic foramen - hip abduction (Trendelenburg)
• Inferior gluteal - L5/S1 - greater sciatic foramen - hip extension (glut max)
• Sciatic nerve - L4-S3 - greater sciatic foramen - posterior compartment of thigh, all of leg
• Pudental - S2-S4 - greater sciatic foramen and ischial spine - perineum

Question 2

Branches of sciatic nerve?

Answer 2

• Posterior compartment of thigh (L5-S1)
• Tibial nerve - S1/S2 - popliteal fossa to posterior compartment of leg
  
  • Gastrocnemius and soleus - ankle plantarflexion
  • Tibialis posterior - ankle inversion
  • Sensation: sole of foot except for lateral part
  • Injury: tarsal tunnel syndrome - pain on sole of foot.
• Common fibular nerve - L4-S2 - lateral popliteal fossa and head of fibula
  
  • Deep fibular nerve: anterior compartment of leg - runs with anterior tibial artery
    
    • tibialis anterior - L4, L5 - foot dorsiflexion
    • extensor hallucis longus - L5 - hallux extension
    • skin between 1st and 2nd toe
  • Superficial fibular nerve: lateral compartment of leg
    
    • fibularis longus and fibularis brevis - eversion and (plantarflexion)
    • dorsum of foot except for in btw 1st and 2nd toe
  • Lateral sural cutaneous - lateral and posterior cutaneous leg

Question 3

Injuries:

• Anterior hip dislocation
• Pelvic fracture
• Lateral knee/fibular neck
• Knee trauma
• Posterior hip dislocation or malpositioned injection

Answer 3

• Anterior hip dislocation: obturator nerve (L2-L4)
  
  • Thigh adduction, medial thigh sensory deficit
• Pelvic fracture: femoral nerve (L2-L4)
  
  • Thigh and knee flexion, anterior thigh and medial leg
• Lateral knee/head of fibula: common fibular (L4-S2)
  
  • Foot drop, dorsum of foot
• Knee trauma: tibial (L4-S3)
  
  • loss of foot inversion and plantarflexion, sole of foot
• Posterior hip dislocation, malpositioned injection
  
  • Superior gluteal (L4-S1): thigh abduction - trendelenburg gait - contralateral hip drop
  • Inferior gluteal (L5-S2): can’t jump or extend thigh.

Question 4

Upper trunk lesion?

Answer 4

• Upper trunk lesion - C5, C6
  
  • Erb’s palsy - “Waiter’s tip”
  • Shoulder dystocia or trauma

Question 5

Long thoracic nerve lesion?

Answer 5

LTN lesion - C5,6,7

winged scapula

injured during breast surgery

Question 6

Lower trunk lesion?

Answer 6

Lower trunk lesion - C8,T1

Klumpke’s palsy - “total claw”; atrophy of thenar and hypothenar eminences

loss of all lumbricals - no flexion at MIP or extension at PIP

finger flexors (C5-C7) and finger extensors (radial nerve) are unopposed

Compressed against cervical rib (thoracic outlet syndrome), grabbing a branch when falling, Pancoast tumor

Question 7

Axillary nerve lesion?

Answer 7

Axillary nerve - C5, C6

Inability to abduct arm; sensory deficit over deltoid muscle.

Fractured surgical neck of humerus or dislocation of humeral head.

Question 8

Radial nerve lesion?

Answer 8

• Radial nerve - C5-T1
• Wrist drop
• Sensory deficit posterior arm, dorsal hand and thumb.
• Fracture at midshaft of humerus or “saturday night palsy”/crutches

Question 9

Median nerve injury?

Answer 9

Median nerve C5-T1

• Proximal: Supracondylar fracture of humerus
  • Loss of lateral finger flexion and thumb opposition (ape hand); also wrist flexion weakness
  • When asked to make fist, “pope’s blessing”
• Distal: carpal tunnel syndrome or dislocated lunate
  • Loss of lateral lumbricals (can’t extend PIP)
  • When asked to extend fingers, 2nd and 3rd remain flexed at PIP - “median claw”

Question 10

Ulnar nerve injury?

Answer 10

Ulnar nerve C8, T1

• Proximal ulnar nerve injury: fracture of medial epicondyle of humerus (funny bone)
  
  • Loss of medial finger flexion, weak wrist flexion, loss of dorsal and palmar interossei
  • “OK sign” upon making a fist (?)
• Distal ulnar nerve injury: falling onto outstretched hand. Injury at hook of hamate.
  
  • Loss of medial finger flexion
  • when extending all fingers, medial flexors remain unopposed at PIP - distal ulnar claw
• For both: atrophy of interossei visible btw knuckles.

Question 11

Sensory corpuscles (4)

Description, location, senses

Answer 11

• Pain and temperature - free nerve endings
  
  • C - slow, unmyelinated
  • A-delta - fast, myelinated
  • all skin and epidermis, some viscera
• Fine touch, proprioception - Meissner’s corpuscles - hairless skin
• Vibration, pressure - Pacinian corpuscles - deep skin, ligaments, joints
• Deep touch - edges - Merkel’s discs - hair follicles, adapt slowly

Question 12

What are the branches of the superior laryngeal nerve?

What do they innervate?

Answer 12

• Internal division
  
  • Runs at the surface of the mucosa covering the piriform sinus; easily injured
  • Descends together with superior laryngeal artery
  • Sensory and autonomic innervation to the larynx above the vocal folds
  • Mediate afferent limb of cough reflex
• External division
  
  • supplies cricothyroid muscle (arch 4), which tenses vocal folds
  • runs with superior thyroid artery