Cranial nerve kesions

• Brain


  A series of wires
• Testing nerves


  1. Overlapping functional wires

  2. Pinpointing non-functional wires

  3. Building up a picture of where there might be a problem
• Simplified example


  • B
  • A
  • D
  • c
• Olfactory nerve (cranial nerve I)


  Responsible for sense of smell
• Optic nerve (CN II)


  Responsible for sense of sight
• Oculomotor nerve (CN III), trochlear nerve (CN IV) and abducens (CN VI)


  Work together to move the eye
• Vestibulocochlear nerve (CN VIII)


  Responsible for sense of balance and hearing
• Accessory nerve (CN XI)


  Function is to move the shoulders
• Hypoglossal nerve (CN XII)


  Function is to move the tongue
• Trigeminal nerve (CN V)


  General sensation to face
• Facial nerve (CN VII)


  Motor to face
• Glossopharyngeal nerve (CN IX)


  General sensation to throat
• Vagus nerve (CN X)

  Motor to throat
• Two tools in life

  • Olfactory
  • Optic, oculomotor, trochlear & abducens
• Olfactory


  1. Olfactory mucosa

  2. Olfactory nerves

  3. Olfactory tracts

  4. Lateral olfactory stria > primary olfactory cortex

  5. Medial olfactory stria > limbic system
• Olfactory


  Responsible for distinctive smells, individual nostrils, may report changes in smell or taste
• Optic, oculomotor, trochlear & abducens

  1. Neurones in retina

  2. Converge to form optic nerve

  3. Hemi-decussate

  4. Travel along optic tract

  5. Synapse in thalamus

  6. Run to primary visual cortex
• Eye testing


  • Visual acuity
  • Visual fields
  • Pupillary reflex
• Pupillary reflex


  1. Light detected by retina

  2. Signal carried by optic nerve

  3. Processed in brain stem

  4. Impulse created in Edinger-Westphal nucleus (parasympathetic nucleus of oculomotor)

  5. Travels along both oculomotor nerves

  6. Synapses in ciliary ganglia

  7. Travels to sphincter pupillae part of irises

  8. Both pupils constrict
• Optic nerve


  • Eye movement
  • Trigeminal sensation
  • Cavernous sinus
  • Trigeminal motor
• Trigeminal motor


  • Paralysis of muscles of mastication
  • Pterygoid action unopposed
  • Mandible differs toward affected side
• Facial motor


  • Corneal reflex
  • Facial pathway
• Hearing and balance


  • Swallowing and speech
  • Gag reflex
• Spinal accessory nerve (CN XI)

  Responsible for shoulder strength and tongue
• Parasympathetics


  • Oculomotor, facial, glossopharyngeal and vagus nerves
  • 'Rest and digest'
  • Increased salivation
  • Pupils constricted
  • Decrease heart rate
  • Decrease respiration rate
• Sympathetics


  • Hitch-hike from thorax into head on internal carotid artery
  • 'Fight or flight'
  • Dry mouth
  • Pupils dilated
  • Increase heart rate
  • Increase respiration rate
  • Cause sweating
• It may or may not be practical to test each nerve in the field
• Feeling unusual sensations that shouldn't be there can be as telling as things that aren't
• Reflexes are probably the most important for you: pupillary, corneal and gag
• Paramedics identify the following as important

  • Know the function of each
  • Cranial nerve exam: Smell, Vision, Eye movement, Taste, PUPILLARY RESPONSE, Facial sensation, Hearing, Balance, Autonomic signs (HR, Skin, RR, pupils), Gag (for intubation), Shoulder strength, Tongue deviation
  • Pupillary
  • Bells
  • Pathways useful
  • Cover the senses
  • Paraesthesia's
  • Diplopia