Week 4- cranial nerves overview Flashcards Preview

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Describe the route of CNI (olfactory nerve)

  • Arises in the forebrain 
  • Runs down the olfactory tracts to the bulbs
  • Then lots of little nerves run through the cribriform foramina in the cribriform plate
  • They sense 'smell' from the olfactory mucosa in the roof of the nasal cavity 


What is the function of the olfactory nerve? (CNI) 

  • Purely special sensory (olfaction/smell)
  • Mucosal membrane of roof of the nasal cavity is the target tissue 


How is the CNI (olfactory) nerve tested?

  • Enquire about sense of smell 
  • Smelling salts
  • Test one nostril at a time 
  • It is rarely formally tested in clinical practice 


What can damage CNI (olfactory) nerve? What can this lead to?

  • Nasal injuries
  • Head injury (shearing forces/basilar skull fracture) 
  • This can cause anosmia (loss of smell) 


What is the commonest cause of anosmia?

  • Colds and other upper respiratory tract infections 


Describe the route of CNII (optic nerve)

  • Arises from the forebrain 
  • Picks up stimuli from the retina (at back of eye)
  • Then passes through the optic canal 
  • The pair of nerves then cross over at the optic chiasm and there is mixing of fibres between the nerves
  • It then goes to the forebrain via the optic tracts


What is the function of CNII (optic nerve)?

  • Purely special sensory (sight/vision)


What pathway is CNII (optic nerve) part of?

  • The visual pathway 


What can adenoma of the pituitary gland cause in relation to the optic nerve (CNII)?

  • There is a close relationship between the optic chiasm and the pituitary so adenoma can cause compression of the chiasm
  • This causes problems in both eyes due to the mixing of fibres


How is CNII (optic nerve) tested?

  • Test one eye at a time 
  • Visual tests and pupils e.g. visual acuity and visual fields 


Why do we get different patterns of visual loss depending on where along the optic nerve a lesion occurs? Give examples of things that can cause damage to the optic nerve 

  • Due to mixing of the fibres between the nerves at the optic chiasm 
  • There is a complex pathway from the retina to visual cortex (occipital lobe) 
  • Things that can cause damage:
    • Optic neuritis 
    • Pituitary tumour 
    • Stroke 


what can we see the optic nerve directly with?

  • Fundoscopy


Describe the route of CNIII (occulomotor nerve)

  • Arises in the midbrain 
  • Passes through the cavernous sinus then through the superior orbital fissure (slit like hole at back of the eye)
  • Then goes to the orbit and supplies structures there 


Describe the role of CNIII (occulomotor nerve)

  • Predominantly motor 
    • Supplies 4 of the 6 occulomotor muscles:
      • Superior rectus 
      • Inferior rectus
      • Medial rectus
      • Inferior oblique 
    • Also supples levator papebrae superioris (lifts the eyelids)
  • Also has autonomic fibres (parasympathetic):
    • Short ciliary nerves which supply muscles in the iris which controls constriction/dilation of the pupil (pupil is essentially a hole) 


Why are dilated pupils often the first sign of raised intracranial pressure?

  • Autonomic fibres of the occulomotor nerve run on the outside of the nerve 
  • So if there is pressure on the nerve these will be affected first 
  • This leads to widening of the pupils
  • Involvement of the rest of the nerve comes later 


Which part of the cavernous sinus is the occulomotor nerve (CNIII) found?

The lateral wall 


How is the occulomotor (CNIII) nerve tested?

  • Inspection of eyelid and pupils
  • Eye movements
  • Pupillary light reflexes (checks autonomic fibres)
  • If there is damage to the nerve the patient often has a 'down and out' eye with severe ptosis +/- pupillary dilation 
    • when checking the position of the eye we may have to lift the eyelid due to paralysis of levator palpibrae superioris 


What is ptosis?

Drooping of the eyelid 


What can damage to the occulomotor CNIII present as?

  • Diplopia (double vision)
  • And 'down and out' position 


Give examples of causes of CNIII (occulomotor) lesions 

  • Raised intracranial pressure (tumour/haemorrhage)
  • Aneurysms (posterior communicating artery)
  • Cavernus sinus thrombosis (clots can travel into the sinus and if there is a blockage then pressure increases and can squash the nerve)
  • Diabetes/hypertension (pupil sparing) 


Describe the route of CNIV (trochlear nerve)

  • Arises from the dorsal aspect of the midbrain (only CN to do this)
  • Passes from the back of the brainstem through the cavernous sinus and superior orbital fissure and into the orbit


Which cranial nerve has the longest intracranial route? 

  • CNIV (trochlear nerve)
  • This means it is more at risk of damage 


What is the role of CNIV (trochlear nerve)? 

  • Motor function 
  • Supplies one oculomotor muscle: 
    • superior oblique 



Which part of the cavernous sinus is the trochlear nerve (CNIV) found?

The lateral wall 


How do we test the trochlear nerve (CNIV)?

  • Test eye movements


Why is damage to the trochlear nerve (CNIV) often missed?

  • It is rare and subtle as it only innervates on muscle
  • Often the patient compensates for the deviation of the eye by slightly tilting their head


Diplopia (double vision) can occur with damage to CNIV (trochlear nerve). When is this worse?

  • On downwards gaze e.g. walking down stairs and reading 


What is the most common cause of acute injury to CNIV (trochlear nerve)? What else can damage it?

  • Most common cause is head injury or any cause of raised intracranial pressure as these can stretch the nerve 
  • Congenital palsies can also cause damage (seen in children) 


Describe the route of CNV (trigeminal) nerve

  • Arises in the pons 
  • The sensory routes all synapse in the trigeminal ganglion before splitting into the 3 divisions:
    • V1 (ophthalmic)
      • goes through the superior orbital fissure
    • V2 (maxillary)
      • Goes through foramen rotundum
      • One branch (infra orbital) goes through infraorbital foramen
    • V3 (mandibular)
      • This is mixed (as also takes the motor fibres of trigeminal with it)
      • Goes through foramen ovale 
      • Branch of mandibular (mental nerve) goes through the mental foramen


what is the function of the trigeminal nerve (CNIV)?

  • Motor function 
    • To muscles of mastication:
      • Masseter
      • Temporal
      • Lateral pterygoid 
      • Medial pterygoid
      • Buccinator
  • General sensory function:
    • Face 
    • Inside of:
      • mouth 
      • Nasal cavities 
      • Sinuses 


Which branches of the trigeminal nerve (CNV) run through the lateral wall of the cavernous sinus?

  • Ophthalamic and maxillary 


How do we test the trigeminal nerve (CNV)?

  • test sensation to the face 
  • Test the muscles of mastication 


If someone gets punched in the face what might they present with in relation to the trigeminal nerve (CNV)?

  • Loss of sensation in the area supplied by the mental and infra orbital nerves (as these are sensory and are superficial) 


Give examples of problems with the trigeminal nerve (CNV)

  • Trigeminal neuralgia 
  • Shingles 
  • Corneal reflex (afferent limb of this reflex) 


Describe the route of the adbducens nerve (CNVI)

  • Arises in the pons 
  • Goes through the cavernous sinus then enters the orbit through the superior orbital fissure


What is the function of the abducens nerve (CNVI)?

  • Motor function 
    • Supplies one muscle:
      • Lateral rectus


Why can the abducens nerve be squashed/stretched if there is raised intracranial pressure?

  • It comes from the junction between the pons and the medulla and so goes round the bulbous bit of the pons running upwards towards the cavernous sinus before running through it
  • Due to its location it is susceptible to being squashed 


How do check the function of abducens nerve (CNVI)?

Test by checking eye movements 


The abducens nerve (CNVI) is susceptible to injury in raised intracranial pressure. Give examples of what can cause this and how it may present

  • Causes 
    • bleed
    • tumour
  • Presents as diplopia (double vision) 


Describe the route of the facial nerve (CNVII) 

  • Arises from the pons
  • Passes into the petrous part of the temporal bone and through the internal acoustic meatus
  • Gives off some branches in the ear and then exits through the stylomastoid foramen giving 5 terminal branches (these pass through the parotid gland)


What is the function of CNVII (facial nerve)?

  • Mostly motor:
    • Muscles of facial expression 
  • Special sensory (taste):
    • Anterior 2/3rds of tongue 
  • Autonomic (parasympathetic):
    • Lacrimal and salivary glands 


How do we test the facial nerve (CNVII)? 

  • Test muscles of facial expression 
  • Taste (check anterior 2/3rds of tongue)
    • This is not often formally tested 


Which other cranial nerve does the facial nerve (CNVII) have a close relationship with?

  • The vestibulocochlear nerve 


Describe Bell's palsy

  • This is facial nerve palsy 
  • Basically becuase of its complex route out of the skull it can become swollen or squashed leading to facial nerve/Bell's palsy 
  • This causes drooping of one side of the face 


Describe the route of the vestibulocochlear (CNVIII) nerve

  • Arises in the pons 
  • Goes through the internal acoustic meatus and terminates inside the ear inside the petrous part of the temporal bone 
  • Then gives branch to the semicircular canal (to do with balance) and a branch to the cochlea (to do with hearing) 


What is the function of the vestibulocochlea nerve (CNVIII)?

  • Special sensory nerve:
    • Cochlear bit allows hearing 
    • Vestibular part controls balance 


How do we test the vestibulocochlear nerve (CNVIII)?

  • Hearing 
  • Rinne's and Weber's test 


If the vestibulocochlear nerve is damaged what can this present as?

  • Hearing loss
  • Vertigo 
  • Tinnitus 


What is an acoustic neuroma?

  • Benign tumour that grows on CNVIII around the internal acoustic meatus
  • It can cause problems with hearing and balance and can cause tinnitus 
  • Because CNVIII is near the facial nerve if this is infiltrated by the tumour this can lead to facial weakness and numbness 


Describe the route of the glossopharyngeal nerve (CNIX) 

  • Arises from the anterior aspect of the medulla 
  • Leaves the cranium via jugular foramen
    • At this point the tympanic nerve arises (has mixed sensory and parasympathetic composition)
  • Extracranial glossopharyngeal nerve descends down the neck anterolateral to the carotid artery 
  • At inferior border of stylopharyngeus several branches arise to provide motor innervation to the muscle
    • Also gives rise to the carotid sinus nerve which provides innervation to carotid sinus and body
  • Nerve enters the pharynx by passing beetween superior and middle pharyngeal constrictors
  • Within pharynx it terminates and divides into terminal branches (lingual, tonsil and pharyngeal) 


Describe the function of the glossopharyngeal nerve (CNIX) 

  • General sensory role 
    • General sensation of soft palate, tonsils, oropharynx and the tympanic membrane (inner surface)
  • Special sensory
    • taste and general sensation of the posterior 1/3 of the tongue 
    • Sensory from the carotid body (signals sent to respiratory centres in the medulla from here) and sinus 
  • Autonomic 
    • From parotid gland
  • Motor
    • Stylopharyngeus


Why can you get referred pain to the ear if you have an infection at the back of the neck?

  • Due to their shared innervation (glossopharyngeal nerve, CNIX)


How do we test the glossopharyngeal nerve (CNIX)?

  • Gag reflex (sensory)
  • Taste is not often formally tested 
  • Tested in conjunction with CNX (provides motor aspect of the gag reflex) 


isolated lesions of which nerves are rare?

  • Glossopharyngeal (CNIX) and vagus (CNX) nerves 


Describe the route of the vagus nerve (CNX) 

  • Arises from the medulla and exits the skull through the jugular foramen then goes through the carotid sheath down the neck
  • Passes down into the abdomen and thorax to supply structures there


Describe the function of the vagus nerve (CNX) 

  • Sensory:
    • Laryngopharynx
    • Larynx
    • Small part to the ear
  • Motor:
    • muscles of the soft palate, pharynx and larynx
  • Autonomic (parasympathetic):
    • Thoracic and abdominal viscera 


How can the vagus nerve (CNX) be tested?

  • Note speech
  • swallow 
  • Cough
  • Gag relfex (this checks the efferent/motor limb)


What does damage to the vagus nerve (CNX) present with?

  • Deviation of the uvula when the soft palate is elevated (happens when you say 'ahhh')
  • Injury to the recurrent laryngeal nerve branch can cause hoarseness and dysphonia (difficulty speaking)


Describe the route of the spinal accessory nerve (CN XI) 

  • Arises from the medulla then goes through the jugular foramen with the glossopharyngeal and vagus nerve 


Describe the role of the spinal accessory nerve (CN XI) 

  • Purely motor:
    • innervates sternocleidomastoid and trapezius 


How do we test the spinal accessory nerve (CNXI)?

  • Test by shrugging shoulders
  • Turn head against resistance 


What is unusual about the spinal accessory nerve (CNXI)? 

  • It receives spinal rootlets from the upper 5/6 cervical segments of the spinal cord; these ascend up the foramen magnum to join the cranial root


Where is the spinal accessory (CNXI) nerve susceptible to injury?

  • In the posterior triangle e.g. lymph node biopsies, stab wounds etc. 


Describe the route of the hypoglossal nerve (CNXII) 

  • Arises from the medulla and passes through the hypoglossal canal 
  • Runs medial to the angle of the mandible and across the internal and external carotid arteries in the neck


What is the function of the hypoglossal nerve (CNXII)? 

  • Purely motor function 
  • Supplies all the muscles of the tongue
  • Each nerve of the pair supplies half of the tongue each 


Why we must be careful when operating on the external and internal carotid arteries? 

  • The hypoglossal nerve (CNXII) runs over these arteries 


How do you test the hypoglossal nerve (CN XII)?

  • Test by inspection of the tongue and by checking the movement of the tongue


Lesions to the hypoglossal nerve are rare. If they occur what do they cause?

  • Weakness and atrophy of the tongue on the ipsilateral side


Which cranial nerves arise from the following areas? 

  • Forebrain 
  • Brainstem:
    • Midbrain
    • Pons  
    • Medulla

  • Forebrain 
    • CNI (olfactory)
    • CNII (optic)
  • Midbrain 
    • CNIII (occulomotor) 
    • CNIV (Trochlear)
  • Pons
    • CNV (trigeminal)
    • CNVI (abducens)
    • CNVII (facial)
    • CNVIII (vestibulocochlear)
  • Medulla:
    • CNIX (glossopharyngeal)
    • CNX (vagus)
    • CNXI (spinal accessory) 
    • CNXII (hypoglossal) 


Are the cranial nerves part of the peripheral or central nervous system?

  • Peripheral nervous system (like spinal nerves) 


What must we remeber about cranial nerves when we think about the areas they innervate?

  • They are all pairs so each nerve itslef only innervates half of the face 


What are differences between cranial and spinal nerves?

  • Cranial nerves arise from the brainstem (except CNI and CNII which arise from the brain
    • Spinal nerves arise from the spinal cord
  • CN arise at irregular intervals from the CNS 
    • Spinal nerves arise in segments 
  • Nerves carry 1000s of axons
    • In spinal nerves all of the nerves have mixed sensory and motor function 
    • In CN some are  mixed but some are also purely sensory or motor 


The numbers of the CN tend to be the order they arise from rostal to caudal. What is the exception?

  • CNXII which arises rostrally to CNXI and CNX 


As the medulla passes through the foramen magnum what does it become?

The spinal cord (these are functionally very different things) 


What are the 3 parts of the brainstem? What is it continuous with caudally and rostrally?

  • Midbrain 
  • Pons
  • Medulla 

Rostrally in contact with the forebrain. Caudally continuous with the brainstem 


The brainstem is the location of the majority of cranial nerve nuclei. What is a nuclei?

  • Collections of the cell bodies of nerve fibres that make up the whole cranial nerve 


What do all strucutres which innervate the eye pass through? What is the exception?

  • The superior orbital fissure
  • The optic nerve (CNII) which passes through the optic canal 


What are the cavernous sinuses? Where do they receive blood from?

  • Clinically important pair of dural sinuses. They are next to the lateral aspect of the body of the sphenoid bone 
  • It receives blood from:
    • the superior and inferior ophthalmic veins
    • Middle superficial cerebral veins 
    • Another dural sinus- the sphenoparietal sinus


What is within the cavernous sinus?

  • Internal carotid artery (crosses the sinus)
    • This allows for cooling of arterial blood before it reaches the brain
  • Abducens nerve (CNVI) (crosses the sinus)
  • Within the lateral wall of each sinus:
    • Occulomotor (CNIII) 
    • Trochlear (CN IV) 
    • Ophthalamic (CNV1)
    • Maxillary (CNV2)


What connects the facial vein to the cavernous sinus? What can this cause?

  • Connected via the superior ophthalamic vein 
  • Facial vein is valveless so blood can reverse direction and flow from the facial vein into the cavernous sinus
  • This provides a pathway by which infection of the face can spread to the venous sinuses 


Which arteries do the right and left recurrent laryngeal nerves turn under?

  • Right recurrent laryngeal nerve 
    • Under right subclavian artery 
  • Left recurrent laryngeal nerve
    • Under the arch of aorta 


  1. Olfactory 
  2. Occulomotor 
  3. Trochlear
  4. Abducens
  5. Vestibulocochlear
  6. Hypoglossal
  7. Cranial accessory 
  8. Optic 
  9. Trigeminal 
  10. Facial
  11. Glossopharyngeal 
  12. Vagus 


Label the nerves of the cavernous sinus 

  1. Occulomotor nerve (CNIII) 
  2. Trochlear nerve (CN IV)
  3. Ophthalamic nerve (CN V1)
  4. Abducen nerve (CNVI)
  5. Maxillary nerve (CNV2)


which cranial nerves pass into the orbit?

  • Optic 
  • Occulomotor
  • Trochlear
  • Ophthalamic branch of trigeminal 
  • Abducens 


How can you remember the names and numbers of the cranial nerves?

  • Ooo (olfactory (CNI))
  • Ooo (optic (CNII))
  • Ooo (occulomotor (CNIII))
  • To (trochlear (CNIV))
  • Touch (trigeminal (CNV))
  • And (abducens (CNVI))
  • Feel (facial (CNVII))
  • Virgin (vestibulocochlear (CNVIII))
  • Girls (Glossopharyngeal (CNIX))
  • Vaginas (Vagus (CNX))
  • And (accessory (CNXI))
  • Hymen (Hypoglossal (CNXII))


What can you use to remember whether each of the cranial nerves are sensory, motor or both?

  • Some (CNI)
  • Say (CNII) 
  • Marry (CNIII)
  • Money (CNIV)
  • But (CNV)
  • My (CNVI)
  • Brother (CNVII)
  • Says (CNVIII)
  • Big (CNIX)
  • Boobs (CNX)
  • Matter (CNXI)
  • Most (CNXII) 


what can you use to remember which foramina each of the cranial nerves pass through?

  • Come (CNI)- cribriform plate 
  • Over (CNII)- optic canal
  • Soon (CNIII)- superior orbital fissure 
  • Soon (CNIV)-  superior orbital fissure
  • Soon (CNV1)- superior orbital fissure
  • Ride (CNV2)- foramen rotundum 
  • On (CNV3)- foramen ovale
  • Some (CNVI)- superior orbital fissure 
  • Intense (CNVII)- Internal acoustic meatus
  • Internal (CNVIII)- Internal acoustic meatus
  • VaJ (CNIX)- jugular foramen 
  • J (CNX)- jugular foramen 
  • J (CNXI)- jugular foramen 
  • Ha! (CNXII)- hypoglossal canal