6) Cranial Nerves Flashcards
How many cranial nerves are there?
Are they part of the CNS or PNS?
12
Part of peripheral nervous system
What are the 3 parts of the brainstem?
Mid-brain, pons and medulla oblongata
What is the role of the brainstem?
Regulation of cardio-respiratory functions and maintaining consciousness
What is cranial nerve I?
Olfactory nerve
What is the function of CN I?
Sense of smell
How would you test CN I?
Test one nostril at a time using smelling salts
What can damage to the olfactory nerve result in?
Anosmia (loss of sense of smell)
What are the causes of anosmia?
URTI
Head injury e.g. basilar skull fracture
Neurodegenerative conditions e.g. Parkinson’s and Alzheimer’s
Describe the route of CN I:
Through foramina of cribriform plate onto olfactory mucosa in roof of nose
What is cranial nerve II?
Optic nerve
What is the function of CN II?
Vision
How would you test CN II?
Test one eye at a time Visual tests (acuity and fields) and puplis
Describe the route of CN II:
Crossover at optic chiasm, through optic canal to retina
What visual problems can a pituitary adenoma cause and why?
Bilateral visual problems due to compression of optic chiasm
Which cranial nerves arise from the forebrain?
Olfactory and optic nerves
What is cranial nerve III?
Oculomotor nerve
What are the functions of CN III?
Innervate extra-ocular nerves (4/6)
PSNS to pupil causes constriction
How would you test CN III?
Eye movements
Pupillary light reflexes
Describe the route of CN III:
Through cavernous sinus and superior orbital fissure into orbit
How does damage to the oculomotor nerve present?
Diplopia (double vision) and eye is in down and out position (blown pupil)
Due to damage to PSNS before cranial nerve
What are the causes of oculomotor nerve lesions?
Raised intracranial pressure
Aneurysms
Cavernous sinus thrombosis
Diabetes/hypertension (pupil sparing)
What is cranial nerve IV?
Trochlear nerve
What is the function of CN IV?
Innervation of extra-ocular muscle - superior oblique
How would you test CN IV?
Patient follows finger and reports double vision
Describe the route of CN IV:
Arises from dorsal aspect of brainstem and travels through cavernous sinus and superior orbital fissure
How does damage to the trochlear nerve present?
Diplopia, worse on downward gaze
What are the causes of trochlear nerve lesions?
Head injury
Raise ICP, stretching nerve
Congenital palsies
What is cranial nerve V?
Trigeminal nerve
What are the functions of CN V?
Innervate muscles of mastication
Main sensory to face
How would you test CN V?
Sensation to face
Muscles of mastication
Corneal reflex
Describe the route of CN V:
V1 ophthalmic - superior orbital fissure
V2 maxillary - foramen rotundum
V3 mandibular - foramen ovale
What can cause trigeminal nerve lesions?
Trigeminal neuralgia
Shingles
How does damage to the trigeminal nerve present?
Absent corneal reflex
Absent sensation
Weakness/wasting of muscles of mastication
What nerves can be damaged through facial trauma?
Hint: from trigeminal nerve
Intra-orbital (V2) and mental (V3)
Travel superficially
What is cranial nerve VI?
Abducens nerve
What is the function of CN VI?
Innervation of extra-ocular muscle - lateral rectus
How would you test CN VI?
Patient follows finger and reports double vision
Describe the route of CN VI:
Through cavernous sinus and superior orbital fissure into orbit
What can cause damage to abducens nerve?
Nerve can be easily stretched in raised ICP due to running under surface of pons
How does damage to abducens nerve present?
Diplopia
Eye can’t be abducted past midline
What nerves arise from the midbrain?
Oculomotor and trochlear nerves
What nerves arise from the pons?
Trigeminal, abducens, facial and vestibulocochlear nerves
What nerves arise from the medulla oblongata?
Glossopharyngeal, vagus, spinal accessory and hypoglossal nerves
What is cranial nerve VII?
Facial nerve
What are the functions of CN VII?
Muscles of facial expression
Anterior 2/3rd of tongue (taste)
PSNS to lacrimal and salivary glands
How would you test CN VII?
Muscles of facial expression
Describe the route of CN VII:
Through petrous part of temporal bone via internal acoustic meatus, gives off branches and travels through stylomastoid foramen to give off terminal branches
What can cause damage to facial nerve and how does it present?
Bell’s palsy
Parotid tumours
Ipsilateral paralysis of muscles
What is cranial nerve VIII?
Vestibulocochlear nerve
What are the functions of CN VIII?
Hearing and balance
How would you test CN VIII?
Hearing test
Rinne’s and Weber’s test
Describe the route of CN VIII:
Through internal acoustic meatus and terminates in ear
What is an acoustic neuroma?
Benign tumour growing on nerve
How does damage to vestibulocochlear nerve present?
Hearing loss
Vertigo/tinnitus
What is cranial nerve IX?
Glossopharyngeal nerve
What are the functions of CN IX?
Sensation or soft palate, tonsils and oropharynx
Taste and sensation of posterior 1/3rd of tongue
Sensory from carotid body and sinus
Autonomic to parotid gland
Innervates stylopharyngeus
How would you test CN IX?
Gag reflex
Describe the route of CN IX:
Through jugular foramen
What is cranial nerve X?
Vagus nerve
What are the functions of CN X?
Sensory to laryngopharynx and larynx
Innervates muscles of soft palate, pharynx and larynx
PSNS to thoracic and abdominal viscera
How does damage to the vagus nerve present?
Deviation of uvula when soft palate is elevated (say Aaah)
Recurrent laryngeal branch - hoarseness and dysphonia
What is cranial nerve XI?
Spinal accessory nerve
What are the functions of CN XI?
Innervate SCM and trapezius
How would you test CN XI?
Shrug shoulder
Turn head against resistance
Describe the route of CN XI:
Through jugular foramen
What anatomical area does the spinal accessory nerve run through and how can it be damaged?
Posterior triangle
Lymph node biopsies and stab wounds
What is cranial nerve XII?
Hypoglossal nerve
What are the functions of CN XII?
Innervate muscles of the tongue
How would you test CN XII?
Inspection and movement of the tongue
Describe the route of CN XII:
Through hypoglossal canal
How does damage to the hypoglossal nerve present?
Weakness and atrophy of the tongue muscles on same side
