Cranial nerves Flashcards
Define nuclei
Collection of cell bodies
How many cranial nerves arise from the forebrain?
Two:
CN I - Olfactory
CN II - Optic
How is sensory information transmitted from the nasal cavity to the Olfactory nerve nucleus?
The receptors are located in the epithelium right at the top of our nasal cavity. They pass up through the roof of the nose and pass through the cribiform foramina in the cribiform plate. They then meet the olfactory bulbs which sits on top of the cribiform plate. The olfactory tracts then take it to the forebrain.
What is the function of the olfactory nerve?
Special sensory - smell
What is the name for loss of sense of smell?
anosmia
Name the causes of a loss of sense of smell
Common cold
Head injury - secondary to shearing forces and/or basilar skull fracture
Intracranial tumours at the base of the frontal lobes
Describe the path of the optic nerve
It leaves the orbit through the optic canal. It enters the cranial cavity and runs along the middle cranial fossa in close proximity to the pituitary gland. The optic nerves from each eye then mix at the optic chiasm. They then form optic tracts which travel to reach the lateral geniculate nucleus (a relay centre in the thalamus). The LGN then tranfers information to the primary visual cortex through the optic radiations.
What is the function of the optic nerve?
Special sensory - vision
How do we clinically test the optic nerve?
Visual tests - visual fields and Snellen charts
Pupillary light reflexes
We can also examine the optic nerve using fundoscopy
Why does the optic nerve swell in raised ICP?
It carries extensions of the meninges
What is the name given to a swollen optic disc observed in raised ICP?
Papillodema
Name the pattern of visual loss seen in a pituitary tumour
Bitemporal hemianopia
Where would a lesion be if visual loss was found in one eye?
The retina or optic nerve -once at the optic chiasm visual loss would be seen in both eyes.
Describe the route of the occulomotor nerve (CN III)
It runs from the midbrain through the cavernous sinus and exits into the orbit through the superior orbital fissure.
What are the functions of the occulomotor nerve?
Motor - supplies most of the extra-ocular muscles and LPS
Autonomic - supplies sphincter pupillae and the cilliary muscle
Describe how the occulomotor nerve can be affected by raised ICP.
The oculomotor nerve runs under the attachment for the tentorium cerebelli. Therefore, when you get raised intracrainal pressure the uncus of the temporal lobe can slip over the tentorium cerebelli and compress the oculomotor nerve.
What is the first sign of occulomotor nerve compression as a consequence of raised ICP?
Blown pupil
The parasympathetic fibres sit around the edge. When you get external compression these will be affected and you will get problems with pupil size and lens size. This is what happens when you get a blown pupil that is dilated. If you continue to compress the nerve, then the other functions will be lost.
How do you test the occulomotor nerve?
Inspect the eyelid and pupils
Eye movements
Pupillary light reflexes
What is the sign of a CN III palsy?
Pupil in the ‘down and out’ position with severe ptosis
What are the causes of a CN III palsy?
Raised intracranial pressure (tumour/haemorrhage)
Anneurysms (posterior communicating artery)
Vascular (secondary to diabetes/hypertension - typically pupil sparing)
Cavernous sinus thrombosis
What is the function of the trochlear nerve (CN IV)?
Motor - supplies superior oblique
Describe the path of the trochlear nerve?
The trochlear nerve also comes off the midbrain and runs through the cavernous sinus. It also exits the superior orbital fissure
What are the clinical signs of a CN IV palsy?
Diplopia (worse on a downward gaze)
Patients often correct the diplopia by tilting their head
What are the most common causes of a CN IV palsy?
Head injury - raised ICP
Congenital palsies in children
Name the three divisions of the trigeminal nerve
Opthalmic (Va) - runs through the superior orbital fissure and supplies sensation to the cornea and conjunctiva of the eye
Maxillary (Vb) - supplies the cheek
Mandibular (Vc) - supplies the jaw
What are the functions of the trigeminal nerve?
Main sensory nerve of the skin of the face and facial structures. It also supplies muscles of mastication (the mandibular branch mainly carries the motor supply for the muscles of mastication)
Name the afferent and efferent arm of the corneal reflex
afferent - trigeminal (V)
efferent - facial (VII)
Which nerve is vulnerable in an orbital blow out fracture?
Infraorbital nerve - branch of the maxillary division of the trigeminal nerve.
The patient will have reduced sensation in the area of the cheek just underneath their orbit
Which branch of the CN Vc is vulnerable in a fracture of the mandible and how will the patient present?
The inferior alveolar nerve
The patient will present with numbness of the lip and chin on the effected side and numbness over their gums and teeth.
The inferior alveolar nerve runs through the bone of the mandible. It enters the bone through the mandibular foramen. It eventually emerges as the mental nerve out of the mental foramen (that is what gives you sensation to your lip and chin.)
Which nerve is often numbed in addition to the alveolar nerve when dentists administer local anaesthetic?
The lingual nerve
Patients get a numb tongue as the alveolar nerve runs in close proximity to the lingual nerve and supplies sensation to the anterior 2/3 of the tongue.
What is the function of the abducens nerve (CN VI)
Motor - supplies lateral rectus
Describe the route of CN VI
The abducens nerve arises from the pons. It runs through the cavernous sinus and through the superior orbital fissure to supply the lateral rectus that abducts the eye
Explain why the abducens nerve is vulnerable when ICP is raised.
The nerve can be easily stretched in raised ICP due to emerging anteriorly at the ponto-medullary junction before running under the surface of the pons towards the cavernous sinus.
Where does CN VII give off its terminal branches?
The parotid gland
What are the functions of the facial nerve?
Motor - muscles of facial expression
Special sensory - taste to the anterior 2/3 of the tongue
Autonomic - parasympathetics to the lacrimal glands and salivary glands
Name the terminal branches of the facial nerve
Temporal (To) Zygomatic (Zanzibar) Buccal (By) Mandibular (Motor) Cervical (Car)
What is the name for an idiopathic facial nerve palsy?
Bell’s palsy
How do we test the facial nerve?
Test muscles of facial expression
Corneal reflex (efferent limb)
Taste (not formally tested, but you can ask about this)
Where in the brain is the primary auditory cortex?
Temporal lobe
What is the function of the vestibulocochlear nerve?
Special sensory - hearing/balance
How is the ventibulocochlear nerve tested?
Rines and Webers tests
Enquire about balance
What type of hearing loss would result from damage to the vestibulocochlear nerve, its nucleus or the cochlea?
Sensorineural
What are the symptoms of damage to the semicircular canals, vestibulococlear nerve or its nucleus?
vertigo and nystagmus
What is the name for old-age related hearing loss?
Presbyacusis
What is the name for a benign tumour involving CN VIII
Acoustic neuroma
What are the symptoms of an acoustic neuroma?
Unilateral hearing loss
Tinnitis
Vertigo
Numbness, pain and weakness down one side of the face
Which cranial nerves arise from the medulla
Glossopharyngeal
Vagus
Accessory
Hypoglossal
Describe the route of the glossopharyngeal nerve
The route of the glossopharangeal nerve runs from the lateral aspects of the medulla through the jugular foramen. It then descends down the neck before heading to parts of the tongue and the pharynx.
Why is it possible to get referred pain in the ear during a respiratory tract infection?
The glossopharyngeal nerve innervates both the pharynx and part of the ear and eardrum
Which nerve senses pressure in a carotid sinus massage?
The glossopharyngeal nerve
it also has some chemoreceptor function in the carotid body
Describe the innervation to the tongue
Anterior 1/3 - taste is supplied by facial nerve and sensation is supplied by the trigeminal nerve.
Posterior 1/3 – taste and general sensation is supplied by the glossopharyngeal nerve
Which nerve supplies the afferent limb of the gag reflex?
Glossopharyngeal nerve
Which nerve supplies the efferent limb of the gag reflex?
Vagus nerve
Describe the functions of the vagus nerve
Motor - supplies the muscles to the soft palate, pharynx and larynx
Sensory - lower pharynx and larynx
Autonomic - parasympathetic supply to the thoracic and abdominal viscera.
Describe the route of the vagus nerve
The vagus nerve originates from the medulla and then travels through the jugular foramen into the neck. It then travels down the length of the carotid sheath behind the artery and vein. It gives off various branches in the neck, but continues down to give down more branches to the thoracic and abdominal viscera.
Which nerves supply the vocal cords?
Left and right recurrent laryngeal nerve (branches of the vagus nerve)
How can an injury to the recurrent laryngeal nerve present?
Hoarsness of voice and dysphonia
How do we test the vagus nerve?
Ask the patient to say ‘ahhh’ and observe the uvula - there should be equal rise of the soft palate muscles on each side, keeping the uvula in the middle. If the uvula is deviated this indicates a lesion (uvula will deviate away from the side of the lesion)
The gag reflex
Noting speech
Swallow and cough
What is the function of the accessory nerve?
Motor - supplies SCM and trapezius
Describe the root of the accessory nerve
The accessory nerve has two roots. One comes off the medulla and the other from the spinal cord. The root that comes from the spinal cord comes up through foramen magnum to join the medullary root. It then exits through the jugular foramen to supply the neck.
(The cranial root joins the vagus nerve)
Which nerve is vulnerable in injuries to the posterior triangle?
The accessory nerve
How is the accessory nerve tested?
Shrug shoulders against resistance
Turn head against resistance
Describe the route of the hypoglossal nerve
It arises from the medulla and exits through the hypoglossal canal on the side of foramen magnum. It exits towards the floor of the tongue.
It then runs medial to the angle of the mandible and crosses the ICA and ECA.
What is the function of the hypoglossal nerve?
Motor - supplies the muscles of the tongue
How do we inspect the hypoglossal nerve?
Examine the movement of the tongue. Damage to the hypoglossal nerve will cause weakness and atrophy of the tongue muscles on the ipsilateral side.
