Topic 7 - Cranial Nerves Flashcards
What are the clinical consequences of facial nerve palsy?
- Weakness/paralysis of muscles of facial expression
- Depending on location of lesion
- Chorda tympani - reduced salivation, loss of taste on ispilateral posterior 2/3 of tongue
- Nerve to stapedius - ipsilateral hyperaccusis (hypersensitive to sound)
- Greater petrosal nerve - ipsilateral reduced lacrimal fluid production
Where does the vagus nerve exit the cranium?
Jugular foramen
What is the function of the mandibular nerve?
- General sensory of anterior 2/3 of tongue, skin over mandible, lower teeth
- Motor - muscles of mastication
List the divisions of the trigeminal nerve
- Ophthalmic
- Maxillary
- Mandibular
Where does the ophthalmic division of the trigeminal nerve exit the skull?
Superior orbital fissure
How is the function of the glossopharyngeal nerve tested clinically?
With the vagus nerve
Where does the mandibular division of the trigeminal nerve exit the skull?
Foramen ovale
Why should irritating substances not be used when testing the function of the olfcatory nerve?
Irritants would stimulate the trigeminal nerve as well as the olfactory nerve, giving a false result
Where does the glossopharyngeal nerve exit the cranium?
Jugular foramen
List the cranial nerves
- Olfactory nerve
- Optic nerve
- Oculomotor nerve
- Trochlear nerve
- Trigeminal nerve
- Abducens nerve
- Facial nerve
- Vestibulocochlear nerve
- Glossopharyngeal nerve
- Vagus nerve
- Accessory nerve
- Hypoglossal nerve
Describe the function of the olfactory nerve
Smell
How are the oculomotor, trochlear and abducens nerves tested clinically?
- Observe normal position of eye (deviation/strabism) and look for spontaneous movements (nystagmus)
- Eye movements - draw H shape with finger, movement should be free and coordinated
Describe the treatment of vestibular schwannomas
Surgery
- Risks of damaging vestibulocochlear nerve and causing loss of hearing
- Also risk damaging surrounding structures e.g. facial nerve
- Use retrosigmoid approach (from behind sigmoid sinuses) to try to preserve hearing
Radiation
Observation - if small and slow growing
Where does the trochlear nerve exit the skull?
Superior orbital fissure
Describe the appearance of an eye with an abducens nerve lesion
Reduced abduction, eye positioned laterally
How is the oculomotor nerve tested clinically?
With the trochlear and abducens nerves
Where does the maxillary division of the trigeminal nerve exit the skull?
Foramen rotundum
Describe the function of the accessory nerve
Innervation of the trapezius and sternocleidomastoid muscles
What is the function of the abducens nerve?
Innervates the lateral rectus muscle
How can an upper and lower motor neuron lesion affecting the face be distinguished?
Upper motor neuron e.g. stroke shows forehead sparing due to bilateral innervation of the forehead
Describe the anatomical course of the facial nerve
- Arises in pons - large motor and small sensory root
- Roots travel through internal acoustic meatus in temporal bone
- Enter facial canal (Z-shaped), roots fuse to give facial nerve, forms geniculate ganglion and gives off the greater petrosal nerve, nerve to stapedius and chorda tympani
- Exits cranium via stylomastoid foramen
- Gives off branches - posterior auricular nerve, nerve to posterior belly of digastric muscle and stylohyoid muscle
- Motor root continues to parotid gland, splits to form 5 terminal branches
Describe the function of the trochlear nerve
Innervates the superior oblique muscle
Where does the accessory nerve exit the cranium?
Jugular foramen
Where does the abducens nerve exit the skull?
Superior orbital fissure
How is the function of the trigeminal nerve tested clinically?
- Sensory
- Light touch in all 3 areas (forehead, cheek, jaw) w/ wisp of cotton wool
- Motor
- Clench teeth - palpate temporalis and massester muscles
- Open mouth - deviation shows weakness of pterygoid muscles
- Jaw jerk reflex
- Corneal reflex - touch cornea with wisp of cotton wool while looking away, normal response is blinking (sensory innervation)
Describe the management of Meniere’s disease
- No cure, manage symptoms
- Dietary changes, salt restriction, diuretics
- Gentamicin injection - risk of hearing loss
- Pressure pulse treatment
- Surgery - cut nerve (rare)
Ramsey-Hunt Syndrome
- Unilateral facial palsy caused by Herpes Zoster virus, reactivation of Varicella zoster virus from geniculate nucleus
- Severe ear pain, facial palsy, vertigo, hyperaccusis, tinnitus
- Vessels of concha, anterior 2/3 tongue, soft palate become visible
What is Meniere’s Disease?
- Inner ear disorder
- Causes tinnitus, vertigo, partial deafness
- No definitive cause known - excess fluid in inner ear
Describe the pathology of a vestibular schwannoma
- Benign, usually slow growing tumour that develops through overproduction of schwann cells around the vestibular/cochlear nerves
- Causes damage to nerves through compression - hearing loss, tinnitus, vertigo
- Can also affect
- Trigeminal nerve - loss of face sensation
- Facial nerve - weakness/paralysis of muscles of facial expression
- Glossopharyngeal/vagus nerves - swallowing difficulties, loss of gag reflex
Describe the function of the glossopharyngeal nerve
- General sensation to posterior 1/3 tongue, external ear, middle ear, carotid body and sinuses
- Taste from posterior 1/3 tongue
- Parotid gland - parasympathetic innervation
- Motor - stylophyaryngeus muscle
Where does the hypoglossal nerve exit the cranium?
Hypoglossal canal
Describe the appearance of an eye with an oculomotor nerve lesion
Ptosis, down and out deviation, fixed and dilated pupil
Describe the appearance of an eye with a trochlear nerve lesion
Torsional (rotational) diploplia, compensatory tilted head
Describe the management of facial nerve palsy
- Most return to normal sponanteously
- Eye care - drops, tarsorrhaphy
- Oral steroids
List the terminal branches of the facial nerve
- Temporal
- Zygomatic
- Buccal
- Marginal mandibular
- Cervical
Describe the function of the vestibulocochlear nerve
- Vestibular fibres - balance
- Cochlear fibres - hearing
Describe the function of the vagus nerve
- Sensory - external ear, larynx, pharynx and thoracic/abdominal viscera
- Taste from epiglottis region of tongue
- Smooth muscle of pharynx, larynx and most of GI tract
Describe how facial nerve function is tested clinically
Motor - raise eyebrows, tightly close eyes, puff out cheeks, purse lups, show teeth
Corneal reflex (motor innervation)
Sensory - change in taste/hearing
Where does the olfactory nerve exit the skull?
Cribiform foramina of the cribiform plate
Describe the anatomical course of the vestibulocochlear nerve
- Vestibular branch from vestibular nuclei complex in pons/medulla, cochlear branch from ventral + dorsal cochlear nuclei in inferior cerebellar peduncles
- Combine in pons, exits cranium via internal acoustic meatus
- Splits in distal internal acoustic meatus, vestibular branch to vestibular organs of inner ear, cochlear to cochlea of inner ear, forming the spiral ganglion
Describe the function of the ophthalmic nerve
Sensory innervation of the scalp, forehead and nose
Why is it important to consider the eye in facial nerve palsy?
Orbicularis oculi muscle supplied by temporal/zygomatic branches of the facial nerve, facial nerve palsy results in inability to close the eye properly, leads to drying of the cornea and damage
Where does the oculomotor nerve exit the skull?
Superior orbital fissure
What is the function of the maxillary nerve?
Sensory innervation of the cheeks, lower eyelid, nasal mucosa, upper lip and teeth and palate
How is the function of the vagus nerve tested clinically?
- With the glossopharyngeal nerve
- Speech - hoarseness/difficulty pronouncing sounds (dysphonia)
- Swallowing (dysphagia)
- Position of palate and uvula (deviation = lesion on opposite side to deviation)
- Gag reflex - not usually done
List the causes of facial nerve palsy
- Middle ear pathology - tumour/infection
- Parotid gland pathology - tumour, parotitis, surgery
- Idiopathic (Bell’s palsy) - viral, diabetes mellitus, pregnancy
- Ramsey-Hunt syndrome
How is the function of the accessory nerve tested clinically?
Raised shoulders and turn cheek against resistance
How is the function of the optic nerve tested clinically?
- Visual field - cover one eye, move finger in all 4 quadrants
- Peripheral fields - move fingers in upper and lower quadrants at periphery, say which finger moves
- Visual acuity - cover one eye and read letters from Snellen chart (start at 6m away, wear glasses if needed)
- Pupil reflexes - direct and consensual responses, swinging flashlight test
Describe the function of the optic nerve
Visual acuity and visual fields
Describe the function of the facial nerve
- Motor (derivatives of 2nd pharyngeal arch)
- Muscles of facial expression
- Posterior belly of digastric muscle
- Stylohyoid muscle
- Sensory
- Area around concha
- Special sensory
- Taste to anterior 2/3 of tongue (chorda tympani)
- Parasympathetic
- Submandibular and sublingual salivary glands (chorda tympani)
- Nasal, palatine and pharyngeal mucous glands
- Lacrimal glands
How is the function of the vestibulocochlear nerve tested clinically?
- Hearing
- Whisper voice test - each ear individually, need 3/6 to pass
- Audiometry
- Rinne test - air vs bone conduction, normal = air > bone, abnormal suggests conductive hearing loss
- Weber test - test symmetrical inner ear function, press tuning fork against forehead
- Balance
- March on spot with eyes closed - turn to side of lesion
- Test vestibulocochlear reflex - turn head quickly
How is the olfactory nerve tested clinically?
Smell tested in each nostril separately, stimuli should be non-irritating and easily identifiable e.g. cinnamon, toothpaste
Describe the function of the oculomotor nerve
Innervates 4 extrinsic eye muscles, levator palpebrae superioris muscle and the pupillary sphincter
Describe the function of the hypoglossal nerve
Innervates the intrinsic and extrinsic muscles of the tongue (except the palatoglossus)
How is the trochlear nerve tested clinically?
With the oculomotor and abducens nerves
Where does the optic nerve exit the skull?
Optic canal
How is the function of the hypoglossal nerve tested clinically?
Stick tongue out - check for deviation (deviates to weak side if lesion)
