Cranial Nerves Flashcards
What are the 3 regions of the brainstem?
Midbrain
Pons
Medulla
What are nuclei in the brain?
Collections of the cell bodies of nerve fibres
How many cranial nerves arise from the brain itself (forebrain)?
2
How many cranial nerves arise from the midbrain?
2
How many cranial nerves arise from the pons?
4
How many cranial nerves arise from the medlla?
4
What is the mneumonic to help remember how many cranial nerves arise from different regions of the brain/brainstem?
2, 2, 4, 4
2 arise from forebrain
2 arise from midbrain
4 arise from pons
4 arise from medulla
Which 2 cranial nerves arise from the forebrain?
Olfactory and optic
CN I and II
How many cranial nerves arise from the brainstem?
10 (III- XII)
What kind of information does the olfactory nerve transmit?
Special sensory
What is the function of the olfactory nerve?
Smell
What is the route and relation of the olfactory nerve to the CNS?
Olfactory nerve -> cribiform foramina -> olfactory bulb -> olfactory tracts -> forebrain
What is anosmia?
The absence of the sense of smell
What skull base cavity does the olfactory nerve (CN I) travel through?
Crimiform foramina of cribiform plate
What is the target tissue of the olfactory nerve?
Mucosal membrane roof of nasal cavity
How is the olfactory nerve tested?
Enquiry about sense of smell, smelling salts
What kind of information does the optic nerve transmit?
Special sensory
What skull base cavity does the optic nerve (CN II) pass through?
Optic canal
What does the anatomical course of the optic nerve describe?
Transmission of special sensory information from the retina to the primary visual cortex
What happens at the optic chiasm?
Optic nerves cross over
What is the point at which the optic nerve enters the retina?
Optic disc
Why can the optic nerve swell due to raised ICP?
Carry extension of meninges - can see evidence of raised ICP on fundoscopy as a swollen optic disc
What would lesions involving the retina or the optic nerve cause?
Visual disturbance affecting only one eye
Where is the primary visual cortex?
Occipital lobe
Why do pituitary tumours cause bilateral visual symptoms?
Compress optic chiasm - both eyes affected
What does the pituitary gland lie in close proximity to?
Optic chiasm (in middle cranial fossa)
What would a patient with bitemporal hemianopia describe?
Tunnel vision (visual defect affecting the peripheral vision in both eyes)
In which bone is the optic chiasm?
Sphenoid
Which two cranial nerves arise from the midbrain?
Oculomotor and Trochlear
CN III and IV
What kind of information does the oculomotor nerve (CN III) transmit?
Motor and autonomic (parasympathetic)
What motor function does the oculomotor nerve serve?
Innervates most extraocular muscles
What do the autonomic components of the oculomotor nerve do?
Supplies sphincter pupillae (pupil) and ciliary muscle (lens)
What are the functions of the oculomotor nerve?
Eye movements, pupil constriction, eyelid opening
What foramen does the oculomotor nerve (CN III) pass through?
Superior orbital fissure
Describe the route of the oculomotor nerve
From the midbrain, runs through lateral wall of cavernous sinus, exits through the SOF, into orbit
What are the three main causes of an oculomotor nerve lesion?
1) Increasing ICP - uncus can squish tentorium cerebelli and thus CN III which is in close proximity
2) Aneurysm of the posterior cerebral artery
3) Cavernous sinus infection or trauma
Why can cavernous sinus infection cause damage to CN III?
Oculomotor nerve runs through the lateral wall of the cavernous sinus
What are the clinical signs of CN III injury?
Oculomotor nerve lesion
1) ptosis - due to paralysis of levator pulpabrae superioris
2) eyeball is down and out - paralysis of rectus muscles and inferior oblique
3) dilated pupil - due to unopposed action of dilator pupillae (can’t costrict)
How is CN III tested?
Inspection of eyelid and pupils, eye movements, pupillary light reflexes
What kind of information is transmitted by the trochlear nerve (CN IV)?
Motor
What is the only nerve to emerge from the dorsal aspect of the brainstem?
Trochlear (CN IV)
Which cranial nerve has the longest intracranial course?
Trochlear (CN IV)
Describe the course of the trochlear nerve
Arises from posterior aspect of midbrain, runs within the subarachnoid space, moves along lateral wall of cavernous sinus, enters orbit of eye via the SOF
Which foramen does the trochlear nerve pass through?
Superior orbital fissure
What single muscle does the trochlear nerve innervate?
Superior oblique
What is the function of the trochlear nerve?
Innervates one extraorbital muscle - superior oblique
What is the overall action of the superior oblique?
Depress and intort the eyeball
How is the trochlear nerve examined?
By testing movements of the eye (eg patient asked to follow a point with their eyes without moving their head)
What is diplopia?
Double vision
How does trochlear nerve palsy present?
Vertical diplopia - exacerbated by looking down and in
Patients can also develop a head tilt away from affected side
Which four cranial nerves arise from the pons?
Trigeminal (CN V)
Abducens (CN VI)
Facial (CN VII)
Vestibulocochear (VIII)
What is the largest cranial nerve?
Trigeminal (CN V)
What kind of information does the trigeminal nerve transmit?
Sensory (all 3 branches) and motor (mandibular branch)
Which branch of the trigeminal nerve has motor fibres?
Mandibular
What is the motor function of the trigeminal nerve?
Mandibular nerve innervates muscles of mastication
What is the sensory function of the trigeminal nerve?
All branches innervate the skin, mucous membranes and sinuses of the face
Which foramen does the opthalmic branch of the trigeminal nerve pass through?
Superior orbital fissure
Which foramen does the maxillary branch of the trigeminal nerve pass through?
Foramen rotundum
Which foramen does the mandibular branch of the trigeminal nerve pass through?
Foramen ovale
What nerve is responsible for the afferent limb of the corneal reflex?
Opthalmic division of the trigeminal nerve (detects the stimuli)
What is the corneal reflex?
Involuntary blinking of the eyelids - stimulated by tactile, thermal or painful stimulation of the cornea
What nerve is responsible for the efferent limb of the corneal reflex?
Facial nerve (contraction of orbicularis ocli muscle)
What is an absent corneal reflex a sign of?
Opthalmic/trigeminal or facial nerve damage
What are the four terminal branches of the mandibular nerve?
Mandibular nerve is a division of the trigeminal nerve
Its terminal branches are:
1) buccal nerve
2) inferior alveolar nerve
3) auriculotemporal nerve
4) lingual nerve
What are the three terminal branches of the opthalmic nerve?
Opthalmic nerve is a division of the trigeminal nerve
Its terminal branches are:
1) frontal
2) lacrimal
3) nasociliary
Describe the sensory supply of the mandibular nerve
Mucous membranes and floor of oral cavity External ear Lower lip Chin Anterior 2/3 of tongue (ONLY SENSATION) Lower molar, incisor and canine teeth
Describe the sensory supply of the opthalmic nerve
Forehead and scalp Frontal and ethmoidal sinus Upper eyelid and conjunctiva Cornea Dorsum of nose
Describe the motor supply of the mandibular nerve
Muscles of mastication
Describe the sensory supply of the maxillary nerve
Lower eyelid and conjunctiva Cheeks, maxillary sinus Nasal cavity Lateral nose Upper lip Upper molar, incisor and canine teeth Superior palate
What does the inferior alveolar nerve (a branch of mandibular nerve) travel through?
Mandibular foramen
What nerve is injured in a blow out fracture?
Infraorbital nerve (branch of maxillary division of trigeminal nerve)
What does the inferior alveolar nerve emerge as to give sensation to the lip and chin?
Mental nerve
What nerve can be damaged in a fractured mandible?
Inferior alveolar/mental nerve
What kind of information does the abducens nerve transmit?
Motor
What muscle is innervated by the abducens nerve?
Lateral rectus
What is the action of the lateral rectus?
Abduction of the eyeball
What presentations could a trigeminal nerve lesion cause?
Loss of corneal reflex
Loss of facial sensation
Paralysis of muscles of mastication
What foramen does the abducens nerve pass through?
Superior orbital fissure
What does abducens nerve palsy result in?
Horizontal diplopia - defective abduction
What is the route of the abducens nerve?
Comes from bottom of pons, through cavernous sinus, through SOF, supplies one muscle of the eye
What nerves are tested when examining eye movements?
CN III, IV and VI
What kind of information is transmitted by the facial nerve?
Motor (muscles of facial expression) Special sensory (taste to anterior 2/3 of tongue) Parasympathetic (salivary glands, nasal glands, lacrimal glands)
What special sensory function does the facial nerve serve?
Taste to anterior 2/3 of tongue
What motor function does the facial nerve serve?
Muscles of facial expression
What autonomic function does the facial nerve serve?
Parasympathetic
Salivary glands, lacrimal glands
What foramen does the facial nerve pass through?
Internal auditory meatus
Briefly outline the route of the facial nerve
Comes from pons, runs through petrous part of temporal bone by going through IAM, gives off a couple of branches inside the petrous bone before exiting through base of skull and giving off its 5 extracranial nerves (TZBMC)
What are the 5 extracranial branches of the facial nerve?
Temporal, zygomatic, buccal, mandibular, cervical
Why would someone with a facial nerve lesion present with hyperacousis?
Injury to nerve to stapedius (which dampens noise)
What is the branch of the facial nerve that gives special sensory fibres to the anterior 2/3 of the tongue?
Chorda tympani
Which branch of the facial nerve gives parasympathetic fibres to glands?
Greater petrosal nerve
What is the most common cause of an intracranial lesion of the facial nerve?
Middle ear pathology
In extracranial lesions, which function of the facial nerve is affected?
Motor function - so paralysis of muscles of facial expression
What is idiopathic facial nerve palsy known as?
Bell’s palsy
What are some causes of extracranial lesions of the facial nerve?
Parotid gland pathology (closely related), infection of the nerve, compression, idiopathic
Which foramen does the vestibulocochlear nerve go through?
Internal auditory meatus
What kind of information does the vestibulocochlear nerve transmit?
Special sensory (hearing and balance)
Where is the primary auditory cortex?
Temporal lobe
What is an acoustic neuroma?
Benign tumour of the schwann cells surrounding the vestibular component of CN VIII
What are the four cranial nerves that arise from the medulla?
Glossopharyngeal (IX)
Vagus (X)
Accessory (XI)
Hypoglossal (XII)
What kind of information is transmitted by the glossopharyngeal nerve?
General sensory - innervation of oropharynx, posterior 1/3 of tongue, middle ear cavity
Special sensory - taste to posterior 1/3 of tongue
Parasympathetic - parotid gland
Motor - stylopharyngeus
What is the motor function of the glossopharyngeal nerve?
Innervates stylopharyngeus
What nerve is responsible for the sensory limb of the gag reflex?
Glossopharyngeal
What is the autonomic function of the glossopharyngeal nerve?
Parotid gland innervation
How is the glossopharyngeal nerve tested?
Gag reflex, tested in conjunction with CN X
What foramen does the glossopharyngeal nerve pass through?
Jugular foramen
What may glossopharyngeal nerve lesions result in?
Hypersensitive carotid sinus reflex
Loss of gag reflex (afferent)
What carries the afferent limb of the gag reflex?
Glossopharyngeal nerve
What carries the efferent limb of the gag reflex?
Vagus nerve
What kind of information is transmitted by the vagus nerve?
General sensory - lower pharynx and larynx
Motor - muscles of the soft palate, pharynx, larynx
Parasympathetic - thoracic and abdominal viscera
What foramen does the vagus nerve pass through to exit the skull?
Jugular foramen
Describe the route of the vagus nerve
Comes from medulla, exits skull through jugular foramen, stays in carotid sheath, runs down length of neck behind artery and vein in carotid sheath, gives off branches in neck, continues into thorax and abdomen
What does the right recurrent laryngeal nerve hook underneath?
Right subclavian artery
What does the left recurrent laryngeal nerve hook underneath?
The arch of the aorta
How may a patient with vagus nerve lesions present?
- Uvula deviation away from site of lesion
- Loss of gag reflex
What foramen does the accessory nerve pass through?
Jugular foramen
What kind of information is transmitted by the accessory nerve?
Motor
What is the function of the accessory nerve?
Supplies trapezius and SCM
How can the accessory nerve be tested?
Shrug shoulders against resistance, turn head against resistance
What does the spinal accessory nerve run down through the neck in?
Posterior triangle - susceptible to injury in this area
What kind of information does the hypoglossal nerve transmit?
Motor
What is the function of the hypoglossal nerve?
Innervates muscles of the tongue
What foramen does the hypoglossal nerve pass through?
Hypoglossal canal (on rim of foramen magnum)
What may be seen in a patient with hypoglossal nerve damage?
Weakened tongue
Tongue may deviate towards side of lesion
Which cranial nerves could be affected by cavernous sinus thrombosis?
Oculomotor, trochlear, trigeminal (Va and Vb) and abducens
