Cranial Nerves Flashcards
What does the brainstem adjoin?
The brain and the spinal cord
What are the parts of the brainstem?
- Mid-brain
- Pons
- Medulla
Is the medulla functionally that different from the spinal cord?
Yes, very different
What is the brainstem continuous with caudally?
The spinal cord
Where does the brainstem have a vital role?
In regulation of cardio-respiratory functions and maintaining consciousness
What runs through brainstem?
Ascending and descending fibres between the brain and the rest of the body run through it
What is the brainstem the location of?
The majority of cranial nerve nuclei
What are nuclei, in terms of the cranial nerves?
Collections of cell bodies of nerve fibres that make up the whole cranial nerve
What are the cranial nerves part of?
The peripheral nervous system
Where do the cranial nerves arise from?
The central nervous system, at the level of the brainstem, or forebrain in the case of olfactory or optic nerve
How many pairs of cranial nerves are there?
12
What does each cranial nerve do?
Innervates halves, as they are in pairs
Describe the intervals that the cranial nerves arise from the brainstem (or brain)
Irregular intervals from CNS, rather than segments as seen in spinal nerves
What does each cranial nerve have for identification?
A roman numeral
What does the numberous of the cranial nerve generally follow?
The order in which they arise (or enter) the brainstem, from rostal to caudal
What do cranial nerves carry?
1000’s of axons
What are the potential types of axons in cranial nerves?
- General sensory
- Special sensory
- Motor
- Autonomic
How many of the cranial nerves are mixed?
Only four
What is meant by a mixed cranial nerve?
Contain both motor and sensory modalities
What is the special sense taste carried within?
Two of the mixed cranial nerves, mainly CN VII and CN IX
How many of the cranial nerves are purely sensory?
3
What do the sensory cranial nerves do?
Carry special sensory function, as opposed to general sensation
What cranial nerve is responsible for hearing and balance?
CN VIII
What cranial nerve is responsible for vision?
CN II
What cranial nerve is responsible for smell?
CN I
How many of the cranial nerves are purely motor?
5
How many of the cranial nerves carry efferent autonomic fibres?
4
Which cranial nerves carry efferent autonomic fibres?
CN III, CN VII, CN IX, and CN X
What are the cranial nerves that carry efferent autonomic fibres known as?
Visceral motor
What cranial nerve is the most rostal?
Olfactory
What is CN I?
Olfactory
What route does CN I take?
Long nerves dangle down through the cribiform plate, into the olfactory mucosa of the roof of the nasal cavity
What is the sensory function of CN I?
Smell
Is CN I motor or sensory?
Sensory
How is CN I tested?
- Test one nostril at time
- Smelling salts, or something quite odouress
Is CN I often formally tested?
No, just ask if they have noticed any change/loss in sense of smell
Is CN I a true cranial nerve?
No, they are paired extensions of the forebrain
What is the clinical term for loss of smell?
Anosmia
What is the most common cause of anosmia?
Upper respiratory tract infection
How can a head injury cause anosmia?
A bump to the head can cause the brain to wobble, which can produce shearing forces or a basilar skull fracture
What is CN II?
Optic nerve
What route does CN II take?
Comes from retina, through optic canal. Cross over at the optic chiasms, to optic tracts, to forebrain
Is CN II motor or sensory?
Sensory
What is the sensory function of CN II?
Vision
How is CN II tested?
- Test one eye at a time
- Visual tests; visual acuity and visual fields
- Test pupils
Is CN II a ‘true’ cranial nerve?
No, paired anterior extensions of the forebrain
How can CN II be seen directly?
With fundoscopy
What is the result of the complex pathway from the retina to the visual cortex of the occipital lobe?
Different lesions give very different patterns of visual loss
What can cause lesions of CN II?
- Optic neuritis
- Pituitary tumour
- Stroke
What is optic neuritis?
Inflammation of optic nerve
What can happen, regarding CN II, when there is a pituitary tumour?
Tumours can squash the chiasm, and because of intermingling here, can cause bilateral visual deficit
What is CN III?
Oculomotor nerve
What route does CN III take?
Passes grom midbrain to the orbit through the superior orbital fissure. Runs through the cavernous sinus
Is CN III motor or sensory?
Motor
What is the motor function of CN III?
- Ciliary muscles
- Sphincter of pupil
- All extrinsic muscles of the eye, except those supplied by CN IV and VI
How is CN III tested?
- Inspection of the eyelids and pupils
- Eye movements
- Pupillary light reflexes
How will a damaged CN III present?
Double vision (diplopia), with eye in down and out position, severe ptosis, and maybe pupillary dilation
What can cause CN III lesions?
- Raised intracranial pressure (tumour or haemorrhage)
- Aneurysms of the posterior communicating artery
- Cavernous sinus thrombosis from infection or clot
- Diabetes/hypertension
What is the first sign of raised intracranial pressure?
Blown pupil
Why does a blown pupil signify raised intracranial pressure?
Superficial parasympathetics run with the oculomotor nerve on the outside, so if pressure exerted from the outside, it affects parasympathetics first. This leads to a loss of sphincter control, and therefore a blown pupil
What CN III lesion will not cause a blown pupil?
Diabetes/hypertension
What is CN IV?
Trochlear
What route does CN IV take?
Longest intracranial route of all CN’s
Arises from the dorsal aspect of the brainstem, so moves right around brain and passes through superior orbital fissure
Is CN IV motor or sensory?
Motor
What is the motor function of CN IV?
Superior oblique muscles of eye
How is CN IV tested?
Eye movements
Is a CN IV lesion commonly seen isolated?
No, rare
What is the problem with recognising CN IV lesions?
Subtle, as only one muscle affected, so often missed
How can the presentation of a CN IV lesion often be corrected?
With a slight tilt of the head
How does a CN IV lesion present?
Diplopia, often worst with downwards gaze
What is the most common cause of acute CN IV injury?
Head injury, or any cause of raised ICP
In whom can congenital palsies of CN IV present?
Children
What is CN V?
Trigeminal
What is the route of CN V?
Arises from the pons, and gives rise to three divisions;
- V1, opthalmic, which goes into the eye through the superoir orbital fissure
- V2, maxillary, which goes through the foramen rotundum
- V3, mandibular, which goes through the foramen ovale
What does the maxillary branch of CN V give off?
The intraorbital nerve
Where does CN V give off the infraorbital nerve?
When it goes through the infra-orbital foramen
What does the mandibular branch of CN V give off?
The mental nerve
Where does CN V give off the mandibular nerve?
When it goes through the mental foramen
How can the mental nerve be injured?
In a fracture of the mandible
What does injury of the mental nerve lead to?
Loss of sensation in the face
Is CN V motor or sensory?
Both
What is the motor function of CN V?
Muscles of mastication
What is the sensory function of CN V?
- Face
- Sinuses
- Teeth
How is CN V tested?
- Sensation to face
- Muscles of mastication testing
What does trigeminal neuralgia cause?
Intense pain from very light touch to certain divisions of the trigeminal nerve on the face
What clinical condition is CN V implicated in?
Shingles
What does CN V provide, regarding the eyes?
The afferent limb of the corneal reflex
What is the function of the corneal reflex?
It senses grit etc on your cornea, and causes you to blink
What is CN VI?
Abducent
What course does CN VI take?
Arises from the pons, through the cavernous sinus, to the superior orbital fissure
Is CN VI motor or sensory?
Motor
What is the motor function of CN VI?
Lateral rectus muscle of the eye
How is CN VI tested?
Eye movements
When is CN VI susceptible to injury?
In raised intracranial pressure, e.g. due to bleed or tumour
Why is CN VI susceptible to injury in raised intracranial pressure?
Due to it running under the surface of the pons upwards towards the cavernous sinus
How do patients with CN VI lesions present?
Diplopia
What is CN VII?
Facial nerve
What route does CN VII take?
Passes into petrous part of temporal bone, goes through the internal acoustic meatus. Through petrous part, gives off branches in the ear. Exits stylomastoid foramen, and gives off 5 terminal branches
Is CN VII motor or sensory?
Both
What is the motor function of CN VII?
- Via it’s primary root-* Muscles of facial expression
- Via the intermediate nerve-* Submandibular, sublingual, and lacrimal glands
What is the sensory function of CN VII?
- Taste to anterior 2/3 of the tongue
- Soft palate
How is CN VII tested?
- Muscles of facial expression
- Taste to anterior 2/3 of tounge (often not formally tested)
Give an example of a facial nerve palsy?
Bells palsy
What happens in Bells Palsy?
Get all muscles of facial expression on one side paralysed, leading to drooping
What can cause CN VII palsies?
Parotid tumours
What is CN VII in close relationship with?
Vestibulococlear nerve
What is CN VIII?
Vestibulocochlear
What are the branches of CN VIII?
- Vestibular nerve
- Cochlear nerve
What course does CN VIII take?
Goes through internal acoustic meatus, terminates inside the ear. Branches to semi-circular canal and cochlear
Is CN VIII motor or sensory?
Sensory
What is the sensory function of the vestibular branch of CN VII?
- Orientation
- Motion
What is the sensory function of the cochlear branch of CN VII?
Hearing
How is CN VIII tested?
- Hearing
- Rinne’s and Weber’s test
What pathologies is CN VIII involved in?
- Hearing loss
- Vertigo
- Tinnitus
What is an acoustic neuroma?
A benign tumour of the vestibular cochlear nerve around the internal acoustic meatus
What is cranial nerve IX?
Glossopharyngeal
Is CN IX motor or sensory?
Both
What is the motor function of CN IX?
- Stylopharyngeus
- Parotid gland
What is the sensory function of CN IX?
- Posterior 1/3 of tongue
- General sensation to pharynx, tonsillar fossa, and pharyngotympanic tube
- Middle ear cavity
- Carotid sinus
Where is the carotid sinus found?
In the internal carotid artery
What does the carotid sinus possess?
Baroreceptors that are sensitive to changes in blood pressure
What does the carotid body possess?
Chemoreceptors
What are the chemoreceptors in the carotid body sensitive to?
Blood and oxygen carbon dioxide levels
What happens when chemoreceptors in the carotid body sense a change in blood oxygen and carbon dioxide?
Afferent signals are sent via CN IX to cardiorespiratory centres in the medulla
How is CN IX tested?
Gag reflex (tests sensory limb)
- Taste often not formally tested.*
- Tested in conjunction with CN X*
Are isolated lesions of CN IX common?
No, rare
What is CN X?
Vagus nerve
What course does CN X take?
Exits skull through jugular foramen, goes into carotid sheath, and down the neck
Is CN X motor or sensory?
Both
What is the motor function of CN X?
- Larynx
- Trachea
- Bronchial tree
- GI tract to left colic flexure
What is the sensory function of CN X?
- Pharynx
- Larynx
- Reflex sensory from tracheobronchial tree
- Lungs
- Heart
- GI tract to left colic flexure
How is CN X tested?
- Noting speech
- Swallow
- Cough
- Gag reflex (efferent limb)
Are isolated lesions of CN X common?
No, rare
What is the clinical sign of isolated CN X lesions?
Deviation of the uvula when soft palate elevated
What can injury to the recurrent laryngeal nerve cause?
Hoarseness and dysphonia
What is CN XI?
Spinal accessory nerve
What route does the spinal accessory nerve take?
Through jugular foramen
Is the spinal accessory nerve motor or sensory?
Motor
By what branches does the spinal accessory nerve give its motor supply?
- Spinal root
- Cranial route
What is the motor function of the spinal root of CN XI?
- Sternocleidomastoid
- Trapezius
What are the motor functions of the cranial root of CN XI?
Most palantine and pharyngeal muscles
How is CN XI tested?
- Shrug shoulders
- Turn head against resistance
Where does CN XI recieve its spinal roots from?
Upper 5/6 cervical segments
How to spinal nerve roots from the upper 5/6 cervical segments contribute to CN XI?
Ascend up foramen magnum to join cranial root
Where does CN XI run down the neck?
Through the posterior triangle
What is the result of CN XI running down the neck through the posterior triangle?
It’s susceptible to injury in this area
How can CN XI be injured in the posterior triangle?
- Lymph node biopsies
- Stab wounds
What is CN XII?
Hypoglossal nerve
What route does CN XII take?
Leaves medulla through hypoglossal canal
Is CN XII motor or sensory?
Motor
What is the motor function of CN XII?
All intrinsic muscles of tongue, except palatoglossus
How is CN XII tested?
Inspection and movement of the tongue
What does damage to CN XII cause?
Weakness and atrophy of the tongue muscles on the ipsilateral side
