Cranial Nerves Flashcards
1
Q
State the number of cranial nerves arising from each part of the brain
A
- 2 from forebrain
- 2 from midbrain
- 4 from pons
- 4 from medulla
2
Q
State the cranial nerves that arise from the forebrain
A
- Olfactory nerve
- Optic nerve
3
Q
State the function of the olfactory nerve
A
Olfaction - special sensory nerve
4
Q
Describe the route of the olfactory nerve to the forebrain
A
Nasal epithelium -> cribiform foramina -> olfactory bulb -> olfactory tracts -> forebrain
5
Q
How is the olfactory nerve tested
A
- Ask for difficulties or changes in sense of smell
- Test one nostril at a time - one damaged nostril can be compensated by the other
6
Q
What is the consequence of damaged olfactory nerve
A
- Loss of sense of smell = ansomia
- Commonest cause of ansomia - common cold
- Head injury can cause ansomia
- Shearing forces which damaged nerve or basilar skull fracture
- Intracranial tumours at base of frontal lobes - interfere with olfaction
7
Q
State the function of the optic nerve
A
Vision
8
Q
State the general optic nerve route from retina
A
Retina -> optic nerve (through optic canal) -> optic chiasm -> optic tract -> primary visual cortex
9
Q
How can you test for optic nerve
A
- Test one eye at a time
- Visual tests - Snellen chart (letters on wall), visual fields
- Testing pupil responses/reflexes - using pen torches
10
Q
How can the optic nerve be damaged from increased ICP
A
- Optic nerve seen directly with ophthalmoscope
- Optic nerve carry extension of meninges thus nerve can swell due to raised intracranial pressure
- ICP can be seen as swollen optic disk (papillodema)
- Optic desk = point at which nerve enters retina
11
Q
How do lesions at different parts of the route of the optic nerve have different consequences
A
- Lesions involving the retina or the optic nerve cause visual field disturbance affecting one eye
- Lesions in the optic chiasm or optic tract involve visual problems in both eyes
- Pituitary tumours compress optic chiasm, causing bitemporal hemianopia (tunnel vision)
12
Q
State the nerves that come from the midbrain
A
- Oculomotor
- Trochlear
13
Q
What are the functions of the oculomotor nerve
A
- Motor - most extra-ocular muscles (move eye)
- Levator palpebrae superioris - opens eyelid
- Autonomic (parasympathetics) - sphincter pupillae - makes pupil smaller
- Ciliary muscle - changes lens size
14
Q
Describe the general route of the oculomotor nerve
A
Midbrain -> cavernous sinus -> superior orbital fissure -> orbit
15
Q
How is the oculomotor nerve commonly compressed
A
- Oculomotor nerve lies on the edge of tentorium cerebelli
- Lies near the uncus, which can slip and squish oculomotor nerve
- Parasympathetic routes are on the outside and will be compressed first
- If intracranial pressure increases, pupil control will be compromised first
16
Q
How do you test the oculomotor nerve
A
- Inspection of eyelid and pupils
- Eye movements - (tests III, IV, VI)
- Pupillary light reflexes
17
Q
What are signs of symptoms of oculomotor nerve damage
A
- Pathology can cause pupillary dilation and/or double vision (diplopia)
- ‘Down and out’ position with severe ptosis (eyelid droops)
18
Q
What are causes of oculomotor nerve damage
A
- Raised intracranial pressure (tumour, haemorrhage)
- Aneurysms
- Vascular - secondary to diabetes/hypertension - pupil sparing
- Cavernous sinus thrombosis
19
Q
State the function of trochlear nerve
A
Motor innervation to superior orbital oblique muscle
20
Q
Describe the general route of the trochlear nerve and the significance of it
A
- Posterior midbrain -> cavernous sinus -> superior orbital fissure
- Only nerve to emerge from dorsal aspect of brainstem - has the longest intracranial distance to travel
- Higher chance of injury
21
Q
How do you test trochlear nerve
A
Eye movements
22
Q
How do patients with trochlear nerve damage present
A
- Diplopia
- Rare and often subtle - patients correct the diplopia with tilt of the head
- Head injury most common cause of injury
- Congenital palsies in children - vertical misalignment of eyes when looking straight
23
Q
State the nerves that arise from the pons
A
- Trigeminal
- Abducents
- Facial
- Vestibulocochlear
24
Q
State the actions of the trigeminal nerve
A
- Main sensory nerve of face
- Muscles of mastication
25
Describe the general route of the branches of the trigeminal nerve
- Ophthalmic (Va) - pons -> superior orbital fissure -> orbit
- Maxillary (Vb) - pons -> foramen rotundum -> pterygopalatine fossa
- Mandibular (Vc) - pons -> foramen ovale -> infratemporal fossa
26
How do you test the trigeminal nerve
- Sensation to face - test dermatomal areas of Va, Vb, Vc
- Muscles of mastication
- Corneal reflex (afferent limb of corneal reflex)
27
State some conditions involving branches of trigeminal nerve
- Trigeminal neuralgia (mild stimulation of face causes pain)
- Shingles - sight threatening due to vesicles/scaring on eyelid
- Corneal ulcer
28
What can happen if the maxillary branch is damaged
- Maxillary nerve -> infraorbital nerve through infraorbital foramen
- If eye hit, floor of orbit can collapse causing blowout fractured - black eye, bruising
- Loss of sensation to eye
29
What can happen if the mandibular branch of trigeminal nerve is damaged
- Loss of sensation to lip and teeth
| - Fracture -> lip/tongue numbness
30
State the action of abducens nerve
Motor innervation to lateral rectus muscle
31
Describe the general route of the abducens nerve
Pons -> cavernous sinus -> superior orbital fissure
32
How do you test abducens nerve
Testing - eye movements
33
How to patients with abducens nerve damage present
- Clinical points - patients present with diplopia
| - Susceptible to injury in raised intracranial pressure as nerve can be easily stretched
34
What are the actions of the facial nerve
- Muscles of facial expression
- Taste to anterior 2/3 tongue
- Parasympathetic innervation to lacrimal and salivary gland
35
Describe the general route of facial nerve
Pons -> internal auditory meatus -> petrous bone -> branches into different nerves
36
How do you test the facial nerve
- Muscles of facial expression
- Corneal reflex (efferent limb)
- Taste
37
How do patients with facial nerve damage present
Idiopathic facial nerve palsy - Bell's palsy
| - loss of facial expression to one half of face
38
State the actions of vestibulocochlear nerve
Hearing, balance
39
Describe the general route of vestibulocochlear nerve
Pons -> internal auditory meatus -> petrous bone -> ear
40
How can the vestibulocochlear nerve be tested
- Test hearing, enquire about balance
| - Rinnes Webers test
41
How can damage to vestibulocochlear nerve present
- Damage to cochlea causes hearing loss
- Presbyacusis - old-age related hearing loss
- Pathology involving semi-circular canals - disturbance of balance (vertigo) and nystagmus (eye makes uncontrolled movements)
- Can damage both vestibulo and cochlear parts causing both hearing and balance problems
42
Describe acoustic neuroma and how it presents
- Benign tumour of Schwann cells surrounding vestibulocochlear nerve
- Compresses whole nerve and other nearby structures
- Sensorineural hearing loss (hearing loss due to damage of inner ear or vestibulocochlear nerve)
- Unilateral hearing loss, tinnitus, vertigo, numbness, pain (CN V) or weakness (CN VII) down one half of face
43
State the nerves which arise from the medulla
- Glossopharyngeal
- Vagus
- Accessory
- Hypoglossal
44
State the actions of glossopharyngeal nerve
- General sensation - of soft palate, tonsils and pharynx (oropharynx)
- Special sensory - middle ear and tympanic membrane
- Referred pain in ear in sore throat
- Sensory from carotid body and sinus
- Taste and general sensation of posterior 1/3 tongue
- Autonomic - parotid gland
45
Describe the general nerve route of glossopharyngeal nerve
Medulla -> jugular foramen -> tongue/pharynx
46
How do you test the glossopharyngeal nerve
- Gag reflex
| - Tested in conjunction with CN X
47
State the actions of the vagus nerve
- Sensory to lower pharynx and larynx
- Muscles of soft palate, pharynx and larynx
- Swallow (pharynx) and talk (larynx)
- Parasympathetic to thoracic and abdominal viscera
48
Describe the nerve route of the vagus nerve
Medulla -> jugular foramen -> length of neck (carotid sheath) -> abdomen
49
How do you test the vagus nerve
- Noting speech
- Swallow and cough
- Say 'Ahhh' and observing uvula - should stay in midline
- Gag reflex
50
How can vagus nerve damage present
- Deviation of the uvula when soft palate elevated when saying 'Ahhh'
- Injury to its recurrent laryngeal nerve branch can cause hoarseness and dysphonia
51
State the function of the accessory nerve
Innervate SCM and trapezius
52
Describe the general route of the accessory nerve
Medulla -> jugular foramen -> muscles
53
How do you test the accessory nerve
- Shrug shoulders against resistance
| - Turn head against resistance
54
How is the accessory nerve susceptible to damage
- Spinal accessory runs down through neck in posterior triangle
- Susceptible to injury in this area - in lymph node biopsies, surgery, stab wound, cancer
55
What is the function of the hypoglossal nerve
- Muscles of the tongue
| - Right hypoglossal nerve innervates the right side of the tongue
56
Describe the general nerve route of the hypoglossal nerve
Medulla -> hypoglossal canal -> tongue
57
How do you test the hypoglossal nerve
Inspection and movement of the tongue
58
How is damage of hypoglossal nerve presented
- Damage to CN XII causes weakness and atrophy of the tongue muscles on ipsilateral side
59
Which cranial nerves travel through superior orbital fissure
III, IV, V1, VI
60
Which cranial nerves travel through jugular foramen
IX, X, XI
