Pathways / Branches
Name the five terminal branches of the facial nerve given off within the parotid gland, from superior to inferior. (5)
Temporal, zygomatic, buccal, marginal mandibular, cervical.
What are the clinical consequences of a maxillary (V2) lesion?
Sensory loss only — over the cheek, lower eyelid, side of the nose, upper lip, upper teeth and gums, and the palatal/maxillary sinus mucosa. There is no motor deficit.
State the afferent and efferent limbs of the jaw jerk
Both limbs are V3
A patient cannot abduct their right eye. Which cranial nerve is affected? (1)
Right CN VI.
Which type of neuron occupies the dorsal half of the spinal cord?
Neurons of the sensory (afferent) system — receiving incoming sensory fibres.
Name the three branches of V1 that pass through the superior orbital fissure. (3)
Lacrimal, frontal and nasociliary.
A lesion at the centre of the optic chiasma produces which field defect, and why?
Bitemporal hemianopia — the decussating nasal retinal fibres, which carry the temporal visual fields, are interrupted.
What is the anatomical basis of the consensual light reflex?
Fibres from the pretectal nucleus project bilaterally to both Edinger–Westphal nuclei, so light shone into one eye constricts both pupils.
A patient has ptosis, a dilated pupil and an eye positioned "down and out". Which cranial nerve(s) is affected?
CN III.
Controls the sphincter pupillae and ciliary muscles
Lateral rectus and superior oblique dominate abducting and pushing eye down
Which cranial nerves are mixed (both motor and sensory)?
CN V (trigeminal), VII (facial), IX (glossopharyngeal), X (vagus).
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Trace the parasympathetic pathway from CN IX to the parotid gland. (5 steps)
Tympanic branch → tympanic plexus → lesser petrosal nerve → through the foramen ovale → otic ganglion (synapse) → parotid, with postganglionic fibres hitch-hiking on the auriculotemporal nerve.
A lesion of the left optic tract produces which visual field defect?
A right homonymous hemianopia — loss of the right half of the visual field of both eyes.
State the afferent and efferent limbs of the pupillary light reflex. (2)
Afferent — CN II (optic nerve)
Efferent — CN III (oculomotor nerve)
On inspection during examination of CN VII, what two abnormalities are you looking for?
Unilateral drooping of the face (facial asymmetry) and ptosis.
What is the key difference between the roots of a spinal nerve and those of a cranial nerve?
Every spinal nerve without exception has both a dorsal (sensory) and a ventral (motor) root.
Cranial nerves vary — some carry only motor fibres, some only sensory, and some both.
Trace the parasympathetic pathway from CN VII to the lacrimal gland (5)
Greater petrosal nerve → joins the deep petrosal nerve to form the nerve of the pterygoid canal → pterygopalatine ganglion (synapse) → then hitch hikes on zygomatic branch of V2, then V1 branch i.e. lacrimal nerve, finally to the lacrimal gland.
A 25-year-old man wakes unable to move the muscles of the right side of his face, with drooling, a dry right eye, discomfort from surrounding sounds and impaired taste. What is the likely cause?
A lower motor neuron lesion of the right facial nerve — Bell’s palsy. Involvement of all the muscles of facial expression, including the forehead, confirms it is LMN rather than UMN.
A patient has facial paralysis and an absent corneal reflex. Explain why the reflex is lost.
Afferent — trigeminal (V1, nasociliary).
Efferent — facial nerve (CN VII), producing bilateral blink via orbicularis oculi.
Corneal sensation is intact (V1 is undamaged), but the patient cannot close the eyelids because orbicularis oculi, supplied by the paralysed facial nerve, cannot contract — the efferent limb has failed.
State the normal result of Rinne’s test and the result in conductive deafness.
Normal (and sensorineural loss): air conduction > bone conduction.
Conductive loss: bone conduction > air conduction.
The lecturer calls CN V "the Uber driver". What does this analogy describe?
The postganglionic parasympathetic fibres of CN III, VII and IX leave their ganglion and hitch-hike along branches of the trigeminal nerve (CN V) to be delivered to their target gland or muscle — regardless of which nerve they originally came from.
Describe the course of the facial nerve (start to end, 4 features)
nternal acoustic meatus
Makes a sharp U-turn at the geniculum (site of the geniculate ganglion)
Runs posteriorly along upper part of medial wall of the middle ear
Goes downwards exiting through stylomastoid foramen
A facial nerve lesion at the stylomastoid foramen produces what deficits (1), what is spared (3)
Paralysis of all ipsilateral muscles of facial expression only.
Taste, lacrimation and stapedius function are spared, since those branches arise more proximally.
Describe how the gag (uvular) reflex is elicited, and state which nerve forms each limb.
Touch the posterior tongue, oropharynx or tip of the uvula; the palate elevates and the pharynx contracts.
Afferent — CN IX; efferent — CN X.
List the four components of the clinical examination of CN II. (4)
Visual acuity (Snellen chart)
Visual fields by confrontation
Colour vision
Fundoscopy — the optic disc
A CN IV palsy produces which type of diplopia, and in which direction of gaze is it worst?
Vertical and torsional diplopia, worst on looking down and inwards — classically descending stairs or reading. The head often tilts away from the affected side.
EXPLANATION: CN IV innervates the superior oblique muscle (SO4), which normally depresses the eye and intorts (rotates its inwards). If you have CN IV palsy, your eye as such rotates outwards a bit and moves up due to loss of superior oblique function. As such you get double vision due to the differing positions of the eyes where the two images will be stacked (as one eye is higher than the other) and one image is also tilted (due to the outwards rotation of the affected eye)
The superior oblique is most active when looking down and inwards and so in those positions (i.e. looking down descending stairs or reading, deficit becomes maximal as one eye cannot do the same as the other eye.
Tilting of head helps to compensate for the superior oblique deficit