26 Questions
Which cranial nerve is responsible for the sense of smell?
Olfactory nerve
What is a characteristic feature of the olfactory nerve?
It is unmyelinated
What is a common cause of damage to the olfactory nerve?
Head injuries
How is the function of the optic nerve tested?
By testing the patient's visual acuity
What is a cause of optic nerve defects?
Stroke
What is the function of the optic nerve?
To transmit sensory information from the retina to the primary visual cortex
What nerve component supplies the muscles of mastication?
V nerve
What is the effect of a UMN lesion on the VII nerve?
Half the face is affected, excluding the forehead
What is the primary function of the VIII nerve?
Sensory function for hearing and balance
What is the primary role of the IX nerve?
Sensory function for taste to the posterior 1/3rd of the tongue
What is the result of a unilateral lesion to the X nerve?
uvula deviation towards the unaffected side
What is the primary function of the XI nerve?
Motor function for spinal cord innervation
What is the primary function of the XII nerve?
Motor function for tongue movement
What is the effect of a LMN lesion on the VII nerve?
Half the face is affected, including the forehead
What is the function of the chorda tympani?
Taste to the anterior 2/3rds of the tongue
What is the result of a bilateral lesion to the X nerve?
Total paralysis of the soft palate
What nerves are involved in the pupillary reflex pathway?
Optic nerve and oculomotor nerve
What is the consequence of a left optic nerve lesion?
Left direct reflex is lost, left consensual reflex is maintained
What is the function of the oculomotor nerve?
Motor function only
What is the consequence of a III nerve palsy?
Eye is fixed down and out
How are nerves III, IV, and VI tested?
Patient is asked to follow a pen as you draw out the letter H
What is the component of function of the trigeminal nerve?
Motor and sensory function
What is the sensory component of the trigeminal nerve divided into?
Ophthalmic, maxillary, and mandibular
What is the cause of a IV nerve palsy?
Trauma
What is the consequence of a VI nerve palsy?
Eye cannot move laterally
What is the component of function of the trochlear and abducens nerves?
Motor function only
Study Notes
Cranial Nerves
- The 12 cranial nerves in order: Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, Hypoglossal
- Shortest cranial nerve: Olfactory nerve
- Olfactory nerve:
- Features: Shortest cranial nerve, unmyelinated, sensory component only
- Function: Sense of smell
- Damage causes: Head injuries, tumours, neurodegenerative disorders
- Testing: Ask about sense of smell changes, identify smells with eyes closed
Optic Nerve
- Function: Transmission of sensory information from retina to primary visual cortex
- Defect causes: Trauma, tumour (e.g., pituitary adenoma), MS (optic neuritis), stroke
- Testing:
- Visual acuity: Ask patient to read from a printed page
- Visual fields: Confrontation test
- Pupillary reflex: Direct and consensual reflex
- Fundoscopy: Ophthalmoscope examination
- Pupillary reflex tests: Optic nerve (afferent pathway) and oculomotor nerve (efferent pathway)
- Blindness types: Monocular (trauma), bitemporal hemianopia (acromegaly), homonymous hemianopia (stroke)
Oculomotor, Trochlear, and Abducens Nerves
- Functions: Motor component; supply extra-ocular muscles
- Oculomotor nerve:
- Supplies: Medial rectus, superior rectus, inferior rectus, inferior oblique, levator palpebrae superioris, parasympathetic fibres
- Formula: SO4LR
- Trochlear nerve:
- Supplies: Superior oblique
- Abducens nerve:
- Supplies: Lateral rectus
- Lesion effects: Diplopia (double vision)
Trigeminal Nerve
- Function: Motor and sensory
- Causes of palsy: UMN lesions (brain cortex), LMN lesions (peripheral nerve fibres)
- Sensory component: Divided into ophthalmic (V1), maxillary (V2), and mandibular (V3)
- Testing:
- Light touch and pin prick
- Inspect and palpate temporalis/masseter muscles
- Ask patient to open jaw against resistance
Facial Nerve
- Functions:
- Sensory: Taste to anterior 2/3 of tongue
- Motor: Muscles of facial expression, nerve to stapedius
- Secretomotor: Lacrimal, submandibular, and sublingual salivary glands
- Causes of palsy:
- UMN lesions (stroke)
- LMN lesions (Bell's palsy, parotid tumour)
- Testing:
- Ask about changes to sense of taste
- Ask about hearing (hyperacusis)
- Facial movements against resistance
Other Cranial Nerves
- Vestibulocochlear nerve:
- Function: Sensory - hearing and balance
- Causes of defects: Acoustic neuroma, Paget's disease
- Testing: Ask about hearing changes, whisper test, Rinne and Weber test
- Glossopharyngeal nerve:
- Functions: Sensory and motor
- Innervations: Taste to posterior 1/3 of tongue, parasympathetic to parotid glands
- Causes of palsy: Trauma, tumour, diptheria
- Testing: Impaired gag reflex
- Vagus nerve:
- Functions: Motor; supplies pharynx, larynx, and soft palate
- Causes of palsy: Trauma, brainstem lesion
- Testing: Ask patient to say 'ah' to visualise uvula and soft palate
- Accessory nerve:
- Function: Motor; supplies spine
- Cause of palsy: Stroke
- Testing: Inspect and palpate trapezius/sternocleidomastoid, shrug shoulder against resistance, turn head against resistance
- Hypoglossal nerve:
- Function: Motor; supplies tongue motor function
- Causes of palsy: Trauma, brainstem lesions
- Testing: Ask patient to protrude tongue, inspect for wasting and fasciculation
Test your knowledge of the 12 cranial nerves, their functions, and characteristics. From the olfactory nerve to the hypoglossal nerve, see how well you know the cranial nerve system.
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