Why is it important to test the sense of smell following a head injury?
A head injury (frontal/back blow to head) can snap/ damage the olfactory nerve
- this ruptured nerve fibres when going through the plate leading to a loss of smell
What clinical term is used to describe the loss of the sense of smell?
Anosmia
What type of visual field defect would occur from a midline compression of the optic chiasm?
Compression leads to both visual fields being damaged = bi temporal heminanopia
What might cause midline compression of the optic chiasm?
- when you fall down
- tumours in pituitary gland, above optic chiasm
What is meant by the term direct and consensual light reflexes?
Direct = pupil construction on eye receiving light only Consensual = light in one eye leads to a change in pupil size in both - should happen in a normal eye
Give 2 unique features of the trochlear nerve
- only nerve exiting the posterior/dorsal brain stem surface
- crosses the midline
What are the characteristics of oculomotor (3rd) nerve palsy?
Exotropia
- when one or both eyes are turned outwards
- another characteristic is a dilated pupil, because the ciliary muscle isn’t active
What are the characteristics of abducens (6th) nerve palsy?
Esotropia (crossed eyes)
- medial rectus overreacts, lateral rectus is paralysed - leads do double vision and diplopia
Through which 3 diff holes does each of the trigeminal nerve branches enter the skull?
Maxillary = foramen rotundum Mandibular = foramen ovale Ophthalmic = superior orbital fissure
Through which 2 holes in the temporal bone does the main motor nerve pass?
- internal auditory meatus
- jugular foramen
What branches of this nerve innervate the obicularis oculi muscles in the eyelids and what happens when this muscle contracts ?
Innervate by facial nerve - contraction closes the eyelid
Damage to both parts of the nerve results in flaccidity of the facial muscles on the same side (Bell’s palsy) but what other symptoms would the px experience?
Dry eyes due to lack of lacrimal gland
What is the main functional diff between the otilithic organs (utricle and saccule) and semi circular canals
Otilithic = sense linear acceleration
Semi circular canals = respond o angular rotation
Which of the otilithic organs or semi circular canals is more important for the VOR and for the eye righting reflex?
Otilithic organs
What are the features of the Olfactory nerve?
- Purely sensory and only involved in the sense of smell (olfaction)
- Comes from olfactory receptors in the nasal cavities
- Has axons that enter the skull through the cribriform plate underneath the frontal lobes of the cerebral cortex, destination of which are neurons located in the olfactory bulbs
How to test for the olfactory nerve?
Present patient with a substance giving a strong odour
How to test the integrity of the Optic nerve and its continuation into the chiasm and tract?
- Assessment of the visual fields in the two eyes, each eye is tested in turn
- Fields can be simply tested by the ‘confrontation technique’
- Interior structure of the eye is typically examined with an opthalmoscope
- Pupil light responses can be easily identified by shining a light directly into each eye
Why are the oculomotor, trochlear and abducent nerves all tested together?
- Because of their combined involvement in the control of eye movements
- Each of these nerves directly innervates one or more of the 6 EOMs
What does a full examination of the oculomotor, trochlear and abducent nerves involve?
1) Assessment of primary gaze ie whether px can look straight ahead with both eyes or shows a manifest deviation (strabismus or squint)
2) Ocular motility ie how well a px is able to move their eyes into diff positions of gaze
3) Pupil reponses (direct, consensual and on convergence, the latter being part of the near reflex)
What are the features of the Trigeminal nerve?
- Mainly sensory and is concerned with somatic ie touch, pain, temp sensation from the entire face
- Also has a smaller motor component which innervates the muscles of mastication (masseter, temporalis and pterygoids) via mandibular branch
What are the 3 major nerves forming the origin of the Trigeminal nerve?
Opthalmic, Maxillary, Mandibular
How to test for the Trigeminal nerve?
- Sensation from face can be tested using a cotton wool bud (touch) or pin (noxious, pain) - facial territories should be tested separately
- Masseter can be palpated on forced jaw closure
- Pterygoids can be checked by asking the subject to move the lower jaw from side to side
What are the features of the Vestibulo Cochlear Nerve?
- Nerve has 2 major parts
- Comprises axons of ganglion cells innervating special sensory receptors (hair cells) of the inner ear inside the petrous temporal bone
- One set of axons (related to spiral ganglion) innervate these receptors in the cochlea involved in hearing
- The other (related to vestibular ganglion) innervate those in the vestibular apparatus, comprising of the otiliths (utricle and saccule) and the 3 semi circular canals
How to test hearing?
- Tested by activating tuning forks that emit vibrations of different sound frequency
- test can be used to differentiate between a conductive hearing loss eg due to problems with middle or outer ear, from a sensori-neutral hearing loss resulting from damage to the cochlear hair cells eg from excessive noise exposure
