Special Senses

Question 1

What structure allows us to smell?

Answer 1

CN I innervates olfactory mucosa of superior concha (part of ethmoid bone) and then travels to olfactory bulb via the cribriform plate carrying sensory neurons to orbital + piriform cortexes with pathways linking to brainstem, limbic system and hypothalamus

Question 2

What is special about olfactory neurons?

Answer 2

They can regenerate - may not if cribriform plate becomes fractured damaging them severely

Question 3

Why might someone get unilateral anosmia?

Answer 3

Meningioma

Anterior cranial fossa trauma

Question 4

How do you clinically test olfaction?

Answer 4

Test EACH nostril individual with familiar scents e.g. orange, coffee (dont use smelling salts as ammonia may irritate nasal mucosa causing false +ve ‘sense of smell) - ask can you smell it? What is it?

Question 5

What is the words for smelling things that aren’t there?

Answer 5

Phantosmia

Cacosmia

Question 6

When do you test a patients olfaction?

Answer 6

Not routinely testing in absence of other signs/issues - patient may complain of loss of taste and/or smell

Question 7

Why might a patient experience anosmia?

Answer 7

Viral infection
Parkinson’s + AD (early sign)
Meningioma (olfactory groove)
Anterior cranial fossa fracture (may present with CSF rhinorrhoea)

Question 8

Where is the piriform cortex?

Answer 8

Part of temporal lobe medially including the amygdala and parahippocampal gyrus

Question 9

What might happen to olfaction in epileptic patients?

Answer 9

Unpleasant olfactory aura preceding a seizure

Question 10

Where are the taste receptors?

Answer 10

On the tongue but also some in the palate/pharynx

Question 11

What cranial nerves (CNs) innervate the tongue?

Answer 11

Taste sensation:
Anterior 2/3rd - CNVII (facial n. via Chorda Tympani n.)
Posterior 1/3rd - CNIX (glossopharyngeal n.)
CNX’s provides a little bit of taste too

Somatic sensory:
CNVc (lingual)
CNIX

Question 12

What are the different taste receptors for?

Answer 12

1. Sweet
2. Sour
3. Salty
4. Bitter
5. Umami (savoury)

Question 13

What is the structure of the tongue?

Answer 13

Covered in papillae e.g. fungiform, filiform (no taste buds) and vallate (across sulcus terminalis)

Question 14

What sensory nucleus do the cranial nerves (CNs) carrying taste synapse on when they come into the brainstem?

Answer 14

Nucleus solitarius

Question 15

Why does the tongue have different innervations?

Answer 15

During embryological development, the tongue develops from different pharyngeal arches so it will have different nervous innervations

Question 16

What can become damaged in a 3rd molar extraction?

Answer 16

Branch of CNVc - inferior alveolar nerve as both provide somatic sensory (lingual) innervation to tongue so patient may not know if they are biting tongue for e.g.

Question 17

What is the structure of the eyeball?

Answer 17

3 layers:

• Retina (photo-receptive/sensory region)
• Choroid
• Sclera (white outer layer)

Fovea centralis = region of greatest visual acuity sitting in middle if macula

Optic papilla = blind spot where all nerves (CNII) and vessels come in

Question 18

How do you examine the retina?

Answer 18

Fundoscopy: first examine cornea and lens when patient is gazing into distance - approach from temporal field (L-L eye, R-R eye), red fundus reflex seen so then move in and adjust dioptre to examine back of eye

Question 19

What is an example of a condition that can cause blindness?

Answer 19

Central retinal arterial occlusion

Pituitary tumours (compress optic chiasm)

LGB damage

Glaucoma (reduces fields)

Retinal issues e.g. retinitis pigmentosa causes tunnel vision, papilloedema (raised disc, engorged veins), retinopathy, emboli, haemorrhage + scars

Question 20

How is light detected by the eye?

Answer 20

1. Light passes through neuronal layers to get to photoreceptors (different cells detect different colours)
2. Neural cells come together off of retina to back of eye to form CNII through optic canal of sphenoid bone
3. Goes through optic chiasm and tract through lateral geniculate body of thalamus
4. Optic radiation (Meyer’s loop) and then loop arches inferiorly down into temporal lobe
5. Projects to primary visual cortex (occipital lobe) gyri around calcarine sulcus

Question 21

What does the visual pathway do to what we see?

Answer 21

Everything ‘seen’ by eye is inverted and flipped as it passes through the lens of the eye and visual field split into a R (L side of retina) and L (R side of retina) half for each eye

Question 22

What are retinal fields?

Answer 22

Anatomical regions of retina named according to its position relative to nose or temporal regions for e.g. in L eye:
Temporal retinal field on L whereas nasal retinal field on R (vice versa for visual fields)

Question 23

How are visual field deficits presented?

Answer 23

Described and drawn from patients POV as if you are seeing as the patient does although patient will not see black as drawn, they will see nothing - depending on size of defect, patient may not be aware of problem

Question 24

How does visual information end up when it reaches the visual cortex?

Answer 24

Information from L side of visual field from both eyes ends up on the R/contralateral side of the brain upside down (vice versa for R visual field) as optic radiation of lower visual field is higher in the brain that fibres portraying upper visual field

Question 25

How is the visual field further split into quadrants?

Answer 25

Meyer's loop = upper visual field (1/4 on each side) Lower visual field above it (1/4 on each side) Macula + foveal vision = tip of occipital pole/lobe/striate area - centre middle circle of visual field

Question 26

What can happen in central scotoma?

Answer 26

Loss of central macula vision so highest area of visual acuity is lost indicating a problem at the occipital lobe (striate area)

Question 27

What can a vascular lesion of the occipital lobe primary visual cortex cause?

Answer 27

Homonymous hemianopia: damage to top and bottom visual fields on same side BUT sparing the central circle i.e. macula sparing where tip of occipital pole (striate area)receives a different blood supply to rest of occipital cortex so escapes harm

Question 28

How do you test the visual fields (CNII)?

Answer 28

Confront patient staring directly ahead at arms length, cover one eye and compare R-L and L-R comparing to own visual field using a large red coloured pin

Question 29

How do you test visual acuity?

Answer 29

Snellen chart: compares what we see at 6m at 6m away from chart (if patient reads 20ft-6m line they have 20/20 vision) - wear glasses/contacts when doing test Under 40s should be able to read 1st 6 lines - acuity of less than 6/9 lines needs investigation When there is poor acuity (e.g. due to optic neuritis, refractive lens error or PS issues) ask patient to count digits, see movement or perceive light

Question 30

How can you clinically test CNII?

Answer 30

``` Visual acuity (Snellen chart) Visual fields Pupil light reflex Accommodation Fundoscopy ```

Question 31

What does the pupillary light reflex test?

Answer 31

Functioning of retina, midbrain and CNII and III as shining light in 1 eye should make both pupils contract (consensual light reflex) due to bilateral distributions of brainstem fibres

Question 32

How does the pupillary light reflex come about?

Answer 32

1. Some retinal cells send afferent info to PTN via CNII 2. PTN linked to eachother by PC and linked to both EWN by interneurons 3. Pre-ganglionic PS fibres enter CNIII synapsing in ciliary ganglion 4. Post-ganglionic PS fibres in short ciliary nerves enter iris controlling sphincter pupillae

Question 33

What should be thought if one function of a CN e.g. visual acuity is not working?

Answer 33

Think WHERE the functions are separate e.g. nuclei, lens of eye etc.

Question 34

What is accommodation?

Answer 34

What enables us to look at and focus upon objects that are close to the eye via vergence, pupillary constriction and lens fattening

Question 35

How does accommodation occur?

Answer 35

1. Retina projects information to 1o visual cortex which affects frontal eye fields 2. CNIII nucleus contracts medial rectus causing vergence 3. EWN has 2 effects on ciliary ganglion: - Contracts sphincter pupillae causing pupil constriction - Contracts ciliary body, relaxing suspensory ligaments enabling lens to recoil + relax making it fatter

Question 36

What are the vestibular and cochlea apparatus?

Answer 36

Structures containing fluid (endolymph and perilymph) that transmit vibrations and shared between the 2 systems - housed in a perfect bony deficit creating a snugly space that fits its contours in the petrous temporal bone within a bone labyrinth

Question 37

How is the cochlea arranged?

Answer 37

In a spiral where the sensory part is the Organ of Corti that has sensory hair cells detecting vibrations so spiral ganglion come together to form the cochlear nerve (part of CNVIII) which transmits back to pons/medulla

Question 38

Where are vibrations transmitted?

Answer 38

From the oval window in the middle ear to the perilymph of the cochlea Vibrations passed to endolymph via vestibular membrane

Question 39

How is high and low frequency sound detected?

Answer 39

When the membrane is narrow and stiff HIGH frequency sound is detected whereas when the membrane is wide and flexible LOW frequency sound is detected

Question 40

How is auditory information transmitted to brain?

Answer 40

Ascends and distributed bilaterally to cortexes with multiple nuclei and decussation points (e.g. auditory relay station inferior colliculus) so primary auditory cortex receives bilateral auditory sensory input so patient will not go deaf if one side is damaged, may just lose sensitivity and stereo placing of sounds

Question 41

What are some examples of hearing disorders?

Answer 41

- Conductive - Sensorineural (drug-linked, viral rubella in utero or mumps) - Loss of stereo-placement sound can indicate cortical/thalamic pathology - Tinnitus (Meniere's, URTI, following exposure to loud sounds or tensor tympani/stapedius myoclonus)

Question 42

What are the 2 parts of the vestibular system?

Answer 42

1. Dynamic: formed from semi-circular canals and crista acting mainly on eye movement via medial-longitudinal fasciculus 2. Static: formed from maculae (utricle + saccule) acting via vestibulospinal pathway picking up static changes of position of head even when still + linear acceleration of head

Question 43

What are maculae?

Answer 43

Provide information relating to head position relative to trunk and sense linear acceleration (e.g. walking, driving, falling)

Question 44

What are the 2 types of macula?

Answer 44

1. Utricle: detect horizontal acceleration (e.g. driving) so active with head in flexion or extension 2. Saccule: detect vertical acceleration (e.g. falling) - extensor activation in a fall (strong extensor thrust) activates vestibulospinal pathway - active with head held to side

Question 45

Where is the vestibular nuclei? What happens when inputs go wrong?

Answer 45

In pontomedullary brainstem with 3 main inputs: 1. Visual via ocular movement 2. Proprioception via cerebellar modulation 3. Vestibular via vestibulospinal tract (1/3 major descending tracts) and neck movement = 1 input can be lost but if 2 are lost, we become unstable losing postural control

Question 46

What is the Romberg test?

Answer 46

Patient closes eyes whilst standing taking away the visual input to the vestibular nuclei and if they sway/fall this is a +ve test whereas if they remain steady, its a -ve test

Question 47

What might be damaged in a positive Romberg test?

Answer 47

Dorsal column can become degenerated in syphilis Fracture through petrous portion of temporal bone which damage inner ear and vestibular system