Senses ✅ Flashcards
How do the senses vary?
- Between different individuals
- Within the same individual, depending on emotional state
What nerves are involved in taste?
Cranial nerves 7 and 9, and partly 10
What detects taste?
Chemoreceptors in the form of papillae distributed over the tongue
How many tastes can be detected?
5
What tastes can be detected?
- Salty
- Sweet
- Sour
- Bitterness
- Umami (savoury/meaty taste of foods)
Why is MSG used as a flavour enhancer?
Receptors for the umami taste are activated by MSG (monosodium glutamate)
Damage to what surfaces might affect taste?
- Damage to cranial nerve 7
- Damage to tongue surface
How does smoking affect taste?
Seems to dull sense of taste, but may be more via its effects on smell
What % of what is interpreted as taste is actually smell?
80-90%
What nerve is responsible for smell?
CN 1
How does CN 1 detect smell?
Axons from thousands of cells expressing the same odour receptor converge in the olfactory bulb
What is the theory behind smell being a potent emotional and memory trigger?
The olfactory systems proximity to the limbic system and hippocampus, which are involved in emotion and memory
Give an example of a cause of temporary loss of smell?
Common cold
What can cause permanent loss of smell?
- Head injuries
- Intracranial tumours
- Kallmann syndrome
What is Kallmann syndrome associated with?
Absent or incomplete pubertal development
What might trigger a false sense of smell?
Some forms of temporal lobe epilepsy - odd smell prior to or during attack
What is a significant feature of olfactory neurones?
Their capacity to regenerate
What does good visual function depend on?
Combination of good visual acuity and sensitivity to targets in the peripheral visual field
What is visual acuity defined as?
Minimal distance that 2 targets need to be separated in order to be seen as distinct
What is considered to be ‘perfect’ vision with regards to visual acuity?
Able to resolve 2 targets separated by one minute of arc (i.e. 1/60 of a degree) - equivalent to 6/6 Snellen vision
How is the Snellen chart used?
It is usually viewed from 6m, and gives the numerator - the denominator is the number printed beneath the smallest line a child can read, e.g. 6/36 means child can read from 6m what most people can read from 36m.
What is the expected visual acuity at birth?
<6/60
How is visual acuity tested at birth?
Fixation to lights
How are visual fields tested at birth?
Not possible
What is the expected visual acuity of a 0-3 month old?
6/60-6/38
What is the expected visual acuity of a 3-24 month old?
6/38, improving to 6/12
What is the expected visual acuity of a 2-4 year old?
6/12-6/9
How is visual acuity measured at 0-3 months old?
Fixation to faces/large toys
How is visual acuity measured at 3-24 month old?
Preferential looking cards (Teller/Cardiff)
How is visual acuity measured at 2-4 years old?
Picture optotype charts
How are visual fields measured up to 4 years (but not newborns)?
- Visually elicited eye movement
- Confrontation techniques
What is the expected visual acuity in 5+ years?
6/9-6/6
How is visual acuity tested in 5+ years?
Letter optotype charts
How are visual fields tested in 5+ years?
Goldmann perimetry/automated perimetry sometimes possible
What are Snellen charts being replaced by?
LogMAR charts (logarithmic minimal angle of resolution)
What logMAR score is equivalent to 6/6 vision on a Snellen chart?
0.0
What does a higher logMAR number mean in terms of visual acuity?
Higher number = worse visual acuity
What can be used when normal visual acuity testing is not possible?
Smart phone apps, e.g. iSight, iChart2000
What electrophysiological test can be used to objectively assess visual acuity?
Visual evoked potential (VEP) pattern reversal test
What happens in VEP test?
Skin electrodes are used to measure the cortical activity stimulated from reversing white/black chequerboard pattern
How is the visual acuity determined by the VEP test?
By the smallest check size to elicit a cortical reaction
When can VEP testing be particularly useful?
In non-organic visual loss
What visual fields are expected by 5 years?
Horizontal field of 150, vertical field of 130
What is a variable angle squint also known as?
Ocular misalignment
Why is variable angle squint common in neonates?
Due to poor visual acuity at that stage of development
When should a variable angle squint no longer be present by?
3 months
Why should a variable angle squint no longer be present by 3 months?
The visual acuity should be sufficient to stimulate ocular alignment
What might a squint after 3 months indicate?
- Poor vision
- Pathological squint
What does ocular and cortical immaturity cause?
Pursuit and saccadic eye movements to be jerky and inaccurate until 3-4 months of age
Give an example of how interpretation of what we see changes with age?
When arranging two objects on a table so one partially obscures another in front a child and asking them to draw what they see, a young child will often draw two seperate objects side by side or one on top of another. An older child can draw an accurate picture.
It is not until mid to late childhood that a child will be able to draw a scene as if from a different viewing position
When is the first visual assessment of a child performed?
Red reflex screening of newborns
When is the next routine visual assessment after red reflex testing?
At 4-5 years
What is the most common condition picked up at 4-5 years routine visual assessment?
Ambylopia
How is amblyopia treated at 4-5 years?
Patching the ‘good’ eye to promote visual pathway development in the weaker eye
When can a fetus hear?
As early as 19 weeks gestation
Hearing to what kind of sounds develops first?
Low frequency sounds
When does reaction to high frequency sounds develop?
30+ weeks gestation
What range of sounds have humans hear?
20-20,000Hz
How can the location of sounds be differentiated?
By processing the difference in amplitude and timing of sound received in 1 ear than the other
When is hearing first screening in children?
Newborn (part of NHS Newborn Hearing Screening Programme)
How is newborn hearing assessed?
Otoacoustic emission (OAE)
What should be done if the newborn OAE suggests hearing loss?
A further OAE and, if required, automated auditory brainstem response (AABR) is performed
What does OAE assess?
The function of the inner ear
What does AABR assess?
The auditory nerve pathway
When is AABR offered as routine alongside OAE?
In infants who are at high risk of hearing impairment
Why might an infant be at high risk of hearing impairment?
- Intensive care
- High serum levels of ototoxic drugs, e.g. gentamicin
Does a clear response to testing in an infant at high risk of hearing loss rule out future hearing loss?
No
What children will be offered further hearing screening after initial newborn assessment?
- Those with family history
- Down’s syndrome
- Cleft palate
- Congenital infection
What does the method used to assess hearing in children depend on?
Developmental level and ability
What response would you expect in a small infant to a gentle rattle or bell near the ear?
Become still and listen to it
When would you expect an infant to actively try and turn to find the source of sound?
6-9 months
How does visual reinforcement audiometry (VRE) work?
Whilst the child is engaged, a speaker emits a tone. If the child stops and looks at the speaker, the examiner provides a visual reinforcement by making a toy placed on the speaker light up.
Is pure tone sweep testing used?
Yes, at school entry, but may be phased out in future
In addition to formal testing, what should prompt further evaluation of children’s hearing?
Any parental or school concern
What problems might be liked to an underlying hearing problem?
- Speech delay
- Speech disorders
- Behavioural difficulties
- Social skill concerns
What is essential if a child or infant is identified with significant hearing impairment?
Early referral to specialist services
What is used in the management of hearing loss?
- Bone anchored hearing aids and cochlear implants
- Use of non-verbal communication strategies such as sign language and Makaton
By what age should infants with hearing loss receive sound amplification?
2-3 months (ideally 6 months at the latest)
What is the advantage of early sound amplification?
Infants who receive early sound amplification are more likely to develop and retain the neural pathways required for later language development
What organ is primarily responsible for touch?
Skin
What sensors are required for touch?
- Mechanoreceptors
- Thermoreceptors
- Nociceptors
What are mechanoreceptors sensitive to?
- Pressure
- Vibration
What are thermoreceptors sensitive to?
Temperature
What are nociceptors sensitive to?
Pain
What are the types of mechanoreceptors?
- Pacinian corpuscles
- Merissner’s corpuscles
- Merkel’s discs
What do Pacinian corpuscles detect?
Vibration and large pressure change
What do Meissner’s corpuscles detect?
Fine touch or vibration
What do Merkel’s disc detect?
Fine discrimination of pressure
What is the largest type of mechanoreceptor?
Pacinian corpuscles
Where are Meissner’s corpuscles located?
Near the surface of the skin
What happens when there is a sustained stimulus to mechanoreceptors?
They adapt, rather than firing repeatedly
What do Ruffini corpuscles detect?
- Changes in temperature
- Stretch (to sense joint position and proprioception)
What are nociceptors?
Free nerve endings that signal adverse stimuli to the brain
