Hearing taste and smell

Question 1

Amplitude and frequency are the two characteristics of sound but what are they responsible for?

Answer 1

frequency/wavelength = pitch of the sound

amplitude = intensity/loudness fo the sound

Question 2

Explain the process of hearing

Answer 2

look at diagram

1) first transduction: sound waves strike the tympanic membrane and become vibrations
2) sound wave energy is transferred to the three bones of middle ear, which vibrate
3) 2nd transduction: stapes is attached to the membrane of the oval window. Vibrations of the oval window create fluid waves within the cochlea
4) 3rd transduction: fluid waves push on the cochlear duct , hair cells bend and release NT
5) 4th transduction: NT release on to sensory neurons creates AP’s that travel through the cochlear nerve ot the brain
6) energy from the waves transfers across the cochlear duct into the tympanic duct and is dissipated back into the middle ear at the round window.

Question 3

What constitutes the outer (external) ear?

Answer 3

• Pinna (auricle)
• External auditory meatus
  + cartilaginous and bony parts are not in the same direction (hence we need to pull the ear posterosuperiorly when examining it)

Question 4

What can you do to differentiate between a TMJ pain and external auditory meatus pain?

Answer 4

tap on the tragus and if it hurts then most like to be EAM

Question 5

what gland is in the EAM and what is its function?

Answer 5

ceruminous glands
- release cerumen (ear wax|) which allows ear drum to be soft and waterproof, prevent laceration of the EAM when under water

Question 6

What nerves supply the EAM?

Answer 6

auricular branch of X

auriculotemporal branch of V

Question 7

explain the structure of the tympanic membrane and what you might see on examination

Answer 7

• concave
• shadow of the handle of the malleus - this splits the membrane into 4 quadrants
• safest quadrant is the antero-inferior but all the fluid also collects here: chorda tympani is in the posterosuperior quadrant
• triangular reflection of light in the AI quadrant (Politzer’s traingle)

Question 8

Explain what is contained within the middle ear

Answer 8

air filled cavity with ossicles, 2 muscles (stapedius and tensor tympani muscle) and nerve (chroda tympani)

• ossicles are attached to the walls by ligaments
• middle ear connected to nasopharyn by the auditory/pharyngotympanic/eustachian tube

Question 9

what is the middle ear supplied by?

Answer 9

glosspharyngeal (because mucous membrane is continuous with pharynx)

Question 10

why are the roof and floor of the middle ear impo?

Answer 10

as they are very thin bones, infection of the middle ear could leak through these. if through the roof could causes meningitis or encephalitis. if through the floor could cause haemorrhage of the int jug vein
infection in ME could also spread into the mastoid sinus

Question 11

by how much do the ossicles magnify the sound as it goes into the inner ear and why?

Answer 11

15x magnification

- because the inner ear is viscous the sound waves need greater energy to move through

Question 12

where do the tensor tympani and stapedius attach and what is their role?

Answer 12

• tensor tympani (mandibular nerve) attaches to the handle of the malleus –> pulling the tympanic membrane medially therefore tensing it during loud sounds as name suggests –> reduce vibration of tympanic membrane
• stapedius (VII) is attached to the stapes –> when contracted it pulls the base fo the stapes away from the oval window therefore not all the vibrations are transferred into the inner ear –> protecting the inner ear from loud sounds

Question 13

what happens if the middle ear muscles are not functioning properly?

Answer 13

hyperacusis- pt have constant tinnitus

Question 14

as the walls of the pheryngotympanic tube are normally collapsed, how can they be actively opened adn why would you want do so?

Answer 14

to restore the nromal pressure within the middle ear the walls can be actively opened through swallowing or blowing while pinching nose

• simultaneous contraction of the tensor veli palatini and salpingopharyngeus muscles to do this

Question 15

how does the pharyngotympanic tube differ in children and why is this impo?

Answer 15

shorter and straighter in children - infection can spread more easily

Question 16

what constitutes the inner ear?

Answer 16

bony labyrinth 
 - vestibule 
   \+ utricle 
   \+ saccule 
 - semicircular canals 
   \+ducts 
 - cochlea 

Membranous labyrinth is within the bony labyrinth containing all of the above and filled with endolymph and surrounded by perilymph

Question 17

where is the spiral ganglia located and what is its function?

Answer 17

located within the cochlea and they are the ganglia for the cochlear nerve

Question 18

what are the three ducts within the cochlea?

Answer 18

• scala vestibuli (end of this is the oval window covered by stapes)
• cochlear duct (more impo in hearing)
• scala tympani (end of this is the round window covered by membrane to allow to compensate for pressure changes when the stapes goes back and forth to create the sound waves)

the two scala ducts are filled with perilymph and connected at the helicotrema (apex/tip of the cochlea) - therefore sound waves goes form oval window –> SV –> helicotrema –> ST –> round window

Question 19

what separates the ducts within the cochlea

Answer 19

• vestibular membrane separates SV from CD

- basilar membrane separates ST from CD

Question 20

Where are the hearing receptors located

Answer 20

organ of corti - on the basilar membrane

tectorial membrane projects over the organ of corti

Question 21

how does the ear differentiate between different frequencies?

Answer 21

the basilar membrane is thicker (short and stiff) at the cochlear base and thin (long and floppy) at the end - high frequency at the base and low at the apex

When the basilar membrane vibrates at the resonant frequency, it absorbs all the kinetic energy of the wave and effectively stops it at that point.

Question 22

how is the signal detected at the organ of corti

Answer 22

upward deflection of the basilar membrane moves the inner and outer hairs laterally with respect to the tectorial membrane

inner hair cells = cochlear nerve endings terminate here

outer hair cells = increase sensitivity of inner hair cells (means we can listen to each with a lot of background noise) - cochlear tuning

Question 23

explain the process of signal transduction that allows us to hear

Answer 23

displacement of the stereocillia in one direction opens K channels, and closes them in the other

Question 24

explain the process of cochlear tuning

Answer 24

inner hair cells depol –> send signal to cochlear nerve –> which is connected to cochlear nuclei –> which is connected to sup olivocochlear nucleus –> fibres alogn this path release Ach onto the inner hair cells causing them to depol and dampening down hearing in areas of pitch which are of no interest (background noise)

Question 25

how are the outer hair cells affected by some antibiotics

Answer 25

kanamycin or gentamycin can preferentially kill outer hair cells in a specific point along the cochlea, resulting in a specific frequency hearing loss at that point

Question 26

what is otoacoustic emission?

Answer 26

sounds of cochlear origin, which can be recorded by a microphone fitted into the ear canal. They are caused by the motion of the cochlea’s sensory hair cells as they energetically respond to auditory stimulation.

Question 27

Explain the auditory pathway from spiral ganglion to the primary auditory cortex

Answer 27

• Hair cells of the organ of Corti generate an electrical signal
• Peripheral extensions of the bipolar neurons at Spiral ganglion synapse with hair cells of the Organ of Corti
• Central extensions of bipolar neurons form the cochlear nerve (1st order)
• Cochlear nerve synapses at anterior and posterior cochlear nuclei
• Central extensions of 2nd order neurons splits up, with some travelling ipsilaterally, but most contralaterally up to the respective superior olivary nucleus
• Lateral lemniscus (3rd order) ascend and synapse at inferior colliculus
• 4th order neurons project to the medial geniculate nucleus of the thalamus where they synapse
• 5th order neurons join the auditory radiation to the auditory cortex => this is connected to association areas as well as reticular formation and the vermis of the cerebellum causing arousal responses to noise

Question 28

how does the ear determine the direction of the sound

Answer 28

1. volume
2. sound shadow (good for higher frequencies) - sound from one side hits the head, which then generates a sound shadow on the other side in which the volume is less. Comparison of signal intensities from both ears determines the ear closest to the sound
3. Sound lag (good for lower frequencies) - sound from a particular direction enters one ear before the other and so there is a slight delay between the sound arriving ipsilaterally at the auditory cortex, and that arriving contralaterally. Enhanced version of this used by owls for prey location

Sound lag = horizontal direction
Neither method detects front to back or above to below
this is achieved by the folds in the pinna

Question 29

What are the two types of the hearing pathologies (deafness)?

Answer 29

Conduction deafness
- blockage in the outer ear
− Infection in either the outer or inner ear
− Ossification of the small bones in the middle ear
− Rupture of the tympanic membrane

Sensory-neural deafness
- Breakdown of the cochlea and associated mechanisms,
− Damage to the auditory nerve
− Damage to the auditory cortex

Question 30

how many decibles are there is two people are 3 feet apart and have to shout to hear each other

Answer 30

85 decibels

Question 31

what is the allowable exposure time for different noise levels

Answer 31

85 decibels = 8 hours 
90 = 4 hours 
100 = 1 hour 
105 = 30 mins 
110 = 15 mins 
115 = 0 mins 

this means if you hear noise of 115 decibels your inner and outer hair cells with start damaging immediately.

first symptom of this is tinnitus and then hearing loss

Question 32

what is normal hearing

Answer 32

you should be able to hear at 20 decibels

look at graph on slide 30 that is a typical presentation of loud noise hearing loss

Question 33

what are the two hearing tests that can be conducted?

Answer 33

Weber test
Rinne test

look at slide 33 to differentiate conductive and sensorineural hearing loss through the results of these tests

Question 34

what is taste and what are the primary tastes

Answer 34

interaction of dissolved moleules with taste buds

five taste are recognised:

1) sweet: sugar, ketones
2) sour: H+ ions
3) salty: NaCl
4) bitter: impo because found in toxic plants (has a low threshold)
5) umami: triggered by glutamate. truffles, meat, aged cheese and tomatoes

taste is closely related to smell - if nose blocked cant taste as well

Question 35

where are taste buds located

Answer 35

tongue, soft palate, pos wall of oropharynx and epiglottis

Question 36

name and identify the papillae

Answer 36

• vallate: supplied by IX (more sensitive to bitter)
• fungiform: supplied by VII (most numerous)
• foliate: poor developed

Question 37

what is the taste nerve supply fo the tongue?

Answer 37

ant 2/3 taste is form geniculate ganglion of facial

pos 1/3 taste is from inf ganglion of IX

epiglottis and soft palate is from X

Question 38

Explain the taste pathway

Answer 38

• all these sensory fibres come together and form the solitary tract
• Tractus solitarius synapse in
  nucleus of tractus solitarius (gustatory nucleus)
  • Axons of 2nd order neurons cross the midline
  • Join medial lemniscus
  • 2nd neurons synapse in thalamus (VPM)
  • 3rd neurons project to the cortex (prim gustatory cortex)

Gustation has a limbic component via the thalamus (tasty things can trigger past memories), and can activate brainstem nuclei for salivation, or vomiting

Question 39

Is olfactory ipsilateral or contralateral

Answer 39

ipsilateral - right side smell will go to right cortex (although it is connected to the left)

sense goes to cortex before thalamus (all other senses go to thalamus first)

Question 40

what is the olfactory system composed of?

Answer 40

• olfactory epithelium
• receptor cells (bipolar cells)
• axons (olfactory nerve) projecting through base of skull to olfactory bulb)
• neuronal tract (olfactory tract) to multiple olfactory destinations in brain

Question 41

what is the life span of olfactory neuroepithelial cells and how are they regenerated?

Answer 41

40-60 days and regenerate from basal cells (which can be used as stem cells)

Question 42

what moistens the olfactory cells

Answer 42

glandular goblet cells (bowman glands) moisten cells which facilitates olfaction

Question 43

what percentage of inhaled air comes in contact with the olfactory receptors and how may you increase the sensitivity

Answer 43

only 2%

sensitivity can be increased by forcefully sniffing

Question 44

describe the process of olfaction

Answer 44

• Odorants are dissolved in mucus secreted by Bowman glands
• Cilia of receptor cells (bipolar neurons) are activated
• Certain chemicals can activate other cranial nerves as well as the olfactory nerves and cause reactions.

medial olfactory stria –> limbic system

lateral olfactory stria –> olfactory cortex in medial temporal lobe

Question 45

what are the causes of anosmia?

Answer 45

• idiopathic (25%)
• nasal/sinus disease (25%)
  + colds
  + polyps
  + other blockages
• head trauma (15%)
  +leading to damage to frontal lobe processing
  +Leading to damage to ascending nerves at cribriform plate
  +Permanent compression of the nasal passages
• alzheimers preceding
• congenital anosmia

Question 46

what is parosmia

Answer 46

distorted often unpleasant sense of smell caused by damage to the lining at the top of the nose
- upper res tract viral infections