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MD4001 > Anatomy and function of hearing, smell and taste > Flashcards

Anatomy and function of hearing, smell and taste Flashcards

1
Q

What dictates the pitch of a sound?

A

The frequency: the higher the frequency, the higher the pitch

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2
Q

What dictates the intensity of sound?

A

The amplitude

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3
Q

Overview of hearing

A
  • First transduction: sound wave strikes the tympanic membrane and becomes vibrations
  • The sound wave’s energy is transferred to the 3 bones of the middle war which vibrate (malleus -> incus -> stapes)
  • Second transduction: the stapes is attached to the membrane of the oval window, vibrations of the oval window create fluid waves within the cochlea
  • Third transduction: fluid waves push on the flexible membranes of the cochlear duct. Hair cells bend and release the neurotransmitter
  • Fourth transduction: neurotransmitter release onto sensory neurones creates action potentials that travel through the cochlear nerve to the brain
  • 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
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4
Q

What makes up the external ear?

A
  • Pinna (auricle)

* External auditory (acoustic) meatus

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5
Q

What is the pinna?

A
  • Also called auricle
  • Single piece of cartilage
  • Ear lobe, tragus, helix etc.
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6
Q

Describe the external auditory (acoustic) meatus

A
  • Cartilaginous and bone parts: not in the same direction
  • Ceruminous glands secrete earwax making it waterproof preventing the maceration of skin and preventing entry of foreign objects
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7
Q

How can you test to see if pain is referred or coming from the ear?

A

Palpate the tragus

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8
Q

What is the supply of the external auditory meatus?

A
  • Auricular branch of the vagus

* Auriculotemporal branch of the trigeminal

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9
Q

Describe the tympanic membrane

A
  • Concave
  • 4 quadrants divided by the (shadow of the) handle of malleus
  • Triangular reflection (Pulitzers triangle) in the anterior inferior quadrant
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10
Q

Which quadrant is chorda tympani found in?

A

Postero- superior quadrant

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11
Q

Which of the quadrants of the tympanic membrane is the safest?

A

• Antero-inferior quadrant

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12
Q

What is the middle ear?

A
  • An air filled cavity with ossicles (malleus, incus and stapes- attached to walls by ligaments), muscles/tendons (tensor tympani and stapedius) and nerves (chorda tympani)
  • it has 4 walls (lat. wall is the tympanic membrane), a roof (bone between the middle ear cavity and the middle cranial fossa) and a floor
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13
Q

What are the ossicles of the ear?

A
  • Malleus
  • stapes
  • Incus
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14
Q

What muscles are found in the middle ear?

A
  • Tensor tympani

* Stapedius

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15
Q

What is the auditory tube? What is the nerve supply?

A
  • Also called pharyngotympanic/ Eustachian tube
  • Mucous membrane continuous with the pharynx
  • Supplied by glossopharyngeus
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16
Q

What happens if there is a fracture to the roof of the middle ear cavity?

A

• CSF will leak through, if the tympanic membrane is ruptured, CSF will leak out of the ear

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17
Q

What is the opening in the posterior aspect of the middle ear cavity?

A
  • Adits as antrum

* Connects to the mastoid antrum and the mastoid air cells

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18
Q

What is chorda tympani a branch of?

A

The facial nerve

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19
Q

What is the role of tensor tympani?

A
  • Pulls the tympanic membrane medially

* Increases the tension in response to loud noises which reduces the vibration of the tympanic membrane

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20
Q

What is the innervation of tensor tympani?

A

• Mandibular nerve (branch of the trigeminal)

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21
Q

What is the role of stapedius?

A
  • Pulls the base of the stapes away from the oval window

* Protects the inner ear from injury from a loud noise

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22
Q

What is the innervation of stapedius?

A

• Facial nerve

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23
Q

What happens if there is injury to the muscles of the inner ear?

A

Hyperacusis

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24
Q

Describe the pharyngotympanic tube

A
  • The walls are normally closed
  • Actively opened by the simultaneous contraction of tensor veli palatini and salpingopharyngeus muscle
  • This forces air into the cavity and equalises pressure
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25
Q

Describe the pharyngotympanic tube in children

A
  • Straight and short

* pharyngeal infections can easily spread to the middle ear

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26
Q

What makes up the inner ear?

A
  • bony labyrinth: vestibule (utricle and saccule), semicircular canals, cochlea
  • Membranous labyrinth
  • Perilymph (between the two labyrinths)
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27
Q

What contains endolymph?

A

The cochlear duct

28
Q

What is the auditory organ and where is it located?

A
  • Organ of corti
  • On the basilar membrane
  • It contains ciliated cells
29
Q

Describe the basilar membrane

A

• Extends from the tip of the osseous spiral lamina to the wall of the spiral canal

30
Q

How is frequency detected?

A
  • The structure of the basilar membrane changes from short and stiff to long and floppy along the length of the cochlea
  • Resonant frequencies vary along the cochlea with 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
  • This is tonotopic organisation
31
Q

Describe signal detection at the organ of corti

A
  • Upward deflection of the basilar membrane moves the inner and outer hairs laterally with respect to the tectorial membrane
  • 95% of the cochlear nerve endings terminate on inner hair cells
  • Outer hair cells increase the sensitivity of the inner hair cells (this can tune the cochlea by amplifying select frequencies)
32
Q

What happens as a result of the displacement of stereo cilia?

A

• One direction opens K channels and closes them in the other

33
Q

Describe how the auditory signal at the centre of a standing wave is enhanced?

A
  • Inner hair cells become depolarised and send signals to the cochlear nerve then to the CNS - mechanical displacement does not provide the sharpness of pitch discrimination recorded
  • Outer hair cells are stimulated by the basilar membrane to depolarise: this causes the cell to contract, and enhances the auditory signal at the centre of the standing wave and inhibits on either side
34
Q

Describe how areas of pitch of no interest are dampened down?

A
  • Olivocochlear neuronal control
  • Fibres along this path release Ach onto the inner hair cells causing them to depolarise
  • This damps down hearing in areas of pitch that are of no interest to the listener
35
Q

Which antibiotic can cause an effect on hearing? What is this effect?

A
  • Kanamycin
  • Preferentially kills outer hair cells in a specific point along the cochlea resulting in specific frequency hearing loss at that point
36
Q

Knockout of prestin

A
  • Prestin in the cell membrane motility protein
  • You lose 40-69 decibels of your hearing at that frequency i.e. the outer hair cell amplifier provides a 40-60 decibel gain in sensitivity
37
Q

What is otoacoustic emission?

A

Sound comes out of the ears (tympanic membrane relieves vibration that has traveled from the cochlea to the middle ear)

38
Q

Describe the auditory pathway

A
  • Hair cells of the organ of corti generate an electrical signal
  • Peripheral extensions of the bipolar neurones at the spinal ganglion synapse with hair cells of the organ of corti
  • Central extensions of bipolar neurones form the cochlear nerve
  • The cochlear nerve synapses at the anterior and posterior cochlear nuclei
  • Central extensions of 2nd order neurones split up with some travelling ipsilaterally, but most contra laterally up to the respective superior olivary nucleus
  • Lateral lemniscus (3rd order) ascend and synapse at inferior colliculus
  • 4th order neurones project to the medial geniculate nucleus of the thalamus where they synapse
  • 5th order neurones join the auditory radiation to the auditory cortex
39
Q

What causes the arousal response to noise?

A

Collaterals from the pathway project into the reticular formation and the vermis of the cerebellum

40
Q

where do secondary projections from the primary and thalamic association area go?

A

To the auditory association cortex - sound is relayed topographically with lower frequencies to the anterior in most maps

41
Q

Describe volume and sound shadow

A
  • Sound from one side hits the head which generates a sound shadow on the other side in which the volume is less
  • The comparison of signal intensities from both ears determines the ear closest to the sound
  • better for higher frequencies
42
Q

Describe sound lag

A
  • Sound from a particular direction enters one ear before the other and so there is a slight delay between the side arriving ipsilaterally at the auditory cortex and that arriving contra laterally
  • Better at lower frequencies
43
Q

What helps to determine horizontal direction of sound?

A

Sound lag

44
Q

How is front/back or above to below detected?

A

Folds in the pinna

45
Q

What is a conduction deafness?

A

• Something that stops vibration reaching the inner ear
For example:
• A blockage in the outer ear
• Infection in either the outer or middle ear
• Ossification of the small bones in the middle ear
• rupture of the tympanic membrane

46
Q

What causes a sensory- neural defect?

A
  • Breakdown of the cochlea and associated mechanisms
  • Damage to the auditory nerve
  • Damage to the auditory cortex
47
Q

What causes tinnitus?

A
  • Damage of outer and inner hair cells

* Usually the first manifestation of auditory damage

48
Q

Which tests can differentiate between a conduction and a sensory-neural deafness?

A

• Weber’s test: tuning fork in the middle of the forehead, heard equally on both sides
- Normal: sound perceived as coming from the midline
- Sensorineural: Sound perceived as coming from the neural ear
- Conductive: sound perceived as coming from the affected ear
• Rinne’s tesat: air conduction is better than bone conduction (AC>BC); if BC>AC then conductive loss

49
Q

How do we taste?

A

Molecules dissolved in saliva interact with taste buds

50
Q

What are the primary tastes?

A
  • Sweet: sugar, glycols, ketones
  • Sour: H+ ions
  • Salty: NaCl
  • bitter: Quinine, alkaloids found in toxic plants
  • Umami: triggered by glutamate
  • Oleogustus: taste of a fatty acid
51
Q

Where are taste buds located?

A

On the oral surface of the soft palate, the posterior wall of the oropharynx and the epiglottis

52
Q

What are the different taste buds?

A
  • Foliate papilla
  • Vallate papilla
  • Filiform
  • Fungiform papilla
53
Q

Vallate papilla

A
  • Along sulcus terminalis
  • Supplied by glossopharyngeal nerve
  • More sensitive to bitter
54
Q

Foliate papilla

A

• Poorly developed

55
Q

Fungiform papilla

A
  • Most numerous

* Supplied by the facial nerve

56
Q

What does chorda tympani innervate?

A

• Taste from anterior 2/3 of the tongue

57
Q

Describe the course of chorda tympani

A
  • Branch of the facial nerve
  • Travels with the lingual nerve
  • Infratemporal fossa -> petrotympanic fissure -> middle ear cavity -> joins facial nerve
58
Q

What is the special sensory afferent nerve supply to the tongue?

A
  • Anterior 2/3 chord tympani: the facial nerve

* Posterior 1/3: glossopharyngeal

59
Q

What conveys taste from the epiglottis and the soft palate?

A

• Vagus

60
Q

Describe the taste pathway

A
  • Central processes of neurones conveying taste from tracts solitaires (solitary tract)
  • Tractus solitarius synapse in the nucleus of tractus solitaires (solitary nucleus, gustatory nucleus)
  • Axons of second order neurones cross the midline
  • Join medial lemniscus
  • 2nd neurones synapse in the thalamus
  • 3rd neurones project to the cortex
  • Gustation has a limbic component via the thalamus and can activate the brainstem nuclei for salivation, or vomiting
61
Q

What do olfactory neuroepithelial cells regenerate from?

A

Basal cells

62
Q

What percentage of air comes into contact with the olfactory receptors?

A
  • 2%

* Sensitivity can be increased by forceful sniffing

63
Q

What facilitates olfaction and moistened the olfactory canal?

A

Mucus produced by the bowman glands

64
Q

What forms the olfactory nerve?

A

• Central processes of receptor cells

65
Q

What causes anosmia?

A
  • Idiopathic
  • Nasal/ sinus disease
  • Head trauma
  • Alzheimer’s preceding
  • Congenital anosmia
  • Parosmia

MD4001 (28 decks)

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