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Physiology Y2 > Hearing > Flashcards

Hearing Flashcards

1
Q

Explain comparative audiometric curves.

A

Sounds important to different animals can vary. Impact how these animals have evolved and the ranges of sound that they can hear. Sensitivity can mean a sound can be at its quietest and still be heard by some species at a certain frequency. Depending how the species has evolved will depict where the sensitivity is.

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2
Q

What are the main roles of the inner, middle and outer ear?

A

Inner ear is sensory. and middle and outer ear are conductive. The middle ear does impedance matching.

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3
Q

Describe the importance of impedance matching.

A
  • Ossicles have lever action
  • Eardrum to oval window surface area = 20:1 for this
  • Approximately x 26 pressure amplification
  • Without impedance matching, only 0.1% energy transfer
  • Unrelated to the cochlear amplifier
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4
Q

Describe the process of impedance matching.

A
  1. Tympanic membrane is vibrating and causes malleus to move and lever action of the incus and stapes.
  2. Stapes pressed up against the oval window, the window into the inner ear, behind this is the fluid of the canal in the inner ear.
  3. Energy in air to energy in fluid, which requires more energy.
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5
Q

Describe the structure of the mammalian cochlea spiral.

A
  • 22mm in length spiral in rat
  • Varies between species
  • Partially developed in some mammals at birth in altricial species
  • Compartments within the tube
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6
Q

What is the name of the mammalian auditory epithelium?

A

Organ of Corti

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7
Q

Describe the structure of the organ of Corti.

A
  • Located on flexible basilar membrane
  • Inner and outer hairs are sensory
  • Spiral ganglion nerve cells
  • Associated supporting and non-sensory cells
  • Hair cells held rigidly while basilar membrane can move
  • Endolymph has high potassium and high potential compared to perilymph with 0mV and low potassium ions. Perilymph bathes basolateral membranes.
  • Tectorial membrane is a jelly like membrane on top of the hair cells.
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8
Q

What are the 3 compartments in the cochlea coil?

A

Perilymph and endolymph. Scala media bear the organ of Corti, which has the sensory hair cells within it.

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9
Q

Distinguish stereocilia in inner and outer hair cells.

A

Inner hair cell: mainly afferent innervation is 10-20 terminals per cell. Inward calcium channels and outward potassium channels. Does sound encoding.

Outer hair cell: little afferent innervation. Prestin motor protein in lateral membranes. Does amplification and tuning

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10
Q

How do sound induced movements cause hair bundle stimulation?

A

At organ of Corti, sound energy set up wave in basilar membrane that moves along the length of the cochlea. Takes hair cells with it and moves hair bundles.

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11
Q

What does hair bundle stimulation cause?

A

Opens ion channels:

  • Tip links – gated springs
  • Mechanically gated transducer channel
  • Movements are tiny – perceptible sound at 0.3nm and saturation at 20nm
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12
Q

How does potassium activate afferent neurones?

A

Potassium moves into cell down concentration gradient via transducer channel. Cell depolarises and voltage gated calcium channels open. Calcium enters cell and neurotransmitter released, which activates afferent neurones.

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13
Q

Describe tonotopy for frequencies higher than 4kHz.

A

Basilar membrane has regional variation in fibrous structure, region of maximal displacement dependent on frequency of stimulus. Basilar separates out these frequencies. Tonotopic map produced from this by the basilar membrane. Neurones near the base have specific frequencies and bands of auditory cortex respond to specific frequencies.

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14
Q

What are the 3 populations of afferent nerves that encode amplitude?

A

High spontaneous rate fibres – easily excited at low sound levels, soon saturated.

Medium spontaneous rate fibres – excited at medium sound levels, will saturate.

Low spontaneous rate fibres – excited when sound levels are high, can detect changes in sound at very high sound levels.

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15
Q

How do outer hair cells act as a cochlear amplifier?

A
  • Depolarisation activates the motor protein, prestin
  • Rigidly held cells contract, amplifying basilar membrane movement
  • OHC loss leads to 60 decibels hearing loss and poor frequency discrimination
  • Amplify motion of basilar membrane and so stimulating the IHCs
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16
Q

List the primary central pathway from cochlea to brain.

A
  1. Spiral ganglion
  2. Ventral cochlear nucleus
  3. Superior olive
  4. Inferior colliculus
  5. MGN
  6. Auditory cortex
17
Q

What is required for sound localisation?

A

The brain compares the timing and intensity of input to the ears.

18
Q

How are horizontal, low frequency and high frequency sounds localised?

A

Horizontal – requires 2 ears and binaural processing.

Low frequency – comparison of the time at which the same phase of a sound arrives at each ear, interaural delay of the peak of the wave.

High frequency – interaural intensity difference

19
Q

What is the role of the pinna?

A

Pinnae motile in most animals. But pinna produce direct and reflected sounds. But properties of the pinna help in sound localisation.

20
Q

What are the conductive causes of deafness?

A

Outer or middle ear
Obstruction – wax, hair or dirt
Tumour
Infection/inflammation
Tympanic membrane damage

21
Q

What are the sensorineural causes of deafness?

A
  • Inner ear: hair cells and/or neurones
  • Congenital - born or progressive. Often associated with lack of pigmentation due to a problem with maintenance of endolymph
  • Noise damage
  • Ototoxic drugs, such as aminoglycoside antibiotics
22
Q

Name 3 ways of detecting deafness.

A

Owner’s observations
Preyer’s reflex
Brainstem auditory evoked response

23
Q

What is Preyer’s reflex?

A
  • Response to sound with movement
  • Startle reflex in mice
  • Elevation and rotation of ears in dogs
24
Q

What is brainstem auditory evoked response?

A
  • Electrodes placed on animals head used to detect neural activity in response to auditory stimulus
  • Most objective measurement
  • Referral – screening for breeding programmes
25
Q

What is kinaesthetic sense?

A

An awareness of the movement and position of parts of the body using sensory inputs. Body movement and position, vision and proprioception contribute to this sense. Balance and equilibrium system also input to this sense and in itself affects this position of the head with respect to gravity and acceleration, so varies across species. Sensory cells are mechanoreceptors: fish have ciliated epithelia in labyrinths, invertebrates have statocysts and birds and mammals have vestibular systems.

26
Q

What 2 sensory organs make up the mammalian vestibular labyrinth?

A

Semi-circular canals and otolithic organs

27
Q

What are the 2 sensory organs used for?

A

Semi-circular canal – critsa: sensitive to head rotation and angular acceleration

Otolithic organs – saccule and utricle: sensitive to gravity/tilt of head and linear acceleration

Both have hair cells

28
Q

Describe vestibular hair cells.

A
  • Mechanotransduction
  • Mechanotransducer channels
  • Hair bundle (stereocilia)
  • Bathed in endolymph
  • Directionally sensitive:
  • Positive – towards the tallest stereocilium (called kinocilium in the vestibular system)
  • Negative – towards the shortest
  • Transduction – similar to inner hair cells of the cochlea
29
Q

Describe transduction and encoding in vestibular hair cells.

A
  • Displacement towards kinocilium – depolarisation. Positive direction
  • Displacement from kinocilium – hyperpolarisation. Negative direction
  • High resting rate of nerve firing
  • Directional sensitivity – orientation is very important
30
Q

How do stereocilia bend in response to movement of the head?

A
  1. Movement of the head due to force
  2. Force acts on otoliths
  3. Moves cap
  4. Deflects stereocilia
  5. Depolarisation, hyperpolarisation or no change to receptor potential
  6. Change in rate of nerve firing
31
Q

How is information encoded by otolithic hair cells?

A
  • Hair cells orientation to transduce all movements, mirror image of organs
  • Curved shape in each of these organs means a constant change in direction of hair cells
  • During any movement, some hair cells excite, ither inhibited
  • CNS processes all information encoded by otolithic hair cells
32
Q

How does the CNS process signals from the semi-circular canals?

A
  • Rotation of the head causes movement of the endolymph fluid in the canals
  • Movement of the endolymph fluid displaces the cupula and the hair bundles
  • Hair cells orientated 1 way in each crista
  • Activation on one side results in inhibition on the other
  • CNS processes signals from all canals
33
Q

What are the central vestibular connections?

A
  • Coordinate and integrate information from vestibular and other systems
  • Control of motor neurones – head, eye and body position
34
Q

What is static balance?

A
  • Maintains posture when animal is still
  • Head may make tiny movements to vary stimulus
  • Utricle and saccule (gravity)
35
Q

What is dynamic balance?

A
  • Maintains posture during movement
  • May involve all vestibular organs but semi-circular canals are most important
36
Q

Describe the vestibulocular reflex.

A
  • Compensatory eye movements to fix a visual target
  • Vestibular and optokinetic input
  • Left canal stimulatory
  • Right canal inhibitory
  • Combined responses of extraocular muscles produce simultaneous, rapid and accurate eye movements
  • Equal and opposite eye movements
37
Q

Describe the species differences of the fixation of gaze.

A

Primates – eye movement in orbit most prominent

Other animals – head movement via neck muscles can be more prominent, but gaze fixing is still essential

Ungulates – reflex serves to keep eyes horizontal during grazing to maintain view of the horizon.

38
Q

Name some peripheral vestibular pathologies.

A
  • Kinetosis – motion sickness. Imbalance of CNS input form eyes and vestibular system. Common in dogs in moving car.
  • Lesions of inflammation
  • Head trauma
  • Middle or inner ear infection
  • Tumour
  • Idiopathic vestibular disease – ‘old dog’. Trauma, infection, tumour ruled out
39
Q

What are the symptoms of vestibular pathologies in domestic animals and why do they occur?

A

Acute, symptomatic or chronic, can compensate (unlike auditory system) using visual stimuli.

  • Exaggerated open stance
  • Head tilt
  • Lack of coordination/balance rolling or falling to one side/circling
  • Nystagmus without appropriate stimulus

Physiology Y2 (14 decks)

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