Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

🧠 Essays > 20.4 Audition > Flashcards

20.4 Audition Flashcards

1
Q

Define hearing

A
  • The ability to perceive sounds by detecting vibrations
    • Vibration = variation in pressure of a physical medium (air/water)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the function of hearing?

A
  • Facilitating communication through speech
    • Important role in spoken language
  • Identifying potential dangers outside of the visual field
  • Aesthetic function in the appreciation of sounds such as music
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Give an introduction to the auditory system as well as well an overview of the peripheral and central auditory systems

A

​

  • The auditory system conducts and transduces sound pressure waves into electrical signals that are then transmitted to and processed by higher cortical centres.
  • Peripheral
    • The peripheral auditory system consists of all structures involved in audition that lie outside of the central nervous system
    • Its anatomical constituents are the ear (external, middle, cochlea) and cochlear branch of the vestibulocochlear nerve (CN VIII)
    • Functions
      • Conduction of sound pressure waves from the environment to internal structures (the external and middle ear)
  • Central
    • The central auditory system consists of CNS structures involved in audition
      • This comprises the brain regions involved in audition (the auditory pathway)
    • Functions
      • Transmission of auditory signals through the CNS
      • Processing of auditory information
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is sound?

A
  • Sound = audible variation in the pressure of a physical medium such as air or water
  • Sound is generated by vibrating objects that displace molecules in the surrounding medium
  • This displacement is propagated as a pressure wave away from the source, characterised by alternating regions of compressions (higher molecular density) and rarefactions (lower molecular density)
    • Compression = increase in density and air pressure
    • Rarefaction = reduction of density and air pressure
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the simplest sound? What are its two defining characteristics?

A
  • Pure tone:
    • The simplest sound is a pure tone, which is a sound wave with a sinusoidal waveform (increases and decreases in pressure) – it follows a sine wave pattern.
    • There are two defining characteristics (components) of a pure tone:
      • Frequency
        • Frequency is the number of wave cycles per second (measured in Hertz)
        • Frequency is perceived centrally as pitch
        • An alternative measure of frequency is wavelength which is the distance between two corresponding points on adjacent cycles
      • Amplitude (intensity)
        • Pressure difference between the wave peak and mean value
          • Maximal displacement of wave from a position of equilibrium
        • It represents the maximal and minimal pressures of the medium being displaced
        • Amplitude is perceived centrally as volume/loudness
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the dynamic range of Pascals and decibels that a human ear can detect

A
  • 2 x 10-6 Pascals to 200 Pascals
  • 0 dB to 140 dB
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Introduction to peripheral audition essay

A

* Define the inner ear

* ​Most medial sub-division of the ear
* Comprised of the **cochlear** and **vestibular apparatus** that form the **membranous labrinth** * **Function**
* The cochlear houses the auditory receptors and functions to **transduce auditory signals into action potentials** that are transmitted to the CNS for the perception of sound (hearing) * **Perceptive**
* Hearing has evolved primarily to alert us of dangers outside of the visual field and provide a means of **communication** by **facilitating speech**
* However, in humans, audition has evolved beyond survival and utilitarian functions, for example the use of **music** to evoke emotion * **Clinical / experimental**
* The loss of transduction of sound from the environment to the CNS by the inner ear can therefore impact these functions, some of the causes of which will be discussed in this essay, alongside current and future treatments that use our understanding of inner ear function
* **Cochlear hearing loss**
* **Sensorineural hearing loss**
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the function of the external ear and middle ear?

A
  • Their role is to conduct sound energy from the surrounding medium (usually air) to the cochlear of the inner ear
  • In the cochlear, sound is transduced into electrical impulses
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the structures of the external ear

A
  • Pinna
    • Cartilaginous structure covered by the skin
  • External auditory meatus
    • Sigmoid shaped tube that conducts sound to the tympanic membrane
      • Outer 1/3 of the tube is cartilaginous
      • Inner 1/3 of the tube is formed by the tympanic part of the temporal bone
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the function of the external ear?

A
  • Protection
    • Protects the tympanic membrane (delicate and susceptible to rupture)
  • Funnel action
    • Acts as a funnel to collect sound and direct it into the ear
      • This is also important for pressure gain
  • Pressure gain
    • The increase in amplitude of sound frequencies by a certain number of decibels
    • Mechanism
      • The different localisations of the sound source result in modification of the amplitude of the sound
      • These result in the generation of spectral cues that mediate monoaural sound localisation in higher centres
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Outline the structures of the middle ear

A
  • Consists of:
    • Tympanic membrane
      • Sheet of tissue attached to the temporal bone by a fibrous ring
      • Fibres from the ring radiate into the central apex
    • Ossicles
      • Series of small bones in the middle ear
    • Malleus (hammer)
      • Largest ossicle
      • Attached to the tympanic membrane via a lateral process (handle)
      • Narrow neck that gives an anterior process that attaches to the body of the incus
    • Incus (anvil)
      • Long limb terminating in a lens-like process which articulates with the head of the stapes
    • Stapes (stirrup)
      • From the head has 2 limbs and a base
      • These connect to the oval window in the medial wall
  • Muscles
    • Attach to the ossicles and move them
  • Tensor tympani
    • From the anterior wall of the tympanic cavity to the handle of the malleus
    • Innervated by the trigeminal nerve (5)
    • Function
      • Pull the tympanic membrane onto the malleus and dampen vibrations caused by high intensity sound
  • Stapedius
    • Attaches to the neck of the stapes
    • Innervated by the facial nerve (7)
    • Functions
      • Dampens the oscillations of the stapes at the oval window and transmission of the inner ear
  • Eustachian tube
    • Connects the nasopharynx to the middle ear
    • Allows pressure equilibration of the middle ear with atmospheric pressure as the tube is opened while swallowing
    • The canal between the nasopharynx and Eustachian tube is not always open but opens when yawning/sleeping to allow pressure to equilibrate
      • Infection of the nasopharynx can reduce the equalisation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the principal function of the middle ear? Describe the mechanism.

A
  • The principal function of the ME is the transmission of sound energy from the EE to the cochlea of the IE by a mechanical coupling mechanism that converts pressure waves in air to pressure waves in the cochlear fluid
  • The ME contains three bones known as ossicles – the malleus, incus and stapes
    • They are attached in sequence by ligaments
  • The malleus is attached to the tympanic membrane (TM) while the footplate of the stapes is attached to the oval window (OW) of the cochlea
  • Displacement of air by the sound wave causes resonant movement of the tympanic membrane
  • Movement of the tympanic membrane causes movement of the ossicles resulting in displacement of the oval window inward and outward and thus displacement of the cochlear fluid
  • Pattern of oval window movement
    • An increase in pressure (compression – positive wave peak) pushes the tympanic membrane and thus oval window inward
    • A decrease in pressure (rarefaction – negative wave peak) pulls the tympanic membrane and oval window outward
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Outline the importance of the ossicles

A
  • Impedance matching
    • The ossicles are important because they match the impedance of air to the impedance of the cochlear fluid
      • Impedance = resistance to displacement
    • The cochlear fluid is denser than the air meaning that a given displacement of air would translate to a smaller displacement of water molecules for the same force applied which would result in loss of pressure and thus amplitude
  • Mechanisms of impedance matching
    • Mechanisms drive an increase in pressure by 40-fold at the oval window compared to the tympanic membrane resulting in a more extreme displacement of the cochlear fluid
    • Underlie the efficient transfer of sound – without it most sound would not reach the inner ear
  • Adaptations
    • Surface area
      • The surface area of the TM is much greater than the OW therefore pressure at the OW is increased by the same scale factor (17-fold)
    • Lever action
      • The malleus is longer than the incus, increasing the movement at the stapes and thus raising the force applied
    • Buckling of the tympanic membrane
      • The TM buckles when moving, further increasing the force transmitted
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Outline the importance of the middle ear reflex and its function

A
  • The muscles are important in the middle ear reflex
    • The reflex contraction of these muscle stiffens the ossicle apparatus, limiting their movement
    • This reduces the transmission of sound through the ME, resulting in a smaller displacement of the OW for a given displacement of the TM and thus lowers the amplitude of the mechanical wave
  • A number of functions have been proposed for this middle ear reflex:
    • Protection
      • Protection of the ear from high intensity/amplitude that could cause damage
        • However, reflex has a delay of 50-100 ms and thus does not protect from sudden loud noises
    • Reduce self-stimulation
      • Reduction of auditory self-stimulation during speech by contracting before vocalisation
      • This increases the sensitivity to external sound
      • Evidence
        • The increased contraction of the muscles at lower frequencies of sound compared to the frequency of speech
        • Measuring the contraction of the muscles shows they contract before the onset of speech but contract with latency with external sound
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Outline conductive hearing loss

A
  • The failure of the external and middle ear to transmit mechanical waves associated with sound to the inner ear
  • External ear causes:
    • Earwax of a foreign body blocking the EAM
    • Infection of the external ear (otitis externa)
    • Congenital stenosis of the EAM
  • Middle ear causes
    • Infection of the middle ear (otitis media) which can lead to the accumulation of fluid (effusion) in the ME cavity that impairs normal transmission
    • It can also result in fibrosis of the tympanic membrane, limiting its movement
    • Bone deposition / growth in the ligaments of the ossicles (ostosclerosis) limit their range of movement
    • Perforation of the tympanic membrane
  • Treatment
    • Otitis media
      • Otitis media can be treated with antibiotics
      • Children with recurrent otitis media can benefit from the surgical implantation of ventilation tube known as a grommet into the TM that provides ME ventilation and drains fluid
    • CHL relating to the middle ear can also be treated surgically through the removal of fibrous tissue or replacement of the conductive apparatus with a prosthesis

*

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What can the Rinne test be used to diagnose? Outline the Rinne test

A
  • CHL can be diagnosed with the Rinne test

​

  • Loudness is compared when the tuning fork is placed near the external auditory canal and then pressed firmly against the skull behind the posterosuperior margin of the pinna
  • The patient is asked whether it sounds louder at the external auditory meatus or on the skull, the air-conducted sound as the meatus is louder than the bone-conducted sound
  • In conductive haring loss (>25 dB air-bone gap), the bone conducted sound will seem louder than the air-conducted sound
    • In bone conduction, the temporal bone acts as the conducting medium to the inner ear
  • If the fork sounds equally loud, this suggest sensorineural hearing loss (damage to the inner ear or neural pathway)
17
Q

Describe the components of cochlear structure

A
  • Components of the cochlear
  • Fluid of the cochlear
  • Organ of Corti
18
Q

Describe the compartments of the cochlear

A
  • The cochlear is divided into 3 fluid-filled compartments visible in the transverse section
  • Scala vestibuli
    • The upper compartment is known as the scala vestibuli (SV) which runs from the oval window at the base of cochlea to the apex of the cochlea
  • Scala tympani
    • The lower compartment is the scala tympani (ST) which is also filled with perilymph
    • The ST runs from the round window at the base of the cochlea to the apex of the cochlea
    • At the apex of the cochlea, the SV and ST are connected by the helicotrema, a hole that makes the fluids continuous with each other
  • Scala media
    • The middle compartment is the scala media (SM) which lies between the SV and ST and terminates at the cochlear apex
    • The SM is separated from the SV by Reissner’s membrane and from the ST by the basilar membrane
19
Q

Desribe the fluid of the cochlear

A
  • Perilymph
    • Has a similar composition to normal extracellular fluid (ECF)
      • High [Na+] (140 mM)
      • Low [K+] (7mM)
  • Endolymph
    • Has a composition like intracellular fluid (ICF)
      • Low [Na+] (1 mM)
      • High [K+] (150 mM)
        • Na+ - 1 to 140
        • K+ - 7 to 150
  • The endolymph ionic composition is generated by the action of the Na+/K+ ATPase in the stria vascularis (SV)
    • Stria vascularis = epithelium lining the lateral wall of the SM
  • Endocochlear potential difference
    • The difference in fluid composition generates an across a potential difference across the basilar membrane between the SM and ST of 80 mV
      • Endolymph is 80mV more positive than the perilymph
      • Important in the transduction process (described later)
20
Q

Describe the Organ of Corti

A
  • Running along the basilar membrane in the SM is the Organ of Corti (OOC)
    • Organ of Corti = sheet of columnar epithelium that acts as the receptor organ of the cochlea
21
Q

Describe the hair cells at the organ of Corti

A
  • Hair cells are epithelial cells that perform mechanoelectrical transduction, acting as the receptor cells of the auditory system
  • Named hair cells due to their apical stereocilia
  • There are two types of auditory hair cell, named by their position relative to the central axis of the modiolus
    • Outer hair cells (OHC)
      • Located on the outer axis of the modiolus
      • Function to mechanically amplify sound energy
        • Amplify BM motion
      • Bundles is V-shaped
        • With the tallest stereocilium at the tip of the V
    • Inner hair cells (IHC)
      • Located on the inner axis of the modiolus
      • They are the main auditory receptor cells that mediate sensory transduction
      • Bundles are arranged in a linear row
  • Stereocilia
    • Each hair cell expresses a bundle of a few hundred apical stereocilia
    • Stereocilia are larger versions of the microvilli expressed on many epithelial cells
    • They contain a core of actin filaments running from base to tip
    • Cross linked with epsin and fimbrin
    • In each bundle, the stereocilia are aligned in height order, giving the bundle a bevelled tip
      • Important in dictating the pattern of displacement during transduction
22
Q

Describe the tectorial membrane

A
  • Tectorial membrane = layer of acellular collagenous gel
  • Above the OOC lies the tectorial membrane
    • (not to be confused with the tympanic membrane)
  • The TM is in direct contact with the OHC stereocilia and is separated from the IHC stereocilia by a thin layer of endolymph
23
Q

Describe the supporting cells

A
  • Pillar cells
    • Support the IHC bases
    • More elastic than inner hair cells so are thought to convey stability to the inner cochlear
  • Deiter cells
    • Support the OHC bases
    • They transmit force and coordinate shift of adjacent hair cells through highly organised microfilaments
24
Q

Outline auditory transduction

A
  1. Basilar membrane displacement
  2. Hair cell transduction
    • ​Depolarisation
    • Hyperpolarisation
25
Q
A

🧠 Essays (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions