Sound Conduction and Transduction Flashcards
What scale is used to measure how loud a sound is?
Decibels (logarithmic scale)
What is pitch? What is the audible range for humans in terms of frequency?
Perception of frequency
20-20,000 Hz
What is the name given to the wing shaped flap of skin and cartilage that makes up the outer ear?
Pinna
Describe the shape of the outer ear and its importance.
Conical: starts off wide at the external auditory meatus + narrows to the tympanic membrane
This focuses the noise + increases the pressure on the tympanic membrane
Is the tympanic cavity fluid-filled or air-filled? What is its function?
Air-filled
Transmits vibrations of tympanic membrane across the cavity to the internal ear; accomplished by 3 interconnected but moveable bones (ossicles)
How do the ossicles increase the pressure of vibration of the tympanic membrane to match the impedance and reduce energy loss?
Incus has a flexible joint with the stapes, the resulting lever action increases force on the oval window
Stapes vibrates against superior oval window to induce pressure wave in inner ear fluid
Round window acts as a pressure release window- moves outwards to equalise pressure when stapes pushes oval window into cochlea
What is the point of the middle ear? Why isn’t the tympanic membrane continuous with the cochlea?
Cochlea contains fluid, in which you are trying to induce a pressure wave
If tympanic membrane was continuous with the cochlea, you would go straight from air to fluid + most of the energy will bounce back due to impedance
Sound waves require more energy to travel through fluid than air so the increase in pressure of vibration is crucial for this conduction
What 2 muscles are involved in making sure that the ossicles aren’t damaged by excessive vibration due to loud noise? What is the name given to this reflex?
Reflex contraction of Tensor Tympani + Stapedius reduce amplitude of vibrations passing through ossicles
Auditory reflex
What does displacement of stereocillia cause?
Opening of ion channels, depolarisation/ hyper polarisation of the nerve synapsing the hair cells
Bending of stereocillia towards the tallest stereocillium changes the internal voltage of the cell producing an electrical signal that goes to the brain (mechanotransduction)
What is the latency period of the auditory reflex?
50-100 ms
What is hyperacusis?
Painful sensitivity to low intensity sounds – can occur in conditions that lead to flaccid paralysis of the auditory reflex muscles (e.g. Bell’s Palsy)
Which test is used to determine the site of damage to the auditory system, that is causing hearing loss?
Weber Test
What are the 2 specialised membranes of the cochlea?
Oval Window
Round Window
What are the 3 chambers of the cochlea? What type of fluid does each contain?
Scala Vestibuli- Perilymph
Scala Media- Endolymph
Scala Tympani- Perilymph
What is the difference in composition of perilymph and endolymph?
Perilymph: Low K+, High Na+
Endolymph: High K+, Low Na+
What structure connects the 2 perilymph chambers?
Helicotrema
Describe the mechanism of sound transduction
Vibration of tympanic membrane moves malleus + incus laterally, pushing the stapes medially onto the oval window, generating a wave in the fluid filled cochlea
The wave moves through the cochlea causing 2ndary tympanic membrane to bulge leading to vibration of the basilar membrane + stimulation of receptor cells
Describe the difference in sensitivity of different parts of the basilar membrane.
Higher frequency sounds = base
Lower frequency sounds = apex
What is the Organ of Corti?
Sense organ of the cochlea, which converts sound signals into nerve impulses that are transmitted to the brain via the cochlear nerve
Where is the Organ of Corti found?
It lies on top of the basilar membrane + beneath the tectorial membrane
What are the 2 types of cell in the organ of corti?
Inner + outer hair cells
Describe 6 features and the function of inner hair cells.
Found alone
Not in contact with tectorial membrane
Send afferents to brain- provide sensory transduction
~3500 per cochlea
Function:
Have stereocilia that move in response to the movement of endolymph in the scala media
Transmit auditory stimulus
Describe 5 features and the functions of outer hair cells.
Found in groups of 3 In contact with tectorial membrane Receive efferents from brain Vulnerable to damage (can result in sensorineural hearing loss) ~11,000 per cochlea Function: Electromotile so can expand + contract to amplify the amount of vibration Control of inner hair cells
Which compartment of the cochlea does the stereocilia of the hair cells project into?
Endolymph (base is in the perilymph)
What internally generated sounds are the outer hair cells responsible for?
Otoacoustic emissions
What are stereocilia connected by? What do these act as? What is activated by stretching these?
Tip links
Act as small springs stretched by stereocillia sliding
Stretching results in opening of ion channels + response currents
What bony conical structure is found at the middle of the cochlea?
Modiolus
Describe what happens when the basilar membrane is displaced upwards.
Depolarisation
Stereocilia move away from the modiolus
K+ channels open
K+ enters from endolymph
Describe what happens when the basilar membrane is displaced downwards.
Hyperpolarisation
Stereocilia move towards the modiolus
K+ channels close
What separates scala vestibuli + scala media? What separates scala media + scala tympani?
Scala Vestibuli-Scala Media: Reissner’s (vestibular) membrane
Scala Media-Scala Tympani: Basilar membrane
Describe the central auditory pathway to the primary auditory cortex.
Hair cells depolarise Synapse with neurones in spiral ganglion Cochlear division of CNVIII synapses with the ipsilateral cochlea nucleus in medulla (dorsally + ventrally) - transmission onwards is bilateral Superior olivary nucleus Inferior colliculus Medial geniculate nucleus Auditory cortex
Up to what point is the auditory pathway from one ear ipsilateral?
Cochlear nuclei
Beyond this point there is bilateral representation
The inferior colliculus receives input from both cochlea. What is the inferior colliculus responsible for?
Reflex associations: turning your head towards loud noise
Describe a phenomenon that is involved in sharpening the signal coming from the cochlea.
Lateral inhibition
To which parts of the CNS do collaterals from the auditory pathway go?
Reticular formation
Cerebellum
In which lobe is the primary auditory cortex?
Temporal
What is the secondary auditory cortex responsible for?
Responding to sounds coming off/on
Responding to the duration of sound
What is the name given to the axons that project from the medial geniculate nucleus to the primary auditory cortex?
Acoustic radiations (travel via the internal capsule)
How do you localise short sound burst?
How do you localise continuous sound?
Short: Interaural time delay
Continuous: Interaural intensity difference
What is conductive hearing loss?
Middle ear damaged
Ear not capable of transmitting vibration of sound waves onto cochlea
Amplification system is eliminated
What is sensorineural hearing loss and what can it be caused by?
Cochlea/ cochlear nerve damaged
Signal transmitted to the primary auditory cortex is reduced/ lost
What is the term used to describe loss of hearing due to the death of hair cells in normal ageing?
Presbyacusis
What is Timbre?
What distinguishes 2 sounds at the same frequency + intensity
What is the hair bundle?
A cluster of modified microvilli called Stereocillia
What does impedance measure?
Reluctance of a system in receiving energy from a source
What is resonant frequency?
Frequency at which the impedance of the system is minimal
What is effected in conductive hearing loss? List 4 causes
Outer + middle ear
Ear is not capable of transmitting the vibration of sound waves onto the cochlea
Fluid accumulation in inner ear, perforated tympanic membrane, ostosclerosis + barotrauma
What generates a difference in pressure between the 2 liquid filled chambers of the cochlea? What is the consequence of this?
Motion of the Stapes
Causes vibration of basilar membrane
What is the Organ of Corti comprised of?
Basilar + Tectorial membranes
Hair cells
Supporting cells
Define intensity and volume
Intensity: Amplitude of sound waves
Volume: Perception of amplitude
What is the external ear composed of?
Pinna (Auricle)
External acoustic meatus (auditory canal)
Tympanic membrane (ear drum)
Name the auditory ossicles and describe their connections
Malleus: connected to tympanic membrane
Incus: connected to malleus by synovial joint
Stapeus: connected to Incus by synovial joint + attached to lateral wall of the internal ear at oval window
What is the internal ear composed of?
Bony labyrinth (3 parts- vestibule, semi-circular canals, cochlea) Membranous labyrinth (Membraneous ducts + sacs within bony cavities)
What is the bony labyrinth lined and filled with?
Lined with periosteum Fluid filled (perilymph)
List the components of the membraneous labyrinth and their functions. What are these spaces filled with?
Semi-circular ducts: balance
Cochlear duct: Hearing
2 sacs: Utricle + Saccule: Balance
All filled with endolymph
How is sound amplified by the structure of the tympanic membrane and oval window?
Focussing the vibrations from large SA of tympanic membrane to small SA of oval window
Decrease in SA results in pressure increase
What maintains the concentration gradient of Na+ and K+ between the different cochlea compartments?
Stria vascularis
Describe the difference in fibres on the basilar membrane
Base= Short + stiff - vibrate in response to high frequency End= Long + loose - vibrate in response to low frequency
What is meant by tonotopic mapping?
Different parts of auditory cortex for different pitches
Low frequencies = ventral neurones
High frequencies = dorsal neurones
What can cause conductive hearing loss?
Wax Infection Otoscleorisis of ossicles Perforated tympanic membrane Barotrauma Fluid accumulation
State 3 causes of pre-lingual hearing loss
Perinatal/ bacterial meningitis
Congenital infection e.g. rubella
Head injury
State 6 common causes of hearing loss in adults
Genetics Ototoxicity (chemotherapy) Infection Tumour Head injury Loud noises
Name 1 solution to address the loss of hair cells causing hearing loss
Bypass dead cells + stimulate nerve fibres directly with cochlear implants
