Sound Conduction and transduction Flashcards
What is frequency of a sound?
The number of wave amplitueds in a certain number of time
What is pitch?
Pitch is the perception of frequency
What is volume (on a physical laevel)
Amplitudes of sound waves
Explain the decibel scale
It shows the intensity of a sound wave (W/m2) in relation to the lowest possible detectable sound intensity of human hearing
This number is log. to get nice numbers (otherwise would be not nice)–> Bel scale
And then times 10 to get deciBel scale
Whar are the names of the osscicels in the middle ear?
What is impedance in context of function of the middle ear?
The term “impedance” in this context describes a medium’s resistance to movement
The major function of the middle ear is to match relatively low-impedance airborne sounds to the higher-impedance fluid of the inner ear.
What is the resonanz frequency?
It is the frequency in which the impedence of.a system is minimal
–> frequency that is the easiest transmittet within the medium
What is the function of the middle ear?
To transmit sound from a (low impedance) air filled space via the tymphanic membrane (ear drum) into the cochlear and amplify it (because needs to be amplified to move into fluid)
What is conductive hearing loss?
Hearing loss because of problems to the middle ear–> no sound conduction from tympanic membrane to cochlear
What are the causes for conductive deafness?
- fluid accumulation in the inner ear (cold)
- A perforated tympanic membrane
- An abnormal growth of bone (otosclerosis)
- Barotrauma is a temporary form of conductive hearing loss. (Valsalva maneuver to reopen the Eustachian tubes)
What is a sterocilium?
It is a cilium on top of a acoustic/vestibular hair cell
Explain theoragnasation of and connection between individual sterocilia
They are organised in groups and get smaller–> on cell has one tallest sterocilium and more that get smaller and smaller
Tey are connevted via tip links. They work as small springs stretched by the stereocilia’s sliding
What is meant by the active process of hair cells?
The hair cell, once generated a responce, actively adapts to the stimmulu by moving itself into the direction dictated by the stimulus –> active genaration + freeing of ion channels
Explain the sprecess from moving of a hair cell into generation of an action potential
What is this process called?
In respnse to a stimulus—> tip links of sterocilia on hair cells move and open mechano-electrical transduction (MET) channels
–> It is called Mechanotransduction
What are the four apsects of the active process in hearing?
- Amplification
- active amplification signal by BM in response to its resonant frequency
- Frequency tuning
- selectively amplifies speceific/single frequencies
- Compressive nonlinearity
- within increasing intensity (volume) of stimulu less amplification can be seen
- Spontaneous ostoacoustic emmission
- generation of hearing sensation without actual stimulus (to counteract viscous drag in cochlear)
Which two types of hair cells are there?
Inner hair cells (IHCs): ~3500 per human cochlea Outer hair cells (OHCs): ~110000 per human cochlea
What is the function of the inner hair cells in the cochlear?
5% of afferent projections (sensory axons that carry signals from the cochlea towards the brain) project from IHCs. IHCs provide sensory transduction.
Via changes of flow in the endolymph induced by movement of the Tectorial membrane
What is the function of the outer ear cells in the cochlear?
Most of the efferent projections (from the brain to the cochlea) connect to OHCs
possibly to enable the active process via the process of electromotiltiy –> shorten and elongation in response to inner voltage changes –> transduct vibration of the basilar membrane on the tectorial membrane to amplify the movement of the liquid that the inner hair cells can sense
What is sensorineural hearing loss?
When the problem lies within the inner ear (cochlear) or nerve conduction
What are possbile reasons for senrsorineural hearing loss?
- Loud noises, headphones at high volume can cause temporary or permanent hearing loss (Club: ~100 dB, Rock concert: ~120 dB)
- Many genetics mutations affect the Organ of Corti
- Aminoglycoside antibiotics are toxic for hair cells
- Congenital diseases (rubella, toxoplasmosis)
- Acoustic neuroma (tumor on the cochlear nerve)
- Ageing (presbycusis)
- • Demyelination = loss of myelin (can be due to inflammation or viral, MS
- Blast injuries can cause disruption in the balance between inhibition and excitation.
Explain the location and the tonotopically organisation of the ventral cochlear nucleus
It is located lateral doralls in the medulla
Its tonotopical mapping has following characteristics:
low frequencies ventrally, high frequencies dorsally
Which part of the hearing apparatus is involved in vertical location of sound in space?
dorsal cochlear nucleus
Which part of the hearing apparatus is involved with localisation of sound in the horizontal plane?
How does it do it?
Lateral superior olive
differences in intensity between the two ears (>2 kHz in humans due to head size). Interaural level difference is used to distinguish and the difference in time of signals
What is the role of the large calyces of Held?
Excitation that arrives ipsilaterally must arrive at the same time as inhibition from the contralateral side.
The contralateral inhibitory signal is carried out via large axons with large synapses (the large calyces of Held). The axons that carry ipsilateral excitations are smaller and conduct more slowly.
–> to localise and percieve sound
Myelinated fibres to I+OHC (from the SOC bilaterally) Unmyelinated to O+IHC(from the SOC ipsilaterally)
What is the role of the superior olive in feedback generation to the cochlear?
Nucleus involved in auditory reflex
SOC neurons send feedback to the hair cells. Activity in these efferent fibres increases the representation of signals in noise and protects it from damage by loud sounds (auditory reflex)
The feedback is used to balance the responses from the two ears, but also to reduce the sensitivity of the cochlea
Explain the role of the inferior colliculus in auditory perception
All ascending auditory pathways in vertebrate converge here
–> many neurons with different function, many carry information about sound location. Precedence effect
What is the role of the Superior colliculus?
Here auditory and visual maps merge. Neurons are tuned to respond tostimuli with specific sound directions.
The auditory map here created is fundamental for reflexes in orienting the head and eyes to acoustic stimuli.
Which part of the auditory system is involved in refelxes?
Superior colliculus
Explain the route of neural information flow from the ear to the autditory cortex
- auditory neural signals detected by the hair cells of the organ of Corti
- → bipolar neurons of the cochlear or spiral ganglion via the 1.cochlear part of the vestibulocochlear nerve
-
Cochlear nucleus →
- ventral(tonotopical mapping, high frequencies dorsally) and
- dorsal nuclei(sound location in vertical plane) (in the medullopontine junction)
- superior olivary nucleus (from the ventral cochlear nucleus bilaterally to the trapezoid body) (horrizontal sound mapping)
- Via the lateral lemniscus pathway
- inferior colliculus (location of sound + reflexes)
- medial geniculate body in thalamus
- primary auditory cortex (superior temporal gyrus in the temporal lobe) and amygdala → auditory association cortex
What is the intensity of a sound?
Amount of energy delivered per second (J/m^2) (energy per area)
–> We can still hear sounds of one Watt spread thorugh the whole area of the UK
What are the two main functions of the middle ear?
- To transduct the sound from the tympanic membrane to the oval window/inner ear
- To Match the Impedance
Which mechanisms of amplification are used in the middle ear to match the changes of impedance?
- Different sizes of the Tympanic membrane and the membrane in the oval window (17:1) –> Same force on smaller area gives higher pressure
- lever arm (Hebelwirkung) because of the different sizes of the individual ossicles
Explain the relationship of the tonotopical mapping of frequencies in the ventral cochlear nucleus and in the basilar membrane
The membrane is more stiff at the apex where low frequencies are sensed and least stiff at the base where high frequencies are sensed –> directly connect fo mapping in superior olive
What is the auditory reflex?
It protects the ear from loud sound and induces
- Contraction of the Musculus stapedius leading to
- stiffnes of the stapes and reduced sound conduction at the oval windov
Explain the pathway for the auditory reflex
- sensing of sound by cochlear nerve
- synapese from cochlear nucleus to superior olive nucelus
- bilateral synapsing onto facial nerve nucleus
- Facial nerve causes contraction of the muscuslus stapedius
What are the different layers of the chochlea?
- Scala vestibuli, scala tympany –> perilymph, are continous with each other and just change directions at the helicotrema
- Scala media in between with the organ of corti
Explain the process of depolerisation at the hair cell
- Movement towards kinocilium causes
- opening of K+ channels –> K+ influx
- depolerisation
- Glutatmate release
- Generation of AP
What are the characteristics of the endolymph?
Where is it present?
Endolymph is present in the scala media
–> high K+, low Na+
Which cells produce endolymph?
stria vascularis produce endolymph (high K+, low Na+)
Explain the direction of perilymph flwo in the chochlea
Perilymph is in the scala vestibule and scala tympany
- Flow from the oval window of the cochlea to the helicotrema in the scala vestibule
- From from the helicotrema to the round window in the scala tympany
