Neurology 10 - Sound Conduction and Transduction Flashcards
List the main causes of hearing loss
- Traumatic loud sounds
- Genetic conditions
- Infections like meningitis, rubella or syphillis
- Drugs (used for heart infections and chemotherapy)
- Aging
Compare the hearing and vision range in humans
- Hearing range from 20Hz to 20kHz
- Vision - static images changing at a rate of 20 times a second are percieved as continuous. The ear works at 20000 times a second
What is pitch?
The perception of frequency
What is timbre?
What distinguishes two sounds at the same frequency and intensity
What movements can the internal ear detect?
Movements as small as a fraction of a nanometer (size of a water molecule)
Describe the volume range of the ear
- Volume is the same as intensity
- Faintest intensity is 10^-12 w/m^2
- Loudest is 12 orders of magnitude larger
How does the ear receive sound?
- The ear detects sound waves in the air and via mechanical couplings, projects the stimuli onto the hair cells
- Hair cells are the sensory receptor of the internal ear
What are hair bundles?
A cluster of modified microvilli called stereocilia, present on the hair cells
What is the function of the ossicles of the ear?
- Three oscicles (malleus, incus and stapes)
- Transmit vibration of the tympanic membrane (caused by air) to the cochlea (filled with liquid)
- Role is to match the impedance and reduce the loss in energy as the vibration goes from the air to the cochlear
What is impedance?
- A measure of the reluctance of a system in receiving energy from a source
- When a sound is recieved, one sound is accepted and one is reflected
What is the resonant frequency?
- The frequency at which the impedance of a system is minimal
- Transmission of energy is maximal
How is the tension of the tympanic membrane controlled?
Tympanic muscle and stapedius muscles adjust the malleus and incus
What is a conductive hearing loss?
- When the ear is not capable of transmitting the vibration of sound waves to the cochlea
- Occurs in infections such as otiti, tumours and cerumen
List the common causes of conductive hearing loss
- In children, fluid accumulation is common
- Wax
- Otitis media
- Perforated tympanic membrane
- Abnormal growth of a bone (otosclerosis) which obstructs the ear canal
- Barotrauma (temporary)
What happens following moton of the stapes?
- Generation of a pressure difference between the two liquid filled chambers of the cochlea
- This in turn causes vibration of the basilar membrane
Describe the location and anatomical structure of the organ of corti
- On the basilar membrane, inside the scala media
- Contains hair cells (more outer than inner, these hair cells synapse with nerve endings)
What is the function and structure of the basillar membrane?
- Elastic, with heterogenous mechanical properties
- Vibrates at different positions in response to different frequencies
- Breaks complex sounds down by distributing the energy of each component frequency along its length
- Hair cells (sensory receptors) are along the whole length of the basilar membrane - tonotopic map
- Basilar membrane is narrow and tough
What is the function of hair cells?
- Sensory receptors of the inner ear
- Hair bundles are deflected by motion of the basilar membrane
- The bending of stereocilia towards the tallest stereocilium changes the internal voltage of the cell, ultimately producing
an electric signal that travels towards the brain. This is called Mechano-transduction (MT)
What are the tip links of sterocilia?
- Connect sterocilia
- Work as small springs stretched by stereocilia sliding
- Tip links share their location with ion channels
- Their disruption abolishes mechanotransduction
- Response currents are the result of opening of ion channels activated by stretching tip links
How is it known that the hair bundle is not passive?
- The hair bundle complies with the direction of the stimulus
- Measured stiffness more negative when the channels open
List the 4 aspects of the active process
- Amplification (a particular segment of a living basilar membrane vibrates more than a dead basilar membrane)
- Frequency tuning (dead basilar membrane produces a broad response, and is not tuned for a specific frequency, while living selectively amplifies frequencies)
- Compressive nonlinearity (motion of the basilar membrane is augmented, amplification diminishes with increasing stimulus intensity)
- Spontaneous otoacoustic emission (70% of noral ears emit pure tones when in a quiet environment)
What are the two types of hair cells?
- Inner hair cells (95% connect to these, 3500 per cochlea)
- Outer hair cells (5% connect to these, 11000 per cochlea)
What is electromotility?
- Outer hair cells shorten and elongate based upon their internal voltage
- Due to reorientation of the protein prestin
How is information transmitted to the cochlear nucleus?
- Hair cells synapse with the sensory neurones in the cochlear ganglion (spiral ganglion)
- Each ganglion responds best at a particular frequency
- Tonotropic map is present