Sensory systems L2: Hearing Flashcards
What are the 3 parts of the ear?
- External ear
- Middle ear (bones –> smallest bone in body)
- Inner ear (Where sound waves are translated into fluid moves)
Why is the hearing system present?
- Translate air movement into fluid movement What is the importance of fluid movement?
- Amplification of the system
- Fluid also activates cells that are specialised to activate the brain (brain can only detect AP eg, sound waves, air movements = won’t be detected in this form)
____ and _____ portions transmit and amplify airborne sound waves to the fluid-filled ____ ear
External; middle; inner
What are 2 sensory systems in the inner ear contains receptors cells?
- Cochlea (for hearing)
- Vestibular apparatus (for equilibrium).
What are 2 aspects of hearing?
- Identification of the sounds (”what”)
- Know what kind of thing is making the sound (eg. can tell that the person is speaking english, if unfamiliar language = is a person that is having a conversation in a language I don’t know or don’t understand
- Localization of the sounds (“where”). Know where sound is coming from
What are sound waves?
mechanical disturbances that displace the molecules of a medium (solid, liquid or gas).
Sound cannot travel through a ______ (example: no sound in outer space).
vacuum
Because you need air (movement)
Sound waves have _____ density regions (compressed air) alternate with _____ density regions.
high; low
What is the speed of sound?
Speed of sound is 300 m/s in air and 1500 m/s in water.
What are the 3 factors factors influencing sound transmission?
- Absorption
- Reflection
- Refraction
- Ambient noise
What is absorption?
- Transformation of acoustic energy into heat energy in the medium or at its boundaries.
- Can be slowed down depending on distance as energy will be absorbed by environment
What is reflection?
When sound wave encounters a medium with different impedance, e.g. wall or water.
What are refraction?
When sound moves between media with different specific acoustic impedances, the direction of the incident sound wave will change due to the different propagation speeds. Change medium = change direction of sound waves
What are ambient noise?
Natural sources of sound caused by weather (e.g. wind, rain) combined with human made noise (e.g. traffic, room full of people).
Need ____ movements and ____ waves to actually hear (to be amplified) Dissipation of energy = less sound heard
air; sound
What are the 3 properties of sound?
- Pitch or tone
- Intensity or loudness
- Timbre or quality of sound
What is pitch or tone? EXAM
determined by the frequency of vibrations.
Humans can detect frequencies between 20 and 20000 Hz, but are more sensitive to 2000-4000 Hz. Animals? Think about bats…
What is intensity or loudness?
depends on the amplitude of the sound waves. Intensity is measured on a logarithmic scale in dB (decibel).
What are timbre or quality of the sound?
depends on overtones: different instruments playing the same note sound different, tuning fork has a pure tone.
What is the hearing threshold?
What is the sound pressure levels in other animals?
What are 3 characteristics of hearing?
- Air movement is important
- Frequency gives tone or pitch
- Amplitude gives loudness or intensity
What are 7 steps for sound transduction?
- Sound waves enter through the external ear (air); • The tympanic membrane vibrates
- The middle ear bones push an oval window: conversion of vibrations into fluid movement
- More energy is needed to start a pressure wave in a fluid compared to air. Sound is amplified around 20 times by structure in the ear:
- Oval window smaller than ear drum;
- Lever action of the ear bones.
- The organ of Corti, the sense organ, rests on the basilar membrane of the cochlea.
- Movement of fluid in the inner ear causes the basilar membrane to vibrate;
Why is the conversion of air to fluid important? EXAM QUESTION
- Activation of specific cells which require liquid movement
- Can change the frequency/amplitude of the movement= way for ears to protect itself
- Amplification of sound by 20 times
What are 2 sound pathways?
- Oval to round window (dissipates energy)
- “shortcut” from scala vestibuli to scala tympani (hearing)
What does the cross section of the cochlea?
What are 2 hair types?
- Outer hair cells
- Inner hair cells
Hair cells are activated by _____ movements = changing in pressure in membrane will change shape of _____ at the top of the cell = activate cells = generate APs = send down nerve fibres to brain
fluid; sterocilia
How do sound waves change to electrical signals?
Specialised receptor cells sensitive to mechanical signals, with around 100 _____ “hairs” each
stereocilia
What are the 4 rows along the length of the basilar membrane in the human cochlea has 1500? EXAM QUESTION
- 3 rows of outer hair cells (enhancing the signal)
- 1 row of inner hair cells (responsible for hearing)
- They can change how close the membrane is to the inner hair cells = where the sounds is actually generated
Hairs make contact with the ______ membrane
tectorial
Differential movement in the tectorial and basilar membranes distorts _____ cells: appropriate signal
hair
Stereocilia are organised from small to large and connect with______
tip links
____ cells are bent backwards and forwards. The movement opens and closes mechanically gated ____ channels
Hair; cation
Cells experiences alternating _____ and _____ potentials with frequency that are tuned to the original sound stimulus
depolarising; hyperpolarising
Movement of hair cells = help to generate the right amount of _____. EXAM QUESTION
AP
When air moving into fluid movement –> fluid moves –> Membrane moves closest to the tallest of the _____ = activation of opening of K+ channels –> more K+ channels –> more K+ flows in –> more Ca++ enters cell –> more neurotransmitter released –> AP *In hair cells –> it is K+ that activates and depolarises the cell not Na++ (unlike usually)
stereocilia
What are 3 steps of inner hair cells?
What is the purpose of outer hair cells?
Not involved in hearing
When outer hair cells are stimulated, how do they change length?
ELECTROMOTILITY
- Depolarisation = shortening
- Hyperpolarasation = lengthening
- Changes in length amplify the movement of the basilar membrane
- Tunes the stimulation of the inner hair cells.
What is electromotility?
- Depolarisation = shortening
- Hyperpolarasation = lengthening
What is the isolated outer hair cells?
Music gets detected by outer hair cells = shortening and lengthening
- Shortening when music comes in
- Lengthening back to normal How much they get activated can be affected by type of music (eg. rock Elvis Vs classical)
What does pitch discrimination depend on?
depends on the region of the basilar membrane that vibrates.
Each frequency only stimulates an area the width of a few hair cells
What does loudness discrimination depend on?
depends on the amplitude of the vibration of the basilar membrane
What does timbre discrimination depend on?
(more than one point along the membrane vibrates) fundamental frequency has the highest amplitude
What is the frequency tuning?
What are 3 characteristics of directional hearing?
- Timing difference between left and right ear
- Shading of head
- Shape of pinna – some animals can change the shape/orientation.
What are 4 characteristics of auditory cortex?
- Primary auditory cortex (Signal comes here) in the temporal lobeis is tonotipically organised
- Each region of the basilar membrane is connected to a specific region of the primary auditory cortex
- Specific cortical neurons are activated by particular frequencies
- Higher-order auditory cortex integrates the separate sounds into meaningful pattern. Eg. hear sound of friend’s voice (able to picture face..etc) Eg. know when crying, dog, cow, mum, cat = learned connection
Air movement -> _____ movement –> _____ movement –> specific activation of ______ hair cells –> basilar membrane –> _____ hair cells helping to shape signal –> generation of______
mechanical; fluid; inner; outer; AP
What is the pre-wired/learned frequency?
Pre-wired/learned to frequency (eg, within 2000-4000Hz = conversational speaking)
Frequency analysis within the ear itself (cochlea in mammals) based on spatial neural code: position along the basilar membrane corresponds to frequency. What does the summary look like?
What are 2 types of hearing loss?
- Conductive deafness
- Sound waves are not conducted due to ruptured ear drum, ear wax, glue ear, fluid build up as part of a middle ear infection or restriction of movement in the ossicles
- Sensory neural deafness
- Sound waves are conducted and the problem lies in the organ of corti or one of the neural tissue
- Presbycusis (age related loss of hair cells)
- Noise (related loss of hair cells).
What is a characteristic of conductive hearing loss?
Sound waves are not conducted due to ruptured ear drum, ear wax, glue ear, fluid build up as part of a middle ear infection or restriction of movement in the ossicles Something happened = can be rescued if the problems are dealt with
What are 3 characteristic of conductive hearing loss?
- Sound waves are conducted and the problem lies in the organ of corti or one of the neural tissue
- Presbycusis (age related loss of hair cells)
- Noise (related loss of hair cells). Neural tissue is affected (inner hair cells) (eg, age related deterioration of hair cells)
How good are hearing aids and cochlear implants for hearing loss?
- Hearing aids are good for conductive deafness as they amplify signal (neural pathways must be there)
- Cochlear implants cannot restore hearing but can give some auditory function.
Where is the problem when listening to hearing?
By passed outer hair cells = no change of membrane (inner hair cells) to modulate soundwaves
