hearing Flashcards
what sound intensity will lead to damage and pain?
between 120 and 140 dB
what is the human hearing range?
20Hz - 20kHz
draw the anatomy of hearing
what makes up each section of the ear?
- Outer
- made up of pinna and auditory canal
- air filled
- Middle
- made up of 3 ossicles – small bones
- air filled
- Inner
- vestibular canals – balance
- cochlear – involved in hearing
- spinal ganglion – project through auditory nerve
- fluid filled
- Vestibular ganglion
- sensory neurons – detect sense of balance
- Vestibular and auditory nerve coalesce to form the vestibular cochlear nerve
draw and label the structures of the middle and inner ear
what is the tympani membrane?
what structures are connected to it?
Junction between outer and middle ear
ossicles connected to it
- maleus, incus, stapes
what are the membranes within the ear
what is the significance of the two membranes
tympanic membrane & foramen ovale
- sound force is amplified between the two membranes due to both
- ossicles
- difference in size of the two membranes
what is the stapes?
what is the importance and function?
ossicle in contact with membrane, foramen ovale
sets up pressure wave within inner ear
- inner ear is filled with fluid
- pressure wave passes through cochlea
how is the presure wave in the cochlea released?
by membrane - foramen rotundum
what are the tendons present?
what is their role? how do they carry out their function?
- stapedius muscle tendon
- tensor tympanum tendon
role :
- prevent excessive noise from damaging middle & inner ear
how :
- rapid contraction locks ossicles in place
describe the pathway of sound waves through the ear
- Start as pressure waves in air – movement of tympani membrane
- Movement of ossicles
- Stapes presses against foramen ovale
- Pressure within inner ear movement around cochlea
draw and label the structures of the cochlea
what sections is it divided into?
The cochlea is divided into 3 chambers:
- scala vestibuli,
- scala tympani
- (contain perilymph)
- scala media
- which is filled with endolymph (high concentrations of K+ and Ca2+ ions)
what is the basilar membrane?
where is it?
what is its role?
Basilar membrane – on floor of scala media
organ of corti lies on it
- converts mechanical energy (movement of basilar membrane) into depolarisation of hair cells which lie on basilar membrane
- therefore into electrical signal
- transmitted via spiral ganglion neurons
what is the structure of the organ of corti?
describe how sound waves have effect on the organ of corti
- sound waves travel through cochlea cause deformation of basilar membrane
- this causes vertical & lateral movement of inner and outer hair cells
- cause bending of apical stereocilia that contact the tectorial membrane
- opening of mechanically gated cation channels and depolarises the polarised hair cells
- glutamate (excitatory neurotransmitter) released from base of hair cells
- glutamate depolarises spiral ganglion neurons
what is the significance of the structure of the basilar membrance?
base of basilar membrane is narrower and stiffer than at the apex
- different frequencies travel up differently
- High frequencies do not travel far
- Low frequencies travel far
therefore sound frequency is mapped on both the basilar membrane and the spiral ganglion neurons
tonotopic map
where is the tonotopic relationship of frequency to position seen within the auditory pathway?
present in : (these all connect to each other) - tonotopic map is maintained throughout
- hair cells
- spiral ganglion neurons
- auditory nerve
- cochlear nucleus
- higher brain levels
describe the auditory pathway from the auditory nerve to the primary auditory cortex
- Sound frequencies mapped in auditory nerve
- synapses with neurons in cochlear nucleus
- projection to third order – superior olivary nucleus
- partial decussation axons from one side to the other allows auditory information from both ears to be sent to both sides of the cortex
- able to determine direction of sound, if it is going towards or away from us
- projection to inferior colliculi neurons – 4th order
- projection to medial geniculate nucleus
* transmit information to the primary auditory cortex
Tonotopic map is maintained throughout
where is the primary auditory cortex?
what maps does it have?
- tucked into the superior-medial surface of the temporal lobe
- tonotopic map of frequency
- others
- from integration of information from both ears
- directional judgement
- distance judgement
- from integration of information from both ears
draw and label the auditory cortices
Wernicke’s area = centre for grammatical analysis of language
- On the opposite hemisphere, this area of secondary cortex is responsive to moving sounds, providing information on direction and distance of sound sources.
