hearing

Question 1

what sound intensity will lead to damage and pain?

Answer 1

between 120 and 140 dB

Question 2

what is the human hearing range?

Answer 2

20Hz - 20kHz

Question 3

draw the anatomy of hearing

what makes up each section of the ear?

Answer 3

• 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

Question 4

draw and label the structures of the middle and inner ear

Answer 4

Question 5

what is the tympani membrane?

what structures are connected to it?

Answer 5

Junction between outer and middle ear

ossicles connected to it

• maleus, incus, stapes

Question 6

what are the membranes within the ear

what is the significance of the two membranes

Answer 6

tympanic membrane & foramen ovale

• sound force is amplified between the two membranes due to both
  
  • ossicles
  • difference in size of the two membranes

Question 7

what is the stapes?

what is the importance and function?

Answer 7

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

Question 8

how is the presure wave in the cochlea released?

Answer 8

by membrane - foramen rotundum

Question 9

what are the tendons present?

what is their role? how do they carry out their function?

Answer 9

• stapedius muscle tendon
• tensor tympanum tendon

role :

• prevent excessive noise from damaging middle & inner ear

how :

• rapid contraction locks ossicles in place

Question 10

describe the pathway of sound waves through the ear

Answer 10

1. Start as pressure waves in air – movement of tympani membrane
2. Movement of ossicles
3. Stapes presses against foramen ovale
4. Pressure within inner ear movement around cochlea

Question 11

draw and label the structures of the cochlea

what sections is it divided into?

Answer 11

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)

Question 12

what is the basilar membrane?

where is it?

what is its role?

Answer 12

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

Question 13

what is the structure of the organ of corti?

Answer 13

Question 14

describe how sound waves have effect on the organ of corti

Answer 14

1. sound waves travel through cochlea cause deformation of basilar membrane
2. this causes vertical & lateral movement of inner and outer hair cells
3. cause bending of apical stereocilia that contact the tectorial membrane
4. opening of mechanically gated cation channels and depolarises the polarised hair cells
5. glutamate (excitatory neurotransmitter) released from base of hair cells
6. glutamate depolarises spiral ganglion neurons

Question 15

what is the significance of the structure of the basilar membrance?

Answer 15

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

Question 16

where is the tonotopic relationship of frequency to position seen within the auditory pathway?

Answer 16

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

Question 17

describe the auditory pathway from the auditory nerve to the primary auditory cortex

Answer 17

1. Sound frequencies mapped in auditory nerve
2. synapses with neurons in cochlear nucleus
3. 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

4. projection to inferior colliculi neurons – 4th order
5. projection to medial geniculate nucleus
   * transmit information to the primary auditory cortex

Tonotopic map is maintained throughout

Question 18

where is the primary auditory cortex?

what maps does it have?

Answer 18

• 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

Question 19

draw and label the auditory cortices

Answer 19

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.