Hearing*

Question 1

Hearing - range? safe amplitude? sound transduction process? cochlea anatomy? organ of Corti? hair cells?

Answer 1

Range between 20-20,000 Hz
Amplitude of 1-80 dB (safe)
Sound transduction turns air waves into mechanical vibrations, then fluid waves, chemical signals and finally APs
Cochlea of the inner ear contains 3 parallel fluid filled channels: cochlear duct, vestibular duct and the tympanic duct
Organ of Corti is contained in the cochlear duct and lies on the basilar mem, it contains hair cells and partially covered by the tectorial mem
Hair cells are topped by flexible cilia, fluid bends the cilia which cause the cells to depolarise and release NuT onto sensory neurons

Question 2

Functions of the outer? middle? and inner ear? (innervation of inner ear?)

Answer 2

Outer ear gathers and conducts sound waves to the eardrum
Middle ear links the eardrum to the cochlea via ossicles
Inner ear comprises the sensory apparatus of the cochlea and vestibular apparatus, innervated by the cochlear nerve

Question 3

Function of the ossicles and the cochlea - canal? tympanic mem? ossicles? oval window? cochlea? round window?

Answer 3

Sound waves conducted down the ear canal vibrate against the thin tympanic membrane causing it to vibrate, this vibrates the malleus to the incus and finally to the stapes, this then vibrates against the oval window, this is then transmitted to the fluid of the cochlea
Vibration at the round window serves to cushion and dampen fluid movement within the cochlea

Question 4

Transmission of sound vibrations into the cochlea - 3 canals? separation of the canals? high vibrate? low vibrate? basilar membrane? hair cell structure? hair displacement?

Answer 4

3 canals such as the tympanic, vestibular and middle canal
The tympanic and vestibular canal are separated by the basilar membrane, which receives sound vibrations
High pitch vibrate the proximal end and low pitch vibrate the distal end
Movement of basilar membrane causes displacement of the organ of Corti (hair cells and cilia which are in contact with the tectorial membrane)
Each hair cell has 3 rows of cilia of progressively increasing heights
Movement of the hair cells due to vibrations of the basilar mem cause the hair cell cilia to displace and lead to increased or decreased firing of the auditory nerve endings

Question 5

Hair cells - supported by (2)? cilia project into? bending the cilia how? cell ion changes? NuT effect? hair movement? hair location translation?

Answer 5

Supported by the Deiter cells and the perilymph
Cillia projection into the endolymph fluid within the tectorial membrane
Bending cilia is caused by the sound vibrations moving the basilar, tectorial and endolymph
Opens Ca ion channels leading to the release of NuTs
Binds to postsynaptic membrane and receptors and depol leading to propagation of an AP
To the right is excitation and to the left is inhibition
Location of hair cells on the membrane creates a code that the brain translates to pitch, amplitude signaled by the degree of displacement and coded in the AP freq generated in the sensory neuron

Question 6

Deafness - types and causes?

Answer 6

Conductive deafness:
- defects in the conduction of sound to the inner ear
- wax build up, blockage of the auditory tube, inflammation and otosclerosis
Sensorineural deafness:
- hair cell damage in the organ of Corti
- Meniere’s disease (increased endolymph)
- trauma, ageing, infection and drugs
Nerve deafness:
- damage to the auditory nerve
- ageing, infection and atherosclerosis

Question 7

Other hearing defects - Tinnitus? Hereditary deafness?

Answer 7

Tinnitus:
- ears ringing can be continuous or discontinuous
- degeneration of organ of Corti
- result from external and middle ear problems
Hereditary deafness:
- variety of phenotypes over 100 mutant genes known

Question 8

Sound equilibrium - definition? balance? dynamic and static component? gravitational change detection? rotational change detection?

Answer 8

Equilibrium is a state of balance that allows us to position our body in 3D space under normal gravitational conditions
Balance via hair cells in the fluid filled vestibular apparatus and in the semicircular canals of the inner ear
Dynamic component sensing rotational movement of the head
Static component that senses head displacement via linear acceleration and the associated gravitational changes
Gravitational via otoliths within the maculae
Rotational by hair cells within the ampulla

Question 9

CNS vestibular pathway - hearing?

Answer 9

Vestibular apparatus via vestibular branch of vestibulocochlear nerve to the cerebellum and vestibular nuclei of medulla