Hearing Flashcards
What are the ossicles?
They are the bones of the middle ear - malleus, incus, stapes.
What is the Organ of Corti and what it it’s function? ?
It is a receptor organ for hearing, located in the cochlea, consisting of highly specialised epithelial hair cells.
It functions to convert mechanical vibrations (energy) into electrical impulses by opening/closing its ion channels.
In what part of the ear is the Cochlea located?
It is contained in the Inner ear.
In what part of the ear is sound waves converted into mechanical vibrations?
Sound waves are converted into mechanical vibrations in the middle ear.
There are two fluid filled labryinths, one inside the other, in the inner ear. What are they called?
The osseous labyrinth (outer) and the membraneous labyrinth (inner).
How many inner and outer hair cells are in the Organ of Corti?
There is 1 row of inner hair cells and 3 rows of outer hair cells.
What are the two roles of the supporting cells?
1) To support the hair cells and connect them to the basilar membrane.
2) To ensure efficient transmission of mechanical vibration to the hair cells.
What cytoskeletal filament is located in cuticular plate at the tips of hair cells?
Actin.
What neurotransmitter is released by the hair cells to convert mechanical vibrations into electrical impulses?
Glutamate.
How do the hair cells transmit mechanical vibrations into electrical impulses?
1) Mechanical vibrations in the basilar membrane create shearing forces that cause the stereocillia to deflect towards the tallest stereocilium.
2) This causes the trandsuction channels to open and for K+ and Ca2+ to enter.
3) This results in membrane depolarisation and the generation of a receptor potential, which will subsequently lead to the release of the neurotransmitter glutamate,
How is the transmission of electrical impulses inhibited in the hair cells?
1) The stereocilia will be deflected away from the tallest stereocilium and so the K+ channels will be closed.
2) This will result in hyperpolarisation of the cell membrane and the K+ leave the cell via the (KCNQ4) basolateral channels.
3) As a consequent, neurotransmitter release will be inhibited.
Which cranial nerve carries the nerve impulses for both hearing and balance from the ear to the brain?
The VIII cranial nerve.
Which 6 genes are involved in K+ recycling, that if mutated will peturb ionic homeostasis and lead to deafness?
KCNQ4 and KCNQ1
Connexins 26, 30, 31 and 32.
Inner and Outer hair cells each have different functions, what are they?
Inner hair cells = acts as transformers to convert mechanical energy into electrical impulses.
Outer hair cells = Act as amplifiers to enhance the response of the inner hair cells (allows us to hear very quiet sounds).
What is the function of Prestin?
Prestin is a motor protein expressed only in outer hair cells that enable the outer hair cells to undergo rapid length changes in response to difference sound frequencies.
Prestin changes its shape in response to depolarising currents.
Why does damage to hair cells lead to permanent hearing impairment?
Because they no not regenerate - they degenerate and are replaced by supporting cells to form a “scar”
What is Epsin and what is its function?
Epsin in an actin cross-linking protein. It functions to aid in the assembly of actin filaments and this stereocilia elongation. Thus, it is important in maintaining stereocilia stability and length.
What do mutations in Epsin result in?
Mutations result in short and stereocilia, hair cell degeneration and deafness.
What is the function of Myosin IIIa?
Myosin III functions to transport epsin and localise it to the apical region of the stereocilia.
What is the function of Myosin VI?
They functions to anchor the stereocillia to the base.
A mutation of what myosin type will lead to short stereocilia?
Myosin XVa
What myosin type plays a role in stereocilia development and actin filament elongation?
Myosin XVa
What is defected in the “Jerker deafness” mouse, “Shaker 1” and “Shaker 2” mouse, “Whirler” mouse, “Waltzer” mouse and “Ames waltzer” mouse?
Jerker = Epsin
Shaker 1 = Myosin VIIa
Shaker 2 = Myosin XVa
Whirler = Whirlin
Waltzer = Cadherin 23
What is the function of Myosin XVa?
It functions to transport whirlin to the tip of the stereocilium.
What does a defect in the Whirlin protein result in?
A mutation in the Whirlin protein will result in disorganised, short and chubby stereocilia.
Why is Whirlin important?
Whirlin is important for the elongation of actin filaments in the stereocilia.
What is Myosin VIIa and what is its role?
Myosin VIIa is an actin motor. It functions to bind to harmonin and SANS to allow for differentiation and organisation of the hair cell stereocilia.
What two molecules allow for the cell-cell adhesion between the stereocilia tip links?
Cadherin 23 and protocadherin 15.
How does Cadherin 23 perform its function?
Cadherin functions to anchor the tip link of a shorter stereocilia to taller one by interacting with harmomin, which will anchor the filament to the actin core.
What two molecules control the opening and closing of the transductions ion channels in the tip links of the hair cells?
Cadherin 23 and Protocadherin 15.
