MD/MS PG Entrance ENT Question

ENT Question ( question Source Edulanche.com)

Q (1): Wrong statement about Organ of Corti?

A.Outer hair cells are much more than inner hair cells in number.
B. Tip of Inner hair cells are embedded in tectoral membrane
C.95% OF Afferent Neurons innervate inner hair cells.
D.Most of the efferent fibres in auditory nerve terminate on outer hair cells.

Explanation

Cochlear and vestibular sensory cells are called hair cells because they are characterized by having a cuticular plate with a tuft of stereocilia bathing in the surrounding endolymph. (Remember that the cell body itself remains in the perilymph compartment. ) 

In the human cochlea, there are 3500 inner hair cells and 12000 outer hair cells.  

The inner hair cells are afferent in nature and outer hair cells are efferent.  

The organ of corti lie in the Scala media and contains the hair cells. The Scala media is filled with endolymph. ( Remember Scala vestibuli and Scala tympani are filled with perilymph ). 

The Scala media contains the organ of corti which includes the Tectorial membrane, the Basilar membrane and the Hair cells in between.  

The acoustics are carried to the brain by the afferent nerves via Inner hair cells.  

Note: The tip of the Outer hair cells, (but NOT Inner hair cells) are embedded in Tectorial membrane.

What is the function of Outer hair cell?  

 1. The outer hair cell are firmly embedded in the overlying Tectorial membrane while the inner hair cell Stereocilia makes only a tenuous connection.  

2. The outer hair cells are located near the centre of the Basilar membrane where vibrations will be greatest. While the Basilar membrane is anchored under the Inner hair cells.  

3. These observations suggest that the movement of Stereocilia is likely to be greatest for outer hair cells than for inner hair cells.  

4. So,the function of the outer hair cell in hearing is now perceived as that of a "Cochlear Amplifier " that refines the sensitivity and frequency selectivity of the mechanical vibrations of the cochlea.  

So answer is  "B" . 

Kindly refer to the first point on the functions of the outer hair cell.

Source :  

1. Baylor College of Medicine  

2. www.cochlea.eu