Question

Why do only some fibres inside the cochlea move when sound is detected?

Answer 1

Human ear can detect a very wide range of frequencies-from very low rumbles to high-pitched (20Hz-20000Hz)

Hair cells are the sensory cells inside the cochlea that detect these sounds.They are spread across basilar membrane(a flat surface )which is rolled like a carpet into a snail shell-shaped structure called the cochlea.

These hair cells are arranged along the basilar membrane according to the frequencies of sound they detect. Those hair cells that sense low pitches are present at one end & those detect high pitches are present at the other end.

Also there about average 30,000 nerve fibers within the cochlear nerve,which travels through the internal auditory canal into auditory cortex which helps in hearing.

Due to particluar arrangement of hair cells based on the frequencies they detect--when a wave of certain frequency enters the ear--Only hair cells which detect that specific frequencies are only vibrated---So only some of the fibres of cochlear nerve which is associated with that hair cells which vibrates only vibrates--so Not all the Fibres inside the cochlea move when a particular sound is detected