Question

Describe how the cochlea responds to the frequency of an incoming sound (include structures from the oval window to the inner hair cells)

Answer 1

When sound Waves (Stimulus)are apporaching------Pinna directs it into the External Audtiory canal------Sound wave reaches Tympanic Membrane----Vibration of Tympanic membrane-----Since malleus (1st ear ossicle is attached to Tympanic Membrane) this causes displacement of Malleus--------Movement of the malleus causes movement of the incus and stapes ------Since footplate of stapes is attached to Oval window---hence movement of Oval window Occur.

Movement of the oval window establishes pressure waves in the perilymph of the vestibular duct----------This pressure wave moves from Oval window to Round window----During this, The pressure wave distorts the basilar membrane on its way to the round window.-----Vibration of Basilar membrane-----Vibration of Hair cells present in the Basilar membrane against the tectorial Membrane(Hair cells present in the Basilar membrane are the sensory receptors for hearing)----Displacement of the stereocilia in the hair cells will stimulates sensory neurons of the cochlear branch of vestibulocochlear nerve.(this is the nerve that carries sensory information about hearing from the Cochlea to Brain)------Information Reaches auditory cortex in the superior temporal gyrus in the temporal lobe(Area in the Brain responsible for Hearing)-----Hearing.

Stimulus:Sound waves

Sensory Receptor:Hair cells

Sensory cell that houses the receptors:Cochlea-Basilar membrane

Supporting structures:OVal window,Round Window,Tectorial membrane..

Nerve:Cochlear branch of vestibulocochlear nerve

Portion of Brain Interpreting the signal-Auditory Cortex present in the Superior temporal gyrus of temporal Lobe.

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