Physiology of hearing (ENT)

Protects the ear from loud frequency sound

160 dB

Grievous Hurt:

• Emasculation.
• Permanent privation of the sight of either eye.
• Permanent privation of the hearing of either ear
• Privation of any member or joint.
• Destruction or permanent impairing of the powers of any member or joint.
• Permanent disfiguration of the head or face.
• Fracture or dislocation of a bone or tooth.
• Any hurt which endangers life or which causes the sufferer to be during the space of twenty days in severe bodily pain or unable to follow his ordinary pursuits.

Noise may be expressed in psycho-acoustic terms – the phon. The phon is a psyho-acoustic index of loudness. It takes into consideration intensity and frequency.

Also remember:

“Octave Band Frequency Analyser,” which measures the noise in octave bands. The resulting plot shows the “sound spectrum” and indicates the characteristics of the noise, whether it is mainly high-pitched, low-pitched or of variable pitch.

Ref: Park’s textbook of Preventive and Social Medicine, 21stedition, page-684

The labyrinth has three components: 

• Cochlea (containing receptors for hearing),
• Semicircular canals (containing receptors that respond to head rotation)
• Otolith organs (containing receptors that respond to gravity and head tilt i.e., linear acceleration).

The otoliths, which are also called otoconia or ear dust, range from 3 to 19 micrometer in length. They are crystals of calcium carbonate embedded in otolithic membrane. 

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Ans. is ‘d’ i.e., 85 

i. Conduction of sound:

• It is done mainly by middle ear. Middle ear not just simply conducts the sound but converts sound of great amplitude and less force to that of less amplitude and greater force.
• This function of the middle ear is called as impedance matching mechanism or the transformer action.

ii. Transduction of mechanical energy to electrical impulse:

• Movements of the stapes footplate causes vibrations in scala vestibuli followed by scala tympani and is transmitted to the cochlear fluids which brings about movement of the basilar membrane.
• This sets up shearing force between the tectorial membrane and the hair cells.
• The distortion of hair cells gives rise to electrical nerve impulse.

A sound wave, depending on its frequency, reaches maximum amplitude on a particular place on the basilar membrane, and stimulates that segment (traveling wave theory of von Bekesy).

Higher frequencies are represented in the basal turn of cochlea and the progressively lower one toward the apex.

The area of tympanic membrane is much larger than area of stapes footplate, the average ratio being 21:1.

As the effectice vibratory area of tympanic membrane is only two thirds, the effectives areal ratio is reducted to 14:1 which helps in impedance matching/ transformer action.

Hair cells: are important receptor cells of hearing and transduce sound energy into electrical energy.

Otolith organs (present in maculae) are concerned with linear acceleration, gravity and head tilt movements and they also help to maintain static equilibrium.