Vibrations now enter the endolymph of scala media followed by the vibrations of Basilar membrane. The sensory hair of organ of corti undergo bending stimulating the sensory cells creating the impulse of hearing which is carried to the brain by the fibres of cochlear branch of auditory nerve.
The high frequency resonance of the basilar membrane occurs near the base, where the sound waves enter the cochlea while low frequency resonance occurs near the apex mainly because of stiffness of fibres of basilar membrane.
Receptor organs of equilibrium are semicircular canal, sacculus and utriculus which are collectively known as vestibular apparatus. g m Equilibrium are of two types – Static and dynamic Static equilibrium refers to orientation of the body (mainly head) relative to gravity.
It is regulated by sacculus and utriculus. Sacculus responds to lateral (sideways) movement of the head.
The hair cells of the saccule are horizontal when the head is upright. Tilting of the head to the left produces a differential response from left and right saccules.
The left receives Autncie increased stimulation as the otoconia pull downwards on the hairs whereas decreased stimulation occurs on the right.
These displacements produce impulses passing to the cerebellum where the orientation of the head is perceived. Utriculus responds to vertical movement when pulling the receptors hairs downwards. Such of the utricle and saccule as when the body is upside down
Dynamic equilibrium refers to the maintenance of body position in response to sudden movement. It is regulated by cristae (ampulla of semicircular canal). The cupula is on the sensory cell of ampulla of the semicircular canal. The sensory hair is in it.
When the speed of rotation acceralates, the endolymph starts to flow and the cupula comes to slant to a side.
Then sensory hair moves. The hair cells of crista come to excite in response to the movement. The lines of sensory hair make a proper nerve impulse.
The receptor cells respond by producing generator potentials leading to action potentials in the vestibular neurones.
The direction and rate of displacement are both detected by the receptor cells. Linear acceleration is detected by both the maculae and cupulae.
Deafness means impairment of hearing. It can occur at any age. Deafness is classified principally as being of two types: conductive loss of hearing and sensorineural deafness. Conductive loss occurs when the ossicular chain (the bones in the middle ear – the hammer, anvil and stirrup) do not function properly.
This type of loss can be surgically treated. Sensorineural deafness occurs from damaged nerves in the inner ear and can generally be treated only by the use of a hearing aid (if there is residual hearing), Sensorineural deafness can result from long exposure to excessive noise levels, diseases such as whooping cough or measles, or the ageing process.