mechanism of hearing and vision .
explain each 4 3marks
Mechanism of hearing:
The ear consists of three sections specializing in different functions. the outer ear consists of the pinna which focuses and collects sound waves into the ear tube (external auditory meatus); the sound waves cause the tympanic membrane (ear drum) to vibrate. In the middle ear, vibrations of the tympanic membrane are transmitted across to the membranous oval window by the movement of three ear ossicles (malleus, incus, stapes). A lever system between these bones and the relative area of contact of the malleus with the tympanic membrane and the stapes with the oval window amplifies the movement of the tympanic membrane. Finally there is the inner ear which consists of a complex system of canals and cavities with in the skull bone. Auditory receptors are found here which help in the conduction of message to the brain for interpretation.
Mechanism of vision:
The eye is a sense organ which receives light of various wavelengths reflected from objects at varying distances. When the light enters the eye, the curved surface of cornea acts as the main structure refracting light towards the retina. The image is formed on the retina which contains rods and cones, and cell body and axons of neurones supplying the optic nerve. Lens is the transparent, elastic biconvex structure which provides fine adjustment for focussing light on the retina and the iris controls the amount of light entering the eye. Once the image is formed of the retina, the optic nerve carries the message to the brain for interpretation.