Page 248 - Biology_F5

Coordination and Irritability

cornea, aqueous humour and pupil there are cone and rod photoreceptors,
(Figure 4.30). The pupil is an opening which are connected to the brain via a
(an aperture), which is controlled by the bundle of fibres called optic nerve. The
iris (like camera shutters) depending information received is processed in the
on the amount of light. The stronger the brain, and consequently, the object can
amount of light, the smaller the size of the be seen. Thus, the role of the retina is to
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aperture is. The lens is positioned between translate light into nerve signals and to
the outer and inner chambers of the eye, allow us to see under various conditions
and its major function is to focus images ranging from starlight to sunlight. It also
on the retina by changing its thickness distinguishes the wavelengths for us to
depending on the amount of light from discriminate colors.
distant or nearby objects. On the retina,

Light
Iris

Retina

Inverted image
of object

Object

Lens Optic nerves

Figure 4.30: Structure of a mammalian eye showing physiology of seeing
4.2.3 The mammalian ear and glands that secrete earwax, which is
located in the upper wall of the auditory
Task 4.9 canal. Ear wax guards the ear against
Search from the internet sources on the entrance of foreign materials such as dust
simulations or videos on the mechanism and microorganisms.
of hearing and body balance make short
notes on the searched information In the middle ear, the tympanic
membrane begins and ends at a bony wall
The mammalian ear consists of three containing two small openings covered by
parts, namely the outer, middle and inner membranes. The two openings are oval
ear. The outer ear comprises an external window (fenestra ovalis) and the round
flap of skin covered by elastic cartilage window (fenestra rotunda). There are
called pinna. The pinna collects sound three connected bones called ear ossicles,
waves and directs them into the ear canal which are held in position by muscles.
(external auditory meatus). Across the These are malleus (hammer), incus (anvil),
end of ear canal is a tympanic membrane and stapes (stirrup). The middle ear is air
or ear drum which separates the outer filled part that depends on the equalization
ear from the middle ear. The opening of of pressure outside and inside the ear to
the auditory canal is lined with fine hairs

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