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The man-Perception
Human being contacts with his environment
and controls his situation and actions
through his five senses consisting of the
senses of sight,hearing,taste,smell and
touch.Each of these senses perceives through
specific receptors the information from
outside and following changing such
information to neural messages,sends them
to the brain.
Eye,the main organ of sight:
The eyeball is located in a lipid space
inside the orbit held in place by eye
muscles.The suscles control its movements.
The appendices of the eye include the
eyelids , lacrimal glands,and muscles.
The orbit is a sphere full of an aqueous
liquid enclosed in a firm external cover
called sclera.The anterior part of sclera,
namely , cornea , is translucent and makes
possible the entry of light into eyes . At
the back of cornea,is situated the iris with
a pore in the middle called pupil.The light,
emitted from objects,enters the eye and
passes through the pupil and lens and reaches
the retina located at the back of the orbit.
Light coming from the objects,after passing
through cornea and following refraction by
the lens,produces a smaller inverted picture
on the retina.This picture is received by
millions of neurons located on retina
membrane and after being changed to neural
messages is sent to the brain.
Ear,the main organ of hearing:
Is an organ that receives sound vibrations
and also is effective in maintaining
ballance.Ear is composed of three main parts:
1.external ear including auricle ecoustic
meatus,and tympanic membrane.2.middle ear
composed of an air cavity containing three
small bones called malleus,incus and stapes.
These three bones are motioned consecutively
and transfer the sound waves transmitted via
ear drum to the malleus from oval window to
the internal ear.3.internal ear is a cavity
full of liquid located at the depth of the
cranium.Part of it contains the cochlea which
receives vibrations from the middle ear.These
vibrations are transmitted to the ear liquid
and perceived by sense cilia.These cilia are
arranged in v-shaped bundles and once being
bent and straightened by the liquid,transmit
the neural messages to the brain.
Semicircular canals and scala vestibuli
located in the internal are control the
ballance of the body.These canals contain
a liquid which vibrates once one moves.
Such vibrations are perceived by sensory
cilia and transmitted to the brain to issue
necessary commands to ballance the body.Its
worth saying that the eustachian tube
connects the middle ear to a pore near the
pharynx to equilibrate air pressure inside
the middle ear cavity with that of the
outside air.Otherwise hearing would be
disturbed and will lead to earache.Usually
during the process of yawning and swallowing,
the eustachian tube open to help the
ballancing process.
Tongue,the main organ of taste:
Tongue is a muco-muscular organ that in
addition to taste perception,participates
in functions of chewing,swallowing and sound
producing . On the mucous surface of the
tongue,there are many small projections
called papillae to which taste nerve endings
terminates.Papillae are distributed as
filiform,and conical elements on the whole
surface of the tongue.Generally the sweet
taste is sensed by tip of the tongue,
sourness by the sides,bitterness with the
end,saltiness with anterior and lateral
parts of the tongue.
Nose,the main organ of smell:
The upper part of the nasal cavity is the
main olfactory section.In this part there
are about 20 million smell receptor neurons
each terminating to some cilia.During
respiration,smell transmitting molecules
enter the nasal cavity and are received by
cilia which produce neural messages.Such
messages are transferred via olfactory bulb
and finally through olfactory nerve to the
brain and in this way we are able to
recognize more than 10000 differents types
of smell.
Skin,the main organ of touch:
Body skin weighing about 4 kg and a surface
area of about 2 square meter is composed of
3 main sections: 1. the superficial part or
epidermis ,supporting underneath layers. On
the surface of this layer,there are flat and
dead cells which are usually separated from
it,through by washing and rubbing and
continuonsly replaced by underneath layer.
2. the more internal layer called dermis
which is full of sense endings which can
reveal sensations of touch,pressure,pain,heat
and cold ) at each square centimeter of skin
there can be found up to 240 nerve endings
called receptors (.This layer also,contains
fat and sweat glands and a profusion of blood
vessels. 3. hypodermis which attaches skin to
other parts of the body and contains half of
the body fat and protects the body against
cold and mechanical blows.
