Special Senses

Special Senses
Special Senses
 Special
senses allow the human body to
react to the environment. Helps the body
to see, hear, taste, smell, and maintain
 Senses occur because the body has
structures that receive the sensation,
nerves that carry the sensory message to
the brain, and a brain that can interpret
and respond to the message.
The Eye
Organ that controls
the special sense of
sight. It does this by
receiving light rays
and transmitting the
light rays to the optic
nerve, which carries
the rays to the brain
where they are
interpreted as vision
or sight.
The Eye
 The
eye is protected by the bony socket of
the skull, eye lashes and lids, and lacrimal
glands which produce tears.
 The conjunctiva is mucous membrane that
protects the eye. It lines the eyelids and
covers the front of the eye.
Three Main Layers of the Eye
 Sclera
The “whites” of the eye is the outermost layer
made up of connective tissue.
Muscles which are responsible for movement
of the eye within the socket are attached to
the outside of the sclera.
On the front of the sclera there is a
transparent part called the cornea which
allows light rays to enter the eye.
Three Main Layers of the Eye
 Choroid
The middle layer of the eye, which has many
blood vessels that nourish the eye.
The pupil is a hole in front of the choroids coat
which allows light to enter.
The iris is the colored portion of the eye and is
a muscle which controls the pupil and
regulates the amount of light entering the eye.
Three Main Layers of the Eye
The retina is the innermost layer of the eye. It is
made up of layers of nerve cells which transmit
the light impulses to the optic nerve.
 There are two special types of cells in the
Cones – Used mainly for light vision, and sensitive
to color. They are located in the area of sharpest
vision on the back surface of the retina.
Rods – are used for dark or dim vision.
The Eye
 Other
special structures of the eye include
the lens located behind the pupil.
Its purpose is to refract or bend light rays so it
can focus on the retina.
The aqueous humor is a clear watery fluid
that helps maintain the curvature of the
eyeball and bends or refracts light rays.
The vitreous humor is a jelly-like substance
that fills the area behind the lens, and also
helps to bend light rays.
The Eye
 When
light rays enter the eye they pass
through a series of parts that bend or
refract the rays to allow the rays to focus
on the retina.
 In the retina, the rays or images are picked
up by the rods and cones, changed into
nerve impulses, and transmitted by the
optic nerve to the occipital lobe of the
brain where sight is interpreted.
Diseases of the Eye
Blurred vision caused by abnormal shape or curvature of the
Also called “lazy eye”
Poor vision in one eye
Lenses become cloudy or opaque, with resulting loss of vision.
Also called “pink eye”
Inflammation of the conjunctiva, usually caused by bacteria or a
Diseases of the Eye
Increased pressure in eye from excess amounts
Leading cause of blindness
Light rays are not refracted properly and the image is
focused behind the retina
Light rays are focused in front of the retina
Diseases of the Eye continued
 Presbyopia
Farsightedness caused by loss of elasticity in
the lens
 Strabismus
Eyes do not move or focus together
May move inward (Cross eyed), or outward,
or up and down
The Ear
The ear is an organ that controls the special
sense of hearing and balance. The ear
transmits impulses from sound waves to the
auditory nerve which carries the nerve
impulses to the brain for interpretation as
Three Main Sections of the Ear
Outer ear
Contain the pinna or auricle, which is the visible part
of the year made up of elastic cartilage covered by
skin. This leads to a canal called the auditory canal.
The auditory canal contains glands which produce
wax called cerumen, to protect the ear.
Sound waves travel through the auditory canal, until
they reach the eardrum or tympanic membrane.
• The tympanic membrane vibrates when sound waves hit it
and transmits the sound waves to the middle ear.
Three Main Sections of the Ear
Middle ear
Contains three small bones
• The malleus, incus and stapes. These are connected and transmit
sound to the inner ear.
Inner ear
Most complex portion of the ear. There is a membrane which
separates the inner and middle ear called the oval window.
The vesibule is the first section or door to the inner ear.
The next section is shaped like a snail’s shell and is called the
• The cochlea contains hair like cells which are the receptors for
sound waves and transmit the impulses to the auditory nerve which
transmits the impulses to the temporal lobe of the cerebrum to be
interpreted as sound.
The Inner Ear continued
 Also
located in the inner ear is the
semicircular canals which contain a liquid
and hair-like cells that bend when the
liquid moves with head and body
 Impulses from this semicircular canal are
sent to the cerebellum to maintain our
sense of balance and equilibrium.
Diseases of the Ear
Hearing loss
Meniere’s disease
Collection of fluid in the inner ear
Otitis externa
Classified as sensory or conductive
Inflammation of the external auditory canal. May be
from swimmers’ ear, inserting bobby pins, Q-tips,
fingernails, ect.
Otitis media
Inflammation of the middle ear. Frequently follows a
sore throat due to bacteria entering the middle ear
from that Eustachian tube.
Other senses
Sense of taste
Dependent upon taste receptors on tongue
Can detect sweet, sour, salty, and bitter
Sense of smell
The nose is the organ of smell. Impulses from the
olfactory receptors in the upper part of the nasal
cavity carry impulses to the brain by the olfactory
Sense of smell is closely related to sense of taste.
Smell is more sensitive than taste.
The human nose can detect over 6,000 different
Skin and General Sense
 General
sense receptors for pressure,
heat, cold, touch, and pain are located
throughout the body in the skin and
connective tissue.
 Messages through these receptors allow
the human body to respond to its
environment and protect it against injury.
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