Special SensesSpecial Senses

Special SensesSpecial Senses

Special senses allow the human body to Special senses allow the human body to react to the environment. Helps the body react to the environment. Helps the body to to seesee, , hearhear, , tastetaste, , smellsmell, and , and maintain maintain balancebalance..

Senses occur because the body has Senses occur because the body has structures that receive the structures that receive the sensationsensation, , nerves that carry the sensory message to nerves that carry the sensory message to the brain, and a brain that can the brain, and a brain that can interpret interpret and respond to the messageand respond to the message..

The EyeThe Eye

Organ that controls Organ that controls the special sense of the special sense of sight. It does this by sight. It does this by receiving light rays receiving light rays and transmitting the and transmitting the light rays to the light rays to the opticoptic nervenerve, which carries , which carries the rays to the brain the rays to the brain where they are where they are interpreted as vision interpreted as vision or sight.or sight.

The EyeThe Eye

The eye is protected by the bony socket of The eye is protected by the bony socket of the skull, the skull, eye lasheseye lashes and and lidslids, and lacrimal , and lacrimal glands which produce tears.glands which produce tears.

The conjunctiva is The conjunctiva is mucous membranemucous membrane that that protects the eye. It lines the eyelids and protects the eye. It lines the eyelids and covers the front of the eye.covers the front of the eye.

Three Main Layers of the EyeThree Main Layers of the Eye

ScleraSclera The “whites” of the eye is the outermost layer The “whites” of the eye is the outermost layer

made up of connective tissue. made up of connective tissue. Muscles which are responsible for movement Muscles which are responsible for movement

of the eye within the socket are attached to of the eye within the socket are attached to the outside of the sclera. the outside of the sclera.

On the front of the sclera there is a On the front of the sclera there is a transparent part called the transparent part called the corneacornea which which allows light rays to enter the eye.allows light rays to enter the eye.

Three Main Layers of the EyeThree Main Layers of the Eye

Choroid CoatChoroid Coat The middle layer of the eye, which has many The middle layer of the eye, which has many

blood vessels that nourish the eye.blood vessels that nourish the eye. The The pupilpupil is a hole in front of the choroids coat is a hole in front of the choroids coat

which allows light to enter.which allows light to enter. The The irisiris is the colored portion of the eye and is is the colored portion of the eye and is

a muscle which controls the pupil and a muscle which controls the pupil and regulates the amount of light entering the eye.regulates the amount of light entering the eye.

Three Main Layers of the EyeThree Main Layers of the Eye

The The retinaretina is the innermost layer of the eye. It is is the innermost layer of the eye. It is made up of layers of nerve cells which transmit made up of layers of nerve cells which transmit the light impulses to the optic nerve.the light impulses to the optic nerve.

There are two special types of cells in the There are two special types of cells in the retina.retina.

1.1. Cones –Cones – Used mainly for light vision, and sensitive to Used mainly for light vision, and sensitive to color. They are located in the area of sharpest vision color. They are located in the area of sharpest vision on the back surface of the retina.on the back surface of the retina.

2.2. RodsRods – are used for dark or dim vision. – are used for dark or dim vision.

The EyeThe Eye

Other special structures of the eye include Other special structures of the eye include the the lenslens located behind the pupil. located behind the pupil. Its purpose is to Its purpose is to refract or bend light raysrefract or bend light rays so it so it

can focus on the retina.can focus on the retina. The The aqueous humoraqueous humor is a clear watery fluid is a clear watery fluid

that helps maintain the curvature of the that helps maintain the curvature of the eyeball and bends or refracts light rays.eyeball and bends or refracts light rays.

The The vitreous humorvitreous humor is a is a jelly-like substancejelly-like substance that fills the area behind the lens, and also that fills the area behind the lens, and also helps to bend light rays.helps to bend light rays.

The EyeThe Eye

When light rays enter the eye they pass When light rays enter the eye they pass through a series of parts that bend or through a series of parts that bend or refract the rays to allow the refract the rays to allow the rays to focus rays to focus on the retinaon the retina..

In the retina, the rays or images are picked In the retina, the rays or images are picked up by the up by the rods and conesrods and cones, changed into , changed into nerve impulses, and transmitted by the nerve impulses, and transmitted by the optic nerve to the occipital lobe of the optic nerve to the occipital lobe of the brain where sight is interpreted.brain where sight is interpreted.

Diseases of the EyeDiseases of the Eye Amblyopia Amblyopia

Also called “lazy eye”Also called “lazy eye” Poor vision in one eyePoor vision in one eye

AstigmatismAstigmatism Blurred vision caused by abnormal shape or curvature of the Blurred vision caused by abnormal shape or curvature of the

cornea.cornea. CataractsCataracts

Lenses become cloudy or opaque, with resulting loss of vision.Lenses become cloudy or opaque, with resulting loss of vision. ConjunctivitisConjunctivitis

Also called “pink eye”Also called “pink eye” Inflammation of the conjunctivaInflammation of the conjunctiva,, usually caused by bacteria or a usually caused by bacteria or a

virusvirus

Diseases of the EyeDiseases of the Eye

GlaucomaGlaucoma Increased pressure in eye from excess amountsIncreased pressure in eye from excess amounts Leading cause of blindnessLeading cause of blindness

Hyperopia Hyperopia FarsightednessFarsightedness Light rays are not refracted properly and the image is Light rays are not refracted properly and the image is

focused behind the retinafocused behind the retina MyopiaMyopia

NearsightednessNearsightedness Light rays are focused in front of the retinaLight rays are focused in front of the retina

Diseases of the Eye continuedDiseases of the Eye continued

PresbyopiaPresbyopia Farsightedness caused by loss of elasticity in Farsightedness caused by loss of elasticity in

the lens the lens StrabismusStrabismus

Eyes do not move or focus togetherEyes do not move or focus together May move inward (Cross eyed), or outward, May move inward (Cross eyed), or outward,

or up and downor up and down

The EarThe Ear

The ear is an organ that controls the special The ear is an organ that controls the special sense of hearing and balance. The ear sense of hearing and balance. The ear transmits impulses from sound waves to the transmits impulses from sound waves to the auditory nerve which carries the nerve auditory nerve which carries the nerve impulses to the brain for interpretation as impulses to the brain for interpretation as hearing.hearing.

Three Main Sections of the EarThree Main Sections of the Ear

Outer earOuter ear Contain the Contain the pinnapinna or or auricleauricle, which is the visible part , which is the visible part

of the year made up of elastic cartilage covered by of the year made up of elastic cartilage covered by skin. This leads to a canal called the auditory canal.skin. This leads to a canal called the auditory canal.

The auditory canal contains glands which produce The auditory canal contains glands which produce wax called wax called cerumencerumen, to protect the ear., to protect the ear.

Sound waves travel through the auditory canal, until Sound waves travel through the auditory canal, until they reach the they reach the eardrumeardrum or or tympanic membranetympanic membrane..

• The tympanic membrane vibrates when sound waves hit it The tympanic membrane vibrates when sound waves hit it and transmits the sound waves to the middle ear.and transmits the sound waves to the middle ear.

Three Main Sections of the EarThree Main Sections of the Ear Middle earMiddle ear

Contains three small bonesContains three small bones• The The malleusmalleus, , incusincus and and stapesstapes. These are connected and transmit . These are connected and transmit

sound to the inner ear.sound to the inner ear. Inner earInner ear

Most complex portion of the ear. There is a membrane which Most complex portion of the ear. There is a membrane which separates the inner and middle ear called the separates the inner and middle ear called the oval windowoval window..

The vesibule is the first section or door to the inner ear.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 next section is shaped like a snail’s shell and is called the

cochlea.cochlea.• The cochlea contains hair like cells which are the receptors for The cochlea contains hair like cells which are the receptors for

sound waves and transmit the impulses to the sound waves and transmit the impulses to the auditory nerveauditory nerve which which transmits the impulses to the transmits the impulses to the temporal lobe of the cerebrumtemporal lobe of the cerebrum to be to be interpreted as sound.interpreted as sound.

The Inner Ear continuedThe Inner Ear continued

Also located in the inner ear is the Also located in the inner ear is the semicircular canalssemicircular canals which contain a liquid which contain a liquid and hair-like cells that bend when the and hair-like cells that bend when the liquid moves with head and body liquid moves with head and body movement.movement.

Impulses from this semicircular canal are Impulses from this semicircular canal are sent to the sent to the cerebellumcerebellum to maintain our to maintain our sense of balance and equilibrium.sense of balance and equilibrium.

Diseases of the EarDiseases of the Ear Hearing lossHearing loss

Classified as Classified as sensory or conductivesensory or conductive Meniere’s diseaseMeniere’s disease

Collection of fluid in the inner earCollection of fluid in the inner ear Otitis externaOtitis externa

Inflammation of the Inflammation of the external auditory canalexternal auditory canal. May be . May be from swimmers’ ear, inserting bobby pins, Q-tips, from swimmers’ ear, inserting bobby pins, Q-tips, fingernails, ect.fingernails, ect.

Otitis mediaOtitis media Inflammation of the middle earInflammation of the middle ear. Frequently follows a . Frequently follows a

sore throat due to bacteria entering the middle ear sore throat due to bacteria entering the middle ear from that Eustachian tube.from that Eustachian tube.

Other sensesOther senses Sense of tasteSense of taste

Dependent upon taste receptors on tongueDependent upon taste receptors on tongue Can detect sweet, sour, salty, and bitterCan detect sweet, sour, salty, and bitter

Sense of smellSense of smell The The nosenose is the organ of smell. Impulses from the is the organ of smell. Impulses from the

olfactory receptors in the upper part of the nasal olfactory receptors in the upper part of the nasal cavity carry impulses to the brain by the cavity carry impulses to the brain by the olfactory olfactory nervenerve..

Sense of smell is closely related to sense of taste. Sense of smell is closely related to sense of taste. Smell is more sensitive than taste.Smell is more sensitive than taste.

The human nose can detect over The human nose can detect over 6,000 different 6,000 different smellssmells

Skin and General SenseSkin and General Sense

General sense receptors for General sense receptors for pressure, pressure, heat, cold, touch, and painheat, cold, touch, and pain are located are located throughout the body in the skin and throughout the body in the skin and connective tissue.connective tissue.

Messages through these receptors allow Messages through these receptors allow the human body to respond to its the human body to respond to its environment and protect it against injury.environment and protect it against injury.