Five Senses (listed in book)  Hearing  Sight  Taste  Smell  Balance Maintenance  However, Touch is often known as the 5 th sense The special senses allow the human body to react to the environment.

Steps to Responding to a Sensory Message 1. Receive the sensation 2. Nerves carry the sensory message to the brain 3. The brain interprets and responds

The Eye  The organ that controls the special sense of sight.

Vision is considered to be the most important sense. About 90% of the information about a person’s surroundings reaches the brain through the eyes.

Main Layers of the Eye Sclera  Outermost Layer  Tough connective tissue  Called “whites” of the eye  Help to maintain the shape of the eye Includes: a. Extrinsic Muscles - moves the eye within the socket b. Cornea – a circular transparent part at the front of the sclera which allows light to enter the eye

Main Layers of the Eye Choroid Coat  Middle Layer  Contains blood vessels Includes:  Pupil – hole in front of choroid coat which allows light rays to enter  Iris – colored portion of the eye, controls the size of the pupil, regulates the light

Main Layers of the Eye Retina  Innermost layer  Contains special cells  Transmits light impulses Special Cells include:  Cones – used mainly for light vision, sensitive to color, located at the Fovea Centralis where the sharpest vision is located  Rods – used for dark or dim vision

View of the Retina

Other Structures of the Eye Lens:  Circular structure located behind the pupil  Refracts or bends light so the rays will focus on the retina Aqueous Humor:  Clear, watery fluid  Fills the space between the cornea and iris  Maintain forward curvature of the eye  Refracts light rays

Other Structures of the Eye Vitreous Humor:  Jellylike substance  Fills the area behind the lens  Maintain the shape of the eyeball  Also, refracts light rays

What Nerve is Responsible for Vision?  The Optic Nerve

Refraction of Light Rays Light passes thru the eye in this order: 1. Cornea 2. Aqueous Humor 3. Pupil 4. Lens 5. Vitreous Humor 6. Retina In the retina, the light rays are picked up by the rods & cones. Finally, the nerve impulses are sent to the optic nerve to the occipital lobe of the brain where the sight is interpreted.

What does 20/20 vision mean?  If you have 20/20 vision, it means when you stand 20 feet away from the eye chart that you can see what the "normal" human being who has good vision can see.  If you have 20/40 vision, it means that when you stand 20 feet away from the chart you can see what a normal human can see when standing 40 feet from the chart (letters will be larger).  20/200 is the cutoff for legal blindness in the United States. Snellen Eye Chart

What Gland Secretes Tears?  Lacrimal Gland  Tears produced in the lacrimal glands constantly clean the eye and keep it moist.

What Protects the Eye? 1) Bony Socket 2) Eyelids 3) Eyelashes 4) Lacrimal Glands (tears) 5) Conjunctiva (thin membrane that lines the eyelids and covers the front of the eye)

Eye Disorders  Amblyopia – poor vision in one eye caused by dominance of the other eye, “lazy eye”

Eye Disorders  Astigmatism – abnormal shape or curvature of the cornea causing blurred vision.

Eye Disorder  Cataract – lens becomes cloudy as a result of aging or trauma.

Eye Disorder  Conjunctivitis – infection of the conjunctiva, “pink eye”

Eye Disorder  Glaucoma – condition resulting from an increased intraocular pressure (inside the eye)

Eye Disorders  Hyperopia – farsightedness, light rays are not refracted properly, the image focuses behind the retina.  Presbyopia – also farsightedness from loss of elasticity in the lens.

Eye Disorders  Myopia – nearsightedness, occurs when light rays are refracted too sharply and the image focuses in front of the retina.

Myopia  Image focuses in front of the retina and image is blurred.  Myopia corrected brings image back to the retina.

Eye Disorders  Strabismus – condition in which the eyes do not move or focus together, “cross- eyed”

The Ear  The organ that controls the special sense of hearing and balance.  The ear transmits impulses from sound waves to the hearing nerve. Divided into 3 main sections:  Outer Ear  Middle Ear  Inner Ear

Outer Ear Contains: a) Pinna or Auricle which is the visible part of the ear (cartilage covered with skin) a) External Auditory Meatus or Auditory Canal that has special ceruminous glands which produce wax called cerumen to protect the ear. a) Tympanic Membrane which separates the external ear and the middle ear. It vibrates when sound waves hit it.

Semicircular Canal

View of Eardrum

Middle Ear Located in the temporal bone Contains Ossicles which are 3 small bones: 1. Malleus 2. Incus 3. Stapes These bones help to transmit sound waves from the tympanic membrane to the inner ear.

Middle Ear (cont)  Eustachian tube connects the middle ear to the pharynx or throat. This tube helps equalize air pressure on both sides of the tympanic membrane.

Inner Ear Most Complex part of the ear Contains: a) Oval Window – separates the middle ear and the inner ear b) Vestibule – entrance of the inner ear c) Cochlea – shaped like a snail’s shell and contains hair-like cells in the Organ of Corti d) Semicircular Canals – contains a liquid and delicate hair-like cells that bend when the liquid moves with head or body movements

Hearing Nerve  The nerve that is responsible for hearing is the Auditory Nerve.  The Cochlea transmits impulses from the sound waves to the auditory nerve that carries the impulses to the temporal lobe of the cerebrum where they are interpreted as hearing.

The Ear What is the membrane between the outer ear and the middle ear?  Tympanic Membrane What is the membrane between the middle ear and the inner ear?  Oval Window The Semicircular Canals send impulses to the cerebellum of the brain to help maintain our sense of balance and equilibrium.

Ear Disorders Hearing Loss – inability to hear correctly due to a Conductive or Sensory problem.  Causes of Conductive Hearing Loss may include wax plug, foreign body, infection, or ruptured tympanic membrane.  Causes of Sensory Hearing Loss may include damage to inner ear or auditory nerve.

Ear Disorders (cont) Otitis Externa – inflammation of the external auditory canal; often a problem with swimmers (known as Swimmer’s Ear)

The Ear Band-It helps to prevent water from getting into the ears.

Ear Disorders Otitis Media – inflammation or infection of the middle ear These middle ear infections are common in children. If a child has repeated ear infections or fluid build-up in the ears, then an ear tube may be needed to allow the eardrum to equalize the pressure.

Tubes for Ear Infections  Doctors suggest tubes for children who have repeat ear infections or when fluid stays behind the eardrum. Ear tubes are plastic and shaped like a hollow spool. This surgery is called a myringotomy. Tubes can help with ear infections because they :  Allow air to enter the middle ear.  Allow fluid to flow out of the middle ear through the Eustachian Tube.  Clears the fluid from the middle ear and can restore hearing.  Prevent future buildup of fluid in the middle ear while they are in place.  Decreases the feeling of pressure in the ears, which reduces pain. Eventually, the tubes will move out of the eardrum and fall into the ear canal.

Ear Disorders  Otosclerosis – a condition in which the stapes becomes immobile causing conductive hearing loss

Taste  The tongue is a mass of muscle tissue with projections called papillae which contain taste buds.  The receptors in the taste buds send a signal to the brain to detect the flavor of the food.

Taste Buds  The average human has about 10,000 taste buds; however, they're not all on the tongue. Some are under the tongue; some are on the inside of the cheeks; some are on the roof of the mouth. Some can even be found on the lips; these are especially sensitive to salt.

Taste – Interesting Facts  Taste is about 75% smell.  A person cannot taste food unless it is mixed with saliva. For example, if strong-tasting substance like salt is placed on your dry tongue, you will not be able to taste it until it starts to dissolve.  Every person has a unique tongue print.  Butterflies taste with their feet.

Four Main Taste on the Tongue  Sweet – located on the tip of the tongue  Salty – located on the front upper sides of the tongue  Sour – located on the sides of the tongue  Bitter – located on the back of the tongue

Smell  The nose is the organ of smell  Olfactory receptors in the upper part of the nasal cavity carry impulses to the Olfactory Nerve of the brain.

Smell – Interesting Facts  Women are born better smellers than men and remain better smellers over life.  Smell function falls off in men after their mid-50s, a decade earlier than in women.  The smell of lavender can help with insomnia and sleep disorders.  The aroma of green apples can help control appetite.

Smell  The sense of smell is closely related to the sense of taste.  How many smells can a human detect? Over 6,000 different smells

General Senses Located throughout the body Includes: 1. Pressure 2. Heat 3. Cold 4. Touch 5. Pain

Works Cited:  Diversified Health Occupations, 7 th Edition by Louise Simmers  ds.htm ds.htm  Created by: Kathy Vidal Health Science Technology