Special Senses

Unit 6.7 (6th Edition)

Chapter 7.7 (7th Edition)1

Learning Objectives

• Identify the five special senses.

• Identify the four general senses.

• Trace the pathway of light rays as they pass

through the eye and how sight works.

• Identify the major parts (anatomy) of the eye.

• Distinguish between the major eye abnormalities.

• Identify the major parts (anatomy) of the ear.

• Trace path of sound waves as pass through ear.

• Explain how the ear helps maintain balance.

• Identify major diseases affecting the ear.

• Distinguish between the four main tastes.

• Explain the role of the nose in our sense of smell.2

Fun Facts About the Special Senses

• Color blindness affects about 1 in 30 people and is

more common in men than women.

• Our sense of smell can tell the difference between

approximately 6,000 smells!

• As you grow older, your sense of smell gets worse.

• A bloodhound can smell at least 1000 times better

than humans.

• If saliva cannot dissolve something, you cannot taste it.

• 2/3 of the human population has less than perfect

vision.

• Everyone has a unique smell, except for

identical twins.3

Special Senses vs. General Senses

• 5 Special Senses

– senses that have specific organs devoted to them

– Sight (eye)

– Hearing (ear)

– Taste (tongue)

– Smell (nose)

– Balance (ear)

• 4 General Senses

– senses that do not have a specialized organ but comes

from all over the body (skin and internal organs)

– Touch

– Pain

– Heat

– Cold 4

How Does Sight Work?• Light rays enter the eye through the cornea and then pupil.

• The convex lens behind the eye focuses the light to form an

image on the screen at the back of the eye (retina).

• This image is upside down.

• Signals from photoreceptors travel along nerve fibers.

• The optic nerve carries impulses to brain (occipital lobe).

• Brain interprets impulses as vision, or sight.

5

Eye Anatomy

6

*Know the highlighted

terms*

Eye Protection & Layers• Protection

– enclosed in bony socket of skull

– eyelids & eyelashes keep out dirt and germs

– lacrimal glands produce tears which moisten and cleanse eye

– conjunctiva is a mucous membrane that lines the eyelids

• Three Eye Layers

– sclera (white)

• tough outermost layer & maintains eye shape

• cornea –transparent part of sclera & allows light to enter eye

– choroid coat

• middle layer of eye

• interlaced with blood vessels that nourish eye

– retina

• innermost layer of eye

• has many nerve cells that transmit impulses to optic nerve

• cones – nerve cells sensitive to color and used when light

• rods – nerve cells used for vision when it is dark 7

Eye Anatomy & Physiology• Iris

– colored portion of eye

– located behind cornea

– pupil is opening (black) in iris center

– contains 2 muscles that control pupil size

– regulates how much light enters the eye

• Lens

– circular structure behind the pupil

– refracts (bends) light rays so that they focus on retina

• Aqueous Humor

– clear, watery fluid that fills space between cornea & iris

– helps maintain forward curvature of eye & refracts light

• Vitreous Humor

– jellylike substance that fills area behind lens

– helps maintain eye shape and also refracts light8

Eye Diseases and Abnormalities• Amblyopia (Lazy Eye)

– occurs in early childhood

– poor vision in one eye causes dominance in the good eye

– if condition not treated by 8-9 years old, blindness may occur

• Astigmatism

– abnormal shape/curvature of cornea (football instead of sphere)

– causes blurred vision

• Cataract

– normally clear lens becomes cloudy or opaque

– typically the result of aging or trauma

• Conjunctivitis (Pink Eye)

– very contagious inflammation of conjunctiva

– usually caused by virus or bacterium

• Glaucoma

– increased pressure in eye caused by excess of aqueous humor

– common after age 40 and is leading cause of blindness 9

Impaired Vision

10

The Ear and Hearing• The Ear

– transmits impulses from sound waves to auditory nerve

– impulses carried to brain for interpretation as hearing

• Three Main Ear Sections

– Outer Ear

• pinna (auricle) – visible part of the ear that leads to auditory canal

• glands in this canal produce cerumen (ear wax) that protects ear

• sound waves travel through canal to tympanic membrane (eardrum)

• eardrum vibrates when waves hit it & transmits waves to middle ear

– Middle Ear

• small cavity in temporal bone that contains three small bones

• ossicles - malleus, incus, and stapes

• bones connect and transmit sound waves from eardrum to inner ear

– Inner Ear

• most complex part of ear

• contains cochlea containing delicate, hair like cells that are receptors

• organ of Corti transmits impulses from sound waves to auditory nerve

• impulses carried to temporal lobe where interpreted as hearing11

Ear Anatomy

12

The Ear and Balance

• Semicircular Canals

• Located in inner ear

• Contain liquid and

delicate hair-like cells

that bend when liquid

moves with head and

body movements

• Impulses sent from these

canals to cerebellum of

brain help to maintain

our sense of balance and

equilibrium13

Ear Diseases and Abnormalities• Conductive Hearing Loss

– occurs when sound waves are not conducted to the inner ear

– possible causes include wax plug, foreign body obstruction, an

infection, or ruptured eardrum

– surgery and hearing aids are common form treatments

• Sensory Hearing Loss (Deafness)

– occurs when there is damage to inner ear or auditory nerve

– cochlear implants can improve severe hearing loss

• Meniere’s Disease

– collection of fluid in labyrinth of inner ear and degeneration of hair cells

– symptoms - severe dizziness, ringing in the ears, nausea, loss of balance

• Otitis Externa

– inflammation of external auditory canal (Swimmer’s Ear)

– caused by pathogenic organism (virus or bacteria)

• Otitis Media

– inflammation or infection of middle ear

– caused by virus or bacterium and frequently follows sore throat

14

The Tongue and Taste

• The Tongue

– mass of muscle tissue with

projections called papillae

– papillae contain taste buds

that are stimulated by flavor

• Four Main Tastes

– Sweet (tip of tongue)

– Salty (tip of tongue)

– Sour (sides of tongue)

– Bitter (back of tongue)

• Taste is influenced by smell

15

The Nose and Smell

• The nose is the organ of smell

• olfactory receptors are located in

upper part of nasal cavity

• impulses from receptors are

carried to brain by the olfactory

nerve

• the sense of smell is more

sensitive than taste

• human nose can detect over

6,000 different smells

• smell and taste are closely linked

• if you have a cold, your sense of

smell and taste are impaired16