Chapter 24

Body Structure and FunctionThe Special Senses

Introduction

This chapter discusses the special senses, which include the structures and organs that make it possible for us to see, hear, smell, taste and feel different sensations.

The Sensory System

ObjectivesReview the anatomy of the eye.Common disorders associated with the eye.Anatomy of the ear.Common disorders associated with the ear.How smell occurs.Discuss the sense of taste and briefly

explain the function of the taste buds.Case study.

The Eye and Sense of VisionThe eye is a fluid-

filled and spherical shaped organ.

Anatomical structures work together to facilitate light.

Light passes through the cornea, pupil, lens and vitreous body to stimulate sensory receptors in the retina.

EyeVision is made possible by the coordinated actions of

the nerves that control the movement of the eyeball, the amount of light admitted by the eyeball, the focusing light on the retina by the lens and the transmission of the resulting impulses to the brain.

Three layers of the eye include:1.The sclera, the white of the eye. The outer layer.2.The choroid layer is the second layer. Blood vessels,

the ciliary muscle and the iris make up the choroid. The iris gives the eye it’s color. The pupil is the opening in the middle of the iris. Pupil size depends on the amount of light entering the eye.

3.The retina is the inner layer of the eye. It contains receptors for vision and the nerve fibers of the optic nerve.

EyeLight enters the eye

through the cornea. The cornea is the transparent part of the outer layer that lies over the eye.

Light rays pass to the lens.

The light is then reflected to the retina and carries to the brain by the optic nerve.

Conjuctiva and Lacrimal apparatus

The tissue located on the underside of the eyelid and the anterior portion of the eyeball is mucous membrane called conjunctiva.

This membrane acts as a protective covering for the exposed surface of the eyeball.

The lacrimal apparatus includes all structures that produce, store and remove tears that cleanse and lubricate the eye.

Common Eye DisordersRefractive errors:1.Myopia2.Hyperopia3.PresbyopiaStrabismusAstigmatismCataract *Conjunctivitis*Glaucoma*Macular

degeneration*

The Ear and Sense of HearingThe ear is the site of hearing and

equilibrium.The ears consists of 3 different

separate sections:1.The external ear2.The middle ear3.The inner ear

The External EarThe external ear is

the visible portion of the ear.

This consists of the pinna(auricle), the auditory canal and the tympanic membrane.

The external ear directs sound waves

Glands produce wax, cerumen, which collects debris.

The Middle EarThe purpose of the

middle ear is to transmit sound.

This space contains the eustachian tube and ossicles.

Ossicles are bones responsible for hearing:

1.Malleus2.Incus3.Stapes

Inner EarConsists of the cochlea

and semicircular canals.

The cochlea contains fluid that carries sound waves from the middle ear to the auditory nerve.

The auditory nerve carries the message to the brain for interpretation.

The semicircular canals maintain balance.

Common Disorders Associated with the Ear

Meniere’s Disease

Presbycusis

Tinnitus

Impacted Cerumen

Sense of SmellThe sense of smell

is dependent on olfactory cells, located on the roof of the nasal cavity.

Once a smell receptor is activated it sends information to the olfactory nerves located in the brain.

Sense of TasteTaste buds are

receptors located on the tongue.

Some can be found on the roof of the mouth and some on the walls of the throat

Four receptors for taste:

1.Sweet-tip2.Salty-sides3.Sour-sides4.Bitter-back

Sense of TouchOldest and most

pervasive senseFirst to experience

and last to lose.Found all over the

bodyTouch originates

from the dermisMore sensitive

areas have more nerve endings

Case StudyWhy do you think

children get otitis media more than adults?

Why do you think a person refuses to eat when their ears hurt?

Why would Tylenol be prescribed for this patient?