special senses - florida technical college -...

Special Senses

Dr. Thorson

Lesson Objectives

Upon completion of this lesson, students should be able to:

1.Define and spell the terms to learn for this chapter.

2.Describe the anatomy of the eye, and briefly explain the function of each structure.

3.Discuss common disorders associated with the eye.

The Special Senses

• Vision

• Hearing

• Smell

• Taste

• Feeling

Critical Thinking Question

1.If you had to lose one of your special senses, which one would you choose to lose and why?

The eyeball and its anatomical structures.

The Eye and the Sense of Vision

• The eye is spherical, fluid-filled organ composed of specialized structures that work together to facilitate vision

• Light rays pass through the cornea, pupil, lens, and vitreous humor to the retina, where they stimulate sensory receptors

• Nervous system plays integral role in the sense of vision


• Nerves of the eye:

• Control the amount of light entering the eye through the pupil

• Focus light on the retina by using the lens

• Transmit the resulting images from the retina to the brain


• Structures of the Eyeball

• Eyeball housed in cavity in skull called orbit

• Eyeball divided into two cavities

• Front (anterior) cavity filled with watery fluid called aqueous humor

• Back (posterior) section located behind the lens and filled with very thick fluid in vitreous chamber, called vitreous humor


• Outer Layer of the Eyeball

• Sclera

• "white" part of the eye

• Cornea

• Frequently referred to as "window" of the eye because it allows the light to enter

• Limbus

• Corneal-scleral junction is area of the eye where the cornea and sclera meet


• Middle Layer of the Eyeball

• Choroid

• Lines the sclera and absorbs extra light entering the eye



• Iris

• Contains the pigment, or eye color, and has a "hole" in the center called the pupil

• Muscular tissue that makes up the iris and pupil allows pupil to constrict and dilate, which is how pupil controls amount of light that enters the eye



• Lens

• Colorless structure behind the iris, sharpens the focus of light rays onto retina; important to accommodation which adjusts eye's optical powers to maintain clear image at various distances



• Ciliary body

• Responsible for holding and moving the lens; secretes aqueous humor, which provides nutrients to the cornea, lens, and other tissues


• Inner Layer of the Eyeball

• Retina

• Back of eyeball, behind vitreous humor

• Photosensitive cells (rods and cones) translate light rays into nerve impulses transmitted to the brain



• Rods react to dim light and are used in night vision

• Cones are sensitive to bright light and are used to see color



• Fovea centralis retinae contains only cones; located in the middle of the macula lutea

• Optic nerve enters at optic disk and carries incoming information from eye to brain


• External Structures of the Eye

• Eyelids (palpebrae) close over eyeballs, protecting them from intense light, foreign matter, and impacts

• Keep eyes moist by preventing moisture in mucosal membrane surface of eye from evaporating

• Eyelashes in margins of eyelids further protect the eye from foreign matter



• Conjunctiva

• Mucous membrane that lines underside of eyelids and anterior part of eyeball; serves protective function

• Six short eye muscles connect eyeball to orbital cavity and supports and enables eyeball to rotate



• Tears produced, stored, and removed by the structures that make up lacrimal apparatus

• Lacrimal gland

• Lacrimal canaliculi

• Lacrimal sac

• Nasolacrimal duct

The lacrimal apparatus.

Common Refractive Disorders

• Most common disorders of the eye

• Characterized by inability of eye to focus correctly

• Caused by factors such as aging and changes in the shape of the eyeball and various eye muscles


• Astigmatism

• Caused by irregularities in curvature of cornea and lens

• Causes light not to focus on retina but rather to spread out over an area

• Blurry near or distant vision


• Astigmatism

• May be accompanied by squinting and headaches

• Corrective lenses or surgery to reshape the cornea


• Strabismus

• Crossed eyes or wall eyes

• Eyes misaligned; do not focus on same image, as one eye turns in, out, up, or down

• Caused by weakness in external eye


• Strabismus

• Poor depth perception and double vision also known as diplopia

• Eyeglasses, eye exercises, wearing a patch over stronger eye to force weaker eye to become stronger, surgery to realign eyes


• Myopia, Hyperopia, and Presbyopia

• Refraction problems, inability to focus correctly, occur because light rays change direction when they pass through the eye

• 75 percent of people living in United States wear corrective lenses to fix these disorders


• Myopia

• Light focuses in front of retina

• Also called nearsightedness

• Objects farther away tend to be blurry and difficult to see

• Easier to see objects closer to the eye

• Corrective lenses

• Radial keratotomy (RK)

• Lasik procedure


• Hyperopia

• Light focuses behind retina

• Farsightedness

• Objects close to eye harder to decipher and blurred

• Easier to see things farther away

• Corrective lenses

• Radial keratotomy (RK)

• Lasik procedure


• Presbyopia

• Loss of elasticity in lens; generally result of aging

• Difficulty focusing and seeing objects that are close

• Resting eyes when reading or working at computer


• Presbyopia

• Close eyes for 20–30 seconds every 20 minutes during visual activity

• Corrective lenses or refractive surgeries

Disorders Related toStructural Irregularities of the Eye

• Blepharoptosis

• Muscles of eyelid aren't strong enough to raise it

• Can be congenital or acquired as a secondary symptom of another disease

• Abnormal drooping of one or both eyelids

• Surgery to correct the drooping eyelid


• Ectropion

• Causes lower eyelid to turn outward

• Can be congenital or result of reaction to a drug, muscle weakness, facial paralysis, skin lesions


• Ectropion

• Eye irritation, excessive tearing of eye or excessive dryness of eye

• Eye ointment or drops

• Permanent treatment surgical intervention


• Entropion

• Causes lower eyelid to turn inward

• Congenital or result of eye infection, muscle weakness, scars from previous surgeries

• Pain and irritation


• Entropion

• Sensitivity to light, watery eyes, decreased or impaired vision

• Skin tape

• Surgery required for permanent solution


• Exophthalmos

• Causes bulging, bug-like appearance of one or both eyes

• Caused by hyperthyroidism, Graves disease, orbital tumor

• Treatment of underlying condition primary goal

• Surgical ablation and radiation are options

Infectious Eye Disorders

• Blepharitis

• Inflammation of the eyelids

• Caused by skin disorders (seborrheic dermatitis, rosacea, lice) and allergies

• Redness, itching, swelling of eyelids, burning sensations

• Treated with warm wet compresses and ophthalmic antibiotic therapy


• Conjunctivitis

• One of the most common and treatable eye infections

• Affects both children and adults

• Commonly known as pink eye

• Highly contagious condition


• Conjunctivitis

• Inflammation of the conjunctiva

• Causes include virus, bacteria, sexually transmitted infections (STIs), allergens, irritants such as chlorine, dirt, or smoke


• Conjunctivitis

• Redness in the sclera

• Increased tear production

• Thick yellow discharge

• Itchy and burning eyes

• Blurred vision


• Conjunctivitis

• Greater sensitivity to light

• Treatment: topical or oral antibiotics; eye drops containing antihistamines or nonsteroidal antiinflammatory agents


• Hordeolums

• Also known as sties

• Very common and frequently contagious

• Caused by Staphylococcus bacterium

• May accompany blocked or infected eyelid glands or inflamed eyelids


• Hordeolums

• Contaminated fingers that touch eye area may cause the infection

• Painful hordeolums can occur under eyelids

A hordeolum


• Hordeolums

• Redness and tenderness

• Itching

• Swelling

• Discomfort in upper or lower eyelid


• Hordeolums

• Often resolve on their own

• Warm, wet compress applied to the area may help relieve pain

• Antibiotics may be taken orally or applied topically to accelerate healing

Age-Related Eye Disorders

• Cataracts

• Clouding or opacity of the lens that prevents light from entering

• Cause is unclear

• May be correlation between formation of cataracts and smoking, diabetes, excessive exposure to sunlight


• Cataracts

• Vision begins to decrease

• Fuzzy, blurred, or filmy vision

• Lack of color intensity

• Night vision problems


• Cataracts

• Double vision or problems with bright lights occurs

• If left untreated, the cataract may eventually cloud the lens severely enough to block vision completely


• Cataracts

• For early or immature cataracts, eyeglasses, magnifying lenses, stronger lighting may be sufficient

• If not successful, surgery is recommended treatment

• Cataract removal very common surgery; it is extremely safe and effective with cure rate of 90 percent


• Retinal Detachment

• Occurs when a retina has separated from the underlying choroid layer

• If left untreated, develop into full detachment



• When such a separation occurs, vision is damaged

• If retina has already detached, vision can frequently be restored by surgery and laser therapy



• Increase in floaters (particles that float slowly within viewer's eyes)

• Flashes of light in the field of vision

• Early treatment is ideal

• Treatment for small holes or tears laser surgery or cryotherapy

• Retinal detachment, more invasive surgery


• Dry Macular Degeneration

• Deterioration of macula (central portion of retina)

• Occurs in 85 to 90 percent of cases

• Small yellow deposits called drusen form under the macula, causing it to thin and dry out, leading to a loss of central vision


• Slower progression than does wet type

• Sometimes turns into wet type




• Decline in central vision

• Increasing haziness of overall vision

• Need for brighter illumination for reading and close work

• No known treatment or cure


• Wet Macular Degeneration

• Abnormal new blood vessels grow under retina and the macula

• These may then bleed and leak fluid, which causes the macula to bulge or lift up, impairing or destroying the central vision

• Vision loss may be rapid and severe


• Wet Macular Degeneration

• Visual distortions

• Blurry spot in central vision

• If performed early, laser surgery may halt the progression of wet macular degeneration, thus preventing a total loss of vision

Other Eye Disorders

• Amblyopia

• Also called "lazy eye"

• Disorder often seen in children

• Occurs when nerve pathway from the eye to the brain does not properly develop

Other Eye Disorders

• Amblyopia

• Causes affected eye to send incorrect images to the brain

• May have a hereditary factor

• Leading cause is strabismus

Other Eye Disorders

• Amblyopia

• Decreased vision

• Eyes that appear to turn in or out

• Faulty depth perception

• Early diagnosis and treatment essential to a positive and lasting outcome

Other Eye Disorders

• Amblyopia

• Treatment for underlying conditions, such as strabismus or refractive disorders

• Patch may be worn over strong eye to force brain to interpret the images from afflicted eye

Other Eye Disorders

• Corneal Abrasion

• Lesion or scratch on cornea; can result from injury, infection, or both

• Very painful and irritating

• Blurred vision

• Excessive tearing

Other Eye Disorders


• Gritty feeling on cornea

• Possible headache

• Very sensitive to light and difficulty opening affected eye

Other Eye Disorders


• Treatment

• Mild analgesics and resting eyes

• If abrasion becomes infected, antibiotic eyedrops or ointments

Other Eye Disorders

• Glaucoma

• Affects people of all ages and all races

• Increased pressure in eye brought on by an excessive amount of aqueous humor

• Left untreated, pressure can lead to damage of the optic nerve and eventual blindness

Other Eye Disorders

• Open-angle (Acute) Glaucoma

• Pressure gradually builds, causing a slow drainage of aqueous humor from the anterior segment of the eye

• About 90 percent of glaucoma cases

Other Eye Disorders

• Closed-angle (Chronic) Glaucoma

• Considered more serious

• Space between iris and cornea narrows, causing a greater degree of pressure to build

Other Eye Disorders

• Glaucoma

• Open-angle is asymptomatic

• Patient may experience tunnel vision; once this symptom begins, damage is severe

Other Eye Disorders

• Glaucoma

• Closed-angle symptoms include sharp eye pain, decreased hazy vision, red swollen eyes

• Glaucoma treated with medications and laser and conventional surgery

Other Eye Disorders

• Nystagmus (Nystaxis)

• Involuntary, repetitive, rhythmic eye movements

• May be inherited or acquired

• Usually results in some loss of vision

Other Eye Disorders

• Nystagmus (Nystaxis)

• Uncontrolled eye movements may be lateral, horizontal, or even circular

• Treatment must address underlying cause: tumor, lesion, alcohol abuse, or retinal maldevelopment

Other Eye Disorders

• Retinopathy

• Disease of the retina caused by recurring or acute damage

• Patients with diabetes prone to diabetic retinopathy

Other Eye Disorders

• Retinopathy

• Nerve damage can result from hypertensive retinopathy caused by hypertension; can lead to permanent blindness

• Sickle cell disease, trauma, and other disorders can cause general retinopathy

Other Eye Disorders

• Retinopathy

• Symptoms vary based on type of retinopathy

• Treatment lies in treating underlying condition causing the disorder

Lesson Objectives


1.Define and spell the terms to learn for this chapter.

2.Describe the anatomy of the ear, and briefly explain the function of each structure.

3.Explain common disorders associated with the ear.

Lesson Objectives


4.Describe the anatomy of the nose, and explain how the sense of smell occurs.

5.Identify the anatomical structures that make up the special senses.

6.Discuss the sense of taste, and briefly explain the function of taste buds.

The ear and its anatomical structures.

The Ear and the Sense of Hearing

• The ear is responsible for hearing and equilibrium, or balance.

• Specialized anatomical structures in the ear are sensitive to sound vibrations, gravity, and head movements.

• Eighth cranial nerve connects these structures to the brain.


• The Outer Ear

• Pinna (auricle)

• Visible portion of ear; funnels sound waves into auditory canal

• Auditory canal (auditory meatus)

• Slightly curved tube; carries sound waves from outer ear to tympanic membrane; secretes cerumen (earwax)


• The Outer Ear

• Tympanic membrane (eardrum)

• Separates outer ear from middle ear and transmits sound vibrations into middle ear

• Fundus

• Floor of tympanic cavity


• The Middle Ear

• Tiny cavity in temporal bone of skull

• Contains three small bones (ossicles)

• Malleus (hammer)

• Incus (anvil)

• Stapes (stirrup)


• The Middle Ear

• Transmits sound vibrations

• Equalizes air pressure on both sides of tympanic membrane

• Protects ear from potentially damaging loud noise

• If eustachian tube blocked, patient may get an infection in middle ear


• The Inner Ear

• Maze of canals within bony labyrinth in temporal bone

• Cochlea, vestibule, three semicircular canals make up labyrinth

• Tiny hair cells in inner ear function as receptors for hearing and balance

• Cochlea (organ of hearing) is bony spiral structure that resembles a snail's shell

The cochlea.


• The Inner Ear

• The Organ of Corti, located in cochlear duct, contains nerve endings that transmit sound vibrations received from stapes to auditory region of the brain via eighth cranial nerve

• Vestibule is fundus of internal auditory meatus

• Vestibular system controls sense of balance

Hearing Loss

• Conductive

• Temporary

• Sound is not conducted efficiently through auditory canal to eardrum and middle ear

• Hearing loss can be medically corrected

Hearing Loss

• Sensorineural

• Permanent

• Caused by damaged cochlea or nerve pathways from inner ear to the brain

• Hearing aids and cochlear implants helpful

Common Disorders Associated with the Outer Ear

• Impacted Cerumen

• Cerumen produced by sebaceous glands to lubricate the ear

• Impacted cerumen obstructs auditory canal

• Affects older adults


• Impacted Cerumen

• Blocked or muffled hearing

• Plugged feeling in ear

• Pain

• Treatment

• Softening wax then flushing with a syringe; if left untreated, leads to tinnitus


• Ruptured Tympanic Membrane

• Objects entering ear perforate membrane or when unequal air pressure on both sides of the membrane causes a rupture

• Known as ruptured eardrum

• Sharp, sudden pain in affected ear may be followed by drainage of fluid, tinnitus, hearing loss, and vertigo (dizziness)


• Ruptured Tympanic Membrane

• Able to heal without any treatment

• Takes a few weeks to fully recover

• Antibiotic medications to prevent infection

• Analgesics to reduce pain

• Cold solutions should never be introduced into the ear

Common Disorders Associated with the Middle Ear

• Otitis Media

• Inflammation of any part of the ear

• Otitis externa (swimmer's ear)

• Inflammation of outer ear canal

• Otitis media

• Inflammation of middle ear


• Otitis Media

• Caused by viral or bacterial infections often secondary to sore throats and colds

• Occurs in children more frequently than adults


• Otitis Media

• Tugging on affected ear

• Irritability or fussiness

• Fever and fluid drainage

• Difficulty sleeping

• Loss of balance


• Otitis Media

• Treatment

• Eliminating cause of infection with oral antibiotics and decongestants

• Tubal insufflation every 1 to 2 days


• Otosclerosis

• Hereditary condition

• Abnormal tissue growth around stapes

• Prevents stapes from transmitting sound vibrations to inner ear

• Hearing loss in one or both ears

• Tinnitus and dizziness

• Treatment: use of a hearing aid or surgery

Common Disorders Associated with the Inner Ear

• Tinnitus

• Symptom associated with many forms of hearing loss and disorders of the ear

• Caused by hearing loss, loud noise, certain medications, other health problems such as allergies and tumors


• Tinnitus

• Ringing or roaring in one or both ears

• No cure

• Hearing aids, maskers, relaxation techniques, hypnosis, acupuncture may bring relief


• Ménière's Disease

• Named after French physician, Prosper Ménière

• Affects balance and hearing



• Changes in fluid volume in labyrinth cause symptoms

• Loss of hearing

• Pressure in the ear

• Vertigo

• Tinnitus



• Symptoms often occur suddenly, without warning; may occur daily or infrequently

• No known cure



• Controlled by lifestyle changes: reducing fluid retention with low-salt diet and avoiding caffeine and alcohol

• Diuretic drugs

• Eliminating tobacco use


• Presbycusis

• Gradual deterioration of sensory receptors in the cochlea

• Seen most frequently in older adults

• Causes

• Prolonged exposure to loud noises, infection, injury, side effects of medications


• Presbycusis

• Occurs in both ears and affects normal and high-pitched tones

• Treatment

• Use of a hearing aid

The Senses of Taste and Smell

• Nose primary organ for the sense of smell

• Olfactory cells of nasal cavity respond to changes in chemical concentrations

• Sends the information to the brain via olfactory nerves

• Sense of taste and sense of smell function together to create a combined effect interpreted by the brain

Nasal cartilage and external structures.

The Senses of Taste and Smell

• Taste buds are microscopic bumps on the tongue, roof of the mouth, walls of throat

• Four types of taste cells

• Sweet

• Sour

• Salty

• Bitter

The Sense of Touch

• Oldest, most primitive sense

• First sense humans experience in the womb and the last one lost before death

• Found over entire body

• Originates in dermis

The Sense of Touch

• Nerve endings in dermis (receptors) transmit information to brain via spinal cord

• More nerve endings = more sensitivity

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