Exercise 17

Special Senses

Portland Community CollegeBI 232

Special Senses• Sensory receptors are extensions of the

nervous system• Contain specialized cells or processes that

relay specific information• A receptor must convert the stimulus to an

action potential (transductions)• The AP must be conducted from the receptor

to the CNS

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General and Special senses• General senses include

touch, pressure, vibration, pain, temperature, proprioception and chemical and fluid pressure.

• Special senses include olfaction, gustation, vision and hearing and equilibrium

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Olfaction• Sensory receptors for

olfaction are located in the olfactory epithelium consists of:

• Olfactory receptor cells

• Supporting cells• Basal cells

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Testing olfactory adaptation• Adaptation refers to a

decreasing sensitivity to a stimulus over time.

• Sensitivity to an odor diminishes over time.

• Do Activity 17.2

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Gustation• Sensory receptors for

gustation are located in taste buds

• Located mainly on the top of the tongue but also in other areas of mouth

• Innervated by cranial nerves VII, IX and X

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Lingual Papilla

• Papilla are epithelial projections on the superior surface of the tongue

• Circumvallate papilla contain about 100 taste buds

• Fungiform papilla contain about 5 -10 taste buds

• Filiform papillae provide friction that helps the tongue move objects around in the mouth, but do not contain taste buds

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Taste Receptors

• Taste buds contain spindle-shaped cells• Basal cells: produce daughter cells that

mature in stages• Gustatory cells: extend microvilli into the

surrounding fluids through a taste pore • Contain the taste receptors

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Taste Bud Histology

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Gustatory Discrimination1. Umami: “Beef”2. Salty3. Sweet4. Bitter5. Sour• Substances must be dissolved (saliva) for

the chemically gated ion channels to open• Olfaction is very important in taste

Lab Activities• Look at the modes that

show oral structures• Look at slides of taste

buds.• Do activity 17.4: Parts

A and B

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Lab Activity 17

Vision

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Histology of the Retina

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Ciliary body

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1

2

A

P

1. Ciliary processes• Ciliary epithelium• Secretes aqueous humor

2. Ciliary muscle - (intrinsic eye muscle)

3. Suspensory ligament of the lensA= anterior chamberP= posterior chamber

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Neural pathway for vision• After optic nerves exit the

eyeballs they meet at the optic chiasm.

• Fibers from medial half of retina cross over to the opposite side.

• Optic tracts project to the lateral geniculate bodies in thalamus

• Some fibers are relayed to superior colliculi

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Lacrimal Apparatus• Consists of the lacrimal

gland and its accessory structures.

• Produces water, alkaline tears.

• Contain antibacterial enzyme called lysozyme for protection from bacterial infections

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Extrinsic Eye Muscles

• Superior oblique: primarily rotates the top of the eye toward the nose and secondarily moves the eye downward• Trochlea: Ligament sling

• Superior rectus: primarily moves the eye upward and secondarily rotates the top of the eye toward the nose

• Lateral rectus: moves the eye away from the nose

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Extrinsic Eye Muscles• Medial rectus: moves the eye toward the

nose• Inferior oblique: primarily rotates the top of

the eye away from the nose and secondarily moves the eye upward

• Inferior rectus: primarily moves the eye downward and secondarily rotates the top of the eye away from the nose

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NoseEar

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Extrinsic Eye Muscles

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Refraction

• Light is bent when it passes from one medium to another medium with a different density

• Light passes through these before it hits the retina:• Cornea• Aqueous humor• Lens• Vitreous humor

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Focal Point & Focal Distance

• Focal Point: The specific point of intersection on the retina.

• Focal distance: The distance between the center of the lens and its focal point. Determined by two factors:

1. Distance from the object to the lens2. Shape of the lens

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Focal Distance

• Distance from the object to the lens: the closer an object is, the greater the focal distance

• Shape of the lens: the rounder the lens, the more refraction occurs, so it has a shorter focal distance

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Accommodation

• Accommodation is an alteration in the curvature of the lens of the eye to focus an image on the retina• Near objects: Lens becomes rounder• Distance objects: Lens becomes flatter

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Accommodation

• Emmetropia is normal vision.

• The image will be focused on the retina’s surface

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Accommodation Problems

• Myopia: Nearsighted• The eyeball is too deep or

the curvature of the lens is too great

• The focal point is in front of the retina, so distance objects are blurry

• Corrected with a diverging lens

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Accommodation Problems

• Hyperopia: Farsighted• The eyeball is too shallow or

the curvature of the lens is too flat

• The focal point is behind of the retina, so near objects are blurry

• Corrected with a converging lens

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Astigmatism

• The degree of curvature in the cornea or lens varies from one axis to another (is uneven or wavy)

• This causes light to focus on more than one area of the retina creating a blurry image.

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Intrinsic Eye Muscles of the Iris

Pupils constrict (Parasympathetic) Close vision and bright light

Pupils dilate (Sympathetic) Distant vision and dim light

Color Blindness• Cones are responsible for

color vision. • 3 types of cones each able

to absorb light at specific wavelengths.

• Lack of one or more types of cone can cause color blindness

• Use Ishihara color plates to test

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Activities

• Dissect cow eye• Perform visual tests

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Lab Activity 18

Hearing & Equilibrium

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Vestibular Portion

Cochlear Portion

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Middle Ear Ossicles (Bones)

Stapes

Malleus Incus

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• The stapes strikes the oval window of the cochlea

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Vestibular Complex

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Cochlea

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• Stapes pushes on fluid of vestibular duct at oval window• At helicotrema, vibration moves into tympanic duct• Fluid vibration dissipated at round window which bulges• The central structure is vibrated (cochlear duct)

helicotrema

vestibular duct

tympanic duct

round window Cochlear duct

containing the Organ of Corti

Cochlea Uncoiledoval window

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Organ of Corti

Neural pathways for hearing• Vestibulocochlear nerve

(CN VIII) has 2 divisions:

• Vestibular division-send impulses to medulla where fibers are crossed and uncrossed to travel to the cerebellum; to the cortex

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Neural pathways for hearing• The cochlear division

receive impulses to the cochlear nuclei in the medulla.

• Some fibers cross over to other side.

• Some remain on the same side.

• Both synapse in the inferior colliculi

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Types of Hearing Loss

• Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the bones of the middle ear.

• Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear to the brain.

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Weber & Rinne Tests

• Weber test: determines if hearing loss is present in one ear, but does not distinguish conductive and sensorineural deafness

• Rinne test : Evaluates an individual’s ability to hear sounds conducted by air or bone

• Used together, these test can distinguish between the two types of hearing loss

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Weber Test• Ring tuning fork and place on center

of head. Ask the subject where they hear the sound.

• Interpreting the test:• Normally, the sound is heard in the

center of the head or equally in both ears.

• Sound localizes toward the poor ear with a conductive loss

• Sound localizes toward the good ear with a sensorineural hearing loss

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Rinne Test

• Place the vibrating tuning fork on the base of the mastoid bone.

• Ask patient to tell you when the sound is no longer heard.

• Immediately move the tuning fork to the front of the ear

• Ask the patient to tell you when the sound is no longer heard.

• Repeat the process putting the tuning fork in front of the ear first

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Rinne Test

• Normally, someone will hear the vibration in the air (in front of the ear) after they stop hearing it on the bone

• Conductive hearing loss: If the person hears the vibration on the bone after they no longer hear it in the air.

• Do Activity 17.8

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The End