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The Sensory SystemThe Sensory System

Chapter 11Chapter 11

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The Sensory System:The Sensory System:

Protects us by detecting changes in the Protects us by detecting changes in the environmentenvironment

Some stimuli arrive from the external Some stimuli arrive from the external environment & are detected at or near the environment & are detected at or near the surface of the bodysurface of the body

Other stimuli can originate internally & help Other stimuli can originate internally & help to maintain homeostasisto maintain homeostasis

Regardless of the type of stimulus, sensations Regardless of the type of stimulus, sensations must be interpreted by the cerebral cortex in must be interpreted by the cerebral cortex in order for us to experience any feelingorder for us to experience any feeling

RECEPTORSRECEPTORS detect a stimulus detect a stimulus

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Special SensesSpecial Senses

Localized in a “special sense” organLocalized in a “special sense” organ Vision: receptors in the eyeVision: receptors in the eye Hearing & Equilibrium: receptors in Hearing & Equilibrium: receptors in

the internal earthe internal ear Taste: receptors on the tongueTaste: receptors on the tongue Smell: receptors in upper nasal Smell: receptors in upper nasal

cavitiescavities

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General SensesGeneral Senses

Widely distributed throughout the Widely distributed throughout the bodybody

Pressure, heat, cold, pain & touch: Pressure, heat, cold, pain & touch: receptors in the skin & internal receptors in the skin & internal organsorgans

Body positioning: receptors in Body positioning: receptors in muscles, joints & tendonsmuscles, joints & tendons

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The Eye & Vision

Protection of the eyeball– Skull bones Skull bones

form the eye form the eye ORBIT (cavity) ORBIT (cavity) protects more protects more than half of than half of the dorsal part the dorsal part of the eyeballof the eyeball

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– Eyelids protect the front of the eye Eyelids protect the front of the eye keeping harmful particles out & keeping harmful particles out & lubricate the eyeball through blinkinglubricate the eyeball through blinking

– Eyelashes & eyebrows assist in keeping Eyelashes & eyebrows assist in keeping foreign matter out of the eyeforeign matter out of the eye

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Lacrimal Glands

Produce tears Produce tears which which lubricate the lubricate the eye, wash eye, wash away small away small foreign objects foreign objects & contain an & contain an enzyme that enzyme that helps protect helps protect against against infectioninfection

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Coats of the EyeballCoats of the Eyeball

1. Sclera “white of the

eye” Outermost coat Made of tough

connective tissue

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2. 2. Choroid Composed of Composed of

delicate tissue with delicate tissue with many blood vesselsmany blood vessels

Contains dark Contains dark brown pigmentbrown pigment

Prevents incoming Prevents incoming light from light from scattering & scattering & reflecting off the reflecting off the inner surface of the inner surface of the eyeeye

Lies between the Lies between the sclera & the retinasclera & the retina

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3. 3. Retina

Innermost coatInnermost coat Receptor layer Receptor layer

of the eyeof the eye Contains Contains RODS

& & CONES which which generate nerve generate nerve impulses in impulses in order for vision order for vision to occurto occur

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Refraction

As light passes toward the retina, it As light passes toward the retina, it undergoes a process called undergoes a process called REFRACTION

The bending of light rays as they pass from one surface to another

Allows light from a large area to be focused on a small surface (the retina) where sight receptors are located

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Refracting Parts of the EyeRefracting Parts of the Eye1. Cornea – the

“window of the eye”

Main refracting structure

Bulges forward slightly

Has no blood vessels

Nourished by fluids that wash over it

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2. 2. Aqueous HumorAqueous Humor

Watery fluid that Watery fluid that fills much of the fills much of the eyeball in front of eyeball in front of the lensthe lens

Helps to maintain Helps to maintain the slight forward the slight forward curve of the corneacurve of the cornea

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3. 3. LensLens (Crystalline Lens) (Crystalline Lens) Clear, circular Clear, circular

structure structure made of firm, made of firm, elastic elastic materialmaterial

Important in Important in light refraction light refraction as it can as it can adjust to focus adjust to focus light for both light for both near & distant near & distant visionvision

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4. 4. Vitreous BodyVitreous Body

Soft, jelly-like Soft, jelly-like substance that fills substance that fills the entire space the entire space behind the lensbehind the lens

Important in Important in maintaining the maintaining the shape of the shape of the eyeballeyeball

Aids in refractionAids in refraction

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Muscles of the Eye Extrinsic Muscles – voluntary muscles – voluntary muscles

attached to the outer surface of the attached to the outer surface of the eyeballeyeball– Seven extrinsic muscles ORIGINATE on Seven extrinsic muscles ORIGINATE on

the bones of the ORBIT & INSERT on the the bones of the ORBIT & INSERT on the surface of the SCLERAsurface of the SCLERA

– These muscles pull on the eyeball in These muscles pull on the eyeball in coordination with each othercoordination with each other

– Center both eyes on one visual fieldCenter both eyes on one visual field– Produce a clear image on the retinaProduce a clear image on the retina

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Intrinsic Muscles – found in two – found in two structures within the eyestructures within the eye

1. Iris – Color part of the eye– Contains the pupil– Regulates the amount of light

entering the eye– Muscles of the iris will reduce or

CONSTRICT the size of the pupil in bright light

– Muscles of the iris will expand or DILATE the size of the pupil in dim light

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2. Ciliary Muscle

Alters the shape of the lens during the process of ACCOMMODATION

Accommodation involves coordinated eye changes to enable a person to focus on near objects

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The Optic Nerve

Carries visual impulses from the rods and Carries visual impulses from the rods and cones to the braincones to the brain

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Eye Disorders1. Hyperopia – Farsightedness

Usually due to an abnormally short eyeball

Focal point is BEHIND the retina Light rays cannot bend sharply enough to

focus ON the retina Objects must be moved AWAY from the

eye to be seen clearly Corrected with a CONVEX lens

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2. 2. Myopia - - NearsightednessNearsightedness

Eyeball is too longEyeball is too long Cornea bends light too sharplyCornea bends light too sharply Focal point is in FRONT of the retinaFocal point is in FRONT of the retina Distant objects appear blurry and Distant objects appear blurry and

must be moved TOWARD the eye to must be moved TOWARD the eye to be seen clearlybe seen clearly

Corrected with a CONCAVE lensCorrected with a CONCAVE lens

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3. 3. Astigmatism

An irregularity in An irregularity in the curvature of the curvature of the cornea or the the cornea or the lenslens

Light rays are Light rays are incorrectly bent, incorrectly bent, causing blurred causing blurred visionvision

Usually found in Usually found in combination with combination with hyperopia or hyperopia or myopiamyopia

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Eye InfectionsEye Infections Conjunctivitis – “Pink Conjunctivitis – “Pink

Eye”Eye”

– Inflammation of the Inflammation of the membrane that lines membrane that lines the eyelidthe eyelid

– Highly contagiousHighly contagious– Causes may include:Causes may include:

Irritants (wind,glare)Irritants (wind,glare) Bacterial InfectionsBacterial Infections

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Inclusion ConjunctivitisInclusion Conjunctivitis Acute infection Acute infection

caused by caused by “chlamydia “chlamydia trachomatis” (also trachomatis” (also causes the STDcauses the STD

History of sexual History of sexual activity and activity and previous sexually previous sexually transmitted disease transmitted disease is important is important

Causes scarring of Causes scarring of cornea & blindnesscornea & blindness

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Eye InjuriesEye Injuries

Scratched Cornea

– Caused by foreign Caused by foreign objects or infectionobjects or infection

– Scarring results; Scarring results; light cannot pass light cannot pass throughthrough

– Blindness may Blindness may resultresult

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CataractsCataracts Covering of the lensCovering of the lens

Can cause gradual Can cause gradual loss of vision or loss of vision or complete losscomplete loss

Age is a factorAge is a factor

Surgery can restore Surgery can restore visionvision

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GlaucomaGlaucoma

Excess pressure on Excess pressure on the aqueous humorthe aqueous humor

Progresses slowlyProgresses slowly

Early diagnosis can Early diagnosis can result in preserving result in preserving visionvision

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Retinal DetachmentRetinal Detachment

Retina separates Retina separates from the rest of the from the rest of the eyeeye

Can result from Can result from head traumahead trauma

Left untreated can Left untreated can cause blindnesscause blindness

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Macular DegenerationMacular Degeneration

Changes in part Changes in part of the retina that of the retina that can distort vision can distort vision & cause & cause blindnessblindness

Factors:Factors:– SmokingSmoking– SunlightSunlight– High cholesterol High cholesterol

dietdiet

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The EarThe Ear

Sensory organ for both hearing and Sensory organ for both hearing and equilibriumequilibrium

Divided into three main sections::– Outer Ear – includes the ear canal– Middle Ear – air space including 3 small

bones (hammer, anvil & stirrup)– Inner Ear – most complex area and

contains the receptors for hearing & equilibrium

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The Eustachian TubeThe Eustachian Tube

The “auditory tube”

Connects the middle ear with the pharynx (throat)

Opens to allow pressure to equalize on both sides of the of the TYMPANIC MEMBRANE (eardrum)

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Disorders of the EarDisorders of the Ear

“Otitis Media” or ear infection of the or ear infection of the middle earmiddle ear

Relatively commonRelatively common

Caused by a variety of bacteria & virusesCaused by a variety of bacteria & viruses

Frequently a complication of measles & Frequently a complication of measles & fluflu

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Hearing LossHearing Loss

Deafness is a complete loss of Deafness is a complete loss of hearinghearing

CONDUCTIVE hearing loss hearing loss– Due to interference with the passage of Due to interference with the passage of

sound waves from the outer to inner ear sound waves from the outer to inner ear by an OBSTRUCTION (wax or a foreign by an OBSTRUCTION (wax or a foreign body)body)

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Sensorineural Hearing LossSensorineural Hearing Loss

Due to prolonged exposure to loud Due to prolonged exposure to loud noises, use of certain drugs for long noises, use of certain drugs for long periods of time or exposure to periods of time or exposure to infection or toxinsinfection or toxins

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TasteTaste

Receptors found in the tongue Receptors found in the tongue

Two nerves carry taste impulses to Two nerves carry taste impulses to the brainthe brain

Receptors (taste buds) are stimulated Receptors (taste buds) are stimulated when saliva mixes with a substancewhen saliva mixes with a substance

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Taste ExperiencesTaste Experiences

SweetSweet – at the TIP – at the TIP

SourSour – at the SIDES – at the SIDES

SaltySalty – on the top – on the top portion of the side portion of the side of the tongueof the tongue

BitterBitter – at the BACK – at the BACK

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SmellSmell Impulses are carried Impulses are carried

by the OLFACTORY by the OLFACTORY nerve to the brainnerve to the brain

Olfactory receptors Olfactory receptors deteriorate with agedeteriorate with age

Closely related to Closely related to taste & is important taste & is important in stimulating in stimulating appetite & flow of appetite & flow of digestive juicesdigestive juices

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General SensesGeneral Senses

Touch

– Receptors found in dermis of skin and hair follicles

– Sensitivity varies with number of receptors

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PressurePressure

– Receptors found in most deep tissue and Receptors found in most deep tissue and jointsjoints

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TemperatureTemperature

– Receptors widely distributed in skinReceptors widely distributed in skin

– Separate receptors for heat and coldSeparate receptors for heat and cold

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PositionPosition

– Receptors found in muscles, tendons & Receptors found in muscles, tendons & jointsjoints

– Aid in judging position & location of Aid in judging position & location of body parts in relation to each otherbody parts in relation to each other

– Inform the brain of the proper amount of Inform the brain of the proper amount of muscle contraction and tendon tensionmuscle contraction and tendon tension

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PainPain

– Receptors widely distributedReceptors widely distributed

– Found in the skin, muscles, joints and Found in the skin, muscles, joints and most internal organsmost internal organs