Introduction to Health ScienceIntroduction to Health ScienceSpecial SensesSpecial Senses

Cranial NervesCranial Nerves

Description of the Special SensesDescription of the Special Senses• SmellSmell– Occurs when specialized cells in the nose Occurs when specialized cells in the nose

(chemoreceptors) detect chemicals (chemoreceptors) detect chemicals – Results in nerve impulses being sent to the brain Results in nerve impulses being sent to the brain

for interpretationfor interpretation

NoseNose• In the upper part of the nasal cavity are specialized nerve cells In the upper part of the nasal cavity are specialized nerve cells

called olfactory receptor cellscalled olfactory receptor cells• These receptor cells contain hair called cilia to which the dissolved These receptor cells contain hair called cilia to which the dissolved

chemicals attachchemicals attach• Transmitted from the olfactory receptors cellsTransmitted from the olfactory receptors cellsolfactory olfactory

bulbbulbolfactory nerveolfactory nervebrain brain • Sense of smell is interpreted then sent back to nasal cavitySense of smell is interpreted then sent back to nasal cavity

• Basic smells include Basic smells include • Putrid (rotting food)Putrid (rotting food)• Pungent (spicy)Pungent (spicy)• Floral (flowers)Floral (flowers)• Ethereal (medicine smell)Ethereal (medicine smell)• MintMint

TasteTaste• Occurs when specialized cells on the tongue Occurs when specialized cells on the tongue

(chemoreceptors) detect chemicals (chemoreceptors) detect chemicals – Results in nerve impulses being sent to the brain Results in nerve impulses being sent to the brain

for interpretationfor interpretation

Mouth and TongueMouth and Tongue• The sense organs that detect dissolved chemicals for the The sense organs that detect dissolved chemicals for the

sense of taste are the taste buds sense of taste are the taste buds – Located in the tongue and throughout the mouth Located in the tongue and throughout the mouth

• When the taste buds are stimulated by chemicals, they When the taste buds are stimulated by chemicals, they generate nerve impulses which are sent to the brain for generate nerve impulses which are sent to the brain for interpretation interpretation

• There are five basic tastes, although they are not limited to There are five basic tastes, although they are not limited to specific parts of the tongue: specific parts of the tongue: – Sweet (sugars and carbohydrates)Sweet (sugars and carbohydrates)– Sour (acids)Sour (acids)– Salt (salt)Salt (salt)– Bitter (caffeine) Bitter (caffeine) – Umami (protein and amino acids)Umami (protein and amino acids)

VisionVision• The sense organs that respond to light are the The sense organs that respond to light are the

eyes eyes – The light waves travel through the eyes until they The light waves travel through the eyes until they

reach the back of the eye called the retina reach the back of the eye called the retina – Nerve impulses are generated by specialized cells Nerve impulses are generated by specialized cells

that are sensitive to light (photoreceptors) that are sensitive to light (photoreceptors) – Nerve impulses travel to the brain Nerve impulses travel to the brain – Interpreted as visual images Interpreted as visual images – Provide much information about the external Provide much information about the external

worldworld– If there is no light, there is no sight!If there is no light, there is no sight!

EyeEye• EyelidEyelid– Structures composed of skin, muscles, and lashesStructures composed of skin, muscles, and lashes– Protect the eye from foreign objects by the blink Protect the eye from foreign objects by the blink

reflexreflex– Moves tears along the surface of the eyeball to Moves tears along the surface of the eyeball to

keep the eyeball moistkeep the eyeball moist

• ConjunctivaConjunctiva– Membrane lining the insides of the eyelids and Membrane lining the insides of the eyelids and

eyeballeyeball– Reduces friction during blinkingReduces friction during blinking

EyeEye• ScleraSclera– The white part of the eyeThe white part of the eye– Provides protection and shape to the eyeProvides protection and shape to the eye

• CorneaCornea– The clear window of the front part of the eyeThe clear window of the front part of the eye– Allows light waves to enter the eyeAllows light waves to enter the eye– Helps to bend the light waves on to the back of Helps to bend the light waves on to the back of

the eye (retina)the eye (retina)

EyeEye• IrisIris– The colored portion of the eye which contains two The colored portion of the eye which contains two

sets of musclessets of muscles– Regulates the size of the pupil to control the amount Regulates the size of the pupil to control the amount

of light entering the eyeof light entering the eye• PupilPupil– An opening in the center of the irisAn opening in the center of the iris– Passage for lightPassage for light

• LensLens– Transparent disc shaped structure located behind the Transparent disc shaped structure located behind the

iris and pupiliris and pupil– Focuses light waves on to the retinaFocuses light waves on to the retina

EyeEye• RetinaRetina– Most inner layer of the eyeball Most inner layer of the eyeball – Located under the scleraLocated under the sclera– Contains the photoreceptors that when stimulated Contains the photoreceptors that when stimulated

by light generate nerve impulses which are then by light generate nerve impulses which are then sent to the brain for interpretationsent to the brain for interpretation

• Optic NerveOptic Nerve– Nerve that sends and receives impulses to and Nerve that sends and receives impulses to and

from the brainfrom the brain

HearingHearing• Involves the movement of sound vibrations Involves the movement of sound vibrations

through the ear through the ear – When they reach a specialized region in the inner When they reach a specialized region in the inner

ear nerve impulses are generated by cells that ear nerve impulses are generated by cells that detect movement (mechanoreceptors)detect movement (mechanoreceptors)

– Nerve impulses travel to the brain where they are Nerve impulses travel to the brain where they are interpreted as soundinterpreted as sound

Outer EarOuter Ear• AuricleAuricle– The visible portion of the ear on the side of the headThe visible portion of the ear on the side of the head– Composed of cartilage Composed of cartilage – Captures sound waves from environmentCaptures sound waves from environment– Directs them toward the auditory canalDirects them toward the auditory canal

• Auditory CanalAuditory Canal– Tube lined with hair and waxTube lined with hair and wax– Assists in the passage of sound waves to the middle Assists in the passage of sound waves to the middle

earear– Provides protection for the ear as particles, debris and Provides protection for the ear as particles, debris and

dust are trapped by the hair and waxdust are trapped by the hair and wax

Middle EarMiddle Ear• Tympanic MembraneTympanic Membrane– Known as the eardrum, it is the first structure of the Known as the eardrum, it is the first structure of the

middle earmiddle ear– It vibrates with the sound waves and passes the It vibrates with the sound waves and passes the

vibrations to the middle ear bonesvibrations to the middle ear bones• Auditory OssiclesAuditory Ossicles– Three tiny bones in the middle ear that continue the Three tiny bones in the middle ear that continue the

passage of sound vibrationspassage of sound vibrations– They also amplify the vibrations twenty timesThey also amplify the vibrations twenty times

• Eustachian Tube (auditory tube)Eustachian Tube (auditory tube)– Small tube extending from the middle ear into the Small tube extending from the middle ear into the

throatthroat– Helps to equalize pressure inside the earHelps to equalize pressure inside the ear

Inner EarInner Ear• CochleaCochlea– Snail shaped structure Snail shaped structure – Membrane-lined fluid-filled canals that continue Membrane-lined fluid-filled canals that continue

to pass along the sound vibrationsto pass along the sound vibrations– Reach a specialized structure of the inner ear Reach a specialized structure of the inner ear

called the Organ of Corti where nerve impulses called the Organ of Corti where nerve impulses are generatedare generated

– The impulses are transmitted to the brain where The impulses are transmitted to the brain where they are interpretedthey are interpreted

• Vestibulocochlear NerveVestibulocochlear Nerve

TouchTouch• Detection of various amounts of pressure by Detection of various amounts of pressure by

the skin the skin • Nerve impulses are generated by cells that are Nerve impulses are generated by cells that are

sensitive to movement (mechanoreceptors) sensitive to movement (mechanoreceptors) and sent to the brain for interpretationand sent to the brain for interpretation

SkinSkin• The skin contains several different types of nerve The skin contains several different types of nerve

receptors receptors – Sensitive to deep pressure like poking or light touchSensitive to deep pressure like poking or light touch

• All regions of the skin are sensitive to touchAll regions of the skin are sensitive to touch– The greatest number of touch receptors are found in the The greatest number of touch receptors are found in the

fingers, toes, and facefingers, toes, and face• Once the nerve impulses for touch are generated, Once the nerve impulses for touch are generated,

they are sent to the brain for interpretationthey are sent to the brain for interpretation

• Learning LogLearning Log

– What problems could we have with our senses?What problems could we have with our senses?– What would cause those problems?What would cause those problems?

Disorders of the Special SensesDisorders of the Special Senses• ConjunctivitisConjunctivitis

– Conjunctivitis is the Conjunctivitis is the inflammation of the inflammation of the conjunctivaconjunctiva

– Can be caused by viruses, Can be caused by viruses, bacteria, fungi, and bacteria, fungi, and allergiesallergies– The most common cause is The most common cause is

viralviral

– ””Pinkeye” is the common Pinkeye” is the common term for conjunctivitisterm for conjunctivitis

Middle Ear Infection (Otitis Media)Middle Ear Infection (Otitis Media)• Causes include anything that Causes include anything that

causes the Eustachian (auditory) causes the Eustachian (auditory) tubes to become blocked, tubes to become blocked, inflamed or irritatedinflamed or irritated– Examples include colds, sinus Examples include colds, sinus

infections, allergies, tobacco smokeinfections, allergies, tobacco smoke– Babies who spend a lot of time Babies who spend a lot of time

drinking in the supine positiondrinking in the supine position• Most common symptom is Most common symptom is

earacheearache• Treatment includes Treatment includes – Antibiotics for bacterial infections Antibiotics for bacterial infections – Use of warm cloths and analgesics Use of warm cloths and analgesics

to relieve painto relieve pain– Possible surgery if ear infections Possible surgery if ear infections

recur frequentlyrecur frequently

DeafnessDeafness

• Complete or partial loss of hearing in one or both ears

• May be caused by a blockage of the sound waves through the middle ear– Wax build up, foreign objects, tumors or

other matter – Generally improves once the blockage is

removed • May also result from damage to the

nerves or to the Organ of Corti– Usually irreversible and may progressively

get worse• Treatment may include removal of the

blockage, hearing aids, or cochlear implants

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MyopiaMyopia

• Nearsightedness Nearsightedness – When a person sees near When a person sees near

objects clearly and distant objects clearly and distant objects are blurred objects are blurred

• Physical length of the eye is Physical length of the eye is greater than the optical greater than the optical lengthlength

• Symptoms include blurred Symptoms include blurred vision of distant objects, vision of distant objects, squinting, eyestrain, and squinting, eyestrain, and sometimes headachessometimes headaches

• Treated with concave lenses Treated with concave lenses or LASIK surgeryor LASIK surgery

HyperopiaHyperopia

• FarsightednessFarsightedness– A person sees far objects clearly A person sees far objects clearly

and near objects are blurredand near objects are blurred• Physical length of the eyeball is Physical length of the eyeball is

too small or the focusing too small or the focusing power of the lens is too weakpower of the lens is too weak

• Symptoms include blurred Symptoms include blurred vision of close objects, eye vision of close objects, eye strain, aching eyes, and strain, aching eyes, and headaches while readingheadaches while reading

• Treated with convex lenses Treated with convex lenses • Surgical options also availableSurgical options also available

PresbyopiaPresbyopia• Normal loss of power of the eye which

occurs as a consequence of aging• Lens becomes less flexible and less able

to bulge or accommodate for near vision • Symptoms are similar to those of

farsightedness and include:– blurring of close objects– eye strain – holding objects further from the face to

focus– headaches or fatigue from focusing on

close objects • Treatments may include the use of

reading glasses or bifocals