The SensesThe Senses

IntroductionIntroduction Sensory receptors detect environmental Sensory receptors detect environmental

changes and trigger nerve impulses that changes and trigger nerve impulses that travel on sensory pathways. The body travel on sensory pathways. The body reacts with a particular feeling or reacts with a particular feeling or sensation.sensation.

Two major categories:Two major categories: Somatic senses: touch, pressure, Somatic senses: touch, pressure,

temperature, and paintemperature, and pain Special senses: smell, taste, hearing, Special senses: smell, taste, hearing,

equilibrium, and visionequilibrium, and vision

Types of ReceptorsTypes of Receptors

Chemoreceptors – changes in the Chemoreceptors – changes in the chemical concentrationchemical concentration

Pain receptors – tissue damagePain receptors – tissue damage Thermoreceptors – change in Thermoreceptors – change in

temperaturetemperature Mechanoreceptors – changes in Mechanoreceptors – changes in

pressure or movementpressure or movement Photoreceptors – light energyPhotoreceptors – light energy

Somatic SensesSomatic Senses

Associated with receptors in the skin, Associated with receptors in the skin, muscles, joints, and visceramuscles, joints, and viscera

Includes touch, pressure, temperature, and Includes touch, pressure, temperature, and painpain Touch/Pressure SensesTouch/Pressure Senses

Sensory nerve fibers – epithelial tissuesSensory nerve fibers – epithelial tissues Connective tissue; lips, fingertips, palms, Connective tissue; lips, fingertips, palms,

soles, nipples, external genitalssoles, nipples, external genitals Connective tissue in subcutaneous Connective tissue in subcutaneous

tissues; tendons and ligaments; deep tissues; tendons and ligaments; deep pressure sensationpressure sensation

Temperature SensesTemperature Senses Depends on free nerve endings in skin; warm Depends on free nerve endings in skin; warm

receptors and cold receptorsreceptors and cold receptors Warm receptors sensitive above 25C (77F), Warm receptors sensitive above 25C (77F),

unresponsive above 113Funresponsive above 113F Cold receptors sensitive between 10C (50F) and Cold receptors sensitive between 10C (50F) and

20C (68F); below 10C produces freezing 20C (68F); below 10C produces freezing sensationsensation

Sense of PainSense of Pain Receptors protect body from tissue damageReceptors protect body from tissue damage Widely distributed throughout skin and internal Widely distributed throughout skin and internal

tissues, except tissues of braintissues, except tissues of brain Visceral pain may not elicit pain sensationsVisceral pain may not elicit pain sensations Referred pain may happen when the pain Referred pain may happen when the pain

sensation feels as if its coming from another sensation feels as if its coming from another part than whats being stimulated.part than whats being stimulated.

Special SensesSpecial Senses

Sensory receptors are within large, Sensory receptors are within large, complex sensory organs in the headcomplex sensory organs in the head

Includes the following:Includes the following: Smell → Olfactory organsSmell → Olfactory organs Taste → taste budsTaste → taste buds Hearing, equilibrium → EarsHearing, equilibrium → Ears Sight → EyesSight → Eyes

Olfactory ReceptorsOlfactory Receptors

Smell receptors are chemoreceptorsSmell receptors are chemoreceptors Smell and taste function closely Smell and taste function closely

together and aid in food selection; we together and aid in food selection; we usually smell food at the same time we usually smell food at the same time we taste it.taste it.

Olfactory bulbs in the ethmoid bone Olfactory bulbs in the ethmoid bone analyze impulsesanalyze impulses

The major interpreting areas are within The major interpreting areas are within the temporal lobes and frontal lobesthe temporal lobes and frontal lobes

TasteTaste Taste buds are taste organsTaste buds are taste organs Located on surface of tongue and associated Located on surface of tongue and associated

with papillaewith papillae Also in roof of mouth and walls of throatAlso in roof of mouth and walls of throat Chemicals must be dissolved in saliva first to Chemicals must be dissolved in saliva first to

be tastedbe tasted Primary taste sensations:Primary taste sensations:

SweetSweet SourSour SaltySalty BitterBitter

HearingHearing

Ear is the hearing organEar is the hearing organ Also can sense equilibriumAlso can sense equilibrium Three parts: External, Middle, and Three parts: External, Middle, and

Inner Ear partsInner Ear parts External Ear – two parts of auricle and External Ear – two parts of auricle and

external auditory meatusexternal auditory meatus Auricle – collects sound waves and directs to Auricle – collects sound waves and directs to

E.A.M.E.A.M.

Middle Ear – tympanic cavity, eardrum, Middle Ear – tympanic cavity, eardrum, and the auditory ossicle bonesand the auditory ossicle bones Tympanic cavity – air-filled space in Tympanic cavity – air-filled space in

temporal bonetemporal bone Eardrum – semitransparent membrane Eardrum – semitransparent membrane

covered by a thin layer of skin and mucous covered by a thin layer of skin and mucous membrane; pressure changes on eardrums membrane; pressure changes on eardrums reproduces vibrations of sound wavesreproduces vibrations of sound waves

Auditory Ossicles (bones) – malleus, incus, Auditory Ossicles (bones) – malleus, incus, stapesstapes

Malleus – vibrates with eardrumMalleus – vibrates with eardrum Incus – vibrates as a result of the malleus Incus – vibrates as a result of the malleus

vibratingvibrating Stapes – vibrates due to incus; vibrations Stapes – vibrates due to incus; vibrations

moves fluid within the inner ear to stimulate moves fluid within the inner ear to stimulate hearing receptorshearing receptors

Auditory ossicles also increase or Auditory ossicles also increase or amplify force of vibrationsamplify force of vibrations

The auditory tube connects the middle The auditory tube connects the middle ear to the throat (eustachian tube)ear to the throat (eustachian tube)

Helps maintain equal air pressure Helps maintain equal air pressure on both sides of the eardrum for on both sides of the eardrum for normal hearing; noticeable in rapid normal hearing; noticeable in rapid change in altitudechange in altitude

Inner EarInner Ear

Inner Ear – communicating chambers and Inner Ear – communicating chambers and tubes called a labyrinthtubes called a labyrinth

The three semicircular canals provide The three semicircular canals provide a sense of equilibriuma sense of equilibrium

Cochlea function in hearingCochlea function in hearing Organ of Corti – contains hearing Organ of Corti – contains hearing

receptorsreceptors

Steps in HearingSteps in Hearing Sound waves enter the E.A.M.Sound waves enter the E.A.M. Waves change the pressure on the eardrum Waves change the pressure on the eardrum

for reproduction of vibrationsfor reproduction of vibrations Auditory ossicles amplify and transmit Auditory ossicles amplify and transmit

vibrations to end of stapesvibrations to end of stapes Stapes movement transmits vibrations to Stapes movement transmits vibrations to

receptor cellsreceptor cells Receptor cells cause release of Receptor cells cause release of

neurotransmitter to stimulate sensory neuronsneurotransmitter to stimulate sensory neurons Sensory impulses are triggered and auditory Sensory impulses are triggered and auditory

cortex of temporal lobe interprets themcortex of temporal lobe interprets them

Sense of EquilibriumSense of Equilibrium

Two senses: static equilibrium and Two senses: static equilibrium and dynamic equilibriumdynamic equilibrium

Static equilibrium – sense head Static equilibrium – sense head position, maintain stability and position, maintain stability and postureposture

Dynamic equilibrium – sense head or Dynamic equilibrium – sense head or body movements or rotations; body movements or rotations; maintain balancemaintain balance

Sight SenseSight Sense

The eye is the organThe eye is the organ Each eyelid has four layers: skin, Each eyelid has four layers: skin,

muscle, connective tissue, conjunctivamuscle, connective tissue, conjunctiva Skin covers outer surfaceSkin covers outer surface Conjunctiva is mucous membrane that Conjunctiva is mucous membrane that

lines inner surfaces of eyelids and covers lines inner surfaces of eyelids and covers eyeball, except for corneaeyeball, except for cornea

Lacrimal glands secretes tearsLacrimal glands secretes tears

Eye StructureEye Structure

Hollow, spherical structure 2.5 cm in Hollow, spherical structure 2.5 cm in diameterdiameter

3 distinct layers:3 distinct layers: Outer tunic – cornea, sclera, optic nerve Outer tunic – cornea, sclera, optic nerve Middle tunic – choroid coat, ciliary body, Middle tunic – choroid coat, ciliary body,

irisiris Inner tunic – retina Inner tunic – retina

Outer TunicOuter Tunic

• Contains a transparent cornea that Contains a transparent cornea that helps the eye focus entering light helps the eye focus entering light raysrays

• Sclera is the white portion of the Sclera is the white portion of the eye; opaque; protects the eye and eye; opaque; protects the eye and is attachment for musclesis attachment for muscles

• Optic nerve – is in the back of the Optic nerve – is in the back of the eye eye

Middle TunicMiddle Tunic

• Choroid coat – joins with the sclera; Choroid coat – joins with the sclera; honeycombed with blood vessels to nourish honeycombed with blood vessels to nourish tissues, contains pigments; melanin tissues, contains pigments; melanin absorbs excess light to keep inside of eye absorbs excess light to keep inside of eye dark.dark.

• Ciliary body – thickest part that forms ring Ciliary body – thickest part that forms ring around front of eye; helps hold lens in placearound front of eye; helps hold lens in place

• Lens – behind iris and pupil, transparent, Lens – behind iris and pupil, transparent, elasticelastic

• Iris – thin, colored portion of eyeIris – thin, colored portion of eye

Inner TunicInner Tunic

• Retina – transparent sheet of tissue continuous Retina – transparent sheet of tissue continuous with optic nerve and inner lining of eyeballwith optic nerve and inner lining of eyeball

– Macula lutea – yellowish spot of retinaMacula lutea – yellowish spot of retina– Fovea centralis – provides sharpest visionFovea centralis – provides sharpest vision– Optic disk – blind spot of the eye; nerve Optic disk – blind spot of the eye; nerve

fibers join optic nervefibers join optic nerve– Posterior cavity – space between lens, Posterior cavity – space between lens,

ciliary body, and retina that is filled with ciliary body, and retina that is filled with jellylike fluid called vitreous humorjellylike fluid called vitreous humor

Light RefractionLight Refraction

• To see something, light waves are given off To see something, light waves are given off or reflected from the objector reflected from the object

• Light waves enter the eye and the image is Light waves enter the eye and the image is focused on the retina by bending the light focused on the retina by bending the light waves; refraction.waves; refraction.

• For normal eye shape, light waves focus on For normal eye shape, light waves focus on retina and the image on the retina is upside retina and the image on the retina is upside down and reversed from left to right. The down and reversed from left to right. The visual cortex interprets the image in its visual cortex interprets the image in its proper positionproper position

Visual ReceptorsVisual Receptors

• Visual receptors are modified neuronsVisual receptors are modified neurons• Rods and cones lie in the retinaRods and cones lie in the retina• Rods – very sensitive to light and provide Rods – very sensitive to light and provide

vision in dim light; produce colorless visionvision in dim light; produce colorless vision• Cones – detect color; provide sharp imagesCones – detect color; provide sharp images• The fovea centralis lacks rods, but packed The fovea centralis lacks rods, but packed

with coneswith cones• For details, people move their eyes so that For details, people move their eyes so that

the image falls on the fovea centralis.the image falls on the fovea centralis.

Visual PigmentsVisual Pigments

• The wavelength of light determines the The wavelength of light determines the color the brain perceives from it.color the brain perceives from it.

• Color blindness results from lack of different Color blindness results from lack of different types of cone pigmentstypes of cone pigments