Somatic and Special SensesSomatic and Special Senses

CategoriesCategories

Somatic SensesSomatic Senses– TouchTouch– PressurePressure– TemperatureTemperature– PainPain

Special SensesSpecial Senses– SmellSmell– TasteTaste– HearingHearing– EquilibriumEquilibrium– visionvision

Types of ReceptorsTypes of Receptors

Chemoreceptors – stimulated by changes Chemoreceptors – stimulated by changes in the chemical concentration of in the chemical concentration of substancessubstances

Pain receptors - … by tissue damagePain receptors - … by tissue damage

Thermoreceptors - … by changes in temp.Thermoreceptors - … by changes in temp.

Mechanoreceptors - … by changes in Mechanoreceptors - … by changes in pressure or movementpressure or movement

Photoreceptors - … by light energyPhotoreceptors - … by light energy

SensationSensation

A feeling that occurs when the brain A feeling that occurs when the brain interprets sensory impulsesinterprets sensory impulses

Depends on which region of the brain Depends on which region of the brain receives the impulsereceives the impulse

Sensory adaptation – ability to ignore Sensory adaptation – ability to ignore unimportant stimuliunimportant stimuli

Somatic SensesSomatic Senses

Senses of touch and pressureSenses of touch and pressure– Free nerve endings (touch and pressure)Free nerve endings (touch and pressure)

– Meissner’s corpuscles (light touch)Meissner’s corpuscles (light touch)Abundant in hairless portions of bodyAbundant in hairless portions of body

– Pacinian corpuscles (heavy pressure)Pacinian corpuscles (heavy pressure)

Temperature sensesTemperature senses– Warm receptorsWarm receptors

Sensitive to 77Sensitive to 77°F and above; become unresponsive at °F and above; become unresponsive at temperatures above 113°Ftemperatures above 113°FAt or above 113°F stimulates pain receptors, producing a At or above 113°F stimulates pain receptors, producing a burning sensationburning sensation

– Cold receptorsCold receptorsSensitive 50Sensitive 50°F to 68°F°F to 68°FBelow Below 5050°F stimulate pain receptors, producing a freezing °F stimulate pain receptors, producing a freezing sensationsensation

Sense of painSense of pain– Widely distributed, except for brainWidely distributed, except for brain– Protect the body b/c tissue damage stimulates themProtect the body b/c tissue damage stimulates them– Pain is perceived as unpleasant and it signals person Pain is perceived as unpleasant and it signals person

to act to remove the simulationto act to remove the simulation– Pain receptors adapt poorlyPain receptors adapt poorly

Visceral painVisceral pain– Localized damage to intestinal organs may Localized damage to intestinal organs may

not elicit pain sensationsnot elicit pain sensations– More widespread stimulation, as when More widespread stimulation, as when

intestinal walls are stretched, a strong pain intestinal walls are stretched, a strong pain sensation may followsensation may follow

– May feel as though it is coming from some May feel as though it is coming from some part of the body other than the part being part of the body other than the part being stimulated, a phenomenon known as stimulated, a phenomenon known as referred referred painpain

Regulation of Pain ImpulsesRegulation of Pain Impulses

Awareness arises when impulses reach the Awareness arises when impulses reach the thalamusthalamusCerebral cortex determines pain intensity, Cerebral cortex determines pain intensity, locates pain’s source, and mediates emotional locates pain’s source, and mediates emotional and motor responses to the painand motor responses to the painGraymatter in midbrain, pons, and medulla Graymatter in midbrain, pons, and medulla oblongata regulate movement of pain impulses oblongata regulate movement of pain impulses from the spinal cordfrom the spinal cordInhibiting substances released (enkephalins, Inhibiting substances released (enkephalins, serotonin, endorphins)serotonin, endorphins)

Sense of SmellSense of Smell

Olfactory organs Olfactory organs contain the olfactory contain the olfactory receptors and are receptors and are yellowish-brown yellowish-brown masses of epithelium masses of epithelium about the size of about the size of postage stamps that postage stamps that cover the upper pars cover the upper pars of the nasal cavityof the nasal cavity

Olfactory receptors are bipolar neurons Olfactory receptors are bipolar neurons surrounded by columnar epithelial cellssurrounded by columnar epithelial cellsThere are 400 types of olfactory receptor There are 400 types of olfactory receptor proteinsproteinsOdorant molecules enter the nasal cavity Odorant molecules enter the nasal cavity as gases, dissolve in watery fluids, and as gases, dissolve in watery fluids, and then bind to the receptors in different then bind to the receptors in different patternspatternsStimulated olfactory receptors cells send Stimulated olfactory receptors cells send nerve impulses along their axons which nerve impulses along their axons which synapse with neurons located in synapse with neurons located in enlargements called olfactory bulbsenlargements called olfactory bulbs

Within the olfactory Within the olfactory bulbs, the impulses bulbs, the impulses travel along the travel along the olfactory tracts to the olfactory tracts to the limbic system within limbic system within the temporal lobe and the temporal lobe and base of the frontal base of the frontal lobes in the brainlobes in the brainSense of smell adapts Sense of smell adapts rapidly but rapidly but adaptations to one adaptations to one scent will not diminish scent will not diminish sensitivity to new sensitivity to new odorsodors

Humans have about Humans have about 12 million olfactory 12 million olfactory receptor cellsreceptor cells

Bloodhounds have 4 Bloodhounds have 4 billion olfactory billion olfactory receptor cellsreceptor cells

Sense of TasteSense of Taste

Taste budsTaste buds are special are special organs of tasteorgans of taste

Our 10,000 taste buds Our 10,000 taste buds are located primarily on are located primarily on surface of the tongue and surface of the tongue and are associated with tiny are associated with tiny elevations called elevations called papillaepapillae

About 1,000 taste buds About 1,000 taste buds are scattered in the roof are scattered in the roof of the mouth and walls of of the mouth and walls of the throatthe throat

Taste receptorsTaste receptors– Each taste bud includes a group of modified Each taste bud includes a group of modified

epithelial cells, the epithelial cells, the gustatory cellsgustatory cells, which , which function as receptors cellsfunction as receptors cells

– Each taste bud has 50-150 receptor cellsEach taste bud has 50-150 receptor cells– Entire structure is spherical with an opening Entire structure is spherical with an opening

called the taste pore and projections called called the taste pore and projections called taste hairs which are the sensitive partstaste hairs which are the sensitive parts

– Nerve fibers wrap around the taste cellsNerve fibers wrap around the taste cells– Stimulation of taste cell triggers an impulse on Stimulation of taste cell triggers an impulse on

a nearby nerve fiber and the impulse travels a nearby nerve fiber and the impulse travels into the braininto the brain

The truth about cats and dogs…The truth about cats and dogs…– They can be satisfied with less varied diets They can be satisfied with less varied diets

than humansthan humans– Cats have 473 taste budsCats have 473 taste buds– Dogs have 1,700 taste budsDogs have 1,700 taste buds

TastingTasting– Chemical must be dissolved in watery fluid Chemical must be dissolved in watery fluid

provided by salivary glandsprovided by salivary glands– Food molecules bind to specific receptors Food molecules bind to specific receptors

embedded in and projecting from taste hairs embedded in and projecting from taste hairs on the taste cellson the taste cells

– Pattern of receptor types generate sensory Pattern of receptor types generate sensory impulses on nearby nerve fibers in interpreted impulses on nearby nerve fibers in interpreted as a particular taste sensationas a particular taste sensation

Taste sensationsTaste sensations– Primary taste Primary taste

sensationssensationsSweetSweet

SourSour

SaltySalty

BitterBitter

– Others recognizedOthers recognizedAlkalineAlkaline

MetallicMetallic

Umami Umami

FlavorFlavor– Results from one or a combination of the Results from one or a combination of the

primary sensationsprimary sensations– Experiencing flavors involves tasting, Experiencing flavors involves tasting,

smelling, and feeling the texture and smelling, and feeling the texture and temperature of foodstemperature of foods

– Some foods, such as chili peppers and Some foods, such as chili peppers and ginger, trigger heat receptorsginger, trigger heat receptors

– Taste sensation undergoes adaptation rapidlyTaste sensation undergoes adaptation rapidly– Moving bits of food over the surface of the Moving bits of food over the surface of the

tongue to stimulate different receptors at tongue to stimulate different receptors at different moments keeps us from losing tastedifferent moments keeps us from losing taste

Sense of HearingSense of Hearing

Outer earOuter ear– Auricle (funnel-like Auricle (funnel-like

structure)structure)– External auditory External auditory

meatus (ear canal)meatus (ear canal)– tympanic membrane tympanic membrane

(ear drum)(ear drum)

Middle earMiddle ear– Air-filled space in the temporal boneAir-filled space in the temporal bone– Contains 3 small bones called auditory ossicles:Contains 3 small bones called auditory ossicles:

MalleusMalleusIncusIncusStapesStapes

– Malleus attaches to eardrum and when the eardrum Malleus attaches to eardrum and when the eardrum vibrates, the malleus vibrates in unison vibrates, the malleus vibrates in unison

– The malleus causes the incus to vibrate, and the The malleus causes the incus to vibrate, and the incus passes the movement on to the stapesincus passes the movement on to the stapes

– Vibration of the stapes at the oval window moves a Vibration of the stapes at the oval window moves a fluid within the inner ear, which stimulates the hearing fluid within the inner ear, which stimulates the hearing receptorsreceptors

– Auditory ossicles also help increase (amplify) Auditory ossicles also help increase (amplify) the force of vibrationsthe force of vibrations

– The pressure that the stapes applies on the The pressure that the stapes applies on the oval window is many times greater than the oval window is many times greater than the pressure that sound waves exert on the pressure that sound waves exert on the eardrumeardrum

Auditory tube (eustachian tube)Auditory tube (eustachian tube)– Connects each middle ear to the throatConnects each middle ear to the throat– Conducts air between the tympanic cavity and Conducts air between the tympanic cavity and

the outside of the body by way of the throatthe outside of the body by way of the throat– Auditory tube helps maintain equal air Auditory tube helps maintain equal air

pressure on both sides of the eardrum, which pressure on both sides of the eardrum, which is necessary for normal hearingis necessary for normal hearing

– Ex. Rapid changes in altitude may push Ex. Rapid changes in altitude may push eardrum inward as air pressure on the outside eardrum inward as air pressure on the outside of the eardrum incerasesof the eardrum incerases

Steps in the generation of sensory impulses Steps in the generation of sensory impulses from the earfrom the ear

– Sound waves enter external acoustic meatusSound waves enter external acoustic meatus

1.1. Waves of changing pressure cause eardrum to Waves of changing pressure cause eardrum to reproduce vibrations coming from sound wave reproduce vibrations coming from sound wave sourcesource

2.2. Auditory ossicles amplify and transmit vibrations to Auditory ossicles amplify and transmit vibrations to end of stapesend of stapes

3.3. Movement of stapes at oval window transmits Movement of stapes at oval window transmits vibrations to perilymph in scala vestibulivibrations to perilymph in scala vestibuli

4.4. Vibrations pass through vestibular membrane and Vibrations pass through vestibular membrane and enter endolymph of cochlear ductenter endolymph of cochlear duct

6.6. Different frequencies of vibration in Different frequencies of vibration in endolymph stimulate different sets of endolymph stimulate different sets of receptor cellsreceptor cells

7.7. As a receptor cell depolarizes, its membrane As a receptor cell depolarizes, its membrane becomes more permeable to calcium ionsbecomes more permeable to calcium ions

8.8. Inward diffusion of calcium ions causes Inward diffusion of calcium ions causes vesicles at the base of the receptor cell to vesicles at the base of the receptor cell to release neurotransmitterrelease neurotransmitter

9.9. Neurotransmitter stimulates ends of nearby Neurotransmitter stimulates ends of nearby sensory neuronssensory neurons

10.10. Sensory impulses are triggered on fibers of Sensory impulses are triggered on fibers of the cochlear branch of vestibulocochlear the cochlear branch of vestibulocochlear nervenerve

11.11. Auditory cortex of temporal lobe interprets Auditory cortex of temporal lobe interprets sensory impulsessensory impulses

Factors of hearing lossFactors of hearing loss– Conductive deafnessConductive deafness

Interference with the transmission of vibrations to Interference with the transmission of vibrations to the inner earthe inner earMay be due to plugging of the external acoustic May be due to plugging of the external acoustic meatus or to changes in the eardrum or auditory meatus or to changes in the eardrum or auditory ossiclesossiclesEardrum may harden as a result of disease and Eardrum may harden as a result of disease and thus be less responsive to sound wavesthus be less responsive to sound wavesDisease or injury may tear or perforate the Disease or injury may tear or perforate the eardrumeardrum

– Sensorineural deafnessSensorineural deafnessDamage to the cochlea, auditory nerve, or auditory Damage to the cochlea, auditory nerve, or auditory nerve pathwaysnerve pathwaysCauses by loud sounds, tumors in the CNS, brain Causes by loud sounds, tumors in the CNS, brain damage as a result of vascular accidents, or use of damage as a result of vascular accidents, or use of certain drugscertain drugs

Sense of EquilibriumSense of Equilibrium

Static equilibriumStatic equilibrium– Sense the position of the head, maintaining Sense the position of the head, maintaining

stability and posture when the head and body stability and posture when the head and body are stillare still

– Organs located with the Organs located with the vestibulevestibule, a bony , a bony chamber between the semicircular canals and chamber between the semicircular canals and the cochleathe cochlea

– A tiny structure called a A tiny structure called a maculamacula contains contains numerous hair cells which serve as sensory numerous hair cells which serve as sensory receptorsreceptors

– When the head is upright, the hairs of the hair cells When the head is upright, the hairs of the hair cells project upward into a mass of gelatinous material, project upward into a mass of gelatinous material, which has grains of calcium carbonate embedded in itwhich has grains of calcium carbonate embedded in it

– Head bending tilt the gelatinous mass and they sag in Head bending tilt the gelatinous mass and they sag in response to gravityresponse to gravity

– Hairs within the mass bends and they signal nerve Hairs within the mass bends and they signal nerve fibersfibers

– Nerve impulses travel into the CNS and informs brain Nerve impulses travel into the CNS and informs brain of head’s new positionof head’s new position

– Brain responds by sending motor impulses to skeletal Brain responds by sending motor impulses to skeletal muscles, which contract or relax to maintain balancemuscles, which contract or relax to maintain balance

Dynamic equilibriumDynamic equilibrium– Aid in maintaining balance when the head and Aid in maintaining balance when the head and

body suddenly move or rotatebody suddenly move or rotate– Organs are the three semicircular canalsOrgans are the three semicircular canals– Each responds to a different anatomical planeEach responds to a different anatomical plane– Each canal ends in a swelling called an Each canal ends in a swelling called an

ampullaampulla which contains the sensory organs which contains the sensory organs crista ampullariscrista ampullaris

– Each of the crista ampullaris contains a Each of the crista ampullaris contains a number of sensory hairs cells which extend number of sensory hairs cells which extend upward in a gelatinous massupward in a gelatinous mass

– Rapid turns of the head or body simulate Rapid turns of the head or body simulate these hair cellsthese hair cells

– Other sensory structures that aid in Other sensory structures that aid in maintaining equilibriummaintaining equilibrium

Mechanoreceptors associated with joinsMechanoreceptors associated with joins

Eyes detect changes in postureEyes detect changes in posture

Motion sicknessMotion sickness– Nausea, vomiting, and Nausea, vomiting, and

headacheheadache– Arise from senses that Arise from senses that

don’t make sensedon’t make sense– Eyes of person reading in a Eyes of person reading in a

moving car, for example, moving car, for example, signal the brain that the signal the brain that the person is stationary, person is stationary, because the print doesn’t because the print doesn’t movemove

– Skin and inner ear, Skin and inner ear, however, detects however, detects movementmovement

– To lessen the misery, focus To lessen the misery, focus on the horizon or an object on the horizon or an object in the distance ahead or in the distance ahead or take dramaminetake dramamine

Sense of SightSense of Sight

Visual accessory organsVisual accessory organs– EyelidEyelid

SkinSkin– Thinnest skin in the bodyThinnest skin in the body– Covers the lid’s outer surface and fuses with its inner Covers the lid’s outer surface and fuses with its inner

lining near the margin of the lidlining near the margin of the lid

MuscleMuscle– Eyelids moved by Eyelids moved by orbicularis oculi orbicularis oculi and and levator palpebrae levator palpebrae

superiorissuperioris

ConjuctiviaConjuctivia– Mucous membrane that lines the inner surfaces of the Mucous membrane that lines the inner surfaces of the

eyelids and fols back to cover the anterior sruface of the eyelids and fols back to cover the anterior sruface of the eyeball, except for its central portion (cornea)eyeball, except for its central portion (cornea)

1.1. CorneaCornea2.2. LensLens3.3. FornixFornix4.4. Marginal conjuctivaMarginal conjuctiva5.5. Lacrimal glandsLacrimal glands6.6. Tarsus, a fibrous Tarsus, a fibrous

connective tissueconnective tissue

– Lacrimal glandsLacrimal glandsSecretes tearsSecretes tearsMoistens and lubricates Moistens and lubricates the surface of the eye and the surface of the eye and the lining of the lidsthe lining of the lidsContain lysozyme that is Contain lysozyme that is an anti-bacterial agent, an anti-bacterial agent, reducing the risk of eye reducing the risk of eye infectionsinfections

– Extrinsic musclesExtrinsic musclesArise from the bones of the orbit and insert by broad tendons Arise from the bones of the orbit and insert by broad tendons on the eye’s tough outer surfaceon the eye’s tough outer surface

Six muscles move the eye in various directionsSix muscles move the eye in various directions

Structure of the eyeStructure of the eye– Hollow, spherical structure about 2.5 cm in Hollow, spherical structure about 2.5 cm in

diameterdiameter– Wall has 3 distinct layersWall has 3 distinct layers

Outer fibrous layerOuter fibrous layer

Middle vascular layerMiddle vascular layer

Inner nervous layerInner nervous layer

– Spaces within the eye are filled with fluids that Spaces within the eye are filled with fluids that support its wall and internal parts and help support its wall and internal parts and help maintain its shapemaintain its shape

Outer layerOuter layer– Outermost layer (1/6 of layer) is transparent Outermost layer (1/6 of layer) is transparent

corneacornea, which is the window of the eye and , which is the window of the eye and helps focus entering light rayshelps focus entering light rays

– Composed largely of connective tissueComposed largely of connective tissue– Very few cells and no blood vesselsVery few cells and no blood vessels– Along its circumference, the cornea is Along its circumference, the cornea is

continuous with the continuous with the sclerasclera, the white portion , the white portion of the eye (5/6 of layer)of the eye (5/6 of layer)

– Opaque due to many large collagenous and Opaque due to many large collagenous and elastic fiberselastic fibers

– Sclera protects the eye and is an attachment Sclera protects the eye and is an attachment for the extrinsic musclesfor the extrinsic muscles

– The optic nerve and blood vessels pierce the The optic nerve and blood vessels pierce the sclera in the back of the eyesclera in the back of the eye

Most common cause of blindness is loss of Most common cause of blindness is loss of transparency of the corneatransparency of the corneaA corneal transplant can replace the central 2/3 A corneal transplant can replace the central 2/3 of the defective cornea with a similar-sized of the defective cornea with a similar-sized portion of cornea from a donor eyeportion of cornea from a donor eye

Middle layerMiddle layer– Choroid coatChoroid coat

Posterior 5/6 of the globe of the eyePosterior 5/6 of the globe of the eyeContains blood vessels which nourish surrounding Contains blood vessels which nourish surrounding tissuetissueContains melanocytesContains melanocytesMelanin absorbs excess light and keeps the inside Melanin absorbs excess light and keeps the inside of the eye darkof the eye dark

– Ciliary bodyCiliary bodyExtends forward from the choroid coat and forms Extends forward from the choroid coat and forms and internal ring around the front of the eyeand internal ring around the front of the eyeContains ciliary musclesContains ciliary muscles

– LensLensTransparent and held in place by suspensory Transparent and held in place by suspensory ligamentsligamentsAdjusts shape to facilitate focusing, called Adjusts shape to facilitate focusing, called accommodationaccommodation

– CataractsCataractsLens or its capsule slowly becomes cloudy and Lens or its capsule slowly becomes cloudy and opaqueopaque

Without treatment, they cause blindnessWithout treatment, they cause blindness

Causes by breakdown of protein within lens after Causes by breakdown of protein within lens after age 45age 45

– IrisIrisThin diaphragm composed mostly of connective Thin diaphragm composed mostly of connective tissue and smooth muscle fiberstissue and smooth muscle fibers

Colored portion of the eyeColored portion of the eye

Lies between the cornea and the lensLies between the cornea and the lens

– Aqueous humorAqueous humorWatery fluid secreted by the ciliary bodyWatery fluid secreted by the ciliary body

Circulates through the Circulates through the pupilpupil (circular opening in the (circular opening in the center of the iris) and into the anterior chambercenter of the iris) and into the anterior chamber

helps nourish cornea and lens and aids in helps nourish cornea and lens and aids in maintaining the shape of the front of the eyemaintaining the shape of the front of the eye

Smooth muscle fibers of iris are organized into two Smooth muscle fibers of iris are organized into two groups, a circular set and a radial setgroups, a circular set and a radial setWhen circular set contracts, pupil gets smaller and When circular set contracts, pupil gets smaller and less light entersless light entersWhen the radial set contracts, the pupil’s diameter When the radial set contracts, the pupil’s diameter increases and more light entersincreases and more light enters

GlaucomaGlaucoma– Disorder in which rate of Disorder in which rate of

aqueous humor formation aqueous humor formation exceeds rate of its removal exceeds rate of its removal

– Fluid pressure squeezes Fluid pressure squeezes shut blood vessels that shut blood vessels that supply the receptor cells of supply the receptor cells of the retinathe retina

– Cells that are robbed of Cells that are robbed of nutrients and oxygen may nutrients and oxygen may die and permanent die and permanent blindness can resultblindness can result

– Treated with drugs, laser Treated with drugs, laser therapy, or surgerytherapy, or surgery

Inner layerInner layer– RetinaRetina

Contains the visual receptor cells (photoreceptors)Contains the visual receptor cells (photoreceptors)Continuous with the optic nerve and extends Continuous with the optic nerve and extends forward as the inner lining of the eyeballforward as the inner lining of the eyeballCentral region is a yellowish spot called the Central region is a yellowish spot called the maculla luteamaculla luteaDepression in its center is called the Depression in its center is called the fovea fovea centraliscentralis which is where the sharpest vision occurs which is where the sharpest vision occursOptic discOptic disc is just medial to the fovea centralis and is just medial to the fovea centralis and contains a central artery and vein which are contains a central artery and vein which are continuous with the capillary networkscontinuous with the capillary networksSpace bounded by the lens, ciliary body, and Space bounded by the lens, ciliary body, and retina is the largest compartment and is filled with retina is the largest compartment and is filled with a transparent, jellylike fluid called a transparent, jellylike fluid called vitreous humorvitreous humorVitreous humor helps eye maintain shapeVitreous humor helps eye maintain shape

Light refractionLight refraction– When a person sees something, either the object is When a person sees something, either the object is

giving off light or light waves are reflected from itgiving off light or light waves are reflected from it– These light waves enter the eye and an image of the These light waves enter the eye and an image of the

object is focused on the retinaobject is focused on the retina– Focusing bends the light waves, a phenomenon Focusing bends the light waves, a phenomenon

called called refractionrefraction– Convex surface of the cornea refracts light waves Convex surface of the cornea refracts light waves

from outside objectsfrom outside objects– Convex surface of lens then refracts the light againConvex surface of lens then refracts the light again– If eye shape is normal, light waves focus sharply on If eye shape is normal, light waves focus sharply on

the retinathe retina– Image that forms is upside down and reversed from Image that forms is upside down and reversed from

left to rightleft to right– Visual cortex interprets the image in its proper Visual cortex interprets the image in its proper

positionposition

interactioninteraction

Visual receptorsVisual receptors– Modified neuronsModified neurons– RodsRods

Have long, thin projections at their endsHave long, thin projections at their endsProvide black and white visionProvide black and white visionProvide general outline of objectsProvide general outline of objects100 times more sensitive to light than cones100 times more sensitive to light than conesHumans have 125 million of themHumans have 125 million of them

– ConesConesShort, blunt projections Short, blunt projections Provide color visionProvide color visionProvide sharp imagesProvide sharp imagesHumans have 7 million of themHumans have 7 million of them

– Stimulated only when light reaches themStimulated only when light reaches them

– Visual pigmentsVisual pigmentsBoth rods and cones contain light-sensitive pigments that Both rods and cones contain light-sensitive pigments that decompose when they absorb light energydecompose when they absorb light energy

Within rods, pigment is called Within rods, pigment is called rhodopsinrhodopsin– In presence of light, these molecules breakdown into a In presence of light, these molecules breakdown into a

colorless protein called opsin and a yellowish substance called colorless protein called opsin and a yellowish substance called retinal that is synthesized from vitamin Aretinal that is synthesized from vitamin A

Poor vision in dim light, called night blindness results from Poor vision in dim light, called night blindness results from vitamin A deficiencyvitamin A deficiency

– Decomposition of rhodopsin activates an enzyme that initiates a Decomposition of rhodopsin activates an enzyme that initiates a series of reactions altering the permeability of the rod cell series of reactions altering the permeability of the rod cell membranemembrane

– As a result, a complex pattern of nerve impulses originates in As a result, a complex pattern of nerve impulses originates in the retina along the optic nerve to the brain, where they are the retina along the optic nerve to the brain, where they are interpreted as visioninterpreted as vision

Within conesWithin cones– Erythrolabe: most sensitive to red light wavesErythrolabe: most sensitive to red light waves

– Chlorolabe: most sensitive to green light wavesChlorolabe: most sensitive to green light waves

– Cyanolabe: most sensitive to blue light wavesCyanolabe: most sensitive to blue light waves

– All 3 stimulated: white; none: blackAll 3 stimulated: white; none: black

Visual nerve pathwayVisual nerve pathway