Inner Chambers and FluidsInner Chambers and Fluids

The lens separates the internal eye into The lens separates the internal eye into anterior and posterior segmentsanterior and posterior segments

The posterior segment is filled with a clear gel The posterior segment is filled with a clear gel called vitreous humor that:called vitreous humor that: Transmits lightTransmits light Supports the posterior surface of the lens Supports the posterior surface of the lens Holds the neural retina firmly against the Holds the neural retina firmly against the

pigmented layerpigmented layer Contributes to intraocular pressureContributes to intraocular pressure

Anterior SegmentAnterior Segment

Composed of two chambersComposed of two chambers Anterior – between the cornea and the irisAnterior – between the cornea and the iris Posterior – between the iris and the lensPosterior – between the iris and the lens

Aqueous humorAqueous humor A plasmalike fluid that fills the anterior segmentA plasmalike fluid that fills the anterior segment Drains via the canal of SchlemmDrains via the canal of Schlemm

Supports, nourishes, and removes wastes Supports, nourishes, and removes wastes

Anterior SegmentAnterior Segment

Figure 15.8

LensLens A biconvex, transparent, flexible, avascular A biconvex, transparent, flexible, avascular

structure that:structure that: Allows precise focusing of light onto the retinaAllows precise focusing of light onto the retina Is composed of epithelium and lens fibersIs composed of epithelium and lens fibers

Lens epithelium – anterior cells that Lens epithelium – anterior cells that differentiate into lens fibersdifferentiate into lens fibers

Lens fibers – cells filled with the transparent Lens fibers – cells filled with the transparent protein crystallinprotein crystallin

With age, the lens becomes more compact and With age, the lens becomes more compact and dense and loses its elasticitydense and loses its elasticity

LightLight

Electromagnetic radiation – all energy waves Electromagnetic radiation – all energy waves from short gamma rays to long radio wavesfrom short gamma rays to long radio waves

Our eyes respond to a small portion of this Our eyes respond to a small portion of this spectrum called the visible spectrumspectrum called the visible spectrum

Different cones in the retina respond to Different cones in the retina respond to different wavelengths of the visible spectrumdifferent wavelengths of the visible spectrum

LightLight

Figure 15.10

Refraction and LensesRefraction and Lenses

When light passes from one transparent When light passes from one transparent medium to another its speed changes and it medium to another its speed changes and it refracts (bends)refracts (bends)

Light passing through a convex lens (as in the Light passing through a convex lens (as in the eye) is bent so that the rays converge to a focal eye) is bent so that the rays converge to a focal pointpoint

When a convex lens forms an image, the When a convex lens forms an image, the image is upside down and reversed right to leftimage is upside down and reversed right to left

Refraction and LensesRefraction and Lenses

Figure 15.12a, b

Focusing Light on the RetinaFocusing Light on the Retina

Pathway of light entering the eye: cornea, Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, and the aqueous humor, lens, vitreous humor, and the neural layer of the retina to the photoreceptorsneural layer of the retina to the photoreceptors

Light is refracted:Light is refracted: At the corneaAt the cornea Entering the lensEntering the lens Leaving the lensLeaving the lens

The lens curvature and shape allow for fine The lens curvature and shape allow for fine focusing of an imagefocusing of an image

Focusing for Distant VisionFocusing for Distant Vision Light from a Light from a

distance needs distance needs little adjustment little adjustment for proper for proper focusingfocusing

Far point of Far point of vision – the vision – the distance beyond distance beyond which the lens which the lens does not need to does not need to change shape to change shape to focus (20 ft.)focus (20 ft.) Figure 15.13a

Focusing for Close VisionFocusing for Close Vision

Close vision requires:Close vision requires: Accommodation – changing the lens shape by Accommodation – changing the lens shape by

ciliary muscles to increase refractory powerciliary muscles to increase refractory power Constriction – the pupillary reflex constricts the Constriction – the pupillary reflex constricts the

pupils to prevent divergent light rays from entering pupils to prevent divergent light rays from entering the eyethe eye

Convergence – medial rotation of the eyeballs Convergence – medial rotation of the eyeballs toward the object being viewedtoward the object being viewed

Focusing for Close VisionFocusing for Close Vision

Figure 15.13b

Problems of RefractionProblems of Refraction

Emmetropic eye – normal eye with light Emmetropic eye – normal eye with light focused properlyfocused properly

Myopic eye (nearsighted) – the focal point is Myopic eye (nearsighted) – the focal point is in front of the retinain front of the retina Corrected with a concave lensCorrected with a concave lens

Hyperopic eye (farsighted) – the focal point is Hyperopic eye (farsighted) – the focal point is behind the retinabehind the retina Corrected with a convex lensCorrected with a convex lens

Problems of RefractionProblems of Refraction

Figure 15.14a, b

Photoreception: Photoreception: Functional Anatomy of Functional Anatomy of

PhotoreceptorsPhotoreceptors Photoreception – process by which the eye Photoreception – process by which the eye

detects light energydetects light energy Rods and cones contain visual pigments Rods and cones contain visual pigments

(photopigments) (photopigments) Arranged in a stack of disklike infoldings of the Arranged in a stack of disklike infoldings of the

plasma membrane that change shape as they absorb plasma membrane that change shape as they absorb lightlight

Figure 15.15a, b

RodsRods

Functional characteristicsFunctional characteristics Sensitive to dim light and best suited for night Sensitive to dim light and best suited for night

visionvision Absorb all wavelengths of visible lightAbsorb all wavelengths of visible light Perceived input is in gray tones onlyPerceived input is in gray tones only Sum of visual input from many rods feeds into a Sum of visual input from many rods feeds into a

single ganglion cell single ganglion cell Results in fuzzy and indistinct imagesResults in fuzzy and indistinct images

ConesCones

Functional characteristics Functional characteristics Need bright light for activation (have low Need bright light for activation (have low

sensitivity)sensitivity) Have pigments that furnish a vividly colored viewHave pigments that furnish a vividly colored view Each cone synapses with a single ganglion cellEach cone synapses with a single ganglion cell Vision is detailed and has high resolutionVision is detailed and has high resolution

Chemistry of Visual PigmentsChemistry of Visual Pigments

Retinal is a light-absorbing moleculeRetinal is a light-absorbing molecule Combines with opsins to form visual pigmentsCombines with opsins to form visual pigments Similar to and is synthesized from vitamin ASimilar to and is synthesized from vitamin A Two isomers: 11-Two isomers: 11-ciscis and all- and all-transtrans

Isomerization of retinal initiates electrical Isomerization of retinal initiates electrical impulses in the optic nerveimpulses in the optic nerve

Excitation of RodsExcitation of Rods The visual pigment of rods is rhodopsin The visual pigment of rods is rhodopsin

(opsin + 11-(opsin + 11-ciscis retinal) retinal) Light phaseLight phase

Rhodopsin breaks down into all-Rhodopsin breaks down into all-transtrans retinal + opsin retinal + opsin (bleaching of the pigment)(bleaching of the pigment)

Dark phaseDark phase All-All-transtrans retinal converts to 11- retinal converts to 11-ciscis form form 11-11-ciscis retinal is also formed from vitamin A retinal is also formed from vitamin A 11-11-ciscis retinal + opsin regenerate rhodopsin retinal + opsin regenerate rhodopsin

CH3

C

C

HH

H2C

H2C C

C

CH3

H

CH3

C

H

C

CH3

C

H

C

H

C

H

C

CH3

C O

H

C

H

C

C

HH

H2C

H2C

H3C

C

C

C

CH3CH3

H

C

H

C

C O

C

H

C H

C

C

C HC

CH3 H CH3 H

Oxidation

Rhodopsin

Opsin

All-trans retinal

–2H

+2HReduction

Vitamin A

Regeneration ofthe pigment:Slow conversionof all-trans retinalto its 11-cis formoccurs in the pig-mented epithelium;requires isomeraseenzyme and ATP.

Dark Light

11-cis retinal

All-trans isomer

11-cis isomer

Bleaching of thepigment:Light absorptionby rhodopsintriggers a seriesof steps in rapidsuccession inwhich retinalchanges shape(11-cis to all-trans)and releasesopsin.

Figure 15.16

Excitation of ConesExcitation of Cones

Visual pigments in cones are similar to rods Visual pigments in cones are similar to rods (retinal + opsins)(retinal + opsins)

There are three types of cones: blue, green, There are three types of cones: blue, green, and redand red

Intermediate colors are perceived by activation Intermediate colors are perceived by activation of more than one type of coneof more than one type of cone

Method of excitation is similar to rodsMethod of excitation is similar to rods

Signal Transmission in the RetinaSignal Transmission in the Retina

Figure 15.17a

PhototransductionPhototransduction Light energy splits rhodopsin into all-Light energy splits rhodopsin into all-transtrans retinal, retinal,

releasing activated opsinreleasing activated opsin The freed opsin activates the G protein transducinThe freed opsin activates the G protein transducin Transducin catalyzes activation of phosphodiesterase Transducin catalyzes activation of phosphodiesterase

(PDE)(PDE) PDE hydrolyzes cGMP to GMP and releases it from PDE hydrolyzes cGMP to GMP and releases it from

sodium channelssodium channels Without bound cGMP, sodium channels close, the Without bound cGMP, sodium channels close, the

membrane hyperpolarizes, and neurotransmitter membrane hyperpolarizes, and neurotransmitter cannot be releasedcannot be released

PhototransductionPhototransduction

Figure 15.18

AdaptationAdaptation Adaptation to bright light (going from dark to Adaptation to bright light (going from dark to

light) involves:light) involves: Dramatic decreases in retinal sensitivity – rod Dramatic decreases in retinal sensitivity – rod

function is lostfunction is lost Switching from the rod to the cone system – visual Switching from the rod to the cone system – visual

acuity is gainedacuity is gained Adaptation to dark is the reverseAdaptation to dark is the reverse

Cones stop functioning in low lightCones stop functioning in low light Rhodopsin accumulates in the dark and retinal Rhodopsin accumulates in the dark and retinal

sensitivity is restoredsensitivity is restored

Visual PathwaysVisual Pathways Axons of retinal ganglion cells form the optic Axons of retinal ganglion cells form the optic

nerve nerve Medial fibers of the optic nerve decussate at Medial fibers of the optic nerve decussate at

the optic chiasmthe optic chiasm Most fibers of the optic tracts continue to the Most fibers of the optic tracts continue to the

lateral geniculate body of the thalamuslateral geniculate body of the thalamus

Visual PathwaysVisual Pathways

Other optic tract fibers end in superior colliculi Other optic tract fibers end in superior colliculi (initiating visual reflexes) and pretectal nuclei (initiating visual reflexes) and pretectal nuclei (involved with pupillary reflexes)(involved with pupillary reflexes)

Optic radiations travel from the thalamus to Optic radiations travel from the thalamus to the visual cortexthe visual cortex

Visual PathwaysVisual Pathways

Figure 15.19

Visual PathwaysVisual Pathways

Some nerve fibers send tracts to the midbrain Some nerve fibers send tracts to the midbrain ending in the superior colliculiending in the superior colliculi

A small subset of visual fibers contain A small subset of visual fibers contain melanopsin (circadian pigment) which:melanopsin (circadian pigment) which: Mediates papillary light reflexesMediates papillary light reflexes Sets daily biorhythmsSets daily biorhythms

Depth PerceptionDepth Perception

Achieved by both eyes viewing the same Achieved by both eyes viewing the same image from slightly different anglesimage from slightly different angles

Three-dimensional vision results from cortical Three-dimensional vision results from cortical fusion of the slightly different imagesfusion of the slightly different images

If only one eye is used, depth perception is lost If only one eye is used, depth perception is lost and the observer must rely on learned clues to and the observer must rely on learned clues to determine depthdetermine depth

On-center fieldsOn-center fields Stimulated by light hitting the center of the fieldStimulated by light hitting the center of the field Inhibited by light hitting the periphery of the fieldInhibited by light hitting the periphery of the field

Off-center fields have the opposite effects Off-center fields have the opposite effects These responses are due to receptor types in These responses are due to receptor types in

the “on” and “off” fieldsthe “on” and “off” fields

Retinal Processing: Receptive Retinal Processing: Receptive Fields of Ganglion CellsFields of Ganglion Cells

Retinal Processing: Receptive Retinal Processing: Receptive Fields of Ganglion CellsFields of Ganglion Cells

Figure 15.20

Thalamic ProcessingThalamic Processing

The lateral geniculate nuclei of the thalamus:The lateral geniculate nuclei of the thalamus: Relay information on movementRelay information on movement Segregate the retinal axons in preparation for depth Segregate the retinal axons in preparation for depth

perceptionperception Emphasize visual inputs from regions of high cone Emphasize visual inputs from regions of high cone

densitydensity Sharpen the contrast information received by the Sharpen the contrast information received by the

retinaretina

Cortical ProcessingCortical Processing

Striate cortex processes Striate cortex processes Basic dark/bright and contrast informationBasic dark/bright and contrast information

Prestriate cortices (association areas) processesPrestriate cortices (association areas) processes Form, color, and movement Form, color, and movement

Visual information then proceeds anteriorly to Visual information then proceeds anteriorly to the:the: Temporal lobe – processes identification of objectsTemporal lobe – processes identification of objects Parietal cortex and postcentral gyrus – processes Parietal cortex and postcentral gyrus – processes

spatial locationspatial location

Chemical SensesChemical Senses

Chemical senses – gustation (taste) and Chemical senses – gustation (taste) and olfaction (smell) olfaction (smell)

Their chemoreceptors respond to chemicals in Their chemoreceptors respond to chemicals in aqueous solutionaqueous solution Taste – to substances dissolved in salivaTaste – to substances dissolved in saliva Smell – to substances dissolved in fluids of the Smell – to substances dissolved in fluids of the

nasal membranesnasal membranes

Sense of SmellSense of Smell

The organ of smell is the olfactory epithelium, The organ of smell is the olfactory epithelium, which covers the superior nasal concha which covers the superior nasal concha

Olfactory receptor cells are bipolar neurons Olfactory receptor cells are bipolar neurons with radiating olfactory ciliawith radiating olfactory cilia

Olfactory receptors are surrounded and Olfactory receptors are surrounded and cushioned by supporting cellscushioned by supporting cells

Basal cells lie at the base of the epitheliumBasal cells lie at the base of the epithelium

Olfactory ReceptorsOlfactory Receptors

Figure 15.21

Physiology of SmellPhysiology of Smell

Olfactory receptors respond to several Olfactory receptors respond to several different odor-causing chemicalsdifferent odor-causing chemicals

When bound to ligand these proteins initiate a When bound to ligand these proteins initiate a G protein mechanism, which uses cAMP as a G protein mechanism, which uses cAMP as a second messengersecond messenger

cAMP opens NacAMP opens Na++ and Ca and Ca2+2+ channels, causing channels, causing depolarization of the receptor membrane that depolarization of the receptor membrane that then triggers an action potentialthen triggers an action potential

Olfactory PathwayOlfactory Pathway

Olfactory receptor cells synapse with mitral Olfactory receptor cells synapse with mitral cellscells

Glomerular mitral cells process odor signalsGlomerular mitral cells process odor signals Mitral cells send impulses to:Mitral cells send impulses to:

The olfactory cortex The olfactory cortex The hypothalamus, amygdala, and limbic systemThe hypothalamus, amygdala, and limbic system

GolfReceptor

Extracellular fluid

Cytoplasm

Odorant Adenylate cyclase

Na+

Ca2+

GTP

GTP GTP

GDP cAMP

cAMP

ATP

1

2 34

5

Figure 15.22

Olfactory Transduction ProcessOlfactory Transduction Process

Taste BudsTaste Buds

Most of the 10,000 or so taste buds are found Most of the 10,000 or so taste buds are found on the tongueon the tongue

Taste buds are found in papillae of the tongue Taste buds are found in papillae of the tongue mucosamucosa

Papillae come in three types: filiform, Papillae come in three types: filiform, fungiform, and circumvallatefungiform, and circumvallate

Fungiform and circumvallate papillae contain Fungiform and circumvallate papillae contain taste budstaste buds

Taste BudsTaste Buds

Figure 15.23

Structure of a Taste BudStructure of a Taste Bud

Each gourd-shaped taste bud consists of three Each gourd-shaped taste bud consists of three major cell typesmajor cell types Supporting cells – insulate the receptor Supporting cells – insulate the receptor Basal cells – dynamic stem cells Basal cells – dynamic stem cells Gustatory cells – taste cellsGustatory cells – taste cells

Taste SensationsTaste Sensations

There are five basic taste sensationsThere are five basic taste sensations Sweet – sugars, saccharin, alcohol, and some Sweet – sugars, saccharin, alcohol, and some

amino acidsamino acids Salt – metal ionsSalt – metal ions Sour – hydrogen ionsSour – hydrogen ions Bitter – alkaloids such as quinine and nicotineBitter – alkaloids such as quinine and nicotine Umami – elicited by the amino acid glutamateUmami – elicited by the amino acid glutamate

Physiology of TastePhysiology of Taste

In order to be tasted, a chemical:In order to be tasted, a chemical: Must be dissolved in salivaMust be dissolved in saliva Must contact gustatory hairsMust contact gustatory hairs

Binding of the food chemical:Binding of the food chemical: Depolarizes the taste cell membrane, releasing Depolarizes the taste cell membrane, releasing

neurotransmitterneurotransmitter Initiates a generator potential that elicits an action Initiates a generator potential that elicits an action

potentialpotential

Taste TransductionTaste Transduction

The stimulus energy of taste is converted into The stimulus energy of taste is converted into a nerve impulse by:a nerve impulse by: NaNa++ influx in salty tastes influx in salty tastes HH++ in sour tastes (by directly entering the cell, by in sour tastes (by directly entering the cell, by

opening cation channels, or by blockade of Kopening cation channels, or by blockade of K++ channels)channels)

Gustducin in sweet and bitter tastesGustducin in sweet and bitter tastes

Gustatory PathwayGustatory Pathway

Cranial Nerves VII and IX carry impulses Cranial Nerves VII and IX carry impulses from taste buds to the solitary nucleus of the from taste buds to the solitary nucleus of the medullamedulla

These impulses then travel to the thalamus, These impulses then travel to the thalamus, and from there fibers branch to the:and from there fibers branch to the: Gustatory cortex (taste)Gustatory cortex (taste) Hypothalamus and limbic system (appreciation of Hypothalamus and limbic system (appreciation of

taste)taste)

Influence of Other Sensations on Influence of Other Sensations on TasteTaste

Taste is 80% smellTaste is 80% smell Thermoreceptors, mechanoreceptors, Thermoreceptors, mechanoreceptors,

nociceptors also influence tastesnociceptors also influence tastes Temperature and texture enhance or detract Temperature and texture enhance or detract

from tastefrom taste

The Ear: Hearing and BalanceThe Ear: Hearing and Balance

The three parts of the ear are the inner, outer, The three parts of the ear are the inner, outer, and middle earand middle ear

The outer and middle ear are involved with The outer and middle ear are involved with hearinghearing

The inner ear functions in both hearing and The inner ear functions in both hearing and equilibriumequilibrium

Receptors for hearing and balance: Receptors for hearing and balance: Respond to separate stimuliRespond to separate stimuli Are activated independentlyAre activated independently

The Ear: Hearing and BalanceThe Ear: Hearing and Balance

Figure 15.25a

Outer EarOuter Ear

The auricle (pinna) is composed of:The auricle (pinna) is composed of: The helix (rim)The helix (rim) The lobule (earlobe)The lobule (earlobe)

External auditory canalExternal auditory canal Short, curved tube filled with ceruminous glandsShort, curved tube filled with ceruminous glands

Outer EarOuter Ear

Tympanic membrane (eardrum)Tympanic membrane (eardrum) Thin connective tissue membrane that vibrates in Thin connective tissue membrane that vibrates in

response to soundresponse to sound Transfers sound energy to the middle ear ossicles Transfers sound energy to the middle ear ossicles Boundary between outer and middle earsBoundary between outer and middle ears

Middle Ear (Tympanic Cavity)Middle Ear (Tympanic Cavity)

A small, air-filled, mucosa-lined cavity A small, air-filled, mucosa-lined cavity Flanked laterally by the eardrumFlanked laterally by the eardrum Flanked medially by the oval and round windowsFlanked medially by the oval and round windows

Epitympanic recess – superior portion of the Epitympanic recess – superior portion of the middle earmiddle ear

Pharyngotympanic tube – connects the middle Pharyngotympanic tube – connects the middle ear to the nasopharynxear to the nasopharynx Equalizes pressure in the middle ear cavity with Equalizes pressure in the middle ear cavity with

the external air pressurethe external air pressure

Middle and Internal EarMiddle and Internal Ear

Figure 15.25b