17 the special senses

© 2012 Pearson Education, Inc.

PowerPoint® Lecture Presentations prepared byJason LaPresLone Star College—North Harris

17The Special Senses


An Introduction to the Special Senses

• Learning Outcomes

• 17-1 Describe the sensory organs of smell, trace the olfactory pathways to their

destinations in the brain, and explain the physiological basis of olfactory discrimination.

• 17-2 Describe the sensory organs of taste, trace the gustatory pathways to their

destinations in the brain, and explain the physiological basis of gustatory discrimination.

• 17-3 Identify the internal and accessory structures of the eye, and explain the functions of

each.



• Learning Outcomes

• 17-4 Explain color and depth perception, describe how light stimulates the production of

nerve impulses, and trace the visual pathways to their destinations in the brain.

• 17-5 Describe the structures of the external, middle, and internal ear, explain their

roles in equilibrium and hearing, and trace the pathways for equilibrium and hearing

to their destinations in the brain.



• Five Special Senses

1. Olfaction

2. Gustation

3. Vision

4. Equilibrium

5. Hearing


17-1 Smell (Olfaction)

• Olfactory Organs

• Provide sense of smell

• Located in nasal cavity on either side of nasal

septum

• Made up of two layers

1. Olfactory epithelium

2. Lamina propria



• Layers of Olfactory Organs

• Olfactory epithelium contains:

• Olfactory receptors

• Supporting cells

• Basal (stem) cells



• Layers of Olfactory Organs

• Lamina propria contains:

• Areolar tissue

• Blood vessels

• Nerves

• Olfactory glands


Figure 17-1a The Olfactory Organs

Olfactoryepithelium

Olfactory Pathway to the Cerebrum

Olfactorynervefibers (N I)

Olfactorybulb

Olfactorytract

Centralnervoussystem

Superiornasal

concha

Cribriformplate

The olfactory organ onthe left side of the nasal septum


Figure 17-1b The Olfactory Organs

Olfactoryepithelium

Cribriformplate

Laminapropria

Basal cell:divides to replaceworn-out olfactory

receptor cells Olfactorygland

Toolfactory

bulb

Olfactorynerve fibers

Developingolfactoryreceptor cell

Olfactoryreceptor cell

Supporting cell

Mucous layer

Knob

Olfactory cilia:surfaces containreceptor proteins(see SpotlightFig. 173)

Subsance being smelled

An olfactory receptor is a modifiedneuron with multiple cilia extendingfrom its free surface.



• Olfactory Glands

• Secretions coat surfaces of olfactory organs

• Olfactory Receptors

• Highly modified neurons

• Olfactory reception

• Involves detecting dissolved chemicals as they interact

with odorant-binding proteins



• Olfactory Pathways

• Axons leaving olfactory epithelium

• Collect into 20 or more bundles

• Penetrate cribriform plate of ethmoid

• Reach olfactory bulbs of cerebrum where first

synapse occurs



• Olfactory Pathways

• Axons leaving olfactory bulb:

• Travel along olfactory tract to reach olfactory cortex,

hypothalamus, and portions of limbic system

• Arriving information reaches information centers

without first synapsing in thalamus



• Olfactory Discrimination

• Can distinguish thousands of chemical stimuli

• CNS interprets smells by the pattern of receptor

activity

• Olfactory Receptor Population

• Considerable turnover

• Number of olfactory receptors declines with age


Figure 17-2 Olfactory and Gustatory Receptors

Olfaction and gustation are specialsenses that provide us with vitalinformation about our environment. Although the sensory information provided is diverse and complex, each special sense originates at receptor cells that may be neurons or specialized receptor cells that communicate with sensory neurons.

Stimulus

Dendrites

Specializedolfactoryneuron

to CNS

StimulusremovedAction

potentials

Stimulus

Threshold

Generator potential



The binding of an odorant to itsreceptor protein leads to theactivation of adenylyl cyclase, theenzyme that converts ATP tocyclic-AMP (cAMP).

The cAMP then openssodium channels in theplasma membrane, which,as a result, begins todepolarize.

If sufficient depolarizationoccurs, an action potential istriggered in the axon, and theinformation is relayed to theCNS.

In general, odorants are small organic molecules. Thestrongest smells are associated with molecules of eitherhigh water or high lipid solubilities. As few as fourodorant molecules can activate an olfactory receptor.

Olfactory reception occurs on the surface membranes ofthe olfactory cilia. Odorantsdissolved chemicals thatstimulate olfactory receptorsinteract with receptors calledodorant- binding proteins on the membrane surface.

Depolarizedmembrane

Sodiumions enter

Closedsodiumchannel

RECEPTORCELL

MUCOUSLAYEROdorant

molecule

Activeenzyme

Inactiveenzyme


17-2 Taste (Gustation)

• Gustation

• Provides information about the foods and liquids

consumed

• Taste Receptors (Gustatory Receptors)

• Are distributed on tongue and portions of pharynx and

larynx

• Clustered into taste buds



• Taste Buds

• Associated with epithelial projections (lingual papillae)

on superior surface of tongue



• Three Types of Lingual Papillae

1. Filiform papillae

• Provide friction

• Do not contain taste buds

2. Fungiform papillae

• Contain five taste buds each

3. Circumvallate papillae

• Contain 100 taste buds each



• Taste Buds

• Contain:

• Basal cells

• Gustatory cells

• Extend taste hairs through taste pore

• Survive only 10 days before replacement

• Monitored by cranial nerves that synapse within solitary

nucleus of medulla oblongata

• Then on to thalamus and primary sensory cortex


Figure 17-3a Gustatory Receptors

Water receptors(pharynx) Umami

Sour

Bitter

Salty

Sweet

Landmarks andreceptors on thetongue


Figure 17-3b Gustatory Receptors

Tastebuds

Circumvallate papilla

Fungiform papilla

Filiform papillae

The structure and representative locationsof the three types of lingual papillae. Tastereceptors are located in taste buds, whichform pockets in the epithelium of fungiform or circumvillate papillae.


Figure 17-3c Gustatory Receptors

Tastebuds

Taste buds

Nucleus oftransitional cell

Nucleus ofgustatory cell

Nucleus ofbasal cell

Taste bud LM 650

LM 280

Transitional cell

Gustatory cell

Basal cell

Taste hairs(microvilli)

Taste pore

Taste buds in a circumvallate papilla.A diagrammatic view of a taste bud,showing gustatory (receptor) cellsand supporting cells.



• Gustatory Discrimination

• Four primary taste sensations

1. Sweet

2. Salty

3. Sour

4. Bitter



• Additional Human Taste Sensations

• Umami

• Characteristic of beef/chicken broths and Parmesan

cheese

• Receptors sensitive to amino acids, small peptides, and

nucleotides

• Water

• Detected by water receptors in the pharynx



• Gustatory Discrimination

• Dissolved chemicals contact taste hairs

• Bind to receptor proteins of gustatory cell

• Salt and sour receptors

• Chemically gated ion channels

• Stimulation produces depolarization of cell

• Sweet, bitter, and umami stimuli

• G proteins

• Gustducins



• End Result of Taste Receptor Stimulation

• Release of neurotransmitters by receptor cell

• Dendrites of sensory afferents wrapped by receptor

membrane

• Neurotransmitters generate action potentials in afferent

fiber



• Taste Sensitivity

• Exhibits significant individual differences

• Some conditions are inherited

• For example, phenylthiocarbamide (PTC)

• 70% of Caucasians taste it but 30% do not

• Number of taste buds

• Begins declining rapidly by age 50



Receptor cell

Stimulusremoved

Stimulus

Threshold

Receptor depolarization

Stimulus

Receptorcell

Synapse

Axon ofsensoryneuron

Stimulus

AxonAction

potentials

Generator potential

Synapticdelay

to CNS



Salt receptors and sour receptors are chemically gated ion channels whose stimulation produces depolarization of the cell.

Salt and Sour Receptors

Receptors responding to stimuli that produce sweet, bitter, and umami sensations are linked to G proteins called gustducins (GUST-doos- inz)protein complexes that use second messengers to produce their effects.

Sweet, Bitter, and Umami Receptors

Sour,salt Gated ion

channel

Resting plasmamembrane

Channel opens

Depolarizedmembrane

Sweet,bitter, orumami

Membranereceptor

ActiveG protein

InactiveG protein

ActiveG protein

Inactive2nd messenger

Active2nd messenger

Depolarization of membranestimulates release of chemicalneurotransmitters.

Activation of second messengers stimulates release of chemical neurotransmitters.


17-3 Accessory Structures of the Eye

• Accessory Structures of the Eye

• Provide protection, lubrication, and support

• Include:

• The palpebrae (eyelids)

• The superficial epithelium of eye

• The lacrimal apparatus



• Eyelids (Palpebrae)

• Continuation of skin

• Blinking keeps surface of eye lubricated, free of dust

and debris

• Palpebral fissure

• Gap that separates free margins of upper and lower

eyelids




• Medial canthus and lateral canthus

• Where two eyelids are connected

• Eyelashes

• Robust hairs that prevent foreign matter from

reaching surface of eye




• Tarsal glands

• Secrete lipid-rich product that helps keep eyelids

from sticking together



• Superficial Epithelium of Eye

• Lacrimal caruncle

• Mass of soft tissue

• Contains glands producing thick secretions

• Contributes to gritty deposits that appear after good

night’s sleep

• Conjunctiva

• Epithelium covering inner surfaces of eyelids

(palpebral conjunctiva) and outer surface of eye

(ocular conjunctiva)


Figure 17-4a External Features and Accessory Structures of the Eye

Gross and superficialanatomy of the accessory structures

Sclera

Lateral canthus

Eyelashes

Pupil

Palpebra

Palpebral fissure

Medial canthus

Lacrimal caruncle

Corneal limbus



• Lacrimal Apparatus

• Produces, distributes, and removes tears

• Fornix

• Pocket where palpebral conjunctiva joins ocular

conjunctiva

• Lacrimal gland (tear gland)

• Secretions contain lysozyme, an antibacterial enzyme



• Tears

• Collect in the lacrimal lake

• Pass through:

• Lacrimal puncta

• Lacrimal canaliculi

• Lacrimal sac

• Nasolacrimal duct

• To reach inferior meatus of nose


Figure 17-4b External Features and Accessory Structures of the Eye

Lacrimalgland ducts

Lacrimal gland

Ocular conjunctiva

Lateral canthus

Lower eyelid

Orbital fat

Inferiorrectus muscle

Inferioroblique muscle

Superiorrectus muscle

Tendon of superioroblique muscle

Lacrimal punctum

Lacrimal caruncle

Superior lacrimalcanaliculusMedial canthusInferior lacrimalcanaliculusLacrimal sac

Nasolacrimal duct

Opening ofnasolacrimal duct

Inferior nasalconcha

The organization of the lacrimalapparatus.


17-3 The Eye

• Three Layers of the Eye

1. Outer fibrous layer

2. Intermediate vascular layer

3. Deep inner layer


17-3 The Eye

• Eyeball

• Is hollow

• Is divided into two cavities

1. Large posterior cavity

2. Smaller anterior cavity


Figure 17-5a The Sectional Anatomy of the Eye

Opticnerve

Fovea

RetinaChoroid

Sclera

Sagittal section of left eye

Lens

FornixPalpebral conjunctiva

EyelashOcular conjunctiva

Cornea

Pupil

Iris

Limbus

Ora serrata


Figure 17-5b The Sectional Anatomy of the Eye

Cornea

Sclera

Neural part

Pigmented part

Fibrouslayer

Neural layer(retina)

Anteriorcavity

Posteriorcavity

Vascular layer(uvea)

Iris

Ciliary body

Choroid

Horizontal section of right eye


Figure 17-5c The Sectional Anatomy of the Eye

Lacrimal punctum

Nose

Lens

Edge ofpupil

Visual axis

Anterior cavity

Posteriorchamber

Anteriorchamber

Lacrimal caruncle

Medial canthus

Ciliaryprocesses

Ciliary body

Ora serrata

Ethmoidallabyrinth

Medial rectusmuscle

Optic disc

Optic nerve

Central arteryand vein

Horizontal dissection of right eye

Orbital fat

Fovea

Lateral rectusmuscle

Posteriorcavity

Retina

Choroid

Sclera

Lateralcanthus

Lower eyelid

Conjunctiva

Corneal limbus

Suspensory ligament of lens

Iris

Cornea


17-3 The Eye

• The Fibrous Layer

• Sclera (white of the eye)

• Cornea

• Corneal limbus (border between cornea and

sclera)


17-3 The Eye

• Vascular Layer (Uvea) Functions

1. Provides route for blood vessels and lymphatics that

supply tissues of eye

2. Regulates amount of light entering eye

3. Secretes and reabsorbs aqueous humor that

circulates within chambers of eye

4. Controls shape of lens, which is essential to

focusing



Lacrimal punctum

Nose

Lens

Edge ofpupil

Visual axis

Anterior cavity

Posteriorchamber

Anteriorchamber

Lacrimal caruncle

Medial canthus

Ciliaryprocesses

Ciliary body

Ora serrata

Ethmoidallabyrinth

Medial rectusmuscle

Optic disc

Optic nerve



Orbital fat

Fovea


Posteriorcavity

Retina

Choroid

Sclera

Lateralcanthus

Lower eyelid

Conjunctiva

Corneal limbus


Iris

Cornea


17-3 The Eye

• The Vascular Layer

• Iris

• Contains papillary muscles

• Change diameter of pupil


Figure 17-6 The Pupillary Muscles

Pupillary constrictor(sphincter)

Pupil

The pupillary dilatormuscles extend radially awayfrom the edge of the pupil.Contraction of these musclesenlarges the pupil.

Pupillary dilator(radial)

Decreased light intensityIncreased sympathetic stimulation

Increased light intensityIncreased parasympathetic stimulation

The pupillary constrictormuscles form a series ofconcentric circles around thepupil. When these sphinctermuscles contract, the diameterof the pupil decreases.


17-3 The Eye


• Ciliary Body

• Extends posteriorly to level of ora serrata

• Serrated anterior edge of thick, inner portion of

neural tunic

• Contains ciliary processes, and ciliary muscle that

attaches to suspensory ligaments of lens


17-3 The Eye


• The choroid

• Vascular layer that separates fibrous and inner layers

posterior to ora serrata

• Delivers oxygen and nutrients to retina


17-3 The Eye

• The Inner Layer

• Outer layer called pigmented part

• Inner called neural part (retina)

• Contains visual receptors and associated neurons

• Rods and cones are types of photoreceptors

• Rods

• Do not discriminate light colors

• Highly sensitive to light

• Cones

• Provide color vision

• Densely clustered in fovea, at center of macula



Lacrimal punctum

Nose

Lens

Edge ofpupil

Visual axis

Anterior cavity

Posteriorchamber

Anteriorchamber

Lacrimal caruncle

Medial canthus

Ciliaryprocesses

Ciliary body

Ora serrata

Ethmoidallabyrinth

Medial rectusmuscle

Optic disc

Optic nerve



Orbital fat

Fovea


Posteriorcavity

Retina

Choroid

Sclera

Lateralcanthus

Lower eyelid

Conjunctiva

Corneal limbus


Iris

Cornea


Figure 17-7a The Organization of the Retina

Amacrine cell

Horizontal cell Cone Rod

Pigmentedpart of retina

Rods andcones

Bipolar cells

Ganglion cells

LIGHT

The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber).


Figure 17-7a The Organization of the Retina

Choroid


Rods andcones

Bipolar cells

Ganglion cells

The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber).

Retina

Nuclei ofganglion cells

Nuclei of rodsand cones

Nuclei ofbipolar cells

LM 350


Figure 17-7b The Organization of the Retina

Central retinal vein

Central retinal artery

Sclera

ChoroidOptic nerve

Optic disc

The optic disc in diagrammatic sagittal section.


Neural part of retina


Figure 17-7c The Organization of the Retina

Fovea

Macula

A photograph of the retina as seen through the pupil.

Central retinal artery and veinemerging from center of optic disc

Optic disc(blind spot)


17-3 The Eye

• Inner Neural Part

• Bipolar cells

• Neurons of rods and cones synapse with ganglion cells

• Horizontal cells

• Extend across outer portion of retina

• Amacrine cells

• Comparable to horizontal cell layer

• Where bipolar cells synapse with ganglion cells


17-3 The Eye

• Horizontal and Amacrine Cells

• Facilitate or inhibit communication between

photoreceptors and ganglion cells

• Alter sensitivity of retina

• Optic Disc

• Circular region just medial to fovea

• Origin of optic nerve

• Blind spot


Figure 17-8 A Demonstration of the Presence of a Blind Spot


17-3 The Eye

• The Chambers of the Eye

• Ciliary body and lens divide eye into:

• Large posterior cavity (vitreous chamber)

• Smaller anterior cavity

• Anterior chamber

• Extends from cornea to iris

• Posterior chamber

• Between iris, ciliary body, and lens


17-3 The Eye

• Aqueous Humor

• Fluid circulates within eye

• Diffuses through walls of anterior chamber into scleral

venous sinus (canal of Schlemm)

• Re-enters circulation

• Intraocular Pressure

• Fluid pressure in aqueous humor

• Helps retain eye shape


Figure 17-9 The Circulation of Aqueous Humor

Cornea

Pupil

Lens

Scleral venous sinus

Body of iris

Conjunctiva

Ciliary body

Sclera

Choroid

Retina

Posterior cavity(vitreous chamber)

Anterior cavity

Anterior chamber

Posterior chamber

Ciliary process

Suspensoryligaments

Pigmentedepithelium


17-3 The Eye

• Large Posterior Cavity (Vitreous Chamber)

• Vitreous body

• Gelatinous mass

• Helps stabilize eye shape and supports retina


17-3 The Eye

• The Lens

• Lens fibers

• Cells in interior of lens

• No nuclei or organelles

• Filled with crystallins, which provide clarity and

focusing power to lens

• Cataract

• Condition in which lens has lost its transparency


17-3 The Eye

• Light Refraction

• Bending of light by cornea and lens

• Focal point

• Specific point of intersection on retina

• Focal distance

• Distance between center of lens and focal point


Figure 17-10 Factors Affecting Focal Distance

Focal distance

Lightfrom

distantsource(object)

Closesource

The closer the light source,the longer the focal distance

Focal distance

Focalpoint

Lens

The rounder the lens,the shorter the focal distance

Focal distance


17-3 The Eye

• Light Refraction of Lens

• Accommodation

• Shape of lens changes to focus image on retina

• Astigmatism

• Condition where light passing through cornea and

lens is not refracted properly

• Visual image is distorted


Figure 17-11 Accommodation

For Close Vision: Ciliary Muscle Contracted, Lens Rounded

Lens rounded

Ciliary musclecontracted

Focal pointon fovea

Lens flattened

Ciliary musclerelaxed

For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened


Figure 17-11a Accommodation

For Close Vision: Ciliary Muscle Contracted, Lens Rounded

Lens rounded

Ciliary musclecontracted

Focal pointon fovea


Figure 17-11b Accommodation

Lens flattened

Ciliary musclerelaxed

For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened


17-3 The Eye

• Light Refraction of Lens

• Image reversal

• Visual acuity

• Clarity of vision

• “Normal” rating is 20/20


Figure 17-12a Image Formation

Light from a point at the top of anobject is focused on the lowerretinal surface.


Figure 17-12b Image Formation

Light from a point at the bottom ofan object is focused on the upperretinal surface.


Figure 17-12c Image Formation

Light rays projected from a verticalobject show why the image arrivesupside down. (Note that the image isalso reversed.)


Figure 17-12d Image Formation

Light rays projected from a horizontalobject show why the image arriveswith a left and right reversal. Theimage also arrives upside down. (Asnoted in the text, these representa-tions are not drawn to scale.)


Figure 17-13 Accommodation Problems

The eye has a fixedfocal length and

focuses by varyingthe shape of the lens.

A camera lens has a fixed size and shape

and focuses by varyingthe distance to the film.



Emmetropia(normal vision)



Diverginglens

Myopiacorrected witha diverging,concavelens

If the eyeball is too deep or the restingcurvature of the lens is too great, theimage of a distant object is projected infront of the retina. The person will seedistant objects as blurry and out of focus. Vision at close range will be normal because the lens is able to round as needed to focus the image on the retina.

Myopia (nearsightedness)



Hyperopia (farsightedness)If the eyeball is too shallow or the lens istoo flat, hyperopia results. The ciliarymuscle must contract to focus even a distant object o the retina. And at closerange the lens cannot provide enoughrefraction to focus an image on the retina. Older people become farsighted as their lenses lose elasticity, a form of hyperopia called presbyopia (presbys, old man).

Hyperopiacorrected witha converging,convexlens

Converginglens



Surgical Correction

Variable successat correcting myopia and hyperopia hasbeen achieved by surgery that reshapes the cornea. In Photorefractivekeratectomy (PRK) a computer-guidedlaser shapes the cornea to exactspecifications. The entire procedure can be done in less than a minute. A variation on PRK is called LASIK (Laser-Assisted in-Situ Keratomileusis). In this procedure the interior layers of the cornea are reshaped and then re-covered by the flap of original outer cornealepithelium. Roughly 70 percent of LASIK patients achieve normal vision, and LASIK has become the most common form of refractive surgery. Even after surgery, many patients still need reading glasses, and both immediate and long-term visual problems can occur.


17-4 Visual Physiology

• Visual Physiology

• Rods

• Respond to almost any photon, regardless of

energy content

• Cones

• Have characteristic ranges of sensitivity



• Anatomy of Rods and Cones

• Outer segment with membranous discs

• Inner segment

• Narrow stalk connects outer segment to inner

segment



• Anatomy of Rods and Cones

• Visual pigments

• Is where light absorption occurs

• Derivatives of rhodopsin (opsin plus retinal)

• Retinal synthesized from vitamin A


Figure 17-14a Structure of Rods, Cones, and Rhodopsin Molecule

Pigment Epithelium

Melanin granules

Outer Segment

Inner Segment

Discs

Connectingstalks

Mitochondria

Golgiapparatus

Nuclei

Cone Rods

In a cone, the discs are infoldings ofthe plasma membrane, and the outersegment tapers to a blunt point.

In a rod, each disc is an independententity, and the outer segment formsan elongated cylinder.

Each photoreceptorsynapses with a bipolar cell.

Bipolar cell

Structure of rods and cones.

LIGHT


Figure 17-14b Structure of Rods, Cones, and Rhodopsin Molecule

In a rod, each disc is an independententity, and the outer segment formsan elongated cylinder.

Rhodopsinmolecule

OpsinRetinal

Structure ofrhodospin molecule.



• Color Vision

• Integration of information from red, green,

and blue cones

• Color blindness

• Inability to detect certain colors


Figure 17-15 Cone Types and Sensitivity to Color

RodsBluecones Green

cones

Redcones

Violet Blue Green Yellow Orange Red

W A V E L E N G T H (nm)

Lig

ht

abso

rpti

on

(per

cen

t o

f m

axim

um

)


Figure 17-16 A Standard Test for Color Vision



• Photoreception

• Photon strikes retinal portion of rhodopsin molecule

embedded in membrane of disc

• Opsin is activated

• Bound retinal molecule has two possible configurations

• 11-cis form

• 11-trans form


Figure 17-17 Photoreception

Opsin activation occurs

The bound retinal molecule has two possibleconfigurations: the 11-cisform and the 11-trans form.

Normally, the molecule is inthe 11-cis form; onabsorbing light it changes to the more linear 11-transform. This change activatesthe opsin molecule.

Photon

Rhodopsin

11-trans retinal

11-cisretinal

Opsin



PDE

Discmembrane

Transducin

Opsin activatestransducin, which in turn activatesphosphodiestease (PDE)

Transducin is a G proteinamembrane-bound enzymecomplex

In this case, transducin isactivated by opsin, andtransducin in turn activatesphosphodiesterase (PDE).



Cyclic-GMP levels decline and gated sodium channels close

Phosphodiesterase is an enzyme that breaks down cGMP.

The removal of cGMP fromthe gated sodium channelsresults in their inactivation.The rate of Na entry intothe cytoplasm is thendecreased.

GMP

cGMP



Dark current is reduced and rate of neurotransmitter release declines

ACTIVE STATE

IN LIGHT



• Recovery after Stimulation

• Bleaching

• Rhodopsin molecule breaks down into retinal and opsin

• Night blindness

• Results from deficiency of vitamin A


Figure 17-18 Bleaching and Regeneration of Visual Pigments

On absorbing light, retinalchanges to a more linear shape.This change activates the opsinmolecule. Opsin activation changes

the Na permeability of theouter segment, and thischanges the rate ofneurotransmitter release bythe inner segment at itssynapse with a bipolar cell.

Na

Na

11-trans retinal

Neuro-transmitterrelease

Bipolarcell

Changes in bipolarcell activity aredetected byone or moreganglion cells.The location ofthe stimulatedganglion cellindicates thespecific portion ofthe retinastimulated by thearriving photons.

Ganglioncell

Opsin11-trans retinal

ADP ATP

enzyme

11-cis retinal

Photon

Opsin

11-cis retinal and opsinare reassembled to form

rhodopsin.

After absorbing aphoton, therhodopsin moleculebegins to break downinto retinal and opsin,a process known asbleaching.

The retinal is convertedto its original shape. Thisconversion requiresenergy in the form of ATP.

Once the retinal has beenconverted, it canrecombine with opsin. Therhodopsin molecule is now ready to repeat the cycle.The regeneration processtakes time; after exposureto very bright light,photoreceptors areinactivated while pigmentregeneration is under way.



• Light and Dark Adaptation

• Dark

• Most visual pigments are fully receptive to stimulation

• Light

• Pupil constricts

• Bleaching of visual pigments occurs



• The Visual Pathways

• Begin at photoreceptors

• End at visual cortex of cerebral hemispheres

• Message crosses two synapses before it heads

toward brain

• Photoreceptor to bipolar cell

• Bipolar cell to ganglion cell



• Ganglion Cells

• Monitor a specific portion of a field of vision

• M Cells

• Are ganglion cells that monitor rods

• Are relatively large

• Provide information about:

• General form of object

• Motion

• Shadows in dim lighting



• Ganglion Cells

• P cells

• Are ganglion cells that monitor cones

• Are smaller, more numerous

• Provide information about edges, fine detail, and color



• Ganglion Cells

• On-center neurons

• Are excited by light arriving in center of their sensory field

• Are inhibited when light strikes edges of their receptive

field

• Off-center neurons

• Inhibited by light in central zone

• Stimulated by illumination at edges


Figure 17-19 Convergence and Ganglion Cell Function

Receptive fieldof ganglion cell

Receptive field

Retinal surface(contacts pigment epithelium)

Photoreceptors

Horizontalcell

Bipolar cell

Amacrinecell

Ganglion cell



• Central Processing of Visual Information

• Axons from ganglion cells converge on optic disc

• Penetrate wall of eye

• Proceed toward diencephalon as optic nerve (II)

• Two optic nerves (one for each eye) reach

diencephalon at optic chiasm



• Visual Data

• From combined field of vision arrive at visual cortex of

opposite occipital lobe

• Left half arrive at right occipital lobe

• Right half arrive at left occipital lobe

• Optic radiation

• Bundle of projection fibers linking lateral geniculate with

visual cortex



• The Field of Vision

• Depth perception

• Obtained by comparing relative positions of

objects between left-eye and right-eye images



• The Brain Stem and Visual Processing

• Circadian rhythm

• Is tied to day-night cycle

• Affects other metabolic processes


Figure 17-20 The Visual Pathways

Combined

Left side Right side

onlyRight eye

onlyBinocular visionLeft eye

Retina

Optic disc

SuprachiasmaticnucleusDiencephalon

andbrain stem

The VisualPathway

Photoreceptorsin retina

Optic nerve(N II)

Optic chiasm

Optic tract

Lateralgeniculate

nucleus

Superiorcolliculus

Right cerebralhemisphere

Left cerebralhemisphere

Projection fibers(optic radiation)

Visual cortexof cerebral

hemispheres

Visual Field


17-5 The Ear

• The External Ear

• Auricle

• Surrounds entrance to external acoustic meatus

• Protects opening of canal

• Provides directional sensitivity


17-5 The Ear


• External acoustic meatus

• Ends at tympanic membrane (eardrum)

• Tympanic membrane

• Is a thin, semitransparent sheet

• Separates external ear from middle ear


Figure 17-21 The Anatomy of the Ear

External Ear

Elastic cartilages

Auricle

External acousticmeatus

Tympanicmembrane

Tympaniccavity

Middle Ear

Auditory ossicles

Ovalwindow

Semicircular canals

Petrous part oftemporal bone

Facial nerve (N VII)

Cochlea

Vestibulocochlearnerve (N VIII)

Bony labyrinthof internal ear

Auditory tube

Tonasopharynx

VestibuleRoundwindow

Internal Ear


17-5 The Ear


• Ceruminous glands

• Integumentary glands along external acoustic meatus

• Secrete waxy material (cerumen)

• Keeps foreign objects out of tympanic membrane

• Slows growth of microorganisms in external

acoustic meatus


17-5 The Ear

• The Middle Ear

• Also called tympanic cavity

• Communicates with nasopharynx via auditory tube

• Permits equalization of pressures on either side of

tympanic membrane

• Encloses and protects three auditory ossicles

1. Malleus (hammer)

2. Incus (anvil)

3. Stapes (stirrup)


Figure 17-22a The Middle Ear

Temporal bone(petrous part)

Malleus Incus Stapes

Ovalwindow Muscles of

the Middle Ear

Tensor tympanimuscle

Stapedius muscle

Round window

Auditory tube

Stabilizingligaments

Branch of facialnerve VII (cut)

Externalacoustic meatus

Tympanic cavity(middle ear)

Tympanicmembrane

The structures of the middle ear.

Auditory Ossicles


Figure 17-22b The Middle Ear

Tendon of tensortympani muscleMalleus

Malleus attached totympanic membrane

Incus

Base of stapesat oval window

Stapes

Stapedius muscle

Inner surface oftympanic membrane

The tympanic membrane and auditory ossicles


17-5 The Ear

• Vibration of Tympanic Membrane

• Converts arriving sound waves into mechanical

movements

• Auditory ossicles conduct vibrations to inner ear

• Tensor tympani muscle

• Stiffens tympanic membrane

• Stapedius muscle

• Reduces movement of stapes at oval window


17-5 The Ear

• The Internal Ear

• Contains fluid called endolymph

• Bony labyrinth surrounds and protects

membranous labyrinth

• Subdivided into:

• Vestibule

• Semicircular canals

• Cochlea


Figure 17-23b The Internal Ear

Semicircular ducts

AnteriorLateral

Posterior

Semicircular canal

Utricle

Saccule

Vestibular duct

Cochlear duct

Vestibule Cristae within ampullae

MaculaeEndolymphatic sac

Membranouslabyrinth

Bony labyrinth

KEY

Cochlea

Spiralorgan

Tympanicduct

The bony and membranous labyrinths. Areas of themembranous labyrinth containing sensory receptors (cristae, maculae, and spiral organ) are shown in purple.


Figure 17-23a The Internal Ear

Perilymph

Bony labyrinth

Endolymph

Membranouslabyrinth

A section through one of thesemicircular canals, showing therelationship between the bony andmembranous labyrinths, and theboundaries of perilymph andendolymph.

Membranouslabyrinth

Bony labyrinth

KEY


17-5 The Ear


• Vestibule

• Encloses saccule and utricle

• Receptors provide sensations of gravity and linear

acceleration

• Semicircular canals

• Contain semicircular ducts

• Receptors stimulated by rotation of head


17-5 The Ear


• Cochlea

• Contains cochlear duct (elongated portion of

membranous labyrinth)

• Receptors provide sense of hearing


17-5 The Ear


• Round window

• Thin, membranous partition

• Separates perilymph from air spaces of middle ear

• Oval window

• Formed of collagen fibers

• Connected to base of stapes


17-5 The Ear

• Stimuli and Location

• Sense of gravity and acceleration

• From hair cells in vestibule

• Sense of rotation

• From semicircular canals

• Sense of sound

• From cochlea


17-5 The Ear

• Equilibrium

• Sensations provided by receptors of vestibular

complex

• Hair cells

• Basic receptors of inner ear

• Provide information about direction and strength of

mechanical stimuli


17-5 The Ear

• The Semicircular Ducts

• Are continuous with utricle

• Each duct contains:

• Ampulla with gelatinous cupula

• Associated sensory receptors

• Stereocilia – resemble long microvilli

• Are on surface of hair cell

• Kinocilium – single large cilium


Figure 17-24a The Semicircular Ducts

Semicircular ductsAnterior

LateralPosterior

Ampulla

Utricle

Saccule Maculae

Vestibular branch (N VIII)

Cochlea

Endolymphatic sac

Endolymphatic duct

An anterior view of the right semicircular ducts, the utricle, and the saccule, showing the locations of sensory receptors


Figure 17-24b The Semicircular Ducts

Cupula

A cross section through theampulla of a semicircular duct

Crista

Supporting cells

Sensory nerve

Ampullafilled with

endolymph

Hair cells


Figure 17-24c The Semicircular Ducts

Endolymph movement along the lengthof the duct moves the cupula andstimulates the hair cells.

At rest

Direction ofduct rotation

Direction of relativeendolymph movement

Semicircular duct

Direction ofduct rotation

Ampulla


Figure 17-24d The Semicircular Ducts

StereociliaKinocilium

Hair cell

Sensorynerve endingSupportingcell

A representative hair cell (receptor) from thevestibular complex. Bending the sterocilia towardthe kinocilium depolarizes the cell and stimulatesthe sensory neuron. Displacement in the opposite direction inhibits the sensory neuron.

Displacement inthis directioninhibits hair cell

Displacement inthis direction

stimulates hair cell


17-5 The Ear

• The Utricle and Saccule

• Provide equilibrium sensations

• Are connected with the endolymphatic duct, which

ends in endolymphatic sac


17-5 The Ear

• The Utricle and Saccule

• Maculae

• Oval structures where hair cells cluster

• Statoconia

• Densely packed calcium carbonate crystals on

surface of gelatinous mass

• Otolith (ear stone) = gelatinous matrix and

statoconia


Figure 17-25ab The Saccule and Utricle

The location ofthe maculae

Otolith

Nervefibers

Hair cells

Statoconia

Gelatinousmaterial

The structure of an individual macula


Figure 17-25c The Saccule and Utricle

Head in normal, upright position

Gravity

GravityHead tilted posteriorly

Receptoroutput

increases

Otolithmoves

“downhill,”distorting haircell processes

A diagrammatic view of macular function when the head is held horizontally and then tilted back 2

1


17-5 The Ear

• Pathways for Equilibrium Sensations

• Vestibular receptors

• Activate sensory neurons of vestibular ganglia

• Axons form vestibular branch of vestibulocochlear

nerve (VIII)

• Synapse within vestibular nuclei


17-5 The Ear

• Four Functions of Vestibular Nuclei

1. Integrate sensory information about balance and

equilibrium from both sides of head

2. Relay information from vestibular complex to cerebellum

3. Relay information from vestibular complex to cerebral

cortex

• Provide conscious sense of head position and

movement

4. Send commands to motor nuclei in brain stem and spinal

cord


Figure 17-26 Pathways for Equilibrium Sensations

Vestibularganglion

Vestibularbranch

Red nucleus

Semicircularcanals

Vestibule

Cochlearbranch

N VI

N IV

N III

Vestibular nucleus

N XI

Vestibulocochlear nerve(N VIII)

Tocerebellum

Vestibulospinaltracts

To superior colliculus andrelay to cerebral cortex


17-5 The Ear

• Eye, Head, and Neck Movements

• Reflexive motor commands

• From vestibular nuclei

• Distributed to motor nuclei for cranial nerves

• Peripheral Muscle Tone, Head, and Neck

Movements

• Instructions descend in vestibulospinal tracts of spinal

cord


17-5 The Ear

• Eye Movements

• Sensations of motion directed by superior colliculi of the midbrain

• Attempt to keep focus on specific point

• If spinning rapidly, eye jumps from point to point

• Nystagmus

• Have trouble controlling eye movements

• Caused by damage to brain stem or inner ear


17-5 The Ear

• Hearing

• Cochlear duct receptors

• Provide sense of hearing


Figure 17-27a The Cochlea

Scala vestibuli

Cochlear duct

Scala tympani

Round window

Stapes atoval window

Cochlearbranch

Vestibularbranch

Vestibulocochlearnerve (N VIII)

The structure of the cochlea

KEY

From oval windowto tip of spiral

From tip of spiralto round window

Semicircularcanals


Figure 17-27b The Cochlea

Vestibularmembrane

Tectorialmembrane

Basilarmembrane

From ovalwindow

To roundwindow


Scala vestibuli(contains perilymph)

Cochlear duct(contains endolymph)

Spiral organ

Spiral ganglion

Scala tympani(contains perilymph)

Cochlear nerve

Vestibulocochlear nerve (N VIII)

Diagrammatic and sectional views of the cochlear spiral


Figure 17-27b The Cochlea

Diagrammatic and sectional views of the cochlear spiral




Spiral organ

Spiral ganglion


Cochlear spiral section LM 60

Vestibularmembrane

Basilarmembrane

Cochlear nerve


17-5 The Ear

• Hearing

• Auditory ossicles

• Convert pressure fluctuation in air into much greater

pressure fluctuations in perilymph of cochlea

• Frequency of sound

• Determined by which part of cochlear duct is stimulated

• Intensity (volume)

• Determined by number of hair cells stimulated


17-5 The Ear

• Hearing

• Cochlear duct receptors

• Basilar membrane

• Separates cochlear duct from tympanic duct

• Hair cells lack kinocilia

• Stereocilia in contact with overlying tectorial

membrane


Figure 17-28a The Spiral Organ

A three-dimensional section of the cochlea, showing thecompartments, tectorialmembrane, and spiral organ

Cochlear branchof N VIII

Spiralganglion

Body cochlear wall

Scala vestibuli

Vestibular membrane

Cochlear duct

Tectorial membrane

Basilar membrane

Scala tympani

Spiral organ


Figure 17-28b The Spiral Organ

Tectorial membrane

Outerhair cell

Basilar membrane Inner hair cell Nerve fibers

Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ


Figure 17-28b The Spiral Organ

Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ

Spiral organ

Cochlear duct (scala media)

Basilarmembrane

Hair cellsof spiral

organ

Spiral ganglioncells of

cochlear nerveLM 125

Vestibular membrane

Tectorial membrane

Scala tympani


17-5 The Ear

• An Introduction to Sound

• Pressure Waves

• Consist of regions where air molecules are crowded

together

• Adjacent zone where molecules are farther apart

• Sine waves

• S-shaped curves


17-5 The Ear

• Pressure Wave

• Wavelength

• Distance between two adjacent wave troughs

• Frequency

• Number of waves that pass fixed reference point at

given time

• Physicists use term cycles instead of waves

• Hertz (Hz) number of cycles per second (cps)


17-5 The Ear

• Pressure Wave

• Pitch

• Our sensory response to frequency

• Amplitude

• Intensity of sound wave

• Sound energy is reported in decibels


Figure 17-29a The Nature of Sound

Wavelength

Tuningfork Air molecules

Tympanicmembrane

Sound waves (here, generated by a tuning fork) travel through the air aspressure waves.


Figure 17-29b The Nature of Sound

A graph showing the sound energyarriving at the tympanic membrane. The distance between wave peaks is the wavelength. The number of wavesarriving each second is the frequency, which we perceive as pitch. Frequencies are reported in cycles per second (cps), or hertz (Hz). The amount of energy in each wave determines the wave’s amplitude, or intensity, which we perceive as the loudness of the sound.

1 wavelength

Amplitude


Figure 17-31a Frequency Discrimination

Stapesat oval

window

Roundwindow

16,000 Hz

Basilar membrane

Cochlea6000 Hz 1000 Hz

The flexibility of the basilar membrane varies along its length, so pressurewaves of different frequencies affect different parts of the membrane.


Figure 17-31b Frequency Discrimination

Stapesmovesinward

Roundwindowpushed

outward

Basilar membrane distortstoward round window

The effects of a vibration of the stapes at a frequency of 6000 Hz. Whenthe stapes moves inward, as shown here, the basilar membrane distortstoward the round window, which bulges into the middle-ear cavity.


Figure 17-31c Frequency Discrimination

Stapesmoves

outwardRound

windowpulled

inward

Basilar membrane distortstoward oval window

When the stapes moves outward, as shown here, the basilarmembrane rebounds and distorts toward the oval window.


Figure 17-30 Sound and Hearing

Externalacousticmeatus

Malleus Incus

Movementof sound

waves

Tympanicmembrane

Roundwindow

Stapes Oval window

Sound wavesarrive attympanicmembrane.

Movement ofthe tympanicmembrane causesdisplacementof the auditoryossicles.

Movement ofthe stapes atthe oval windowestablishespressurewaves in theperilymphof the scalavestibuli.


Figure 17-30 Sound and Hearing

Cochlear branchof cranial nerve VIII


Vestibular membrane



The pressurewaves distortthe basilarmembrane ontheir way to theround windowof the scalatympani.

Vibration of the basilarmembranecauses vibrationof hair cellsagainst thetectorialmembrane.

Information about the region and the intensity of stimulation isrelayed to the CNS over the cochlear branch of cranial nerve VIII.

Basilar membrane


17-5 The Ear

• Auditory Pathways

• Cochlear branch

• Formed by afferent fibers of spiral ganglion neurons

• Enters medulla oblongata

• Synapses at dorsal and ventral cochlear nuclei

• Information crosses to opposite side of brain

• Ascends to inferior colliculus of midbrain


17-5 The Ear

• Auditory Pathways

• Ascending auditory sensations

• Synapse in medial geniculate nucleus of thalamus

• Projection fibers deliver information to auditory cortex of

temporal lobe


Figure 17-32 Pathways for Auditory Sensations

Stimulation of hair cells ata specific location alongthe basilar membraneactivates sensory neurons.

Cochlea

Low-frequencysounds

High-frequencysounds

Vestibularbranch

KEY

Sensory neurons carry thesound information in thecochlear branch of thevestibulocochlear nerve (VIII)to the cochlear nucleus onthat side.

Primary pathwaySecondary pathway

Motor output

Vestibulocochlearnerve (VIII)


Figure 17-32 Pathways for Auditory Sensations

KEYPrimary pathwaySecondary pathwayMotor output

Motor outputto spinal cordthrough the

tectospinal tracts

To reticular formation and motor nuclei of cranial nerves

Information ascends from each cochlearnucleus to the inferior colliculi of the midbrain.

The inferior colliculi direct a variety ofunconscious motor responses to sounds.

Ascending acousticinformation goes to themedial geniculate nucleus.

Low-frequencysounds

High-frequency

soundsThalamus

Projection fibers thendeliver the information tospecific locations withinthe auditory cortex of thetemporal lobe.

Tocerebellum


17-5 The Ear

• Hearing Range

• From softest to loudest represents trillionfold increase

in power

• Never use full potential

• Young children have greatest range


Table 17-1 Intensity of Representative Sounds


17-5 The Ear

• Effects of Aging on the Ear

• With age, damage accumulates

• Tympanic membrane gets less flexible

• Articulations between ossicles stiffen

• Round window may begin to ossify

17 the special senses

Documents