BIO 210 LabInstructor: Dr. Rebecca Clarke

Chapter 17:The Special Senses

Figure 17–1a

Smell (Olfaction)

Olfactory Organs

Provide sense of smell

Located in nasal cavity on either side of nasal

septum

Made up of two layers

Olfactory epithelium

Lamina propria

Figure 17–1a

Smell (Olfaction)

Layers of olfactory organsOlfactory epithelium contains

Olfactory receptors

Supporting cells

Basal (stem) cells

Lamina propria containsAreolar tissue

Blood vessels

Nerves

Olfactory glands

Smell (Olfaction)

Smell (Olfaction)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

Smell (Olfaction)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

Axons leaving olfactory bulb:

travel along olfactory tract to reach olfactory cortex,

hypothalamus, and portions of limbic system

Accessory Structures of the EyeProvide protection, lubrication, supportInclude:

Palpebrae (eyelids)Conjunctiva (superficial epithelium)Lacrimal apparatus

Figure 17–3

Accessory Structures of the Eye

Palpebrae:Superior/Inferior Palpebra

Continuation of skinSeparated by

palpebral fissureBlinking keeps surface

of eye lubricated, free of dust, and debris

Can close to protect delicate surface

Palpebral Structuresmedial canthus and lateral canthus

where eyelids are connected at corners of eyeeyelashes

Hairs that grow along margins of eyelidsprevent foreign matter from reaching surface of eye

(lacrimal) carunclesoft tissue mass at medial canthuscontains glands thick secretions at night gritty deposits

(“sand” in eyes)

Tarsal (Meibomian) Glandslarge sebaceous glands associated with

eyelashes oily product that keeps eyelids from

sticking togetherchalazion – sty; painful, localized swelling

associated with infection of tarsal gland

Eyelid MusclesOrbicularis oculi – closes eyelids Levator palpebrae superioris – opens

eyelids

Eyelid Muscle:Levator Palpebrae Superioris

Opens eyelid

Eyelid Muscle: Orbicularis Oculi

Closes eyelids

Conjunctiva Epithelium covering:

Inner surfaces of eyelids (palpebral conjunctiva)Anterior surface of eye (ocular conjunctiva)Cornea = corneal epithelium; continuous with

ocular conjunctiva

Figure 17–3b

Figure 17–4a

Fornix

Pocket where palpebral conjunctiva joins ocular conjunctiva

Conjunctivitis (Pinkeye) Results from damage to conjunctival

surface

Functions of Tears

reduce frictionremove debrisprevent bacterial infection ( antibacterial

lysozyme)provide nutrients and O2 to conjunctival

epithelium+ sebum (waxy secretion on hairs) “oil

slick” that lubricates, slows evaporation

Lacrimal Apparatus Structures that produce, distribute, and

remove tears:Lacrimal gland, lake, puncta, canaliculi, sac and

nasolacrimal duct

Figure 17–3b

Lacrimal ApparatusTear gland:

Located in:Lateral depression in frontal bone

Produces tears (watery, slightly alkaline secretion, with antibacterial enzyme)

Lacrimal lake:Where tears accumulate at the medial canthusCovers lacrimal caruncle

Lacrimal puncta – 2 small pores that drain the lacrimal lake; empty into…

Lacrimal canaliculi – small canals that lead to… Lacrimal sac – nestles in lacrimal sulcus of orbitNasolacrimal duct – leads from lacrimal sac to

nasal cavity

Tears Large quantities of tears go into the nasal

cavity runny noseIf lacrimal puncta can’t provide enough

drainage, lacrimal lake overflows and tears run down face

Figure 17–3b

Figure 17–4b

Outer Eye: Contains 3 LayersFibrous tunic (outer)Vascular tunic (middle)Neural tunic (inner)

Figure 17–4b

Outer Eye: Fibrous TunicStructures:

Sclera (white of eye)Cornea

Outer Eye: Fibrous Tunic

Figure 17–4c

Fibrous TunicFunctions:

Provides mechanical support and physical protection

Serves as attachment site for extrinsic eye muscles

Fibrous Tunic: Scleradense fibrous CT that covers most of the

ocular surfacethinnest over anterior surface, thickest over

posterior near where optic nerve exitssurface contains nerves and small blood

vessels ( thin red lines on opaque background)

Fibrous Tunic: CorneaTransparentoverlies iris and pupilstructurally continuous with sclerano blood vessels; obtains nutrients and O2

from tears that wash surfacenumerous nerve endings so is most

sensitive portion of eye

Figure 17–4b

Outer Eye: Vascular TunicStructures:

ChoroidCiliary body (of choroid)Iris

Outer Eye: Vascular Tunic

Figure 17–4c

Outer Eye: Vascular TunicFunctions:

Provides route for blood and lymphatic vessels that supply eye

Regulates amount of light that enters eyeControls shape of lens, essential to focusing

images on retinaSecretes and reabsorbs aqueous humor

Contains many blood vessels, lymphatic vessels and intrinsic eye muscles

Vascular Tunic: Choroid

covered by sclerasupplies O2 and nutrients to retina

Vascular Tunic: Ciliary BodyContains:

Ciliary muscle - extends around outer edge of lens

Ciliary processes:folds of ciliary bodysecrete aqueous humor

Suspensory ligaments (of lens):Attach lens to ciliary processesHolds lens centered on pupil so light passing through

pupil will also pass through lens

Ciliary Body

Figure 17–4c

Ciliary Body

Figure 17–8

Vascular Tunic: IrisRound, colored area visible through

transparent cornea; pupil = central openingContains:

Pigment cells (melanocytes)In CT and epitheliumDensity and distribution determine eye color

Blood vesselsPupillary muscles (smooth muscles)

Pupillary MusclesChange pupil diameter (central opening of

iris) when they contract and relaxControlled by ANS

Pupillary MusclesConstrictor muscles (sphincter):

Concentric; constrict pupilDilator muscles:

Radial; dilate/enlarge pupil

Figure 17–4b

Outer Eye: Neural Tunic (Retina)Consists of two layers:

Pigmented partNeural part

Outer Eye: Neural Tunic (Retina)

Figure 17–4c

Neural Tunic: Pigmented PartThin outer layerSingle layer of cellsAbsorbs light that passes through neural

part

Neural Tunic: Neural PartThick inner layer with several layers of cellsLines posterior cavityContains:

Photoreceptors = visual (light) receptorsRods – light sensitiveCones – color sensitive

Associated neurons (bipolar, horizontal, amacrine cells)

Blood vessels (supply tissues that line posterior cavity)

Retina

Figure 17–6a

PhotoreceptorsNot evenly distributedOptic disk:

Has no photoreceptorsorigin of optic nerve (N II = cranial nerve II)blind spot; don’t notice because involuntary eye

movements keep visual image moving (Fig 17-7 – find your blind spots)

Macula lutea:concentration of cones, no rodsfovea (fovea centralis) – middle of macula lutea,

highest concentration of cones sharpest vision

macular degeneration – age-related deterioration loss of visual field

Optic Disc and Macula Lutea

Figure 17–6b, c

Central Retinal Artery and Veinpass through center of N II (optic nerve)emerge on surface of optic discsupply retina

Optic Chiasma(a)where optic nerves crossover on way to

visual cortex of occipital lobe of cerebrum (Fig 17-19)

Note: brain devotes approx 35% of its power to vision!

Inner EyeEyeball is “hollow” filled with fluid or

gelatinous materialDivided into 2 cavities:

Smaller anterior cavityLarge posterior cavity

Figure 17–4b

Anterior CavitySubdivided into:

anterior chamber: extends from cornea to iris

posterior chamber: between iris, ciliary body, and lens

Filled with aqueous humor

Aqueous Humorclear fluid; similar to CSFformed by epithelial cells of ciliary processes

and secreted into posterior chamberpasses between chambers through pupilDiffuses through anterior chamber walls into

canal of Schlemm:passageway that encircles eye at level of limbus

(where cornea meets sclera)delivers aqueous humor to veins of sclera

Circulation of Aqueous Humor

Ciliary processes posterior chamber pupil anterior chamber canal of Schlemm veins of sclera

Figure 17–8

Aqueous HumorFunctions:Circulation provides important route for

nutrient and waste transportforms fluid cushion

Intraocular Pressure

fluid pressure in aqueous humorhelps retain eye shapestabilizes position of retina, pressing neural

part against pigmented partinadequate drainage of aqueous humor at

canal of Schlemm: inc intraocular pressure = glaucomacan result in atrophy of optic nerve and

blindness

Posterior (Vitreous) ChamberLarge chamberFilled with gelatinous mass (vitreous

body/humor)Vitreous body:

formed during development of eye; not replaced

helps stabilize shape of eyegives additional physical support to retina

Lens Lies posterior to cornea Forms anterior boundary of posterior cavity

Held in place by suspensory ligaments that originate on ciliary body of choroid

Primary function:to focus visual image on photoreceptors

accomplished by changing shape

Lens Structure Consists of concentric layers of precisely organized cells:Covered by fibrous capsule with elastic fibersMakes lens spherical when contracted

Cells in center:Have no nuclei or other organellesAppear transparentContain transparent proteins

(crystallins) that clarity and focusing power of lens

CataractAbnormal, cloudy lens with reduced

transparencyAge-, disease-, drug-relatedMost common cause of blindness in adults

Extrinsic Eye MusclesExternal muscles that rotate the eyeballOriginate on surface of the eyeball4 rectus muscles – attach straight behind the

eyeballsuperior rectusinferior rectusmedial rectuslateral rectus

2 oblique muscles – that attach from the side of the eyeballsuperior oblique – along medial wall, passes through

trochlea (loop on medial wall of orbit) and turns laterallyinferior oblique – from lateral wall of orbit, on inferior side

of eyeball

Extrinsic Eye Muscles

Extrinsic Eye Muscles

Summary: Extrinsic Eye Muscles

Table 11–3

EarDivided into 3 anatomical regions:

External/outer earMiddle earInner ear

Figure 17–20

External/Outer Ear

Visible portion of earCollects and directs sound waves toward

middle earStructures:

Auricle (pinna)External acoustic/auditory canalTympanic membrane

External Ear

Figure 17–20

Auricle (Pinna)Fleshy, cartilaginous flapSurrounds/protects entrance to external

acoustic canalProvides directional sensitivityBlocks sound waves from behindCollected from side/front and channeled

into canal

External Acoustic CanalPassageway from outside to tympanic

membrane (eardrum)

Tympanic MembraneThin, delicate, semitransparent sheetSeparates external ear from middle ear

Ceruminous Glands Integumentary glands along external

acoustic canalSecrete waxy material (cerumen):

With hairs projecting from canal walls, traps foreign objects

Slows growth of microorganisms in canal and reduces chance of infection

Middle Ear

Figure 17–20

Middle EarSeparated from external ear by tympanic

membraneCollects sound waves and transmits to inner

earAir-filled chamber in petrous portion of

temporal boneCommunicates with nasopharynx via auditory

(eustachian) tubeEncloses and protects 3 auditory ossicles

Auditory TubeAllows equalization of pressures

inside/outside tympanic membraneAlso allows microorganisms to invade

middle ear middle ear infection (otitis media)

Auditory OssiclesConnect tympanic membrane to receptor

complexes of the inner earConvert sound waves into mechanical

movements3 tiny bones:

Malleus (hammer) – attaches at 3 places on tympanic membrane;

Incus (anvil) – attaches outer ossicle (malleus) to inner (stapes)

Stapes (stirrup) – edges of base are bound to edges of oval window = opening in bone surrounding inner ear

Note: articulations between auditory ossicles are smallest synovial joints in body

Middle Ear

Figure 17–21

Muscles Protect tympanic membrane and

ossicles from violent movementsTensor tympani muscle:

Inserts on malleusStiffens tympanic membrane

Stapedius muscle:Inserts on stapesReduces movement of stapes at oval window

Inner Ear

Figure 17–20

Inner Ear Also in petrous part of temporal boneContains sensory organs for:

hearing – enables us to detect and interpret sound waves

equilibrium – establishes position of head by monitoring gravity, linear acceleration, rotation

Receptor mechanism same for both sensesReceptors = hair cells (simple

mechanoreceptors)Structures:

Bony labyrinthMembranous labyrinth

Maculae of Hair Cells

Figure 17–23

Inner Ear: 2 Labyrinths Labyrinth = network of canalsBony labyrinth:

Surrounds and protects membranous labyrinthInner contours follow contours of membranous

labyrinthContains perilymph (similar to CSF) that flows

between two labyrinthsMembranous labyrinth

Fluid-filled ducts and chambers inside bony labyrinth

Site of sensory receptorsContains endolymph = fluid with different

electrolyte concentrations than those of body

Inner Ear

Figure 17–22

Inner Ear: Bony Labyrinth3 regions:

VestibuleSemicircular canalsCochlea

Vestibule Bony structure that encloses 2 membranous

sacs:Utricle – superior, larger, nearer semicircular

canalsSaccule – inferior, smaller, closer to cochlea

Receptors (hair cells) clustered in oval structures (maculae)

Provide sensations of gravity and linear acceleration

Connected with endolymphatic duct which ends in endolymphatic sac

Semicircular Canals Continuous with utricle of vestibuleEnclose 3 semicircular ductsEach duct has an ampulla = expanded

region that contains hair cells (sensory receptors)

Receptors in ducts respond to rotation of head

Vestibular Complex Combination of vestibule and semicircular

canals

Cochlea Spiral-shaped bony chamber (“snail shell”)Size of a split peaContains 3 ducts (parts of membranous labyrinth):

Cochlear duct:spiraling central duct within cochlea; contains endolymph;

suspended between…Vestibular duct:

superior to cochlear duct; starts at oval window, and Tympanic duct:

inferior to cochlear duct; ends at round windowVestibular and tympanic ducts interconnect at tip

of cochlear spiral one long perilymphatic chamber (contains perilymph)

Organ of Corti:Inside cochlear ductContains hearing receptors

Hearing Process

Figure 17–29

Organ of Corti

Figure 17–27

Organ of CortiInside cochlear ductContains hearing receptorsConsists of:

Vestibular membrane – separates cochlear duct from vestibular duct

Basilar membrane – separates cochlear duct from tympanic duct

Hair cells – hearing receptors set in rows along basilar membrane

Tectorial membrane – thick membrane above hairs of hair cells; attached to inner wall of cochlea

Cochlear Windows Oval window:

Collagen fibers connect to stapes Round window:

Thin partition that separates air space of middle ear from perilymph of cochlea

Figure 17–20

Vestibulocochlear Nerves (N VIII): Vestibular BranchCarries neural information on orientation

and movement of head

Figure 17–25

Vestibulocochlear Nerves (N VIII): Cochlear Branch

Carries neural signals for hearing

Figure 17–31