Chapter 17:
The Special Senses
BIO 210 Lab
Instructor: Dr. Rebecca Clarke
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 organs
 Olfactory epithelium contains
 Olfactory receptors
 Supporting cells
 Basal (stem) cells
 Lamina propria contains
 Areolar tissue
 Blood vessels
 Nerves
 Olfactory glands
Figure 17–1a
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 Eye
 Provide protection, lubrication, support
 Include:
 Palpebrae (eyelids)
 Conjunctiva (superficial epithelium)
 Lacrimal apparatus
Accessory Structures of the Eye
Figure 17–3
Palpebrae:
Superior/Inferior Palpebra
 Continuation of skin
 Separated by palpebral fissure
 Blinking keeps surface of eye
lubricated, free of dust, and
debris
 Can close to protect delicate
surface
Palpebral Structures
 medial canthus and lateral canthus
 where eyelids are connected at corners of eye
 eyelashes
 Hairs that grow along margins of eyelids
 prevent foreign matter from reaching surface of eye
 (lacrimal) caruncle
 soft tissue mass at medial canthus
 contains glands  thick secretions at night  gritty deposits (“sand” in eyes)
Tarsal (Meibomian) Glands
 large sebaceous glands associated with eyelashes
  oily product that keeps eyelids from sticking together
 chalazion – sty; painful, localized swelling associated with
infection of tarsal gland
Eyelid Muscles
 Orbicularis 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
Fornix
 Pocket where palpebral conjunctiva joins ocular conjunctiva
Figure 17–4a
Conjunctivitis (Pinkeye)
 Results from damage to conjunctival surface
Functions of Tears
 reduce friction
 remove debris
 prevent 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 Apparatus
 Tear 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 canthus
 Covers 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 orbit
 Nasolacrimal duct – leads from lacrimal sac to nasal cavity
Tears
 Large quantities of tears go into the nasal cavity  runny
nose
 If lacrimal puncta can’t provide enough drainage, lacrimal
lake overflows and tears run down face
Figure 17–3b
Outer Eye: Contains 3 Layers
 Fibrous tunic (outer)
 Vascular tunic (middle)
 Neural tunic (inner)
Figure 17–4b
Outer Eye: Fibrous Tunic
 Structures:
 Sclera (white of eye)
 Cornea
Figure 17–4b
Outer Eye: Fibrous Tunic
Figure 17–4c
Fibrous Tunic
 Functions:
 Provides mechanical support and physical protection
 Serves as attachment site for extrinsic eye muscles
Fibrous Tunic: Sclera
 dense fibrous CT that covers most of the ocular surface
 thinnest over anterior surface, thickest over posterior near where
optic nerve exits
 surface contains nerves and small blood vessels ( thin red lines
on opaque background)
Fibrous Tunic: Cornea
 Transparent
 overlies iris and pupil
 structurally continuous with sclera
 no blood vessels; obtains nutrients and O2 from tears that
wash surface
 numerous nerve endings so is most sensitive portion of eye
Outer Eye: Vascular Tunic
 Structures:
 Choroid
 Ciliary body (of choroid)
 Iris
Figure 17–4b
Outer Eye: Vascular Tunic
Figure 17–4c
Outer Eye: Vascular Tunic
 Functions:
 Provides route for blood and lymphatic vessels that supply eye
 Regulates amount of light that enters eye
 Controls shape of lens, essential to focusing images on retina
 Secretes and reabsorbs aqueous humor
 Contains many blood vessels, lymphatic vessels and intrinsic
eye muscles
Vascular Tunic: Choroid
 covered by sclera
 supplies O2 and nutrients to retina
Vascular Tunic: Ciliary Body
 Contains:
 Ciliary muscle - extends around outer edge of lens
 Ciliary processes:
 folds of ciliary body
 secrete aqueous humor
 Suspensory ligaments (of lens):
 Attach lens to ciliary processes
 Holds 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: Iris
 Round, colored area visible through transparent cornea; pupil =
central opening
 Contains:
 Pigment cells (melanocytes)
 In CT and epithelium
 Density and distribution determine eye color
 Blood vessels
 Pupillary muscles (smooth muscles)
Pupillary Muscles
 Change pupil diameter (central opening of iris) when they
contract and relax
 Controlled by ANS
Pupillary Muscles
 Constrictor muscles (sphincter):
 Concentric; constrict pupil
 Dilator muscles:
 Radial; dilate/enlarge pupil
Outer Eye: Neural Tunic (Retina)
 Consists of two layers:
 Pigmented part
 Neural part
Figure 17–4b
Outer Eye: Neural Tunic (Retina)
Figure 17–4c
Neural Tunic: Pigmented Part
 Thin outer layer
 Single layer of cells
 Absorbs light that passes through neural part
Neural Tunic: Neural Part
 Thick inner layer with several layers of cells
 Lines posterior cavity
 Contains:
 Photoreceptors = visual (light) receptors
 Rods – light sensitive
 Cones – color sensitive
 Associated neurons (bipolar, horizontal, amacrine cells)
 Blood vessels (supply tissues that line posterior cavity)
Retina
Figure 17–6a
Photoreceptors
 Not evenly distributed
 Optic disk:
 Has no photoreceptors
 origin 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 rods
 fovea (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 Vein
 pass through center of N II (optic nerve)
 emerge on surface of optic disc
 supply 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 Eye
 Eyeball is “hollow” filled with fluid or gelatinous material
 Divided into 2 cavities:
 Smaller anterior cavity
 Large posterior cavity
Figure 17–4b
Anterior Cavity
 Subdivided into:
 anterior chamber:
 extends from cornea to iris
 posterior chamber:
 between iris, ciliary body, and lens
 Filled with aqueous humor
Aqueous Humor
 clear fluid; similar to CSF
 formed by epithelial cells of ciliary processes and secreted into
posterior chamber
 passes between chambers through pupil
 Diffuses 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 Humor
 Functions:
 Circulation provides important route for nutrient and waste
transport
 forms fluid cushion
Intraocular Pressure
 fluid pressure in aqueous humor
 helps retain eye shape
 stabilizes position of retina, pressing neural part against
pigmented part
 inadequate drainage of aqueous humor at canal of Schlemm:
  inc intraocular pressure = glaucoma
 can result in atrophy of optic nerve and blindness
Posterior (Vitreous) Chamber
 Large chamber
 Filled with gelatinous mass (vitreous body/humor)
 Vitreous body:
 formed during development of eye; not replaced
 helps stabilize shape of eye
 gives 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 fibers
 Makes lens spherical when contracted
 Cells in center:
 Have no nuclei or other organelles
 Appear transparent
 Contain transparent proteins (crystallins) that  clarity
and focusing power of lens
Cataract
 Abnormal, cloudy lens with reduced transparency
 Age-, disease-, drug-related
 Most common cause of blindness in adults
Extrinsic Eye Muscles
 External muscles that rotate the eyeball
 Originate on surface of the eyeball
 4 rectus muscles – attach straight behind the eyeball
 superior rectus
 inferior rectus
 medial rectus
 lateral rectus
 2 oblique muscles – that attach from the side of the eyeball
 superior oblique – along medial wall, passes through trochlea (loop on medial wall
of orbit) and turns laterally
 inferior oblique – from lateral wall of orbit, on inferior side of eyeball
Extrinsic Eye Muscles
Extrinsic Eye Muscles
Summary: Extrinsic Eye Muscles
Table 11–3
Ear
 Divided into 3 anatomical regions:
 External/outer ear
 Middle ear
 Inner ear
Figure 17–20
External/Outer Ear
 Visible portion of ear
 Collects and directs sound waves toward middle ear
 Structures:
 Auricle (pinna)
 External acoustic/auditory canal
 Tympanic membrane
External Ear
Figure 17–20
Auricle (Pinna)
 Fleshy, cartilaginous flap
 Surrounds/protects entrance to external acoustic canal
 Provides directional sensitivity
 Blocks sound waves from behind
 Collected from side/front and channeled into canal
External Acoustic Canal
 Passageway from outside to tympanic membrane (eardrum)
Tympanic Membrane
 Thin, delicate, semitransparent sheet
 Separates external ear from middle ear
Ceruminous Glands
 Integumentary glands along external acoustic canal
 Secrete 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 Ear
 Separated from external ear by tympanic membrane
 Collects sound waves and transmits to inner ear
 Air-filled chamber in petrous portion of temporal bone
 Communicates with nasopharynx via auditory (eustachian) tube
 Encloses and protects 3 auditory ossicles
Auditory Tube
 Allows equalization of pressures inside/outside tympanic
membrane
 Also allows microorganisms to invade middle ear  middle
ear infection (otitis media)
Auditory Ossicles
 Connect tympanic membrane to receptor complexes of
the inner ear
 Convert sound waves into mechanical movements
 3 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
movements
 Tensor tympani muscle:
 Inserts on malleus
 Stiffens tympanic membrane
 Stapedius muscle:
 Inserts on stapes
 Reduces movement of stapes at oval window
Inner Ear
Figure 17–20
Inner Ear
 Also in petrous part of temporal bone
 Contains 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 senses
 Receptors = hair cells (simple mechanoreceptors)
 Structures:
 Bony labyrinth
 Membranous labyrinth
Maculae of Hair Cells
Figure 17–23
Inner Ear: 2 Labyrinths
 Labyrinth = network of canals
 Bony labyrinth:
 Surrounds and protects membranous labyrinth
 Inner contours follow contours of membranous labyrinth
 Contains perilymph (similar to CSF) that flows between two
labyrinths
 Membranous labyrinth
 Fluid-filled ducts and chambers inside bony labyrinth
 Site of sensory receptors
 Contains endolymph = fluid with different electrolyte
concentrations than those of body
Inner Ear
Figure 17–22
Inner Ear: Bony Labyrinth
 3 regions:
 Vestibule
 Semicircular canals
 Cochlea
Vestibule
 Bony structure that encloses 2 membranous sacs:
 Utricle – superior, larger, nearer semicircular canals
 Saccule – 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 vestibule
 Enclose 3 semicircular ducts
 Each 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 pea
 Contains 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 window
 Vestibular and tympanic ducts interconnect at tip of cochlear spiral 
one long perilymphatic chamber (contains perilymph)
 Organ of Corti:
 Inside cochlear duct
 Contains hearing receptors
Hearing Process
Figure 17–29
Organ of Corti
Figure 17–27
Organ of Corti
 Inside cochlear duct
 Contains hearing receptors
 Consists 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 Branch
 Carries 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