Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 8
Special Senses
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slides 8.1 – 8.54
Special Senses
Lecture Slides in PowerPoint by Jerry L. Cook
The SensesThe Senses
General senses of touch
Temperature
Pressure
Pain
Special senses
•Special sensereceptors are eitherlarge, complexsensory organs
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Special senses
Smell
Taste
Sight
Hearing
Equilibrium
sensory organs(eyes and ears) orlocalized clusters orreceptors (tastebuds and olfactoryepithelium)
The Eye and VisionThe Eye and Vision
70 percent of all sensory receptors arein the eyes
Each eye has over a million nerve fibers
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Each eye has over a million nerve fibers
Protection for the eye
Most of the eye is enclosed in a bony orbit
A cushion of fat surrounds most of the eye
Accessory Structures of the EyeAccessory Structures of the Eye Eyelids
Eyelashes
Meibomian glands– modifiedsebaceous
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sebaceousglandsproduce anoily secretionto lubricatethe eye Figure 8.1b
Accessory Structures of the EyeAccessory Structures of the Eye
Ciliary glands – modified sweat glandsbetween the eyelashes
Conjunctiva
Membrane thatlines the eyelids
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lines the eyelids
Connects to thesurface of the eye
Secretes mucusto lubricate the eye
Figure 8.1b
Accessory Structures of the EyeAccessory Structures of the Eye
Lacrimalapparatus
Lacrimal gland –produces lacrimal
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produces lacrimalfluid
Lacrimal canals –drains lacrimalfluid from eyes
Figure 8.1a
Accessory Structures of the EyeAccessory Structures of the Eye
Lacrimal sac –provides passageof lacrimal fluidtowards nasalcavity
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cavity
Nasolacrimal duct– empties lacrimalfluid into the nasalcavity
Figure 8.1a
Function of the Lacrimal ApparatusFunction of the Lacrimal Apparatus
Properties of lacrimal fluid
Dilute salt solution (tears)
Contains antibodies and lysozyme
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Contains antibodies and lysozyme
Protects, moistens, and lubricates theeye
Empties into the nasal cavity
Extrinsic (External) Eye MusclesExtrinsic (External) Eye Muscles
Muscles attach to the outer surface of theeye
Produce gross eye movements and make itpossible to follow moving objects
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Figure 8.2
Structure of the EyeStructure of the Eye
The wall is composed of three tunics – coatswhile the interior is filled with fluids called humors
Fibrous tunic (sclera)–outside layer
Choroid –
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Choroid –middlelayer
Sensorytunic –insidelayer Figure 8.3a
The Fibrous TunicThe Fibrous Tunic
Sclera
White connective tissue layer
Seen anteriorly as the “white of the eye”
Cornea
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Cornea
Transparent, central anterior portion
Allows for light to pass through
Repairs itself easily
The only human tissue that can be transplantedwithout fear of rejection – no blood vessels
Choroid LayerChoroid Layer
Blood-rich nutritive tunic
Dark pigment prevents light from scatteringinside the eye
Modified interiorly into two structures
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Ciliary body – smooth muscle to which the lendsis attached
Iris
Pigmented layer that gives eye color
Pupil – rounded opening in the iris for light toenter
Sensory Tunic (Retina)Sensory Tunic (Retina)
Contains receptor cells (photoreceptors)
Rods
Cones
Signals pass from photoreceptors via a
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Signals pass from photoreceptors via atwo-neuron chain
Bipolar neurons
Ganglion cells
Signals leave the retina toward the brainthrough the optic nerve
Neurons of the RetinaNeurons of the Retina
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Figure 8.4
Neurons of the Retina and VisionNeurons of the Retina and Vision
Rods
Most are found towards the edges of theretina
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retina
Allow dim light vision and peripheral vision
Perception is all in gray tones
Neurons of the Retina and VisionNeurons of the Retina and Vision
Cones
Allow for detailed color vision in bright light
Densest in the center of the retina
Fovea centralis – area of the retina with
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Fovea centralis – area of the retina withonly cones – lateral to each blind spot
No photoreceptor cells are at the opticdisk, or blind spot – where the opticnerve leaves the eyeball
Cone SensitivityCone Sensitivity There are three types of
cones
Different cones aresensitive to differentwavelengths
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wavelengths
Color blindness is the resultof lack of one cone type
Impulses received at thesame time are interpretedas intermediate colors
Figure 8.6
LensLens
Biconvex crystal-like structure
Held in place by a suspensory ligamentattached to the ciliary body
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Figure 8.3a
Internal Eye Chamber FluidsInternal Eye Chamber Fluids
Aqueous humor
Watery fluid found in chamber between thelens and cornea
Similar to blood plasma
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Similar to blood plasma
Helps maintain intraocular pressure
Provides nutrients for the lens and cornea
Reabsorbed into venous blood through thecanal of Schlemm
Internal Eye Chamber FluidsInternal Eye Chamber Fluids
Vitreous humor
Gel-like substance behind the lens
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Gel-like substance behind the lens
Keeps the eye from collapsing inward byreinforcing it internally
Lasts a lifetime and is not replaced
Internal Eye Chamber FluidsInternal Eye Chamber Fluids
Cataracts form when thelens becomes increasinglyhard and opaque over timerequiring a transplant orspecial glasses
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special glasses
Glaucoma results when the drainage ofaqueous humor is blocked and pressurewithin the eye increases dramatically andcompresses the delicate retina and opticnerve causing pain and blindness
Lens AccommodationLens Accommodation
Light must be focusedto a point on the retinafor optimal vision –done by the lens
The resting eye is setfor distance vision
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for distance vision(over 20 ft away)
The lens must changeshape to focus forcloser objects –accommodation
Figure 8.9
Images Formed on the RetinaImages Formed on the Retina
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Figure 8.10
•Real image (reversed left to right, andupside down) formed on the retina
Visual PathwayVisual Pathway
Photoreceptors ofthe retina
Optic nerve
Optic nerve crosses
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Optic nerve crossesat the optic chiasmato the opposite side
Fiber tracts thatresult are the optictracts
Figure 8.11
Visual PathwayVisual Pathway Optic tracts contains fibers
from the lateral side of theeye on the same side andthe medial side of theopposite eye
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The optic tract fiberssynapse with neurons inthe thalamus, whose axonsform optic radiation
Visual cortex of theoccipital lobe
Figure 8.11
Eye ReflexesEye Reflexes
Internal muscles are controlled by theautonomic nervous system
Bright light causes pupils to constrict throughaction of radial and ciliary muscles –photopupillary reflex
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Viewing close objects causes accommodation– accommodation pupillary reflex
External muscles control eye movement tofollow objects
Viewing close objects causes convergence(eyes moving medially (toward nose))
The EarThe Ear
Houses two senses
Hearing
Equilibrium (balance)
Receptors are mechanoreceptors –
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Receptors are mechanoreceptors –respond to physical forces
Although these two sense organs arehoused together in the ear, their receptorsrespond to different stimuli and areactivated independently
Anatomy of the EarAnatomy of the Ear
The ear is divided intothree areas
Outer (external)ear
Middle
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Middleear
Inner (internal)ear
Outer and middle ear structures involved inhearing only while inner ear functions in bothequilibrium and hearing
Figure 8.12
The External EarThe External Ear
Structures ofthe external ear
Pinna (auricle) –the ear
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Externalauditory canal
Figure 8.12
The External Auditory CanalThe External Auditory Canal
Narrow chamber in the temporal bone
Lined with skin
Ceruminous (wax) glands are present
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Ceruminous (wax) glands are presentthat secrete earwax – cerumen
Ends at the tympanic membrane(eardrum) where sound waves hit andcause vibrations
The Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity Air-filled cavity within the temporal bone
Two tubes are associated with the inner ear– the oval window and the inferior, membrane-covered round window
The opening from the auditory canal is
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The opening from the auditory canal iscovered by the tympanic membrane
The auditory tube connecting the middle earwith the throat
Allows for equalizing pressure during yawningor swallowing – This tube is otherwisecollapsed
Bones of the Tympanic CavityBones of the Tympanic Cavity
Three bones spanthe cavity – theossicles
Malleus (hammer)
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Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Figure 8.12
Bones of the Tympanic CavityBones of the Tympanic Cavity
Vibrations fromeardrum movethe malleus
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the malleus
These bonestransfer soundto the inner ear
Figure 8.12
Inner Ear or Bony LabrynthInner Ear or Bony Labrynth
A maze of bony chambers within the temporalbone called the osseous or bony labyrinth
Cochlea
Vestibule
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Vestibule
Semicircularcanals
Filled with a plasma-like fluid called perilymph
Inside is a membranous labyrinth that containsa thicker fluid called endolymph
Figure 8.12
Organs of HearingOrgans of Hearing
Organ of Corti
Located within the cochlea
Receptors = hair cells on the basilarmembrane – hearing receptors
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membrane – hearing receptors
Gel-like tectorial membrane is capable ofbending hair cells
Cochlear nerve attached to hair cellstransmits nerve impulses to auditory cortexon temporal lobe
Organs of HearingOrgans of Hearing
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Figure 8.13
Mechanisms of HearingMechanisms of Hearing
Vibrations from sound waves movetectorial membrane
Hair cells are bent by the membrane
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An action potential starts in the cochlearnerve
Continued stimulation can lead toadaptation – stop responding to thosesounds
Mechanisms of HearingMechanisms of Hearing
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Figure 8.14
Organs of EquilibriumOrgans of Equilibrium
Receptor cells are in two structures
Vestibule
Semicircular canals
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Figure 8.16a, b
Organs of EquilibriumOrgans of Equilibrium
Equilibrium has two functional parts
Static equilibrium
Dynamic equilibrium
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Figure 8.16a, b
Static EquilibriumStatic Equilibrium
Maculae – receptors in the vestibule
Report on the position of the head with respect togravity – help determine up from down
Send information via the vestibular nerve
Anatomy of the maculae
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Anatomy of the maculae
Hair cells are embedded in the otolithic membrane
Otoliths (tiny stones) float in a gel around the haircells
Movements cause otoliths to bend the hair cellswhich send impulses along the vestibular nerve tothe cerebellum
Function of MaculaeFunction of Maculae
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Figure 8.15
Dynamic EquilibriumDynamic Equilibrium
Crista ampullaris –receptors in thesemicircular canals
Tuft of hair cells
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Tuft of hair cells
Cupula (gelatinous cap)covers the hair cells
Figure 8.16c
Dynamic EquilibriumDynamic Equilibrium
Receptors respond to angular or rotatorymovements of the head
Action of angular headmovements
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movements
The cupula stimulates thehair cells – gelatinous cap
An impulse is sent via thevestibular nerve to the cerebellum
Figure 8.16c
Chemical SensesChemical Senses –– Taste and SmellTaste and Smell
Both senses use chemoreceptors
Stimulated by chemicals in solution
Taste has four types of receptors
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Taste has four types of receptors
Smell can differentiate a large range ofchemicals
Both senses complement each otherand respond to many of the samestimuli
OlfactionOlfaction –– The Sense of SmellThe Sense of Smell
Olfactory receptors are in the roof of thenasal cavity
Neurons with long cilia – olfactory hairs
Chemicals must be dissolved in mucus for
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Chemicals must be dissolved in mucus fordetection
Impulses are transmitted via the olfactoryfilaments which makes up the olfactory nerve
Interpretation of smells is made in theolfactory cortex
Olfactory EpitheliumOlfactory Epithelium
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Figure 8.17
The Sense of TasteThe Sense of Taste
Taste budshouse thereceptororgans
Location of
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Location oftaste buds
Most are onthe tongue
Soft palate
Inner cheeks Figure 8.18a, b
The Tongue and TasteThe Tongue and Taste
The dorsal tongue is covered withprojections called papillae
Filiform papillae – sharp with no taste buds
Fungiform papillae – rounded with taste
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Fungiform papillae – rounded with tastebuds
Circumvallate papillae – large papillae withtaste buds
Taste buds are found on the sides ofpapillae
Structure of Taste BudsStructure of Taste Buds
The specific cells that respond to chemicaldissolved in saliva are epithelial cells -Gustatory cells are the receptors
Surrounded by supporting cells in the taste
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Surrounded by supporting cells in the tastebud
Have gustatory hairs (long microvilli)
Hairs are stimulated by chemicals dissolved insaliva
Structure of Taste BudsStructure of Taste Buds
Impulses are carried to the gustatorycomplex by several cranial nervesbecause taste buds are found in differentareas
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Facial nerve – anterior tongue specifically
Glossopharyngeal nerve
Vagus nerve
Anatomy of Taste BudsAnatomy of Taste Buds
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Figure 8.18
Taste SensationsTaste Sensations Sweet receptors
Sugars
Saccharine
Some amino acids
Sour receptors
•May respond to the OH-
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Sour receptors
Acids
May respond to the H+
Bitter receptors
Alkaloids
Salty receptors
Metal ions in solution
Developmental Aspects of theDevelopmental Aspects of theSpecial SensesSpecial Senses
Formed early in embryonic development
Eyes are outgrowths of the brain
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Eyes are outgrowths of the brain
All special senses are functional at birth