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