Sense Organs Chapter 38: pp. 701 - 716 1. Outline Chemical Senses Taste Smell Sense of Vision Human Eye Focusing Photoreceptors Sense of Hearing Sense

Sense Organs

Chapter 38: pp. 701 - 716

1

OutlineOutline

Chemical SensesTaste

Smell

Sense of VisionHuman Eye

Focusing

Photoreceptors

Sense of HearingSense of Balance

2

Chemical SensesChemical Senses

Sensory receptors responsible for taste and smell are termed chemoreceptors

Chemoreception is found almost universally in animals

Thought to be most primitive sense

3

Sense of TasteSense of Taste

In humans, taste buds are located primarily on the tongue◦Taste buds open at a taste pore◦Have supporting cells and elongated taste cells

that end in microvilli◦Four primary tastes

Bitter, sour, salty, sweet Taste buds for each are concentrated on the

tongue in particular regions

4

Taste Buds in HumansTaste Buds in Humans

5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

b(All): © Omikron/SPL/Photo Researchers, Inc.b. Papillae d. One taste bud

epiglottistonsils

taste bud

supporting cell

microvillitaste cellconnective tissue

papillae

sensory nerve fiber taste pore

a. Tongue c. Taste buds

10 µm

Sense of SmellSense of Smell

Sense of taste and smell◦Work together to create a combined effect◦Interpreted by the cerebral cortex

Dependent on olfactory cells◦Located within olfactory epithelium◦In the roof of the nasal cavity

Nerve fibers from olfactory cells lead to neuron in the olfactory bulb

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Olfactory Cell Location and Olfactory Cell Location and AnatomyAnatomy

7


olfactory bulb

olfactory epithelium

nasal cavity

olfactory bulb

odor molecules

olfactory tractneuron

a.

b.

frontal lobe ofcerebral hemisphere

odormolecules

olfactory cilia ofolfactory cell

olfactorycell

supportingcell

olfactoryepithelium

sensorynerve fibers

Sense of VisionSense of Vision

Photoreceptors are light sensory receptors◦Photoreceptors generate nerve impulses which

pass to the brain by way of optic nerve fibersArthropods

◦Eyes are compound◦Insects have limited color vision

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Compound EyeCompound Eye

9


crystalline cone

cornea

Fly head Ommatidium

Compoundeye

opticnervefibers

pigmentcells

photoreceptorcells

© Farley Bridges

Nectar GuidesNectar Guides

10


nectar guides

(Both): © Heather Angel/Natural Visions

Sense of VisionSense of Vision

Vertebrates and certain molluscs have a camera-type eye◦Single lens focuses an image of the visual field

on closely-packed photoreceptors

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The Human EyeThe Human Eye

Three Layers◦Sclera - Opaque outer layer

Fibrous layer◦Choroid - Thin middle layer

Iris regulates size of pupil◦Retina - Inner layer

Contains rod cells and cone cells

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Anatomy of the Human EyeAnatomy of the Human Eye

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ciliary body

pupil

cornea

optic nerve

fovea centralis

retina

choroid

sclera

retina

choroid

sclera

lens

iris

retinal bloodvessels

posterior compartmentfilled with vitreous humor

suspensoryligament

anteriorcompartmentfilled withaqueous humor

Focusing the EyeFocusing the Eye

Light rays pass through the pupil and are focused on the retina

Focusing starts at the cornea and continues as rays pass through the lens and humor◦Shape of lens is controlled by ciliary muscles

Distant Object - Muscles Relaxed Near Object - Muscles Contracted

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Focusing the EyeFocusing the Eye

With normal aging, the lens loses its ability to accommodate for near objects◦Also may make lens subject to cataracts

Nearsighted◦Elongated eyeball - Wear concave lenses

Farsighted◦Shortened eyeball - Wear convex lenses

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Functions of the Parts of the Functions of the Parts of the EyeEye

16

Focusing of the Human EyeFocusing of the Human Eye

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light rays

ciliary muscle contracted

lens rounded

suspensory ligament relaxed

ciliary body

ciliary muscle relaxed

lens flattened

suspensory ligament tauta. Focusing on distant object

b. Focusing on near object

Common Abnormalities of the Eye Common Abnormalities of the Eye withwithPossible Corrective LensesPossible Corrective Lenses

18


a. Nearsightedness

b. Farsightedness

normaleyeball

Long eyeball; rays focus in front ofretina when viewing distant objects.

Concave lens allows subjectto see distant objects.

Convex lens allows subjectto see close objects.

Short eyeball; rays focus behindretina when viewing close objects.

normaleyeball

Uneven cornea;rays do not focus evenly.

c. Astigmatism

Uneven lens allows subjectto see objects clearly.

Photoreceptors of the EyePhotoreceptors of the Eye

Both rods and cones have an outer segment joined to an inner segment

Pigment molecules are embedded in membrane of disks in the outer segmentRhodopsin

Rods permit vision in low lightPeripheral vision and motion

Cones permit vision in bright lightFine detail and color

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Photoreceptors in the EyePhotoreceptors in the Eye

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© Lennart Nilsson, from The Incredible Machine

cell body

cone cell

rod cell

nucleus

inner segment

outer segment

synaptic endings

membrane of disk

retinal

opsin

synapticvesicles

20 µm

ion channelsin plasmamembrane

lightrays

membraneof disk

Rhodopsin molecule(opsin + retinal)

ionchannelsclose

Integration of Visual Signals in the Integration of Visual Signals in the RetinaRetinaRetina has three layers of neurons

◦Layer closest to choroid contains rod and cone cells

◦Middle layer contains bipolar cells◦Innermost layer contains ganglion cells

Synaptic integration and processing◦Begin in the retina ◦Then impulses are sent to the brain

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Structure and Function of the Structure and Function of the RetinaRetina

22


to optic nerve

sclera

choroid

retina

choroid

a. Location of retina

b. Micrograph of retina

light rays

axons ofganglion cells

blindspot

opticnerve

ganglioncell layer

bipolarcell layer

rod celland conecell layer

b: © Biophoto Associates/Photo Researchers, Inc.

Sense of Hearing and BalanceSense of Hearing and Balance

Anatomy of the EarOuter ear - Pinna and auditory canalMiddle ear begins at tympanic membrane and ends

at oval and round windowsOssicles found between tympanic membrane and the

windowsAuditory tube (eustachian tube) extends from middle

ear to nasopharynxInner ear has three areas

Semicircular canalsVestibuleCochlea

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Anatomy of the Human EarAnatomy of the Human Ear

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round window

cochlea

earlobe

vestibule

stapes semicircular canals

incus

malleus

Outer ear Middle ear Inner ear

pinna

tympanicmembrane

auditorycanal

auditorytube

cochlearnerve

vestibularnerve

Process of HearingProcess of Hearing

Sound waves enter the auditory canalStrike tympanic membrane, causing it to

vibrate◦Malleus takes pressure from inner surface of

tympanic membrane◦Passes it to the stapes, multiplying the pressure

along the way◦Stapes strikes membrane of oval window,

passing pressure to fluid within cochlea

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AnimationAnimation

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Process of HearingProcess of Hearing

Spiral Organ, hair cells of cochlear canal, synapse with nerve fibers of cochlear nerve

Mechanoreceptors for sound are the hair cells of cochlear canal◦Sound causes basilar membrane to vibrate◦The stereocilia of the hair cells bend◦Stimulates nerve cells leading to the auditory

center

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Mechanoreceptors for Mechanoreceptors for HearingHearing

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2 µm

Cochlea cross section

Organ of Corti

tectorial membrane

hair cell

stereocilia

cochlear nerve

oval window

stapes

cochlea

round window

Stereocilia

semicircularcanals

vestibularcanal

cochlearcanal

tympaniccanal

cochlearnerve

basilarmembrane

tympaniccanal

Sense of BalanceSense of Balance

Mechanoreceptors of rotational equilibrium are in semicircular canalsDetect rotational and/or angular movements of the

headMaintain rotational equilibriumCupula

Mechanoreceptors of gravitational equilibrium are in the utricle and sacculeDetect straight-line movements of the head in any

directionMaintain gravitational equilibrium Otolithic Membrane

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Mechanoreceptors for Mechanoreceptors for EquilibriumEquilibrium

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vestibular nerve

vestibular nerve

receptor in ampulla endolymph

ampullae

cochlea

b.Gravitational equilibrium: receptors in utricle and saccule of vestibule

kinocilium

supporting cell

hair cell

hair cell

otolithscupula

endolymph

flow of endolymph

stereocilia

stereocilia

utricle

saccule

semicircularcanals

otolithicmembrane

supportingcell

vestibularnerve

flow of otolithicmembrane

a. Rotational equilibrium: receptors in ampullae of semicircular canal

Sensory Receptors in Other Sensory Receptors in Other AnimalsAnimals

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hair cells

a.

b.

statolith

ciliaskin

cupula

external openingwater scale

haircell

dendritesof sensoryneurons

lateral linenerve

lateral linecanal

ReviewReview

Chemical SensesTaste

Smell

Sense of VisionHuman Eye

Focusing

Photoreceptors

Sense of HearingSense of Balance

32

Sense Organs

Chapter 38: pp. 701 - 716

33

(Both): Courtesy of The Virginia Bloodhound Search and Rescue Association


Documents

Sense Organs Chapter 38: pp. 701 - 716 1. Outline Chemical Senses Taste Smell Sense of Vision Human Eye Focusing Photoreceptors Sense of Hearing Sense