powerpoint to accompany hole’s human anatomy and ... 12.1: introduction • general senses •...

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

Chapter 12

*Lecture Outline

*.

2

12.1: Introduction

• General senses

• Receptors that are widely distributed throughout the body

• Skin, various organs and joints

• Special senses

• Specialized receptors confined to structures in the head

• Eyes, ears, nose and mouth

3

12.2: Receptors, Sensation,

and Perception

• Sensory receptors

• Specialized cells or multicellular structures that collect

information from the environment

• Stimulate neurons to send impulses along sensory

(afferent) fibers to the brain

• Sensation

• A feeling that occurs when brain becomes aware of

sensory impulse

• Perception

• A person’s view of the stimulus; the way the brain

interprets the information

4

Pathways From Sensation to Perception

(Example of an Apple)

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

TABLE 12.1 | Information Flow from the Environment Through the Nervous System

Sensory receptors Olfactory receptor

cells

Taste bud receptor cells Rods and cones in retina Hair cells in cochlea

Impulse in sensory fibers Olfactory nerve fibers Sensory fibers in various cranial nerves Optic nerve fibers Auditory nerve fibers

Midbrain and cerebral cortex Midbrain and cerebral cortex

Sensation (new experience,

recalled memory)

A sweet taste A small, round, red object

Information Flow Smell Taste Sight Hearing

Impulse reaches CNS Cerebral cortex Cerebral cortex

A crunching sound

Perception The smell of an apple The taste of an apple The sight of an apple The sound of biting into an apple

A pleasant smell

5

Receptor Types

• Chemoreceptors

• Respond to changes in chemical concentrations

• Pain receptors (nociceptors)

• Respond to chemicals released during tissue damage

• Thermoreceptors

• Respond to changes in temperature

• Mechanoreceptors

• Respond to mechanical forces (touch, stretch, pressure)

• Photoreceptors

• Respond to light

6

Sensory Impulses

• Stimulation of receptor causes local change in its receptor potential

• A graded electrical current is generated that reflects intensity of

stimulation

• If receptor is part of a neuron, the membrane potential may generate

an action potential

• If receptor is not part of a neuron, the receptor potential must be

transferred to a neuron to trigger an action potential

• Peripheral nerves transmit impulses to CNS where they are analyzed

and interpreted in the brain

7

Sensations and Perception

• Projection

• Process in which the brain projects the sensation back to

the apparent source

• It allows a person to pinpoint the region of stimulation

8

Sensory Adaptation

• Ability to ignore unimportant stimuli

• Involves a decreased response to a particular stimulus

from the receptors (peripheral adaptation) or along the

CNS pathways leading to the cerebral cortex (central

adaptation)

• Sensory impulses become less frequent and may cease

• Stronger stimulus is required to trigger impulses

9

12.3: General Senses

• Senses associated with skin, muscles, joints and viscera

• Three (3) groups: • Exteroceptive senses (exteroceptors)

• Senses associated with body surface such as touch,

pressure, temperature, and pain

• Visceroceptive senses (interoceptors)

• Senses associated with changes in the viscera such as

blood pressure stretching blood vessels and ingestion of a

meal

• Proprioceptive senses

• Senses associated with changes in muscles and tendons

such as at joints

10

Touch and Pressure Senses

Free nerve endings

• Common in epithelial

tissues

• Simplest receptors

• Sense itching

Tactile (Meissners) corpuscles

• Abundant in hairless portions of

skin and lips

• Detect fine touch and texture

Lamellated (Pacinian) corpuscles

• Common in deeper subcutaneous

tissues, tendons and ligaments

• Detect heavy pressure and vibrations

11

Touch and Pressure Receptors

Epidermis

Dermis

(a)

(b)

(c)

Section of

skin

Free nerve

endings

Epithelial

cells

Sensory (afferent)

nerve fiber

Epithelial

cells

Tactile

(Meissners)

corpuscle

(touch receptor)

Sensory (afferent)

nerve fiber

Lamellated

(Pacinian)

corpuscle

(pressure receptor)

Connective tissue

cells

Sensory (afferent)

nerve fiber


© Ed Reschke

12

Temperature Senses

• Warm receptors

• Sensitive to temperatures above 25oC (77o F)

• Unresponsive to temperature above 45oC (113oF)

• Cold receptors

• Sensitive to temperatures between 10oC (50oF) and 20oC

(68oF)

• Pain receptors

• Respond to temperatures below 10oC

• Respond to temperatures above 45oC

13

Sense of Pain

• Pain receptors/nociceptors

• Free nerve endings

• Widely distributed

• Nervous tissue of brain lacks pain receptors

• Stimulated by tissue damage, chemical, mechanical forces, or

extremes in temperature

• Adapt very little, if at all

14

Visceral Pain

• Pain receptors are the only receptors in viscera whose

stimulation produces sensations

• Pain receptors respond differently to stimulation

• Pain receptors are not well localized

• Pain receptors may feel as if coming from some other part of

the body

• Known as referred pain…

15

Referred Pain

• May occur due to sensory impulses from two regions

following a common nerve pathway to brain

Appendix

Ureter

Lung and

diaphragm

Heart

Stomach

Pancreas

Colon

Kidney

Urinary bladder

Liver and

gallbladder

Small

intestine Ovary

(female)

Liver and

gallbladder


16

Pain Pathways

• Acute pain fibers

• A-delta fibers

• Myelinated

• Conduct impulses rapidly

• Associated with sharp pain

• Well localized

• Chronic pain fibers

• C fibers

• Unmyelinated

• Conduct impulses more

slowly

• Associated with dull,

aching pain

• Difficult to pinpoint

• Blocked by narcotics

(controlled substances)

• CCC (Chronic, C fibers,

Controlled substances)

17

Regulation of Pain Impulses

• Thalamus

• Allows person to be aware of pain

• Cerebral cortex

• Judges intensity of pain

• Locates source of pain

• Produces emotional and motor responses to pain

• Pain inhibiting substances:

• Enkephalins

• Serotonin

• Endorphins

18

12.1 Clinical Application

Treating Pain

19

Proprioception

• Mechanoreceptors

• Send information to spinal cord and CNS about body

position and length, and tension of muscles

• Main kinds of proprioceptors:

• Pacinian corpuscles – in joints

• Muscle spindles – in skeletal muscles*

• Golgi tendon organs – in tendons*

*considered to be stretch receptors

20

Stretch Receptors

(a)

Muscle spindle Skeletal muscle fiber

Golgi tendon organ

Tendon

(b)

Sensory

(afferent)

nerve fiber

Sensory

nerve endings

Sensory

(afferent)

nerve fiber

Connective

tissue sheath

Intrafusal

fiber

Skeletal muscle

fiber


21

Visceral Senses

• Receptors in internal organs

• Convey information that includes the sense of

fullness after eating a meal as well as the

discomfort of intestinal gas and the pain that

signals a heart attack

22

Summary of Receptors of the

General Senses

23

12.4: Special Senses

• Sensory receptors are within large,

complex sensory organs in the head

• Smell in olfactory organs

• Taste in taste buds

• Hearing and equilibrium in ears

• Sight in eyes

24


Mixed-Up Senses: Synesthesia

http://www.youtube.com/watch?v=FTr1VnXKr4A

http://www.youtube.com/watch?v=FTr1VnXKr4A

25

Sense of Smell

• Olfactory receptors

• Chemoreceptors

• Respond to chemicals dissolved in liquids

• Olfactory organs

• Contain olfactory receptor cells and supporting epithelial

cells

• Cover parts of nasal cavity, superior nasal conchae, and a

portion of the nasal septum

26

Olfactory Receptors


Nasal cavity

Cilia

(b) (a)

Cribriform

plate

Olfactory area of

nasal cavity

Superior nasal

concha

Olfactory

bulb

Olfactory

tract

Nerve fibers within

the olfactory bulb

Olfactory

receptor cells

Columnar

epithelial cells Cribriform

plate

27

Olfactory Nerve Pathways

• Once olfactory receptors are stimulated, nerve impulses

travel through openings in cribiform plates

• Olfactory nerves olfactory bulbs olfactory

tracts limbic system (for emotions) and olfactory

cortex (for interpretation)

28

Olfactory Stimulation

• Olfactory code

• Hypothesis

• Odor that is stimulated by a distinct set of receptor cells and

its associated receptor proteins

• Olfactory organs located high in the nasal cavity above the

usual pathway of inhaled air

• Olfactory receptors undergo sensory adaptation rapidly

• Sense of smell drops by 50% within a second after

stimulation

29

Sense of Taste

• Taste buds

• Organs of taste

• Located on papillae of tongue, roof of mouth, linings of

cheeks and walls of pharynx

• Taste receptors

• Chemoreceptors

• Taste cells – modified epithelial cells that function as

receptors

• Taste hairs –microvilli that protrude from taste cells through

pores of taste buds; sensitive parts of taste cells

30

Taste Receptors

Papillae

(a)

(b)

Connective

tissue

Sensory (afferent)

nerve fibers

Epithelium

of tongue

Supporting

cell

Taste

pore

Taste hair

Taste cell

Taste buds


31

Taste Sensations

• Five primary taste sensations

• Sweet - stimulated by carbohydrates

• Sour - stimulated by acids

• Salty - stimulated by salts

• Bitter - stimulated by many organic compounds

• Umami – stimulated by some amino acids

• Spicy foods activate pain receptors

• Taste receptors undergo rapid adaptation

32

Taste Nerve Pathways

• Sensory impulses from taste receptors travel along:

• Cranial nerves VII, IX, and X to…

• Medulla oblongata to…

• Thalamus to…

• Gustatory cortex (for interpretation)

33


Smell and Taste Disorders

http://www.youtube.com/watch?v=Dm1YahV5JeE

http://www.youtube.com/watch?v=Dm1YahV5JeE

The Importance of Olfaction

Beyond Smell

&

Memory and Smell

34

http://www.youtube.com/watch?v=R-TTHK40u4w

http://www.youtube.com/watch?v=8ybA6SScQ8A







35

Sense of Hearing

• Ear

• Organ of hearing

• Three (3) sections:

• Outer/External ear

• Middle ear

• Inner/Internal ear

36

External Ear

• Auricle

• Collects sounds

waves

• External acoustic meatus

• Lined with

ceruminous glands

• Carries sound to

tympanic membrane

• Terminates with

tympanic membrane

• Tympanic membrane

• Vibrates in response

to sound waves


Round window

Pharynx Auditory tube

Auricle

Oval window

(under stapes)

Cochlea

Malleus

Incus Stapes

External acoustic

meatus

Semicircular

canals

Vestibulocochlear

nerve

Tympanic cavity

Tympanic

membrane

37

Middle Ear


Round window


Auricle

Oval window

(under stapes)

Cochlea

Malleus

Incus Stapes

External acoustic

meatus

Semicircular

canals

Vestibulocochlear

nerve

Tympanic cavity

Tympanic

membrane

• Tympanic cavity

• Air-filled space in

temporal bone

• Auditory ossicles

• Vibrate in response to

tympanic membrane

• Malleus, incus and stapes

• Hammer, anvil and stirrup

• Oval window

• Opening in wall of tympanic

cavity

• Stapes vibrates against it to

move fluids in inner ear

• Tympanic Reflex

• Muscle contractions that occur during loud sounds to tighten bridge of

auditory ossicles

• Muscles involved are tensor tympani and stapedius

38

Middle Ear

Temporal

bone

Malleus

Incus

Tympanic

cavity

Tendon of

stapedius m.

Stapes

Tympanic

membrane

(a)

Auditory

tube

Round

window

Oval window

Tensor tympani m.

Tendon of

tensor tympani m.

Stapedius m.

Stapedius

tendon

Stapes

Incus

(b)


39

Auditory Tube


Round window


Auricle

Oval window

(under stapes)

Cochlea

Malleus

Incus Stapes

External acoustic

meatus

Semicircular

canals

Vestibulocochlear

nerve

Tympanic cavity

Tympanic

membrane

• Also known as the

eustachian tube

• Connects middle ear to

throat

• Helps maintain equal

pressure on both sides of

tympanic membrane

• Usually closed by valve-

like flaps in throat

Inner Ear

• Complex system of

labyrinths

• Osseous labyrinth

• Bony canal in

temporal bone

• Filled with

perilymph

• Membranous labyrinth

• Tube within osseous

labyrinth

• Filled with

endolymph

Cochlear nerve

Maculae

Utricle

(a)

Cochlea

Saccule

Ampullae

Endolymph

Perilymph

Membranous

labyrinth

Bony labyrinth

Vestibular nerve

Scala

vestibuli (cut)

Scala

tympani (cut)

Cochlear

duct (cut)

containing

endolymph

Vestibule Oval

window

Round

window

Semicircular

canals

Bony labyrinth

(contains perilymph)

Membranous labyrinth

(contains endolymph)


40

Inner Ear

Cochlear nerve

Maculae

Utricle

(a)

Cochlea

Saccule

Ampullae

Endolymph

Perilymph

Membranous

labyrinth

Bony labyrinth

Vestibular nerve

Scala

vestibuli (cut)

Scala

tympani (cut)

Cochlear

duct (cut)

containing

endolymph

Vestibule Oval

window

Round

window

Semicircular

canals

Bony labyrinth


Membranous labyrinth



41

• Three (3) parts of labyrinths:

• Cochlea

• Functions in hearing

• Semicircular canals

• Functions in

equilibrium

• Vestibule

• Functions in

equilibrium

42

Cochlea

• Scala vestibuli

• Upper compartment

• Leads from oval

window to apex of

spiral

• Part of bony labyrinth

• Scala tympani

• Lower compartment

• Extends from apex of

the cochlea to round

window

• Part of bony labyrinth

Stapes vibrating in

oval window

Scala vestibuli

filled with perilymph

Vestibular

membrane

Basilar

membrane

Scala tympani

filled with

perilymph

Round window

Helicotrema

Membranous

labyrinth

Cochlear duct

filled with endolymph


43

Cochlea

• Cochlear duct

• Portion of membranous

labyrinth in cochlea

• Vestibular membrane

• Separates cochlear duct

from scala vestibuli

• Basilar membrane

• Separates cochlear duct

from scala tympani

•Tectorial membrane

• Extends partially into

cochlear duct

Spiral organ (organ of Corti)

Basilar membrane

(a)

Scala vestibuli


Vestibular membrane

Cochlear duct


Scala tympani


Branch of

cochlear

nerve


44

Getting a Cochlear Implant

http://www.youtube.com/watch?v=GTKMJ-El0sA

Cochlea




45

Spiral Organ (Organ of Corti)

• Group of hearing receptor cells (hair

cells)

• On upper surface of basilar

membrane, just below tectorial

membrane

• Different frequencies of vibration

move different parts of basilar

membrane

• Particular sound frequencies cause

hairs of receptor cells to bend as they

push up against the tectorial

membrane

• Nerve impulse generated

Spiral organ (organ of Corti)

Hair cells

Basilar membrane

(a)

(b)

Scala vestibuli


Cochlear duct


Scala tympani


Branch of

cochlear

nerve

Tectorial

membrane

Basilar

membrane

Supporting

cells

Nerve

fibers

Branch of

cochlear nerve

Vestibular membrane


46

Spiral Organ (Organ of Corti)

Cochlear duct

Scala tympani Hair cells

(a)

(b)

Basilar

membrane

Tectorial membrane


a: © John D. Cunningham/Visuals Unlimited; b: © Fred Hossler/Visuals Unlimited

47

Spiral Organ (Organ of Corti) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Vestibular

membrane

Malleus Incus

Stapes

Cochlear duct

(endolymph)

Tectorial

membrane

Facial nerve

Oval window

Tympanic

membrane

Tympanic

cavity

Round

window

20,000 cps 1,500 cps 500 cps 20 cps

Receptors

(hair cells)

Scala vestibuli (perilymph)

Scala tympani (perilymph)

48

Auditory Pathways

Midbrain

Pons

Thalamus

Auditory cortex

(temporal lobe)

Medial geniculate

body of thalamus

Superior

olivary

nucleus

Medulla

oblongata

Vestibulocochlear

nerve

Cochlear

nuclei


49


Hearing Loss

50

Summary of the Generation of

Sensory Impulses from the Ear

51

Sense of Equilibrium

• Static equilibrium

• Vestibule

• Senses position of

head when body is not

moving

• Dynamic Equilibrium

• Semicircular canals

• Senses rotation and

movement of head and

body

52

Static Equilibrium

• Macula

• Organ of static

equilibrium

• Hair cells and support

cells in wall of utricle

and saccule

• Utricle and saccule

are portions of the

membranous labyrinth

of the vestibule

• Saccule

Utricle Cochlea

Maculae

Ampullae of

semicircular

canals

Vestibulocochlear

nerve

Cochlear

duct


Vestibule

Macula

• Macula has hair cells

embedded in gelatinous

material filled with

otoliths

• Gravity pulls on

gelatinous mass

• Bending of hairs

results in generation of

nerve impulse

Hair cells

Sensory (afferent) nerve fiber Supporting cells

Otoliths

(a) Head upright (b) Head bent forward

Macula

of utricle

Hairs of

hair cells bend

Gelatinous

material sags

Gravitational

force


53

54

Dynamic Equilibrium

• Three (3) canals at right angles

• Ampulla

• Swelling of membranous

labyrinth that communicates with

the vestibule

• Crista ampullaris

• Sensory organ for dynamic

equilibrium

• Hair cells and supporting cells

• Located in ampulla of each

semicircular canal

• Consists of hair cells whose hairs

extend upward into dome-saped

gelatinous mass (cupula)

• Rapid turns of head or body

stimulate hair cells

• Nerve impulse

Saccule

Utricle Cochlea

Maculae

Ampullae of

semicircular

canals

Vestibulocochlear

nerve

Cochlear

duct


Vestibule

55

Crista Ampullaris

Hair cell

Supporting cells

Sensory (afferent)

nerve fibers

Hairs

Cupula Crista

ampullaris

(a) Head in still position

(b) Head rotating


(c)

Crista ampullaris

Semicircular canal

Endolymph

Ampulla


56

Sense of Sight

• Visual accessory organs

• Eyelids

• Lacrimal apparatus

• Extrinsic eye muscles

Eyelid

• Palpebra

• Composed of four (4) layers:

• Skin

• Muscle

• Connective tissue

• Conjunctiva

• Orbicularis oculi – closes eyelid

• Levator palpebrae superioris –

opens eyelid

• Tarsal glands – secrete oil onto

eyelashes

• Conjunctiva – mucous

membrane; lines eyelid and covers

portion of eyeball

Eyelash

Cornea

Conjunctiva

Eyelid

Tendon of levator

palpebrae superioris

Superior

rectus

Orbicularis

oculi

Inferior

rectus

Tarsal glands


57

Lacrimal Apparatus

• Lacrimal gland

• Lateral to eye

• Secretes tears

• Canaliculi

• Collect tears

• Lacrimal sac

• Collects from

canaliculi

• Nasolacrimal duct

• Collects from lacrimal

sac

• Empties tears into nasal

cavity

Lacrimal gland

Lacrimal sac

Superior and

inferior canaliculi

Nasolacrimal

duct


58

Extrinsic Eye Muscles

Inferior rectus Inferior oblique

Medial

rectus

Superior

rectus

Superior

oblique

Lateral

rectus

(cut)


• Superior rectus

• Rotates eye up and

medially

• Inferior rectus

• Rotates eye down

and medially

• Medial rectus

• Rotates eye

medially

59

Extrinsic Eye Muscles

Inferior rectus Inferior oblique

Medial

rectus

Superior

rectus

Superior

oblique

Lateral

rectus

(cut)


• Lateral rectus

• Rotates eye

laterally

• Superior oblique

• Rotates eye down

and laterally

• Inferior oblique

• Rotates eye up and

laterally

60

61

Structure of the Eye

• Hollow

• Spherical

• Wall has three (3) layers:

•Outer fibrous tunic

•Middle vascular tunic

•Inner nervous tunic

Ciliary body Retina

Choroid coat

Sclera

Fovea centralis

Optic nerve

Lens

Iris

Pupil

Cornea

Lateral rectus

Medial rectus

Optic disc

Posterior cavity

Vitreous humor

Posterior

chamber

Anterior

chamber

Aqueous

humor

Suspensory

ligaments


Anterior

cavity

62

Outer Tunic

Ciliary body Retina

Choroid coat

Sclera

Fovea centralis

Optic nerve

Lens

Iris

Pupil

Cornea

Lateral rectus

Medial rectus

Optic disc

Posterior cavity

Vitreous humor

Posterior

chamber

Anterior

chamber

Aqueous

humor

Suspensory

ligaments


Anterior

cavity

• Cornea

• Anterior portion

• Transparent

• Light transmission

• Light refraction

• Sclera

• Posterior portion

• Opaque

• Protection

• Pierced by optic nerve

and blood vessels

63

Middle Tunic

Ciliary body Retina

Choroid coat

Sclera

Fovea centralis

Optic nerve

Lens

Iris

Pupil

Cornea

Lateral rectus

Medial rectus

Optic disc

Posterior cavity

Vitreous humor

Posterior

chamber

Anterior

chamber

Aqueous

humor

Suspensory

ligaments


Anterior

cavity

• Iris


• In front of lens

• Pigmented

• Controls light intensity

• Ciliary body


• Pigmented

• Holds lens

• Moves lens for focusing

• Choroid coat

• Provides blood supply

• Contains melanocytes

• Pigments absorb extra light

64

Anterior Portion of Eye

• Filled with aqueous humor

Conjunctiva

Iris

Lens

Ciliary process

Ciliary muscles

Sclera

Cornea Anterior chamber

Vitreous

humor

Suspensory

ligaments

Posterior

chamber

Ciliary

body


65

Lens

Conjunctiva

Iris

Lens

Ciliary process

Ciliary muscles

Sclera

Cornea Anterior chamber

Vitreous

humor

Suspensory

ligaments

Posterior

chamber

Ciliary

body


Transparent, Biconvex , Lies behind iris, Composed of lens fibers,

Elastic, Held in place by suspensory ligaments of ciliary body

66

Ciliary Body

• Forms internal ring around the front of the eye

• Ciliary processes – radiating folds

• Ciliary muscles – contract and relax to move lens

Retina

Choroid coat

Sclera

Lens

Ciliary processes

of ciliary body

Suspensory

ligaments


67

Accommodation

• Lens changes shape to view objects

(a)

Lens thick

Lens thin

(b)

Ciliary muscle

fibers contracted

Suspensory

ligaments relaxed

Ciliary muscle

fibers relaxed

Suspensory

ligaments taut


• Lens thickens

when focusing on

close object

• Lens thins when

focusing on distant

objects

• Bright light

stimulates circular

muscles and pupil

constricts

68

Iris

Sympathetic

motor nerve

fiber

In dim light


Radially arranged

Smooth muscle fibers

of the iris

Circularly arranged

smooth muscle fibers

of the iris

Pupil

In normal light In bright light

Parasympathetic

ganglion

Parasympathetic

motor nerve fiber

• Composed of

connective tissue and

smooth muscle

• Pupil is hole in iris

• Dim light stimulates

radial muscles and

pupil dilates

• Bright light

stimulates circular

muscles and pupil

constricts

• Amount and

distribution of

melanin helps

determine eye color

69

Aqueous Humor

• Fluid in anterior cavity of eye

• Secreted by epithelium on inner surface of the ciliary body

• Provides nutrients

• Maintains shape of anterior portion of eye

• Leaves cavity through Canal of Schlemm

Sclera

Iris

Lens

Aqueous humor

Cornea

Vitreous humor

Ciliary process

Ciliary muscles


Posterior

chamber

Ciliary

body

Scleral venous sinus

(canal of Schlemm)

Anterior

chamber

70

Inner Tunic

• Retina

• Contains visual receptors

• Continuous with optic nerve

• Ends just behind margin of the ciliary body

• Composed of several layers

• Macula lutea – yellowish spot in retina

• Fovea centralis – center of macula lutea; produces

sharpest vision

• Optic disc – blind spot; contains no visual receptors

• Vitreous humor – thick gel that holds retina flat against

choroid coat

71

Posterior Cavity

• Contains vitreous humor – thick gel that holds retina flat

against choroid coat

Ciliary body

Retina

Choroid coat

Sclera

Fovea centralis

Optic nerve

Lens

Iris

Pupil

Cornea

Lateral rectus

Medial rectus

Optic disc

Posterior cavity

Vitreous humor

Posterior

chamber

Anterior

chamber

Aqueous

humor

Suspensory

ligaments


Anterior

cavity

72

Major Groups of Retinal Neurons

• Receptor cells, bipolar cells, and ganglion cells - provide pathway

for impulses triggered by photoreceptors to reach the optic nerve

• Horizontal cells and amacrine cells – modify impulses

Sclera

Receptor cells Rod

Cone

Retina Bipolar neuron

Ganglion cell

Nerve fibers

Horizontal cell

Amacrine cell

Light waves

Retinal pigment

epithelium

Pigmented

choroid

coat

Impulses

to optic

nerve

Vitreous humor

Layer of

connecting

neurons


73

Layers of the Eye

74

Light Refraction

• Refraction

• Bending of light

• Occurs when light waves pass at an oblique angle into

mediums of different densities

Light wave

Perpendicular line

Air

Glass

Refracted

light wave


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Types of Lenses

• Convex lenses cause

light waves to converge

• Concave lenses cause

light waves to diverge

Air

Glass

(a) (b) Diverging

light waves

Convex

surface

Light

wave

Converging

light waves

Concave

surface


76

Focusing On Retina

• As light enters eye, it is refracted by:

• Convex surface of cornea

• Convex surface of lens • Image focused on retina is upside down and reversed from left

to right

Light waves

Object Cornea

Image

Retina


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Visual Receptors

• Rods

• Long, thin projections

• Contain light sensitive

pigment called rhodopsin

• Hundreds of times more

sensitive to light than cones

• Provide vision in dim light

• Produce colorless vision

• Produce outlines of objects

• Cones

• Short, blunt projections

• Contain light sensitive

pigments called

erythrolabe, chlorolabe, and

cyanolabe

• Provide vision in bright

light

• Produce sharp images

• Produce color vision

• Fovea centralis contains

just cones

78

Rods and Cones

Cones Rods

Rod

Cone

(c)

Many sensory (afferent)

nerve fibers

(b)

Single sensory

(afferent) nerve fiber

(a)

Retinal

pigment

epithelium


c: © Frank S. Werblin, PhD.

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Refraction Disorders

• Concave lens corrects

nearsightedness

• Convex lens corrects

farsightedness

Light waves

Light waves

Light waves

Cornea Lens

Retina

(a) Eye too long (myopia)

(b) Normal eye

(c) Eye too short (hyperopia)

Point

of focus

Point

of focus

Point

of focus

Light waves

Concave lens

Convex lens

(a)

(b)

Uncorrected

point of focus

Corrected

point of focus

Uncorrected

point of focus

Corrected

point of focus


80

Visual Pigments

• Rhodopsin

• Light-sensitive pigment in rods

• Decomposes in presence of light

• Triggers a complex series of

reactions that initiate nerve

impulses

• Impulses travel along optic nerve

• Pigments on cones

• Each set contains different light-

sensitive pigment

• Each set is sensitive to different

wavelengths

• Color perceived depends on

which sets of cones are stimulated

• Erythrolabe – responds to red

• Chlorolabe – responds to green

• Cyanolabe – responds to blue

81

Rod Cells

Mitochondria

Nucleus

Discs of

membrane

within cell

Synaptic

ending


82

Stereoscopic Vision

• Provides perception of distance and depth

• Results from formation of two slightly different retinal images

Light

waves

Right eye Left eye


83

Visual Nerve Pathway

Optic tract

Eye

Fibers from

nasal (medial) half

of each retina

crossing over

Visual cortex of

occipital lobe

Lateral

geniculate

body of

thalamus

Optic

chiasma

Optic

nerve

Optic

radiations


84

12.5: Lifespan Changes

• Age related hearing loss due to:

• Damage of hair cells in organ of Corti

• Degeneration of nerve pathways to the brain

• Tinnitus

• Age-related visual problems include:

• Dry eyes

• Floaters (crystals in vitreous humor)

• Loss of elasticity of lens, decreasing accommodation

• Glaucoma

• Cataracts

• Macular degeneration

•Age related smell and taste problems due to:

• Loss of olfactory receptors

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Important Points in Chapter 12:

Outcomes to be Assessed

12.1: Introduction

Differentiate between general senses and special senses.

12.2: Receptors, Sensation, and Perception

Name the five types of receptors and state the function of each.

Explain how receptors trigger sensory impulses.

Explain sensation and adaptation.

12.3: General Senses

Describe the differences among receptors associated with the senses

of touch, pressure, temperature, and pain.

Describe how the sensation of pain is produced.

Explain the importance of stretch receptors in muscles and tendons.

86

Important Points in Chapter 12:

Outcomes to be Assessed

12.4: Special Senses

Explain the relationship between the senses of smell and taste.

Describe how the sensations of smell and taste are produced and

interpreted.

Name the parts of the ear and explain the function of each part.

Distinguish between static and dynamic equilibrium.

Describe the roles of the accessory organs to the eye.

Name the parts of the eye and explain the function of each part.

Explain how the eye refracts light.

Explain how the brain perceives depth and distance.

Explain the visual nerve pathways.

12.5: Life-Span Changes

Describe aging-associated changes that diminish the senses.

87

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Quiz 12

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