16-chapt18 lecture - Nassau Community College [Compatibility...• Some receptors are free nerve...

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Chapter 18

Lecture Outline

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

See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without

notes.

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18.1 Sensory Receptors and Sensations

• Sensory Receptors

– Specialized cells to detect specific stimuli

– Interoceptors - detect stimuli inside body

• Include receptors for blood pressure, blood volume, and blood pH

• Directly involved in homeostasis, regulated by negative feedback

– Exteroceptors - detect stimuli outside body

• Include receptors for taste, smell, vision, hearing, and equilibrium

• Function to inform CNS about environmental state

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Types of Sensory Receptors

• Chemoreceptors respond to chemicals.

– Taste, smell, blood pH

• Photoreceptors respond to light energy.

– Vision (light)

• Mechanoreceptors are stimulated by mechanical forces.

– Hearing, gravity, motion, body position

• Thermoreceptors are stimulated by changes in

temperature.

• Located in the hypothalamus and skin

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How Sensation Occurs

• Detection occurs when environmental changes, such as pressure to the fingertips or

light to the eye, stimulate sensory receptors.

• Sensation occurs when nerve impulses arrive

at the cerebral cortex of the brain.

• Perception occurs when the brain interprets

the meaning of stimuli.

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stimulusPeripheral

Nervous System

sensory receptor

nerve impulses

along sensory

fiber

brain

spinal cord

Central

Nervous System


Figure 18.1

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• We are aware of a reflex action when sensory information reaches the brain.

• The brain integrates this information with other

information received from other sensory receptors.

• Some receptors are free nerve endings.

• Others are specialized cells associated with neurons.

• The plasma membrane of a sensory receptor contains proteins that react to the stimulus.

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• Sensory Transduction

– Energy from a chemical or physical stimulus is

converted into an electrical signal (nerve

impulse).

• The stronger the stimulus, the more frequent the action potentials.

– The sensation that results depends on the part of

the brain receiving the nerve impulse.

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• Integration occurs before sensory receptors initiate nerve impulses.

– Summing up of environmental signals by sensory

receptors

– Sensory Adaptation

• Decrease in response to a stimulus (not being

consciously aware of a stimulus)

• Two possible explanations

– Sensory receptors have stopped sending impulses.

– The thalamus has filtered out the ongoing stimulus.

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18.2 Somatic Senses

• Somatic senses are those whose receptors

are associated with the skin, muscles, joints and viscera.

• Three types of somatic sensory receptors

– Proprioceptors

– Cutaneous receptors

– Pain receptors

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Proprioceptors

• Proprioceptors are mechanoreceptors

involved in reflex actions.

– Help maintain muscle tone

– Muscle spindles increase the degree of muscle

contraction

– Golgi tendon organs decrease the degree of

muscle contraction

– Result is proper muscle length and tension (tone)

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Muscle Spindle

tendon

1

2

1

2

3

muscle spindle

muscle fiber

bundle of

muscle fibers

Golgi tendon organ

sensory neuron

to spinal cord

quadriceps

muscle


Figure 18.2

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Cutaneous Receptors

• Both layers of the skin contain cutaneous receptors.

– Fine touch receptors

• Meissner corpuscles and Krause end bulbs -fingertips, lips, palms, penis, clitoris

• Merkel disks - junction of epidermis and dermis

• Root hair plexus - free nerve endings at base of follicles

– Allows sensation when hair is touched

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Cutaneous Receptors

• Pressure receptors

– Pacinian corpuscles - onion-shaped, deep in

dermis

– Ruffini endings - encapsulated receptors with complex nerve networks

• Temperature receptors - free nerve endings

– Some respond to cold; more numerous

– Some respond to warmth

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epidermis

dermis

Cutaneous Receptors in theHuman Skin


Figure 18.3

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Cutaneous Receptors in the Human Skin

free nerve endings

(pain, heat, cold)

Merkel disks (touch)

Krause end

bulbs (touch)

root hair

plexus (touch)

epidermis

Meissner

corpuscles (touch)

Pacinian corpuscles

(pressure)

Ruffini endings

(pressure)

dermis


Figure 18.3

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Pain Receptors

• Pain receptors (or free nerve endings – nociceptors)

– Stimulated by chemicals released by damaged

tissue

– Alert us to possible danger

– Referred pain

• In some areas stimulation of internal pain receptors is

also perceived as pain from the skin.

• Most likely explanation is that impulses from internal pain

receptors also synapse in cord with neurons receiving

pain impulses from the skin.

– Ex: pain originating in heart is also referred to left arm and

shoulder

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18.3 Senses of Taste and

Smell• Taste and smell are called chemical senses

because their receptors are sensitive to

molecules in the food we eat and in the air we breathe.

• Taste cells and olfactory cells are classified as chemoreceptors.

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Sense of Taste

• Taste buds contain chemoreceptors and are located primarily in the tongue.

– Many lie along the walls of the papillae.

• Isolated taste buds are also found in the hard palate, pharynx, epiglottis.

– Different receptors exist for salty, sour, bitter, sweet tastes and umami.

• “Umami” receptors detect the amino acid glutamate

– Present in the flavor enhancer monsodium glutamate

(MSG)

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How the Brain Receives Taste Information

• Taste buds open at a taste pore.

– The taste pore is surrounded by supporting cells

and taste cells.

– Taste cells have microvilli with receptors.

– The gustatory cortex interprets as particular tastes.

– The brain appears to survey the overall pattern of

incoming impulses and takes a “weighted average”

is the perceived taste.

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Taste Buds in Humansepiglottistonsils

Tongue


Figure 18.4a

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Taste Buds in Humans

papillae10µm

Papillae

© Omikron/SPL/Photo Researchers, Inc.


Figure 18.4b

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Taste Buds in HumansCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Taste buds

taste bud

© Omikron/SPL/Photo Researchers, Inc.Figure 18.4c

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taste cellOne taste bud

connective tissue microvilli

sensory nerve fiber supporting cell taste pore

Figure 18.4d

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epiglottistonsils

taste cell

a. Tongue

papillae10µµµµm

b. Papillae c. Taste buds d. One taste bud

connective tissue microvilli

sensory nerve fiber supporting cell taste pore

taste bud

© Omikron/SPL/Photo Researchers, Inc.

Figure 18.4

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Sense of Smell

• Sense of smell

– 80-90% of what we perceive as taste is due actually to smell.

– Olfactory cells

• Chemoreceptors (modified neurons) are located high in the nasal cavity.

• Olfactory cells have a tuft of olfactory cilia with receptors for odor molecules.

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How the Brain Receives Odor Information

• Each olfactory cell has only one out of about 1,000 different types of receptor proteins.

• Nerve fibers lead to the olfactory bulb, an extension of the brain.

• A single odor is composed of many different molecules which activate a characteristic combination of receptor proteins.

• An odor’s “signature” is interpreted by the brain.

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Olfactory Cell Location and AnatomyCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

frontal lobe ofcerebral hemisphere

olfactory bulb

olfactory epithelium

nasal cavity

odormolecules

Figure 18.5a

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odor molecules

sensorynerve fibers

olfactoryepithelium

supporting

cell

olfactory

cell

olfactory cilia ofolfactory cell

olfactory bulb neuron olfactory tract

Figure 18.5b

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odor molecules

a.

frontal lobe ofcerebral hemisphere

olfactory bulb

olfactory epithelium

nasal cavity

odormolecules

sensorynerve fibers

olfactoryepithelium

b.

supporting

cell

olfactory

cell

olfactory cilia ofolfactory cell

olfactory tractneuronolfactory bulb

Figure 18.5

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18.4 Sense of Vision

• Vision requires the work of the eyes and the

brain.

• It is believed that at least a third of the

cerebral cortex takes part in processing

visual information.

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Anatomy and Physiology of the Eye

• The eye is an elongated sphere about 2.5 cm in diameter made of three layers.

– Sclera – outer layer, white and fibrous

• The cornea is made of transparent collagen fibers.

• The conjuctiva is a membrane that covers the sclera.

– Choroid –middle layer, darkly pigmented and vascular

• Toward the front, the choroid becomes a donut-shaped iris.

• The iris contains smooth muscle to control the size of the pupil.

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• Choroid (continued)

– Behind the iris, the choroid thickens into the ciliary body.

– The ciliary body contains the ciliary muscle, which controls the lens shape for near and far vision.

– The lens divides the eye into two compartments.

• The anterior compartment is in front of the lens and is filled with aqueous humor, a clear watery fluid.

• The posterior compartment is behind the lens.

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• Retina – the third layer, located in the posterior compartment

– Filled with a clear, gelatinous material, vitrous humor

– Contains photoreceptor cells, rods and cones

– Has a special region called the fovea centralis, where cone cells are densely packed

– Optic nerve, which takes impulses to the visual cortex, is formed from sensory nerve fibers from the retina.

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Function of the Lens

• Lens focuses images on the retina

– Starts with the cornea and continues as the rays pass through the lens and humors

• Visual accommodation

– For viewing close objects

• Lens rounds up to bring the image into focus on retina

• Lens shape is controlled by the ciliary muscle

• Ciliary muscle contracts and lens rounds up to elasticity

• Elasticity of the lens may decrease with age

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pupil

lens

iris

sclera

choroid

retina

retinal blood

vessels

optic nerve

fovea centralis

posterior compartment

filled with vitreous humor

retina

choroid

sclera

anterior

compartment

filled with

aqueous humor

suspensory

ligament

ciliary body

cornea

Anatomy of the Human EyeCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Figure 18.6

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Functions of the Parts of the Eye

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Focusing the Human EyeCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

ciliary muscle relaxed

lens flattened

light rays

suspensory ligament tautFocusing on

distant object

Figure 18.7a

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Focusing the Human EyeCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

ciliary muscle contracted

ciliary body

lens rounded

suspensory ligament relaxedFocusing on

near object

Figure 18.7b

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Focusing the Human Eyeciliary muscle relaxed

lens flattened

light rays

suspensory ligament taut

ciliary muscle contracted

ciliary body

lens rounded

suspensory ligament relaxedb. Focusing on

near object

a. Focusing on

distant object


Figure 18.7

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Visual Pathway to the Brain

• Vision begins once light has been focused on photoreceptors in the retina.

• Some integration occurs in the retina, where

nerve impulses begin.

• Then the optic nerve transmits the integrated impulses to the brain.

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• Function of photoreceptors

– Rod cells– Visual pigment is rhodopsin

• Very sensitive to light, important for night vision

• Provide peripheral vision and the perception of motion

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– Cone cells

• Located primarily in fovea centralis

• Activated by bright light

• Permits fine detail and color perception

• Three different kinds of cones

– Blue, green and red

– Different combinations of stimulation produce different colors

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Photoreceptors in the EyeCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

cell body

cone cell

rod cell

20 µµµµm

membrane of disk

synapticvesicles

nucleus

outer segment

ion channelsin plasmamembrane

synaptic endings

inner segment

© Lennart Nilsson, from "The Incredible Machine"

Figure 18.8

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Photoreceptors in the Eye

ionchannels

close

lightrays

retinal

opsin

Rhodopsin molecule(opsin + retinal)

membraneof disk


Figure 18.8

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cell body

cone cell

membrane of disk

synaptic

vesicles

nucleus

outer segment

ion channels

in plasma

membrane

synaptic endings

ion

channels

close

light

rays

retinal

opsin

Rhodopsin molecule

(opsin + retinal)

membrane

of disk

20 µm

rod cell

inner segment

© Lennart Nilsson, from "The Incredible Machine"

Figure 18.8

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• Function of the retina

– Three layers of neurons

• Layer closest to choroid contains rods and cones.

• Middle layer is composed of bipolar cells.

• Inner layer is composed of ganglion cells.

– Sensory fibers become the optic nerve

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opticnerve

retina

blindspot

Location of retina

Structure and Function of the RetinaCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Figure 18.9a

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to optic nerve

axons ofganglion cells

light rays

ganglioncell layer

bipolarcell layer

rod celland conecell layer

choroid

Figure 18.9a

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ganglioncell layer

bipolarcell layer

rod celland conecell layer

Micrograph of retina

sclera

choroid

© Biophoto Associates/Photo Researchers, Inc.Figure 18.9b

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optic

nerve

retina

blind

spot

a. Location of retina

to optic nerve

axons of

ganglion cells

light rays

ganglion

cell layer

bipolar

cell layer

rod cell

and cone

cell layer

b . Micrograph of retina

sclera

choroid

b: © Biophoto Associates/Photo Researchers, Inc.

Figure 18.9

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• Function of the retina

– Rod and cone cells synapse with bipolar cells

which synapse with ganglion cells.

• Axons become the optic nerve.

– Sensitivity of cones versus rods is due in part to

how directly they connect to ganglion cells.

• As many as 150 rods may synapse on the same ganglion cell.

• Some cone cells in the fovea centralis activate only one ganglion cell.

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• Blind spot

– No rods and cones where the optic nerve

exits the retina

– No vision is possible in this area

opticnerve

retina

blindspot

Location of retina


Figure 18.9a

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• From the retina to the visual cortex

– Optic nerves from each eye travel to the optic

chiasma.

– Some of the axons cross over at the optic

chiasma.

• Fibers from the right half of each retina join together to form the right optic tract.

• Fibers from the left half of each retina join together to form the left optic tract.

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• From the retina to the visual cortex

• Optic tracts travel around the hypothalamus and

most fibers synapse with nuclei in the thalamus.

– Axons from the thalamic nuclei form optic radiations that carry impulses to the visual area.

– Right and left visual areas must communicate for us to see entire visual field.

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primary visual

area of occipital

lobe

thalamic nucleus

optic tract

optic chiasma

optic nerve

Right

visual

field

Left visual

field

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

Figure 18.10

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18.5 Sense of Hearing

• The ear has two sensory functions -

hearing and balance (equilibrium)

– Sensory receptors for both of these are located in the inner ear.

– Each consists of hair cells with stereocilia(long microvilli) that are sensitive to

mechanical stimulation.

• Mechanoreceptors

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Anatomy of the Ear

• The ear has three divisions

– Outer ear – consists of the pinna

• Pinna collects and funnels sounds to the auditory canal.

• The opening of the canal is lined with fine hairs and sweat glands.

• Modified sweat glands secrete earwax.

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Anatomy of the Ear

• Middle ear – begins at the tympanic membrane and ends at a bony wall with openings called oval

window and round window

– Between the tympanic membrane and oval window are three bones, the ossicles.

• Malleus, incus and stapes

– An auditory tube extends from the middle ear to the nasopharynx, permitting equalization of air pressure.

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Anatomy of the Ear

• Inner ear – the only part that is fluid-filled

– Three areas

• Semicircular canals – role in equilibrium

• Vestibule – role in equilibrium

• Cochlea – role in hearing

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Anatomy of the Human EarCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

earlobe

Outer ear Middle ear

stapes

incus

malleus

Inner ear

semicircular canals

vestibularnerve

cochlearnerve

cochlea

round window auditorytube

tympanicmembrane

auditorycanal

pinna

Figure 18.11

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Auditory Pathway to the Brain

• Through the auditory canal and middle

ear

– Process begins when sound waves enter the auditory canal

– Tympanic membrane (ear drum) begins to vibrate

– Vibrations are amplified across the middle ear bones

– Stapes touches the oval window

– Oval window vibrates and transmits vibrations to fluid inside the cochlea

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• From the cochlea to the auditory cortex

– Cochlea has three fluid-filled canals

• Vestibular canal - fluid is perilymph

• Cochlear canal – fluid is endolymph

– Sense organ for hearing is called organ of Corti

– Hair cells sit on basilar membrane with stereocilia embedded in tectorial membrane

• Tympanic canal - fluid is perilymph

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• From the cochlea to the auditory cortex

– When the stapes strikes the oval window membrane, pressure waves move from the vestibular canal to

tympanic canal across basilar membrane.

– Basilar membrane moves up and down, and the stereocilia in the tectorial membrane bend.

– Then nerve impulses begin in the cochlear nerve and travel to the brain.

– When they reach the auditory cortex in the temporal lobe, they are interpreted as a sound.

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• Each part of the organ of Corti is sensitive to different wave frequencies, or pitch.

• Near the tip, it responds to low pitches.

• Near the base, it responds to higher pitches.

• The pitch sensation depends upon which region of

the basilar membrane vibrates and which area of the auditory complex is stimulated.

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• Volume is a function of the amplitude of sound waves.

– Loud noises cause fluid in the vestibular canal to

exert more pressure and the basilar membrane to vibrate more.

– The brain interprets the increased stimulation as

volume.

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semicircular

canals

oval

window

stapes

round window

cochlea

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

Figure 18.12

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Mechanoreceptors for Hearing

vestibularcanal

cochlearcanal

cochlearnerve

tympaniccanal

Cochlea cross section


Figure 18.12

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hair cell

tectorial membrane

stereocilia

basilarmembrane

cochlear nerve

tympaniccanal

Spiral organ

Figure 18.12

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Stereocilia2 µµµµm

© P. Motta/SPL/Photo Researchers, Inc.

Figure 18.12

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hair cell

semicircularcanals

ovalwindow

stapes

round window

vestibularcanal

cochlearcanal

cochlea

cochlearnerve

tympaniccanal

Cochlea cross section

tectorial membrane

stereocilia

basilarmembrane

cochlear nervetympaniccanal

Spiral organ

Stereocilia2 µµµµm

© P. Motta/SPL/Photo Researchers, Inc.Figure 18.12

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Rotational Equilibrium Pathway

• Three semicircular canals are arranged so that one is in each dimension of space.

• Each semicircular canal has an enlarged base called an ampulla.

– Each ampulla contains hair cells with stereocilia embedded in a

cupula.

• As fluid within a canal flows and bends a cupula, stereocilia are bent; this changes the pattern of impulses carried in vestibular nerve to cerebellum and cerebrum.

– Brain uses this information to make postural corrections

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Gravitational Equilibrium Pathway

• Depends on utricle and saccule

– Utricle is sensitive to horizontal movements of the head.

– Saccule is sensitive to vertical movements of the head.

– Both contain hair cells with stereocilia embedded in an otolithic membrane.

• Large central cilium called the kinetocilium

• Calcium carbonate granules (otoliths) rest on otolithic membrane

– When head or body moves in horizontal or vertical plane, the

otoliths are displaced and the otolithic membrane sags, bending stereocilia.

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

liquid

semicircularcanals

ampullae

cupula

stereocilia

hair cell

supporting cell

vestibular nerve

flow of liquid

receptorinampulla

vestibularnerve

cochlea

Rotational equilibrium: receptorsin ampullae of semicircular canalFigure 18.13a

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liquid

hair cell

otoliths

Gravitational equilibrium: receptorsin utricle and saccule of vestibule

stereocilia

kinocilium

flow of otolithicmembrane

otolithicmembrane

supportingcell

vestibularnerve

utricle

saccule

Figure 18.13b

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liquid

hair cell

otoliths

liquid

semicircularcanals

ampullae

cupula

stereocilia

hair cell

supporting cell

vestibular nerve

flow of liquid

receptorinampulla

vestibularnerve

cochlea

b . Gravitational equilibrium: receptorsin utricle and saccule of vestibulea. Rotational equilibrium: receptorsin ampullae of semicircular canal

stereocilia

kinocilium

flow of otolithicmembrane

otolithicmembrane

supportingcell

vestibularnerve

utricle

saccule

Figure 18.13

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18.7 Disorders that Affect the SensesDisorders of Taste and Smell

• Sense of smell begins to decline after age 60.

• Some people born without sense of smell (anosmia).

• Other factors can contribute to a decrease in ability to taste and/or smell.

– Upper respiratory infections

– Allergies

– Exposure to certain drugs or chemicals (including tobacco smoke)

– Brain trauma

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Disorders of the Eye

• Color blindness and problems with visual

focus are two common abnormalities of the eye.

• More serious disorders can result in blindness.

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Color Blindness

• Complete colorblindness is rare.

– In most instances a particular cone is lacking or

deficient in number.

• Red-green colorblindness is the most

common type.

– X-linked recessive trait

– 5-8% of males

– 0.5% of females

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Testing for Color Blindness

Figure 18.14

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Visual Focus

• Nearsightedness

– Can see close objects better than distant ones

– Eye is elongated so image is brought to point focus in front of the retina

– Corrected by concave lenses which diverge light rays so point focus is farther back

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Visual Focus

• Farsightedness

– Can see distant objects better than close ones

– Eye is shortened so image is brought to point

focus behind the lens

– Corrected by convex lenses to increase bending

of light rays so point focus is farther forward

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Visual Focus

• Astigmatism

– The cornea or lens is uneven, producing a fuzzy image.

– The light rays are not evenly focused on the

retina.

– This can be corrected by wearing an unevenly ground lens to compensate for the uneven cornea.

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Corrective Abnormalities of the Eye

and Possible Corrective LensesCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Concave lens allows subjectto see distant objects.

normaleyeball

Nearsightedness

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

Figure 18.15a

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Convex lens allows subjectto see close objects.

normaleyeball

Short eyeball; rays focus behindretina when viewing close objects.

Farsightedness

Figure 18.15b

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Uneven lens allows subjectto see objects clearly.

Uneven cornea;Rays do not focus evenly.

Astigmatism

Figure 18.15c

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Concave lens allows subjectto see distant objects.

Convex lens allows subjectto see close objects.

Uneven lens allows subjectto see objects clearly.

normaleyeball

a. Nearsightedness

normaleyeball

Short eyeball; rays focus behindretina when viewing close objects.

b.Farsightedness

Uneven cornea;Rays do not focus evenly.

c. Astigmatism

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

Figure 18.15

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Common Causes of Blindness

• Retinal Disorders

– Diabetic retinopathy - capillaries to the retina may become damaged

• Hemorrhages and blocked vessels can occur

– Macular degeneration - cones are destroyed

because thickened choroid vessels no longer function

– Retinal detachment - following trauma, the retina is torn or separated from the choroid

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Common Causes of Blindness

• Glaucoma

– Fluid builds up in the eye because the drainage

system fails

– Causes an increase in pressure

– Nerve fibers associated with peripheral vision are destroyed due to pressure

• Cataracts

– Cloudy spots on lens, eventually cover whole lens

– Risk factors - exposure to UV light, diabetes, heavy alcohol consumption, smoking

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Cataract in a Human Eye

Figure 18.16

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Disorders of Hearing and Equilibrium

• Hearing loss can develop gradually or suddenly

and has many potential causes.

– One in three people over age 60 have hearing loss.

– The middle ear is subject to infections that can lead to impairment if not properly treated.

– The first signs are problems understanding conversation with background noise.

– Hearing problems may begin around age 20.

• Mobility of ossicles decreases with age.

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Disorders of Hearing and

Equilibrium• Sudden Deafness

– Usually occurs in only one ear

– Causes include infections, trauma, and side

effects of some drugs

– Sometimes resolves itself

• Deafness at Birth

– Genetic disorders

– German measles or mumps virus infecting mother during pregnancy

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• Disorders of equilibrium

– Vertigo

• Feeling that a person or the environment is moving when no motion is occurring

• Can be caused by problems in the brain or inner ear

• Benign positional vertigo (BPV) due to particles in semicircular canals

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– Meniere’s Disease

• Caused by an increased fluid volume in the inner ear

• Characterized by vertigo, a feeling of fullness in affected ear(s), tinnitus (ringing in the ears), and hearing loss

16-chapt18 lecture - Nassau Community College [Compatibility...• Some receptors are free nerve...

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