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Chapter 8

Special Senses

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Outline• Types of Sensory Receptors• Functions of Sensory Receptors• Sensations and Perceptions• Cutaneous Receptors • Sense of Position in Space- Posture• Sense of Taste• Sense of Smell• Sense of Hearing• Sense of Balance (Equilibrium)• Sense of Vision• Homeostasis

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Types of Sensory Receptors• Sensory receptors are specialized to detect certain

types of stimuli. Can be modified dendrites of sensory neurons or specialized cells that release neurotransmitters that stimulate nearby sensory neuron.

– Exteroceptors detect stimuli outside the body. Taste, smell, vision. Indirectly linked to homeostasis.

– Interoceptors detect stimuli inside the body. Blood pressure, blood volume, pH. Directly linked to homeostasis.

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Subtypes of Sensory Receptors• Chemoreceptors.

– Respond to chemical substances in the immediate vicinity.

Pain Receptors (Nociceptors). Respond to chemicals released by damaged

tissue from intense pressure, temperature, light.

• Photoreceptors.– Respond to light energy.

• Mechanoreceptors.– Stimulated by mechanical forces.

• Thermoreceptors.– Stimulated by changes in temperature.

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Functions of Sensory Receptors• To provide information for the proper

maintenance of the body.• Significant contributors to homeostasis.• Interoceptors are directly involved by

monitoring vital functions such as blood pressure and pH.

• Exteroceptors are indirectly involved by monitoring our external environment, but are just as important; we see the oncoming car and get out of the way; we put a coat on so as not to freeze to death.

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Sensations and Perceptions• Sensation occurs when nerve impulses

arrive at the cerebral cortex of the brain.• Perception occurs when the cerebral cortex

interprets the meaning of sensations.– Sensory receptors initiate nerve impulses;

perception depends on the part of the brain receiving the nerve impulses.

– Strength of stimulus related to frequency of firing of nerve impulses.

– Have integration at level of sensory receptor, spinal cord, and brain.

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Cutaneous Receptors

• The dermis contains cutaneous receptors, which include:– Mechanoreceptors.

Sensitive to touch.– Nociceptors.

Sensitive to pain.– Thermoreceptors.

Sensitive to temperature.

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Cutaneous Receptors

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Sense of Position in Space- Posture

• Proprioceptors are mechanoreceptors that help determine limb position in space by detecting the degree of muscle relaxation, stretch of tendons, and movement of ligaments.– Muscle spindles detect the stretching of

muscles; act to increase the degree of muscle contraction.

– Tendon receptors detect the tension in the tendons of muscles; act to decrease it.

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Muscle Spindle

© 2012 Pearson Education, Inc. Figure 12.3

Sensory neurons of muscle spindle

a) Muscle spindle. A muscle spindle responds tomuscle length. Passive stretch of a muscle stretchesthe muscle spindle, stimulating mechanoreceptors inthe nerve endings of the sensory neurons. Conversely,muscle contraction shortens the muscle spindle,reducing muscle spindle mechanoreceptor stimulation.

Muscle spindle

Tendon

Bone

Tendonreceptor

Skeletalmuscle

Tendonconnecting bone tomuscle

b) Tendon receptor. A tendon receptor responds totension in tendons. When a muscle contracts andalso when it is stretched passively, tension on thetendon increases, activating tendon receptors.

Sensory neuronof tendonstretch receptor

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Sense of Taste• Chemoreceptors for taste are found in taste

buds located primarily embedded in tongue epithelium.

Five primary tastes. Sweet. Sour. Salty. Bitter. Umami

Weighted average integrated response.

© 2015 Pearson Education, Inc.

Figure 8.19 Location and structure of taste buds.

Epiglottis

Palatine tonsil

Lingual tonsil

Surface ofthe tongue

Vallate papilla

Epithelium of tongue

Taste bud

Connectivetissue

Gustatory(taste) cell

Basalcell

Sensorynervefiber

Gustatory hairs(microvilli) emergingfrom a taste pore

(c)

Fungiformpapillae

Taste buds(a)

(b)

Sense of Taste

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Sense of Smell• Dependent on chemoreceptors on olfactory

cells located within olfactory epithelium high in the roof of the nasal cavity.

– Each olfactory cell (sensory neuron) has only one type of chemoreceptor; there are ~1500 types; odor made up of multiple molecules; multiple different cells stimulated- integration.

– Olfactory bulbs have direct connections with the limbic system and its centers for emotions and memory.

– Sense of taste and smell work together to create a combined effect.

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Sense of SmellCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

odormolecules

nasal cavity

frontal lobe ofcerebral hemisphere

olfactory bulb neuron olfactory tract

bone ofskull

sensorynerve fibers

olfactoryepithelium

olfactorycell

odor molecules

olfactory cilia ofolfactory cell

b.

a.

supportingcell

olfactory epithelium

olfactory bulb

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Sense of Hearing• Anatomy of the Ear.

– Outer ear: pinna; auditory canal.– Middle ear: tympanic membrane; malleus,

incus, and stapes (ossicles); round window; oval window.

– Inner ear: semicircular canals, vestibule, and cochlea.

© 2015 Pearson Education, Inc.

Figure 8.12 Anatomy of the ear.

External (outer) ear Middle ear

Internal (inner) ear

Vestibulocochlearnerve

SemicircularcanalsOval window

Cochlea

Vestibule

Round window

Pharyngotympanic(auditory) tube

Hammer(malleus)

Anvil(incus)

Stirrup(stapes)

Tympanicmembrane(eardrum)

External acousticmeatus(auditory canal)

Auricle(pinna)

Auditory ossicles

© 2012 Pearson Education, Inc.

Frequency(cycles/sec)

Soft,low tone

Loud,low tone

Soft,high tone

Loud,high tone

Amplitude

Time (msec)

0 1 2 3 4 5

Figure 12.8

© 2012 Pearson Education, Inc.

High-frequencysounds

Low-frequencysounds

Round windowOvalwindow

Soundwave

a) The cochlea as it might appear if it were uncoiled. Higher-frequency sounds are converted to impulses near the oval window, whereas lower-frequency sounds are converted near the tapered tip.

Vestibularcanal

Cochlearduct

Auditory tube

Organof Corti

Hairs ofhair cells

Tectorial membrane

Hair cells

To auditorynerve

Tympaniccanal

Basilarmembrane

Haircells

c) A section through part of the cochlea,showing hair cells with their hairs embeddedin the tectorial membrane. Vibration of thebasilar membrane bends the hairs, ultimatelygenerating impulses in sensory neurons.

b) A cross section through the cochlea. Pressure waves passing from the vestibular canal to the tympanic canal through the cochlear duct cause the basilar membrane to vibrate.

d) SEM ( 4,200) of healthy hair cells.

Figure 12.10

Loudness determined by number of hair cells stimulated.

Pitch determined by region of basilar membrane stimulated.

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© 2012 Pearson Education, Inc. Figure 12.11

“Hairs” ofhair cell

Sensoryneuron

Actionpotentials

Moreneurotransmitter

Lessneurotransmitter

c) Hairs moving in other direction.

b) Hairs moving in one direction.

a) Hair cell at rest.

Neurotransmitter

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Sense of Balance (Equilibrium)

• Rotational Equilibrium– Cupula movement within the semicircular

canals detects rotation and/or angular movement of the head.

• Gravitational Equilibrium.– Movement of the otolithic membrane

within the utricle and the saccule detects position of the head in the vertical and horizontal planes compared to gravity and detects acceleration.

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The inner ear: BalanceCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Flow of otolithicmembrane

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

otoliths

otolithicmembrane

supportingcellvestibularnerve

kinocilium

stereocilia

saccule

utricle

endolymph

hair cell

receptor in ampulla

a. Rotational equilibrium: receptors in ampullae of semicircular canal

Vestibular nerve

Supporting cell

Hair cell

stereocilia

cupula

ampullae

semicircularcanals

Vestibular nerve

cochlea

endolymph

flow of endolymph

The mechanoreceptors of the inner ear and the sense of balance.

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Sense of Vision

• The eyeball has three layers.– Sclera.– Choroid.– Retina.

• The retina contains two types of photoreceptors.– Rod cells.– Cone cells.

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Anatomy of the Human Eye

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Anatomy of the Human Eye (Cont.)

• The Lacrimal Apparatus & Conjunctiva– Lacrimal glands- lateral end of each eye; release tears

continuously, flush across eyes; contains lysozyme- antibacterial protein

– Lacrimal canaliculi- channels that help drain tears– Lacrimal sac- drains tears into nasolacrimal duct– Nasolacrimal duct- tube that conducts tears to nasal

cavity– Conjunctiva- thin membranes line eyelids & covers

surface of eyes; produces mucus, helps lubricate eye movements & keeps surface moist

© 2015 Pearson Education, Inc.

Figure 8.2 Accessory structures of the eye.

Lacrimalgland

Conjunctiva

Anterioraspect

Eyelid

Eyelashes

Tarsalglands

Eyelid(a) (b)

Nostril

Excretory ductof lacrimal gland

Inferior meatusof nasal cavity

Nasolacrimal duct

Lacrimal canaliculus

Excretory ductsof lacrimal gland

Lacrimalgland

Lacrimal sac

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Focusing

• Observing object, light rays pass through the cornea, the aqueous humor, the pupil, the lens, the vitreous humor, and are focused on the retina.

– Focusing involves the cornea, the lens and the humors.

– Focusing for close objects (accommodation) involves the ciliary muscles and the changing shape of the lens.

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Focusing

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Figure 8.9 Relative convexity of the lens during focusing for distant and close vision.

Retina

Focal point

Focal point

Retina

Light from distant source

Light from near source

(a)

(b)

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Photoreceptors

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

– Rod cells; black and white vision; very sensitive to light; provide night and peripheral vision.

– Cone cells allow detection of fine detail and color.

Color vision depends on three different kinds of cones which are sensitive to different wavelengths (kinds of light); blue, green, and red light.

Cone Sensitivity to Light

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Photoreceptors in the Eye

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Integration of Visual Signals in the Retina• The retina has three layers.

– Layer closest to choroid contains rod cells and cone cells.

– Middle layer contains bipolar cells.– Innermost layer contains ganglion cells.

• Rod and cone cells in back of retina thus light must penetrate to the back before they are stimulated.

• Many rod cells connected to one ganglion cell.

• One cone cell connected to one ganglion cell (within fovea centralis).

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Integration of Visual Signals in the Retina

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Integration of Visual Signals in the Brain

• The visual pathway begins in the retina and passes through the thalamus before reaching the cerebral cortex.

– The visual fields from both eyes overlap allow you to see depth & around edges (three-dimensional vision).

– The pathway and visual cortex take the visual field apart, possibly to extract more information like color, form, motion.

– The cortex rebuilds it so we correctly perceive the field and with possibly a better understanding of it.

© 2015 Pearson Education, Inc.

Figure 8.11 Visual fields of the eyes and visual pathway to the brain.

Fixation point

Left eye

Opticnerve

Optictract

Right eye

Opticchiasma

Thalamus

Opticradiation

Occipital lobe(visual cortex)

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Integration of Visual Signals in the Brain

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Abnormalities of the Eye

• Color blindness.– Particular type of cone is lacking.

• Distance Vision– Nearsighted.

Elongated eyeball.– Farsighted.

Shortened eyeball.• Astigmatism.

– Uneven cornea.

© 2012 Pearson Education, Inc.

Focal plane

a) The normal eye.

Correction

Concave lens

b) Nearsightedness (myopia). Nearsighted persons can see nearobjects clearly, but distant objects are out of focus because the focalpoint is in front of the retina.

Convex lens

c) Farsightedness (hyperopia). Farsighted persons can see distantobjects clearly, but near objects are out of focus.

d) Astigmatism. Astigmatism is due to an abnormal curvature of eitherthe cornea or the lens.

Figure 12.17

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Homeostasis• To provide information for the proper

maintenance of the body.• Significant contributors to homeostasis.• Interoceptors are directly involved by

monitoring vital functions such as blood pressure and pH.

• Exteroceptors are indirectly involved by monitoring our external environment, but are just as important; we see the oncoming car and get out of the way; we put a coat on so as not to freeze to death.

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Need to Know1. Types of Sensory Receptors

A. Exteroceptors

B. Interoceptors

2. Subtypes of Sensory ReceptorsA. Chemo

Pain

B. Photo

C. Mechano

D. Thermo

3. Function in Homeostasis of Sensory ReceptorA. Proper functioning of body

B. Interoceptors monitor vital functions

C. Exteroceptors monitor external environment

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Need to Know (Cont.)4. Difference Between Sensation and

PerceptionA. Sensation: nerve impulses to the brainB. Perception: the meaning of sensationsC. Part of perception is strength: comes from frequencyD. Part of perception is integration: occurs at receptors,

spinal cord, brain

5. Sense of VisionA. Basic anatomy including lacrimal apparatus & conjunctivaB. Focusing: how it worksC. Photoreceptors: rod and cone cells; what they are

sensitive toD. Integration of visual signals: many rod cells, one ganglion

cell; one cone cell, one ganglion cell

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Need to Know (Cont.)6. Sense of Hearing

A. Basic anatomy

B. How sound is transferred to cochlea: malleus, incus, stapes

C. How Organ of Corti works: hair cells and basilar membrane

7. Sense of Smell

A. Basic anatomy

B. Each olfactory cell has only one chemoreceptor type

C. Odor involves multiple cell stimulation; integration

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Need to Know (Cont.)8. Sense of Taste

A. Basic anatomyB. Taste cells respond to sweet, sour, salty, bitter, umami

C. Integration of incoming signals with sense of smell

9. Sense of Position in SpaceA. Basic anatomy

B. Proprioceptors: sensitive to stretch; tell brain where our limbs are

10. Sense of Balance (Equilibrium)A. Rotational Equilibrium: cupula in semicircular

channels

B. Gravitational Equilibrium: otolithic membrane in utricle and saccule of vestibule