Transcript Ch 8 Powerpoint Special Senses

Essentials of Human Anatomy & Physiology
Elaine N. Marieb
Seventh Edition
Chapter 8
Special Senses
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Senses
 General senses of touch
 Temperature
 Pressure
 Pain
 Special senses
 Smell
 Taste
 Sight
 Hearing
 Equilibrium
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 8.1
The Eye and Vision
 70 percent of all sensory receptors are
in the eyes, only see 1/6th of eye
 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
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Slide 8.2
Accessory Structures of the Eye
 Eyelids
Meets at
medial
and
lateral
canthus
(crease)
 Eyelashes
Figure 8.1b
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Slide 8.3a
Accessory Structures of the Eye
 Eyelashes
 Meibomian
glands - modified
sebacious
glands
produce an
oily secretion
to lubricate
the eye
Figure 8.1b
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Slide 8.3b
Accessory Structures of the Eye
 Ciliary glands –
modified
sweat glands
between the
eyelashes
Figure 8.1b
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Slide 8.3c
Accessory Structures of the Eye
 Conjunctiva
 Membrane that lines eyelids
 Connects to the surface of eye
 Secretes mucus to lubricate eye
 When inflamed, conjunctivitis
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Slide 8.4a
Accessory Structures of the Eye
 Lacrimal
apparatus
Glands,
ducts, (eye),
canals, sac,
nasolacrimal
duct
Tears:
antibodies,
lysozymes,
stress?
Figure 8.1a
Slide 8.4b
Extrinsic Eye Muscles
 Muscles attach to the outer surface of
the eye
 Produce eye movements
Figure 8.2
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Slide 8.6
Structure of the Eye
 The wall is composed of three tunics
 Sclera & Cornea
fibrous outside
layer
 Choroid –
middle
layer
 Sensory
tunic –
(retina) inside
layer
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Figure 8.3a
Slide 8.7
The Fibrous Tunic
 Sclera
 White connective tissue layer
 Seen anteriorly as the “white of the eye”
 Cornea
 Transparent, central anterior portion
 Allows for light to pass through
 Repairs itself easily
 The only human tissue that can be
transplanted without fear of rejection
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Slide 8.8
Choroid Layer
 Blood-rich, nutritive tunic
 Pigment prevents light from scattering
 Modified interiorly into two structures
 Ciliary body – smooth muscle
 Iris
 Pigmented layer that gives eye color
 Pupil – rounded opening in the iris
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Slide 8.9
Sensory Tunic (Retina)
 Contains receptor cells (photoreceptors)
 Rods-
Most are found towards the edges of the retina
Allow dim light vision and peripheral vision
Perception in gray tones
 Cones – 3 types detect different colors
Densest in the center of the retina
Fovea centralis – area of the retina with only cones
Lack of one type = color blindness
 Signals pass from photoreceptors; leave the retina
toward the brain through the optic nerve
 No photoreceptor cells are at the optic disk, or blind spot
Neurons of the Retina
Figure 8.4
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Slide 8.11
Lens
 Biconvex crystal-like structure
 Held in place by a suspensory ligament attached to the
ciliary body
Internal Eye Chamber Fluids
 Aqueous humor in Anterior Segment
 Watery fluid found in chamber between
lens and cornea
 Similar to blood plasma
 Helps maintain intraocular pressure
 Provides nutrients for the lens and cornea
 Reabsorbed into venous blood
 Blocked drainage = inc pressure =
glaucoma
Internal Eye Chamber Fluids
 Vitreous humor in Posterior Segment
 Gel-like substance behind lens
 Keeps the eye from collapsing
 Lasts a lifetime and is not replaced
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Slide
Lens Accommodation
 Light must be
focused to point on
retina for optimal
vision
 The eye is set for
distance vision
(over 20 ft away)
 The lens must
change shape to
focus for closer
objects
Correcting the Eye
• Correct Focus = emmetropia
• Nearsightedness = myopia
– Focus of light in front of retina
– Eyeball too long or lens too strong
– Distant objects are blurry
• Farsightedness = hyperopia
– Focus of light beyond the retina
– Short eyeball or lazy lens
– Near objects are blurry.
Emmetropia
Hyperopia
Astigmatism
• Unequal curvatures in cornea & lens
The Ear
 Houses two senses
 Hearing
 Equilibrium (balance)
 Receptors are mechanoreceptors
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Slide 8.20
Anatomy of the Ear
 The ear is divided into 3 areas
 Outer
(external)
ear
 Middle
ear
 Inner
ear
The External Ear
 Involved in
hearing only
 Structures of
external ear
 Pinna
(auricle)
 External
auditory canal
The External Auditory Canal
 Narrow chamber in the temporal bone
 Lined with skin
 Ceruminous (wax) glands present
 Ends at the tympanic membrane (ear
drum)
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Slide 8.23
The Middle Ear or Tympanic Cavity
 Air-filled cavity within temporal bone
 Only involved in sense of hearing
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Slide
The Middle Ear or Tympanic Cavity
 2 tubes are associated with the ear
 opening from auditory canal is covered by the tympanic membrane
 auditory tube (Eustachian tube) connecting middle ear with throat
 equalizing pressure during yawning or swallowing
 otherwise collapsed
Bones of the Tympanic Cavity
 Three bones
span cavity
 Malleus
(hammer)
 Incus (anvil)
 Stapes (stirrip)
Figure 8.12
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Bones of the Tympanic Cavity
 Vibrations from
eardrum move
malleus
 These bones
transfer sound
to inner ear
Figure 8.12
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Slide
Inner Ear or Bony Labyrinth
 Includes sense organs for hearing and
balance
 Filled with
perilymph
(liquid)
Figure 8.12
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Slide
Inner Ear or Bony Labrynth
 Maze of bony chambers within temporal
bone
 Cochlea
 Vestibule
 Semicircular
canals
Organs of
Hearing
 Organ of Corti
 Located within cochlea
 Receptors = hair cells on basilar membrane
 Gel-like tactorial membrane is capable of bending
hair cells
 Cochlear nerve attached to hair cells transmits
nerve impulses to auditory cortex on temporal lobe
Organs of Hearing
Figure 8.13
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Slide
Mechanisms of Hearing
 Vibrations from sound waves move
tectorial membrane
 Hair cells are bent by the membrane
 An action potential starts in the cochlear
nerve
 Continued stimulation can lead to
adaptation
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Slide 8.28
Mechanisms of Hearing
Figure 8.14
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Slide 8.29
Mechanisms of Hearing
Uncoiled cochlea: sound waves below level of hearing travel w/o
exciting hair cells
1- Higher pitched sounds make pressure waves that penetrate
through cochlea and reach scala tympani
2- Membrane vibrates and response to frequencies of sound,
stimulating hair cells
Figure 8.14
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Slide 8.29
Organs of Equilibrium
 Receptor cells are in two structures
 Vestibule
 Semicircular canals
Figure 8.16a, b
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Slide
Organs of Equilibrium
 Equilibrium has two functional parts
 Static equilibrium – sense of gravity at rest
 Dynamic equilibrium – angular and rotary
head movements
Figure 8.16a, b
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Slide
Static Equilibrium - Rest
 Maculae – receptors in the vestibule
 Report on position of head
 Send information via vestibular nerve
 Anatomy of the maculae
 Hair cells are embedded in otolithic
membrane
 Otoliths (tiny stones) float in a gel around
hair cells
 Movements cause otoliths to bend hair
cells
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Slide 8.31
Function of Maculae
Figure 8.15
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Slide 8.32
Dynamic Equilibrium - Movement
 Crista ampullaris –
receptors in the
semicircular canals
 Tuft of hair cells
 Cupula (gelatinous cap)
covers hair cells
Figure 8.16c
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Slide
Dynamic Equilibrium
 Action of angular head
movements
 The cupula stimulates hair
cells
 An impulse is sent via
vestibular nerve to
cerebellum
Figure 8.16c
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Slide
Chemical Senses
Taste and Smell
 Both senses use chemoreceptors
 Both stimulated by chemicals in solution
 Taste has 4 types of receptors
 Smell can differentiate a large range of
chemicals
 Both senses complement each other
and respond to many of same stimuli!
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Slide 8.34
Olfaction – The Sense of Smell
 Olfactory receptors are in roof of the
nasal cavity
 Neurons with long cilia
 Chemicals must be dissolved in mucus for
detection
Olfaction – The Sense of Smell
 Impulses are transmitted via olfactory
nerve
 Interpretation of smells made in cortex
The Sense of Taste
 Taste buds
house the
receptor
organs
 Location of
taste buds
 Most are on
the tongue
 Soft palate
 Cheeks
Figure 8.18a, b
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Slide 8.37
The Tongue and Taste
 The tongue is
covered w/
projections,or
papillae
 Filiform papillae
sharp w/ no taste buds
 Fungifiorm papillae
rounded w/ taste buds
 Circumvallate
papillae
large w/ taste buds
The Tongue and Taste
Taste buds
are found on
the sides of
papillae
Structure of Taste Buds
 Gustatory cells are the receptors
 Have gustatory hairs (long microvilli)
 Hairs stimulated by chemicals dissolved in saliva
Structure of Taste Buds
 Impulses carried to gustatory complex
by several cranial nerves b/c taste buds
found in different areas
Facial, Glossopharyngeal & Vagus nerves
Taste Sensations
 Sweet receptors
 Sugars
 Saccharine
 Some amino acids
 indicates
energy-rich
nutrients
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Slide 8.41
Taste Sensations
 Sour receptors
 Acids
Slide 8.41
Taste Sensations
 Bitter receptors
allows sensing diverse
natural toxins
Taste Sensations
 Salty receptors
allows modulating
diet for electrolyte
balance
Developmental Aspects of
All Special Senses
 Formed early in embryonic development
 Eyes are outgrowths of the brain
 All special senses are functional at
birth
Short taste intro
Relationship between
smell and taste