Transcript Unit 3- Special Senses

PowerPoint® Lecture Slide Presentation
by Patty Bostwick-Taylor,
Florence-Darlington Technical College
Special Senses
8
PART A
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Types of Receptors
5 receptors
1. Chemoreceptor- stimulated by changes in chemicals in
solution
2. Pain receptor- stimulated by damage to tissue
3. Thermoreceptor- stimulated by changes in temperature
4. Mechanoreceptor5. Photoreceptor-
stimulated by changes in touch or sound
stimulated by light energy
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Somatic Senses- Touch
 Types of Touch Receptors
 Naked Nerve Endings (Pain Receptor)
 Meissner’s Corpuscle (Touch Receptor)
 Pacinian Corpuscle (Pressure Receptor)
 Warm and Cold Receptors (Temperature)
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What about that Two-Point Discriminator Test?
 Which type of receptors?
 Why were there differences?
 What part of the brain perceives touch?
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Two-Point Discriminator
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The Senses
 Special senses
 Smell
 Taste
 Sight
 Hearing
 Equilibrium
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What do you see?
What do
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Bellwork
 Thinking back to the 2-pt discriminator test, was
there a “blind-spot” in our sense of touch? Why?
 Is there a blind spot in our vision? Why?
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Structure of the Eye
Figure 8.4a
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The Oculomotor Muscles
 Six muscles attached to eye
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Table 14.2 (3 of 12)
Keep staring at the black dot. After a while
the gray haze around it will appear to
shrink.
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Three Major Layers
 Fibrous
 Vascular
 Sensory
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Structure of the Eye: The Fibrous Layer
 Sclera
 White connective
tissue layer
 Seen anteriorly as the
“white of the eye”
 Cornea
 Transparent, central
anterior portion of
sclera
 Allows for light to pass
through
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Three Major Layers
 Fibrous
 Vascular
 Sensory
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Structure of the Eye: Vascular Layer
 Choroid is a blood-rich layer in the posterior of the eye
 Modified anteriorly into two smooth muscle
structures:
 Ciliary body
 smooth muscle attached to lens
 Helps regulate lens shape
 Iris
 Pigmented layer that gives eye color
 Pupil—rounded opening in the iris that
regulates amount of light entering eye
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Stare into your classmate’s eyes
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Blind Spot Test
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Three Major Layers
 Fibrous
 Vascular
 Sensory
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Structure of the Eye: Sensory Layer
 Retina
 Contains receptor
cells
(photoreceptors)
 Rods
 Cones
 No photoreceptor
cells are at the
optic disc, or blind
spot
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Structure of the Eye: Sensory Layer
Figure 8.5a
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Structure of the Eye: Sensory Layer
 Rods
 Allow dim light vision and peripheral
vision
 Most are found towards the edges of the
retina
 All perception is in gray tones
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Structure of the Eye: Sensory Layer
 Cones
 Allow for detailed
color vision
 Work best in
bright light
 Densest in the
center of the
retina
 Fovea centralis—
area of the retina
with only cones
PLAY The Eye: The Retina
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Structure of the Eye: Sensory Layer
 Cone sensitivity
 Three types of cones (blue, green, red)
 Different cones are sensitive to different
wavelengths
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Sensitivities of Cones to Different Wavelengths
Figure 8.6
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Color Perception Test
 Look at the marker colors on the board
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How sight works
Neural layer of retina
Pigmented
layer of
retina
Choroid
Sclera
Pathway of light
Optic disc
Central artery
and vein of retina
Optic
nerve
(a) Posterior aspect of the eyeball
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Photoreceptors- How sight works
Process
of bipolar
cell
 Both have an inner and outer segment
 Outer segments are receptor regions where light
absorbing pigments are present
Rod cell
body
Rod
cell
body
Nuclei
Cone
cell
body
Outer
fiber
Mitochondria
Connecting
cilia
Inner
segment
 Light particles modify the visual pigment and generate a
nerve impulse
Synaptic
terminals
Inner
fibers
Pigmented
layer
Outer
segment
Apical
microvillus
Discs
containing
visual pigments
Melanin
granules
Discs being
phagocytized
Pigment
cell
nucleus
Basal lamina
(border with
choroid)
Figure 16.9
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The Retina: Sensory Tunic
Bipolar
Ganglion cells
cells
Photoreceptors
Rod
Cone
 Photoreceptor cells  bipolar
cells ganglion
 Axons from ganglion cells
exit through the optic disc to
form the optic nerve
Amacrine cell
Horizontal cell
Pathway of signal output
Pigmented
Pathway of light
layer of retina
(b) Cells of the neural layer of the retina
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Posterior Aspect of the Eyeball
Neural layer of retina
Pigmented
layer of
retina
Choroid
Sclera
Pathway of light
Optic disc
Central artery
and vein of retina
Optic
nerve
(a) Posterior aspect of the eyeball
Figure 16.8a
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Visual Pathways to the
Brain Begins at the
Retina
Both eyes
Fixation point
 Light activates photoreceptors:
 Bipolar cells  ganglion cells
axons exit as the optic nerve
 Optic disc (blind spot) is where the
optic nerve leaves the eyeball
Right eye
Left eye
Optic nerve
Suprachiasmatic
nucleus
Pretectal
nucleus
Optic chiasma
Optic tract
 Cannot see images focused on the
optic disc
 Fibers go to primary visual cortex
(occipital lobe)
Uncrossed
(ipsilateral) fiber
Crossed
(contralateral) fiber
Optic
radiation
Lateral
geniculate
nucleus of
thalamus
Superior
colliculus
Occipital
lobe
(primary visual
cortex)
(a) The visual fields of the two eyes overlap considerably. Note that fibers
from the lateral portion of each retinal field do not cross at the optic chiasma.
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Is the left center circle bigger?
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Do you see the three faces?
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Count the black dots!
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Lens
 Biconvex crystal-like structure
 Held in place by a suspensory ligament attached
to the ciliary body
PLAY The Eye: Lens and Retina
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Lens
Figure 8.4a
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Two Segments, or Chambers, of the Eye
 Anterior (aqueous) segment
 Anterior to the lens
 Contains aqueous humor

Watery fluid found between lens and cornea

Helps maintain intraocular pressure

Provides nutrients for the lens and cornea
 Posterior (vitreous) segment
 Posterior to the lens
 Contains vitreous humor

Gel-like substance posterior to the lens

Prevents the eye from collapsing

Helps maintain intraocular pressure
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Pathway of Light to the Eye
 FOCUS ACTIVITY
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Pathway of Light Through the Eye
 Light must be focused to a point on the retina for
optimal vision
 The eye is set for distance vision
(over 20 feet away)
 Accommodation—the lens must change shape to
focus on closer objects (less than 20 feet away)
 Ciliary body contraction changes shape of the
lense
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Pathway of Light Through the Eye
Figure 8.9
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Pathway of Light Through the Eye
 Image formed on the retina is a real image
 Real images are
 Reversed from left to right
 Upside down
 Smaller than the object
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Images Formed on the Retina
Figure 8.10
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Disorders
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Lens
 Cataracts result when the lens becomes hard and
opaque with age
 Vision becomes hazy and distorted
 Eventually causes blindness in affected eye
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Lens
Figure 8.7
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A Closer Look
 Emmetropia—eye focuses images correctly on
the retina
 Myopia (nearsighted)
 Distant objects appear blurry
 Light from those objects fails to reach the
retina and are focused in front of it
 Results from an eyeball that is too long
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A Closer Look
 Hyperopia (farsighted)
 Near objects are blurry while distant objects
are clear
 Distant objects are focused behind the retina
 Results from an eyeball that is too short or
from a “lazy lens”
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A Closer Look
 Astigmatism
 Images are blurry
 Results from light focusing as lines, not
points, on the retina due to unequal
curvatures of the cornea or lens
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Homeostatic Imbalances of the Eyes
 Night blindness—inhibited rod function that
hinders the ability to see at night
 Color blindness—genetic conditions that result in
the inability to see certain colors
 Due to the lack of one type of cone (partial
color blindness)
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Homeostatic Imbalances of the Eyes
 Glaucoma—can cause blindness due to
increasing pressure within the eye
 Hemianopia—loss of the same side of the visual
field of both eyes; results from damage to the
visual cortex on one side only
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Bellwork
 Is there a comparable “Blind Spot” in hearing as
there is in vision?
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The Ear
 Houses two senses
 Hearing
 Equilibrium (balance)
 Receptors are mechanoreceptors
 Different organs house receptors for each sense
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Anatomy of the Ear
 The ear is divided into three areas
 External (outer) ear
 Middle ear (tympanic cavity)
 Inner ear (bony labyrinth)
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Anatomy of the Ear
Figure 8.12
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The External Ear
 Involved in hearing only
 Structures of the external ear
 Auricle (pinna)
 External acoustic meatus (auditory canal)
 Narrow chamber in the temporal bone
 Lined with skin and ceruminous (wax)
glands
 Ends at the tympanic membrane
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Anatomy of the Ear
Figure 8.12
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The Middle Ear (Tympanic Cavity)
 Air-filled cavity within the temporal bone
 Only involved in the sense of hearing
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Anatomy of the Ear
Figure 8.12
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Bones of the Middle Ear (Tympanic Cavity)
 Three bones (ossicles) span the cavity
 Malleus (hammer)
 Incus (anvil)
 Stapes (stirrip)
 Function
 Vibrations from eardrum (tympanic
membrane) move the malleus  anvil 
stirrup  inner ear
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Anatomy of the Ear
Figure 8.12
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Inner Ear or Bony Labyrinth
 Includes sense organs for hearing and balance
 A maze of bony chambers within the temporal
bone
 Cochlea
 Vestibule (static equilibrium – position of
head)
 Semicircular canals (dynamic equilibrium –
movement of head)
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Organs of Equilibrium
Figure 8.14a–b
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Mechanism of Hearing
Figure 8.16a
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Anatomy of the Ear
Oval window
(deep to stapes)
Semicircular
canals
Entrance to mastoid
antrum in the
epitympanic recess
Malleus
(hammer)
Incus
Auditory
(anvil)
ossicles
Stapes
(stirrup)
Vestibule
Vestibular
nerve
Cochlear
nerve
Cochlea
Tympanic
membrane
Pharyngotympanic
(auditory) tube
Round window
(b) Middle and internal ear
Figure 8.12
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Organs of Hearing
 Organ of Corti
 Located within the
cochlea
 Receptors = hair cells
on the basilar
membrane
 Gel-like tectorial
membrane is capable
of bending hair cells
 Cochlear nerve
attached to hair cells
transmits nerve
impulses to auditory
cortex on temporal
lobe
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How We Hear Sound
1) Vibrating waves of air enter the outer
ear (pinna) and strike the eardrum
(tympanic membrane).
2) The eardrum transmits vibrations to 3
ossicles (hammer, anvil & stirrup).
3)The ossicles pass the vibrations to the
cochlea (primary organ of hearing) in the
inner ear.
4) The cochlea passes the vibrations along
the basilar membrane (inside cochlea)
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How We Hear Sound
 5) The swaying of tiny hairs on the basilar
membrane stimulates sensory nerve endings and
the excited neurons transform the mechanical
vibrations into neural activity (action potential).
 6) Now the neural message leaves the cochlea in
a bundle of neurons called the cochlear nerve
(VIII-vestibulocochlear).
 7) The neurons from the two ears meet in the
brainstem.
 8) The brainstem passes the auditory information
to the auditory cortex (temporal lobe) of the brain
for interpretation of sound or hearing occurs.
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Tectorial membrane
Inner hair cell
Hairs (stereocilia)
Afferent nerve fibers
Outer hair cells
Supporting cells
Fibers of
cochlear
nerve
Basilar
membrane
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The Role of the Cochlea in Hearing
1 Sound waves vibrate the
tympanic membrane.
Auditory ossicles
Malleus Incus
Stapes
2 Auditory ossicles vibrate.
Pressure is amplified.
Cochlear nerve
Scala vestibuli
Oval
window Helicotrema
3
4a
Scala tympani
Cochlear duct
2
3
4b
Basilar
membrane
1
4a
Pressure waves created by the
stapes pushing on the oval
window move through fluid in
the scala vestibuli.
Sounds with frequencies below
hearing travel through the
helicotrema and do not excite hair
cells.
4b Sounds in the hearing range go
Tympanic
membrane
through the cochlear duct,
vibrating the basilar membrane,
deflecting hairs on inner hair cells.
Round
window
Figure 16.21
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Mechanisms of Hearing
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Blind Spot?
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Olfaction—The Sense of Smell
 Olfactory receptors are in the roof of the nasal
cavity
 Neurons with long cilia
 Chemicals must be dissolved in mucus for
detection
 Impulses are transmitted via the olfactory nerve
 Interpretation of smells is made in the olfactory
cortex (temporal lobe)
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Olfactory Epithelium
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The Olfactory Pathway
 Olfactory (CN I) nerve: olfactory bulb
and olfactory tract
 Olfaction: only sensations to reach the
cerebral cortex without first synapsing in
the thalamus
 Axons of the olfactory tract project to
the primary olfactory area
 Inferiomedial surface of the temporal lobe
Copyright 2012 John
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Blind Spot?
 We have about 400 types of olfactory receptors
 5-6 million olfactory receptors in total
 Dogs have 220 million
 Rabbits 100 million
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The Sense of Taste
 Taste buds house the receptor organs
 Location of taste buds
 Most are on the tongue
 Soft palate
 Cheeks
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Taste Buds
 Found in papillae
 Elevations on the tongue
 Taste buds are on sides of papillae
 Three types contain taste buds
 Circumvallate (vallate) contain 100 –
300 taste buds
 Fungiform papillae contain about five
taste buds
 Foliate papillae most of their taste
buds degenerate in early childhood
 Filiform papillae contain tactile
receptors but no taste buds
 Increase friction between the tongue
and food
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Taste Buds
Figure 8.18
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The Tongue and Taste
 The Structure of Tastebuds
 Gustatory cells are the receptors
 Have gustatory hairs (long microvilli)
 Hairs are stimulated by chemicals dissolved in
saliva
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The Tongue and Taste
 Impulses are carried to the gustatory cortex
(parietal lobe) by several cranial nerves because
taste buds are found in different areas
 Facial nerve
 Glossopharyngeal nerve
 Vagus nerve
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Taste Sensations
 Sweet receptors
(sugars)
 Saccharine
 Some amino acids
 Sour receptors
 Acids
 Bitter receptors
 Alkaloids
 Salty receptors
 Metal ions
 Umami (delicious)
 Steak, soy sauce
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Frontal plane
Primary
gustatory
area of
cerebral
cortex
Thalamus
View
Vagus CN X
Gustatory
nucleus
Glossopharynge
al CN IX
Facial CN
VII
Tongue
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Blind Spot?
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Chemical Senses: Taste and Smell
 Both senses use chemoreceptors
 Stimulated by chemicals in solution
 Taste has five types of receptors
 Smell can differentiate a large range of
chemicals
 Both senses complement each other and respond
to many of the same stimuli
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