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CHAPTER 8
SPECIAL SENSES
Special Senses
 Special Senses: smell, taste, sight,
hearing and equilibrium
 The special sense receptors are either
lar...
Special Senses
 Remember, these senses are overlapping!
 What you sense of “feel” is a blending of
stimulus effects
THE EYE AND VISION
Anatomy of the Eye
 The adult eye is a sphere about 1 in. in
diameter
 Only 1/6 of the anterior surface can be
seen
 Th...
Anatomy of the Eye
 The accessory structures include:
◦ Extrinsic eye muscles
◦ Eyelids
◦ Conjunctiva
◦ Lacrimal apparatus
Anatomy of the Eye
 The eyelids offer anterior protection of the
eye
 Meet at the medial and lateral
commissure (canthus)
Anatomy of the Eye
 The palpebral fissure is the space between
the eyelids in an open eye
 The eyelashes protect the bor...
Anatomy of the Eye
 The conjunctiva is a delicate membrane
that lines the eyelids and covers part of
the outer surface of...
Anatomy of the Eye
 Conjunctivitis is an
irritation and
inflammation of the
conjunctiva
 Pinkeye is a
infectious form of...
Anatomy of the Eye
 The lacrimal
apparatus consists
of the lacrimal gland
and a number of
ducts that drain the
lacrimal s...
Anatomy of the Eye
 The lacrimal glands continually release a
salt solution (your tears!) onto the
anterior surface of th...
Anatomy of the Eye
Anatomy of the Eye
 Lacrimal secretions are high in antibodies
and lysozyme to help cleanse and protect
the eye from fore...
Anatomy of the Eye
 There are six extrinsic or external eye
muscles
 Attached to the outer surface to each eye
 Produce...
Anatomy of the Eye
Anatomy of the Eye
 The eye itself, commonly called the
eyeball, is a hollow sphere
 The wall is composed of three layer...
Anatomy of the Eye
 The lens is the main focusing apparatus of
the eye and is supported upright within
the eye cavity, se...
Anatomy of the Eye
 Three layers of the
eyeball wall:
 1. Fibrous
 2. Vascular
 3. Sensory
Anatomy of the Eye
 1. The Fibrous Layer
 Outermost layer
 Consists of the sclera (protective layer)
and cornea (transp...
Anatomy of the Eye
 1. Fibrous Layer
 Sclera - the white of the eye
◦ Thick, connective tissue
 Cornea – the window of ...
Anatomy of the Eye
 Fun Fact: the cornea is the only tissue in
the body that can be transplanted from
one person to anoth...
Anatomy of the Eye
Anatomy of the Eye
 2. Vascular Layer
 3 distinguishable regions
◦ 1. Choroid (blood-rich, contains dark
pigment)
◦ Prev...
Anatomy of the Eye
Anatomy of the Eye
 2. Vascular Layer
 Circularly and radially arranged smooth
muscle fibers form the iris
 Regulates t...
Anatomy of the Eye
Anatomy of the Eye
 3. Sensory Layer
 Two-layered retina
 Extends anteriorly to the ciliary body
Anatomy of the Eye
 3. Sensory Layer
 The outer pigmented layer of the retina is
full of pigmented cells that absorb lig...
Anatomy of the Eye
 3. Sensory Layer
 The inner neural layer of the retina
contains millions of photoreceptors – rods
an...
Anatomy of the Eye
 3. Sensory Layer
 Electrical signals
pass from the
photoreceptors via
a 2 neuron chain,
then leave v...
Anatomy of the Eye
 3. Sensory Layer
 Photoreceptors are over the entire retina
except at the optic disc, where the opti...
Anatomy of the Eye
 Rods allow us
to see in gray
tones and dim
light
 Peripheral
vision
 More dense at
the edges or
per...
Anatomy of the Eye
 Night Blindness
(Nyctalopia)
 Interferes with rod
function and limits the
ability to see at night
 ...
Anatomy of the Eye
 Cones allow for details and color to be
seen in bright light
 Densest in the center of the retina
Anatomy of the Eye
 Lateral to each blind spot is the fovea
centralis, a tiny pit that contains only
cones
 Greatest vis...
Anatomy of the Eye
 There are three varieties of cones:
 “blue”
 “green”
 “red” (actually responds to green and red)
Anatomy of the Eye
 Impulses received at the same time from
more than one type of cone by the visual
cortex are interpret...
Anatomy of the Eye
 When all three types of cones are
stimulated we see white
 “mixing” of colors occurs in the brain, n...
Anatomy of the Eye
 Color blindness
 Lack of one type of
cone leads to
partial color
blindness
 Lack of all three
cones...
Color Blindness Test #1
Color Blindness Test #2
Color Blindness Test #3
Anatomy of the Eye
 Lens: a flexible biconvex crystal-like
structure
 Light entering the eye is focused on the
retina by...
Anatomy of the Eye
Anatomy of the Eye
 The lens divides the eye into two
segments:
 1. anterior (aqueous) segment
◦ Contains aqueous humor
...
Anatomy of the Eye
Anatomy of the Eye
 Aqueous humor is reabsorbed into the
venous blood through the scleral venous
sinus, or the canal of S...
Anatomy of the Eye
 Cataracts
 In youth, the lens is transparent and a
hardened jelly-like texture
 As we age, it becom...
Anatomy of the Eye
 Cataracts cause vision to become hazy
and distorted, and eventually cause
blindness
 Risk factors: T...
Cataract Surgery
Anatomy of the Eye
 Glaucoma
 Occurs when the drainage of the aqueous
humor is blocked, and fluids back up
 Pressure on...
Anatomy of the Eye
 Glaucoma causes
pain and possible
blindness
 Progresses slowly
and painlessly until
the damage is do...
Anatomy of the Eye
 Glaucoma is commonly treated with
eyedrops that increase the rate of
drainage
 Laser or surgical enl...
Anatomy of the Eye
 An ophthalmoscope is
an instrument used to
illuminate the interior of
the eyeball
 Conditions such a...
Anatomy of the Eye
 Ophthalmascope
Anatomy of the Eye
 Ophthalmascope
Anatomy of the Eye
Pathway of Light/Light Refraction
Pathway of Light
 When light passes from one substance to
another substance of a different density,
it’s speed changes an...
Pathway of Light
 The refractive powers of the corneas and
humors are constant
 The refractive power of the lens changes...
Pathway of Light
Pathway of Light
 The greater the lens convexity (bulge) the
more it bends the light
 The flatter the lens, the less it ...
Pathway of Light
 The resting eye is set for distant vision
 Light from a distant source (+20ft)
approaches the eye in p...
Pathway of Light
 Light from a near source tends to scatter
or diverge
 The lens must bulge to make clear vision
possibl...
Pathway of Light
 Accommodation: the ability of the eye to
focus specifically on close objects
Pathway of Light
Pathway of Light
 The image formed on the retina as a
result of the light-bending activity of the
lens is a real image – ...
Pathway of Light
Pathway of Light
 The normal eye can accommodate
properly
 Vision problems occur when the lens is
too strong or too weak...
Pathway of Light
Pathway of Light
 The eye that focuses images correctly on
the retina is said to have emmetropia
Pathway of Light
 Myopia is nearsightedness
 It occurs when the parallel light rays from
distant objects fail to reach t...
Pathway of Light
Pathway of Light
 Hyperopia is farsightedness
 It occurs when the parallel light rays from
distant objects are focused b...
Pathway of Light
Pathway of Light
 Unequal curvatures in
different parts of the
cornea or lens cause
astigmatism
 In this condition, imag...
Pathway of Light
Visual Fields and Visual Pathways
to the Brain
Visual Fields and Pathways
 The optic nerve is
located in back of
the eye, and
carries impulses
form the retina to
the br...
Visual Fields and Pathways
 At the optic chiasma the fibers from the
medial side of each eye cross over to the
opposite s...
Visual Fields and Pathways
 The fiber tracts
that result are
called the optic
tracts
 Each optic tract
contains fibers
f...
Visual Fields and Pathways
 The optic tract
fibers synapse with
neurons in the
thalamus, whose
axons form the
optic radia...
Visual Fields and Pathways
 There they
synapse with the
cortical cells, and
visual
interpretation, or
seeing, occurs.
Visual Fields and Pathways
 Each side of the brain
receives visual input
from both eyes
 Lateral of the same
side eye, m...
Visual Fields and Pathways
 Each eye “sees” a slightly different view
 The visual fields of each eye overlap
 Humans ha...
Visual Fields and Pathways
 Hemianopia: the loss of the same side of
the visual field in both eyes
 Results from damage ...
Visual Fields and Pathways
 People who suffer from
hemianopia are not
able to see things past
the middle of the
visual fi...
Visual Fields and Pathways
Eye Reflexes
Eye Reflexes
 Both the internal and external eye
muscles are needed for proper eye
function
 The external muscles, as me...
Eye Reflexes
 Convergence: the
reflexive movement of
the eyes medially
when viewing close
objects
 Both eyes are aimed
t...
Eye Reflexes
 When the eyes are suddenly exposed to
bright light, the pupils instantly constrict
 This is called the pho...
Eye Reflexes
 The photopupillary reflex prevents
excessively bright light from damaging
the photoreceptors
Eye Reflexes
 The accomodation
pupillary reflex also
constricts the pupil,
but occurs when
viewing close
objects
 It all...
Eye Reflexes
 Reading requires almost continuous work
by both sets of muscles
 Ciliary fibers cause the lens to bulge, t...
Ears
Hearing and Balance
The Ear
 Ears are key to the senses of hearing and
balance
 Sound vibrations move fluids to stimulate
hearing receptors
...
The Ear
 Receptors that respond to physical forces
are called mechanoreceptors
 These two sense organs are housed in the...
Anatomy of the Ear
Anatomy of the Ear
 Anatomically, the ear is divided into 3
major sections:
 1. external (outer) ear - hearing
 2. midd...
Anatomy of the Ear
External Ear
 The external (outer) ear is composed of
the auricle and the external acoustic
meatus
External Ear
 The auricle (pinna) is
“the ear,” the shell-
shaped structure
surrounding the
auditory canal opening
 It c...
External Ear
 The external acoustic meatus (auditory
canal) is a short, narrow chamber (1x.25
in) carved into the tempora...
External Ear
 The auditory
external acoustic
meatus has skin-
lined walls with
ceruminous glands
which secrete
cerumen (e...
External Ear
 Sound waves entering the auditory canal
eventually hit the tympanic membrane
(eardrum) and cause it to vibr...
Middle Ear
 The tympanic cavity or middle ear is a
small, air-filled, mucosa-lined cavity
within the temporal bone
Middle Ear
Middle Ear
 It is flanked laterally
by the eardrum and
medially by a bony
wall with two
openings, the oval
window and the...
Middle Ear
 The pharyngotympanic (auditory) tube
also called the eustachian tube runs
obliquely downward to link the midd...
Middle Ear
 Normally the auditory tube is flattened
and closed
 Swallowing and yawning opens this tube
briefly to equali...
Middle Ear
 When the pressures are
unequal, the eardrum
bulges inward or
outward making hearing
difficult or causes
earac...
Middle Ear
 An inflammation of the otitis media is
common in children with sore throats
 The eardrum becomes inflamed, b...
Middle Ear
Middle Ear
 The tympanic membrane is spanned by
the three smallest bones in the body, the
ossicles
 The ossicles transmi...
Middle Ear
 The ossicles are named for their shape:
 Hammer (malleus)
 Anvil (incus)
 Stirrup (stapes)
Middle Ear
 When the eardrum moves, the hammer
moves as well, and transfers the vibration
to the anvil
 The anvil passes...
Middle Ear
 The stirrup which presses on the oval
window of the inner ear
 The movement at the oval window sets
the flui...
Inner Ear
 The internal ear is a
maze of bony
chambers called the
bony, or osseous,
labyrinth, located
deep within the
te...
Inner Ear
 The three subdivisions of the bony
labyrinth are the:
 1. cochlea (spiral, pea size)
 2. vestibule
 3. semi...
Inner Ear
 The inner ear is a
cavity filled with a
plasmalike fluid called
perilymph
 Suspended in the
perilymph is a
me...
Inner Ear
 Suspended in the
perilymph is a
membranous
labyrinth, a system of
membrane sacs that
more or less follow
the s...
Mechanisms of Equilibrium
Mechanisms of Equilibrium
 Equilibrium is not an easy sense to
describe
 It responds to various head movements
 The equ...
Mechanisms of Equilibrium
 The vestibular apparatus can be divided
into two functional aspects:
 1. static equilibrium
...
Static Equilibrium
Static Equilibrium
 Within the membrane
sacs of the vestibule
are receptors called
maculae
 The maculae are
essential to...
Static Equilibrium
 The maculae report on changes in the
position of the head in space with respect
to the pull of gravit...
Static Equilibrium
Static Equilibrium
 Each macula is a patch of receptor (hair)
cells with their “hairs” embedded in the
otolithic hair mem...
Static Equilibrium
 As the head
moves, the
otoliths roll in
response to
changes in
gravitational pull
 The surrounding
g...
Static Equilibrium
Static Equilibrium
 This movement activates the hair cells,
which send impulses along the vestibular
nerve to the cerebel...
Dynamic Equilibrium
Dynamic Equilibrium
 Dynamic equilibrium receptors, found in
the semicircular canals, respond to
angular or rotary moveme...
Dynamic Equilibrium
 Within the ampulla, a swollen region at
the base of each membranous
semicircular canal is a receptor...
Dynamic Equilibrium
 The crista consists of a tuft of hair cells
covered with a gelatinous cap called
cupula
 When your ...
Dynamic Equilibrium
 As the cupula drags against the stationary
endolymph the cupula bends with the
body’s motion
Dynamic Equilibrium
 This motion
stimulates the hair
cells, and impulses
are transmitted up
the vestibular
nerve to the
c...
Dynamic Equilibrium
 When you are
moving at a
constant rate, the
receptors gradually
stop sending
impulses, and you
no lo...
Dynamic Equilibrium
 The receptors of the semicircular canal
and vestibule are responsible for dynamic
and static equilib...
Dynamic Equilibrium
 Besides these equilibrium senses, sight
and proprioceptors of the muscles and
tendons are also impor...
Mechanism of Hearing
Mechanism of Hearing
 Within the cochlear duct, the endolymph-
containing membranous labyrinth of the
cochlea is the spir...
Mechanism of Hearing
 The scalae, chambers, above and below
the cochlear duct contain perilymph
 Sound waves that reach ...
Mechanism of Hearing
 As the sound waves are transmitted by
the ossicles, their force is increased by
the lever activity ...
Mechanism of Hearing
 The pressure waves set up vibrations in
the basilar membrane
 The receptor cells are stimulated wh...
Mechanism of Hearing
Mechanism of Hearing
 The length of the fibers spanning the
basilar membrane “tunes” specific regions
to vibrate at speci...
Mechanism of Hearing
Mechanism of Hearing
 Once stimulated, the hair cells transmit
impulses along the cochlear nerve to the
auditory cortex
Mechanism of Hearing
 Sound usually reaches the two ears at
different times, or “in stereo”
 This helps us determine the...
Mechanism of Hearing
 We are able to habituate, or adapt, to
constant, repetitive sounds
Mechanism of Hearing
 Hearing is also the last sense to leave us
when we fall asleep and the first to return
when we wake...
Hearing and Equilibrium Deficits
Hearing and Equilibrium Deficits
 Deafness: hearing loss of any degree
 Two main kinds:
 1. conduction
 2. sensorineur...
Hearing and Equilibrium Deficits
 Temporary or
permanent
conduction
deafness results
when something
interferes with
the c...
Hearing and Equilibrium Deficits
 Conduction
deafness can be
caused by
 Earwax
 Otosclerosis, the
fusion of the
ossicle...
Hearing and Equilibrium Deficits
 Sensorineural deafness occurs when there
is degeneration or damage to the receptor
cell...
Hearing and Equilibrium Deficits
 Hearing aids use the
skull bones to conduct
sound vibrations to
the inner ear
 They ar...
Hearing and Equilibrium Deficits
 Equilibrium problems are usually obvious;
nausea, dizziness, and problems in
maintainin...
Hearing and Equilibrium Deficits
 Meniere’s Syndrome
causes progressive
deafness of the inner
ear
 Sufferers become
naus...
Hearing and Equilibrium Deficits
 Vertigo: a sense of spinning so severe
that they cannot stand up without
extreme discom...
Chemical Senses - Taste and Smell
Taste and Smell
 Both senses use chemoreceptors
Stimulated by chemicals in solutions
Taste has four types of receptors
...
Olfaction - Smell
 Olfactory
receptors are in
the roof of the
nasal cavity
Neurons with
long cilia
Chemicals must
be di...
Olfaction - Smell
Olfaction - Smell
 Impulses are transmitted via the olfactory
nerve
 Interpretation of smells is made in the cortex
(olf...
http://asb.aecom.yu.edu/histology/labs/images/slides/A74_OlfactoryEpith_40X.jpg
Taste
 Taste buds house the receptor
organs
 Location of taste buds
Most on the tongue
Soft palate
Cheeks
Tongue and Taste
 The tongue is covered
with projections called
papillae
 Filiform papillae –
sharp with no taste
buds
...
http://neuromedia.neurobio.ucla.edu/campbell/oral_cavity/wp_images/96_fungiform.gif
http://www.esg.montana.edu/esg/kla/ta/vallate.jpg
Structure of Taste Buds
 Gustatory cells
are the
receptors
Have gustatory
hairs (long
microvilli)
Hairs are
stimulated ...
Structure of taste buds
Structure of taste buds
 Impulses are carried to the gustatory
complex (parietal lobe) by several
cranial nerves because ...
http://www.biosci.ohiou.edu/introbioslab/Bios171/images/lab6/Tastebuds.JPG
Taste Sensations
 Sweet receptors
Sugars
Saccharine
Some amino acids
 Sour receptors
Acids
 Bitter receptors
Alkal...
Development of the Special
Senses
 Formed early in embryonic development
 Eyes are outgrowths of the brain
 All special...
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Chapter 8 - Special Senses

Chapter 8 - Special Senses

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Chapter 8 - Special Senses

  1. 1. CHAPTER 8 SPECIAL SENSES
  2. 2. Special Senses  Special Senses: smell, taste, sight, hearing and equilibrium  The special sense receptors are either large, complex sensory organs (eyes/ears) or localized clusters of receptors (tastebuds/olfactory epithelium)
  3. 3. Special Senses  Remember, these senses are overlapping!  What you sense of “feel” is a blending of stimulus effects
  4. 4. THE EYE AND VISION
  5. 5. Anatomy of the Eye  The adult eye is a sphere about 1 in. in diameter  Only 1/6 of the anterior surface can be seen  The rest of the eye is covered and protected by fat and the walls of the bony orbit
  6. 6. Anatomy of the Eye  The accessory structures include: ◦ Extrinsic eye muscles ◦ Eyelids ◦ Conjunctiva ◦ Lacrimal apparatus
  7. 7. Anatomy of the Eye  The eyelids offer anterior protection of the eye  Meet at the medial and lateral commissure (canthus)
  8. 8. Anatomy of the Eye  The palpebral fissure is the space between the eyelids in an open eye  The eyelashes protect the borders of each eyelid  The tarsal glands are modified sebaceous glands associated with the eyelids
  9. 9. Anatomy of the Eye  The conjunctiva is a delicate membrane that lines the eyelids and covers part of the outer surface of the eyeball
  10. 10. Anatomy of the Eye  Conjunctivitis is an irritation and inflammation of the conjunctiva  Pinkeye is a infectious form of Conjunctivitis caused by bacteria or viruses
  11. 11. Anatomy of the Eye  The lacrimal apparatus consists of the lacrimal gland and a number of ducts that drain the lacrimal secretions into the nasal cavity  The lacrimal glands are located above the lateral end of each eye
  12. 12. Anatomy of the Eye  The lacrimal glands continually release a salt solution (your tears!) onto the anterior surface of the eye  Tears flush across the eyeball into the lacrimal canaliculi medially, then into the lacrimal sac and finally into the nasolacrimal duct which empties into the nasal cavity
  13. 13. Anatomy of the Eye
  14. 14. Anatomy of the Eye  Lacrimal secretions are high in antibodies and lysozyme to help cleanse and protect the eye from foreign substances
  15. 15. Anatomy of the Eye  There are six extrinsic or external eye muscles  Attached to the outer surface to each eye  Produce gross eye movement  Make it possible to follow objects  Controlled by the cranial nerves (abducens, oculomotor, trochlear)
  16. 16. Anatomy of the Eye
  17. 17. Anatomy of the Eye  The eye itself, commonly called the eyeball, is a hollow sphere  The wall is composed of three layers  The interior is filled with fluids called humors that help maintain its shape
  18. 18. Anatomy of the Eye  The lens is the main focusing apparatus of the eye and is supported upright within the eye cavity, separating it into two chambers
  19. 19. Anatomy of the Eye  Three layers of the eyeball wall:  1. Fibrous  2. Vascular  3. Sensory
  20. 20. Anatomy of the Eye  1. The Fibrous Layer  Outermost layer  Consists of the sclera (protective layer) and cornea (transparent layer)
  21. 21. Anatomy of the Eye  1. Fibrous Layer  Sclera - the white of the eye ◦ Thick, connective tissue  Cornea – the window of the eye, where light enters the eye ◦ Many nerve endings (pain fibers) ◦ Most exposed part of the eye ◦ Self-repairing
  22. 22. Anatomy of the Eye  Fun Fact: the cornea is the only tissue in the body that can be transplanted from one person to another without the worry of rejection  Because the cornea has no blood vessels, it is beyond the reach of the immune system
  23. 23. Anatomy of the Eye
  24. 24. Anatomy of the Eye  2. Vascular Layer  3 distinguishable regions ◦ 1. Choroid (blood-rich, contains dark pigment) ◦ Prevents light scattering inside the eye ◦ 2. Ciliary body (smooth muscle to which the lens is attached by the ciliary zonule) ◦ 3. Iris (pigmented part of the eye) ◦ Includes the pupil, where light passes
  25. 25. Anatomy of the Eye
  26. 26. Anatomy of the Eye  2. Vascular Layer  Circularly and radially arranged smooth muscle fibers form the iris  Regulates the amount of light entering the eye to see clearly in available light  In bright light/close vision the pupil contracts, in dim light/distant vision the pupil dilates
  27. 27. Anatomy of the Eye
  28. 28. Anatomy of the Eye  3. Sensory Layer  Two-layered retina  Extends anteriorly to the ciliary body
  29. 29. Anatomy of the Eye  3. Sensory Layer  The outer pigmented layer of the retina is full of pigmented cells that absorb light and prevent light scattering  Also act as phagocytes, and store vitamin A
  30. 30. Anatomy of the Eye  3. Sensory Layer  The inner neural layer of the retina contains millions of photoreceptors – rods and cones
  31. 31. Anatomy of the Eye  3. Sensory Layer  Electrical signals pass from the photoreceptors via a 2 neuron chain, then leave via the optic nerve  This nerve impulse is transmitted to the optic cortex and results in vision
  32. 32. Anatomy of the Eye  3. Sensory Layer  Photoreceptors are over the entire retina except at the optic disc, where the optic nerve leaves the eyeball  This is your blind spot!
  33. 33. Anatomy of the Eye  Rods allow us to see in gray tones and dim light  Peripheral vision  More dense at the edges or periphery of the retina
  34. 34. Anatomy of the Eye  Night Blindness (Nyctalopia)  Interferes with rod function and limits the ability to see at night  Usually results from prolonged vitamin A deficiency ◦ Causes neural retina deterioration
  35. 35. Anatomy of the Eye  Cones allow for details and color to be seen in bright light  Densest in the center of the retina
  36. 36. Anatomy of the Eye  Lateral to each blind spot is the fovea centralis, a tiny pit that contains only cones  Greatest visual acuity (sharpest vision)
  37. 37. Anatomy of the Eye  There are three varieties of cones:  “blue”  “green”  “red” (actually responds to green and red)
  38. 38. Anatomy of the Eye  Impulses received at the same time from more than one type of cone by the visual cortex are interpreted as intermediate colors  Ex. both blue and red result in purple
  39. 39. Anatomy of the Eye  When all three types of cones are stimulated we see white  “mixing” of colors occurs in the brain, not the retina
  40. 40. Anatomy of the Eye  Color blindness  Lack of one type of cone leads to partial color blindness  Lack of all three cones leads to total color blindness  Sex-linked trait, almost exclusively in males
  41. 41. Color Blindness Test #1
  42. 42. Color Blindness Test #2
  43. 43. Color Blindness Test #3
  44. 44. Anatomy of the Eye  Lens: a flexible biconvex crystal-like structure  Light entering the eye is focused on the retina by the lens  Lens is held upright by the ciliary zonule
  45. 45. Anatomy of the Eye
  46. 46. Anatomy of the Eye  The lens divides the eye into two segments:  1. anterior (aqueous) segment ◦ Contains aqueous humor ◦ Provides nutrients for lens and cornea  2. posterior (vitreous) segment ◦ Filled with vitreous humor ◦ Keeps eyeball from collapsing inward  Both provide intraocular pressure
  47. 47. Anatomy of the Eye
  48. 48. Anatomy of the Eye  Aqueous humor is reabsorbed into the venous blood through the scleral venous sinus, or the canal of Schlemm
  49. 49. Anatomy of the Eye  Cataracts  In youth, the lens is transparent and a hardened jelly-like texture  As we age, it becomes increasingly hard and opaque
  50. 50. Anatomy of the Eye  Cataracts cause vision to become hazy and distorted, and eventually cause blindness  Risk factors: Type II diabetes, exposure to intense sunlight, heavy smoking  Current treatments: surgical removal, replacement lens implants or specialized glasses
  51. 51. Cataract Surgery
  52. 52. Anatomy of the Eye  Glaucoma  Occurs when the drainage of the aqueous humor is blocked, and fluids back up  Pressure on the eye increases, compressing the retina and optic nerve
  53. 53. Anatomy of the Eye  Glaucoma causes pain and possible blindness  Progresses slowly and painlessly until the damage is done  Tonometer is used to test intraocular pressure
  54. 54. Anatomy of the Eye  Glaucoma is commonly treated with eyedrops that increase the rate of drainage  Laser or surgical enlargement of the drainage channel can also be used
  55. 55. Anatomy of the Eye  An ophthalmoscope is an instrument used to illuminate the interior of the eyeball  Conditions such as diabetes, arteriosclerosis, and degeneration of the optic nerve and retina, can be detected by examination with an ophthalmoscope
  56. 56. Anatomy of the Eye  Ophthalmascope
  57. 57. Anatomy of the Eye  Ophthalmascope
  58. 58. Anatomy of the Eye
  59. 59. Pathway of Light/Light Refraction
  60. 60. Pathway of Light  When light passes from one substance to another substance of a different density, it’s speed changes and the rays are bent or refracted  Light rays are refracted in the eye when they encounter the cornea, aqueous humor lens and vitreous humor
  61. 61. Pathway of Light  The refractive powers of the corneas and humors are constant  The refractive power of the lens changes by changing its shape
  62. 62. Pathway of Light
  63. 63. Pathway of Light  The greater the lens convexity (bulge) the more it bends the light  The flatter the lens, the less it bends light
  64. 64. Pathway of Light  The resting eye is set for distant vision  Light from a distant source (+20ft) approaches the eye in parallel rays  The lens does not need to change shape to focus
  65. 65. Pathway of Light  Light from a near source tends to scatter or diverge  The lens must bulge to make clear vision possible  In order to bulge, the ciliary body contracts, and the lens becomes more convex
  66. 66. Pathway of Light  Accommodation: the ability of the eye to focus specifically on close objects
  67. 67. Pathway of Light
  68. 68. Pathway of Light  The image formed on the retina as a result of the light-bending activity of the lens is a real image – it is reversed from left to right, upside down, and smaller than the object  The farther away the object is, the smaller its image on the retina
  69. 69. Pathway of Light
  70. 70. Pathway of Light  The normal eye can accommodate properly  Vision problems occur when the lens is too strong or too weak, or from structural problems
  71. 71. Pathway of Light
  72. 72. Pathway of Light  The eye that focuses images correctly on the retina is said to have emmetropia
  73. 73. Pathway of Light  Myopia is nearsightedness  It occurs when the parallel light rays from distant objects fail to reach the retina and instead are focused in front of it  Results from eyeball that is too long, a lens that is too strong, or a cornea that is too curved  Requires concave corrective lenses
  74. 74. Pathway of Light
  75. 75. Pathway of Light  Hyperopia is farsightedness  It occurs when the parallel light rays from distant objects are focused behind the retina  Lens is usually short or “lazy”  Often subject to eyestrain  Requires convex corrective lenses
  76. 76. Pathway of Light
  77. 77. Pathway of Light  Unequal curvatures in different parts of the cornea or lens cause astigmatism  In this condition, images occur because points of light are focused not on points on the retina but as lines  Special cylindrically ground lenses or contacts are used to correct this problem
  78. 78. Pathway of Light
  79. 79. Visual Fields and Visual Pathways to the Brain
  80. 80. Visual Fields and Pathways  The optic nerve is located in back of the eye, and carries impulses form the retina to the brain
  81. 81. Visual Fields and Pathways  At the optic chiasma the fibers from the medial side of each eye cross over to the opposite site of the brain
  82. 82. Visual Fields and Pathways  The fiber tracts that result are called the optic tracts  Each optic tract contains fibers from the lateral side of the eye on the same side and the medial side of the opposite eye
  83. 83. Visual Fields and Pathways  The optic tract fibers synapse with neurons in the thalamus, whose axons form the optic radiation.  This runs to the occipital lobe of the brain
  84. 84. Visual Fields and Pathways  There they synapse with the cortical cells, and visual interpretation, or seeing, occurs.
  85. 85. Visual Fields and Pathways  Each side of the brain receives visual input from both eyes  Lateral of the same side eye, medial form the other eye
  86. 86. Visual Fields and Pathways  Each eye “sees” a slightly different view  The visual fields of each eye overlap  Humans have binocular vision, “two-eyed” vision  Allows for depth perception as the visual cortex fuses the two images
  87. 87. Visual Fields and Pathways  Hemianopia: the loss of the same side of the visual field in both eyes  Results from damage to the visual cortex
  88. 88. Visual Fields and Pathways  People who suffer from hemianopia are not able to see things past the middle of the visual field on either the left or right side
  89. 89. Visual Fields and Pathways
  90. 90. Eye Reflexes
  91. 91. Eye Reflexes  Both the internal and external eye muscles are needed for proper eye function  The external muscles, as mentioned earlier, are responsible for following moving objects  They are also responsible for convergence
  92. 92. Eye Reflexes  Convergence: the reflexive movement of the eyes medially when viewing close objects  Both eyes are aimed toward the near object being viewed
  93. 93. Eye Reflexes  When the eyes are suddenly exposed to bright light, the pupils instantly constrict  This is called the photopupillary reflex
  94. 94. Eye Reflexes  The photopupillary reflex prevents excessively bright light from damaging the photoreceptors
  95. 95. Eye Reflexes  The accomodation pupillary reflex also constricts the pupil, but occurs when viewing close objects  It allows for more acute vision
  96. 96. Eye Reflexes  Reading requires almost continuous work by both sets of muscles  Ciliary fibers cause the lens to bulge, the iris constricts the pupil, convergence occurs  This is why eyestrain often occurs
  97. 97. Ears Hearing and Balance
  98. 98. The Ear  Ears are key to the senses of hearing and balance  Sound vibrations move fluids to stimulate hearing receptors  Gross movements of the head move fluids in the balance organs
  99. 99. The Ear  Receptors that respond to physical forces are called mechanoreceptors  These two sense organs are housed in the ear  They respond to different stimuli and are activated independently of one another
  100. 100. Anatomy of the Ear
  101. 101. Anatomy of the Ear  Anatomically, the ear is divided into 3 major sections:  1. external (outer) ear - hearing  2. middle ear - hearing  3. internal (inner) ear – hearing and equilibrium
  102. 102. Anatomy of the Ear
  103. 103. External Ear  The external (outer) ear is composed of the auricle and the external acoustic meatus
  104. 104. External Ear  The auricle (pinna) is “the ear,” the shell- shaped structure surrounding the auditory canal opening  It collects and directs sound waves into the auditory canal  Function is weak in humans
  105. 105. External Ear  The external acoustic meatus (auditory canal) is a short, narrow chamber (1x.25 in) carved into the temporal bone of the skull
  106. 106. External Ear  The auditory external acoustic meatus has skin- lined walls with ceruminous glands which secrete cerumen (earwax)  It provides a sticky trap for foreign bodies and repels insects
  107. 107. External Ear  Sound waves entering the auditory canal eventually hit the tympanic membrane (eardrum) and cause it to vibrate  The canal ends at the eardrum, which separate the external from the middle ear
  108. 108. Middle Ear  The tympanic cavity or middle ear is a small, air-filled, mucosa-lined cavity within the temporal bone
  109. 109. Middle Ear
  110. 110. Middle Ear  It is flanked laterally by the eardrum and medially by a bony wall with two openings, the oval window and the inferior, membrane- covered round window
  111. 111. Middle Ear  The pharyngotympanic (auditory) tube also called the eustachian tube runs obliquely downward to link the middle ear cavity with the throat, and the mucosae lining the two regions are continuous
  112. 112. Middle Ear  Normally the auditory tube is flattened and closed  Swallowing and yawning opens this tube briefly to equalize the pressure in the middle ear cavity  The eardrum does not vibrate freely unless the pressure on both surfaces is the same
  113. 113. Middle Ear  When the pressures are unequal, the eardrum bulges inward or outward making hearing difficult or causes earaches  The sensation of ear- popping is the equalizing of pressures
  114. 114. Middle Ear  An inflammation of the otitis media is common in children with sore throats  The eardrum becomes inflamed, bulges and often the cavity fills with fluid or pus  A myringotomy is sometimes required to relieve the pressure  A tiny tube can also be used for drainage
  115. 115. Middle Ear
  116. 116. Middle Ear  The tympanic membrane is spanned by the three smallest bones in the body, the ossicles  The ossicles transmit the vibratory motion of the eardrum to the fluids of the inner ear
  117. 117. Middle Ear  The ossicles are named for their shape:  Hammer (malleus)  Anvil (incus)  Stirrup (stapes)
  118. 118. Middle Ear  When the eardrum moves, the hammer moves as well, and transfers the vibration to the anvil  The anvil passes the vibration to the stirrup
  119. 119. Middle Ear  The stirrup which presses on the oval window of the inner ear  The movement at the oval window sets the fluids of the inner ear into motion, eventually exciting the hearing receptors  How Hearing Works
  120. 120. Inner Ear  The internal ear is a maze of bony chambers called the bony, or osseous, labyrinth, located deep within the temporal bone behind the eye socket
  121. 121. Inner Ear  The three subdivisions of the bony labyrinth are the:  1. cochlea (spiral, pea size)  2. vestibule  3. semicircular canals
  122. 122. Inner Ear  The inner ear is a cavity filled with a plasmalike fluid called perilymph  Suspended in the perilymph is a membraneous labyrinth, a system of membrane sacs that more or less follow the shape of the bony labyrinth
  123. 123. Inner Ear  Suspended in the perilymph is a membranous labyrinth, a system of membrane sacs that more or less follow the shape of the bony labyrinth  The membranous labyrinth itself contains a thicker fluid called endolymph  How Hearing Works
  124. 124. Mechanisms of Equilibrium
  125. 125. Mechanisms of Equilibrium  Equilibrium is not an easy sense to describe  It responds to various head movements  The equilibrium receptors of the inner ear, are collectively called the vestibular apparatus
  126. 126. Mechanisms of Equilibrium  The vestibular apparatus can be divided into two functional aspects:  1. static equilibrium  2. dynamic equilibrium
  127. 127. Static Equilibrium
  128. 128. Static Equilibrium  Within the membrane sacs of the vestibule are receptors called maculae  The maculae are essential to the sense of static equilibrium: balance concerned with changes in the position of the head
  129. 129. Static Equilibrium  The maculae report on changes in the position of the head in space with respect to the pull of gravity when the body is not moving  Give information on which way is up or down  Help keep the head erect
  130. 130. Static Equilibrium
  131. 131. Static Equilibrium  Each macula is a patch of receptor (hair) cells with their “hairs” embedded in the otolithic hair membrane, a jellylike mass studded with otoliths or “earstones,” tiny stones made of calcium salts
  132. 132. Static Equilibrium  As the head moves, the otoliths roll in response to changes in gravitational pull  The surrounding gel pulls, slides over the hair cells, bending the hairs
  133. 133. Static Equilibrium
  134. 134. Static Equilibrium  This movement activates the hair cells, which send impulses along the vestibular nerve to the cerebellum of the brain, giving information on head position in space
  135. 135. Dynamic Equilibrium
  136. 136. Dynamic Equilibrium  Dynamic equilibrium receptors, found in the semicircular canals, respond to angular or rotary movements of the head
  137. 137. Dynamic Equilibrium  Within the ampulla, a swollen region at the base of each membranous semicircular canal is a receptor region called a crista ampulliaris or crista
  138. 138. Dynamic Equilibrium  The crista consists of a tuft of hair cells covered with a gelatinous cap called cupula  When your head moves in arclike/angular motion, the endolymph lags behind
  139. 139. Dynamic Equilibrium  As the cupula drags against the stationary endolymph the cupula bends with the body’s motion
  140. 140. Dynamic Equilibrium  This motion stimulates the hair cells, and impulses are transmitted up the vestibular nerve to the cerebellum  Bending the cupula in the opposite direction reduces impulse generation
  141. 141. Dynamic Equilibrium  When you are moving at a constant rate, the receptors gradually stop sending impulses, and you no longer have the sensation of motion until your speed or direction of movement changes
  142. 142. Dynamic Equilibrium  The receptors of the semicircular canal and vestibule are responsible for dynamic and static equilibrium separately, they usually act together
  143. 143. Dynamic Equilibrium  Besides these equilibrium senses, sight and proprioceptors of the muscles and tendons are also important in providing information used to control balance to the cerebellum
  144. 144. Mechanism of Hearing
  145. 145. Mechanism of Hearing  Within the cochlear duct, the endolymph- containing membranous labyrinth of the cochlea is the spiral organ of Corti  This contains the hearing receptors, or hair cells
  146. 146. Mechanism of Hearing  The scalae, chambers, above and below the cochlear duct contain perilymph  Sound waves that reach the cochlea through vibrations of the eardrum, ossicles and oval window set the cochlear fluids in motion
  147. 147. Mechanism of Hearing  As the sound waves are transmitted by the ossicles, their force is increased by the lever activity of the ossicles  The total force exerted in the large eardrum reaches the oval window, which sets the inner ear fluids in motion
  148. 148. Mechanism of Hearing  The pressure waves set up vibrations in the basilar membrane  The receptor cells are stimulated when the hairs are bent or tweaked by the movement of the tectorial membrane
  149. 149. Mechanism of Hearing
  150. 150. Mechanism of Hearing  The length of the fibers spanning the basilar membrane “tunes” specific regions to vibrate at specific frequencies  Shorter fibers are disturbed by high- pitched sounds  Longer fibers are disturbed by low-pitched sounds
  151. 151. Mechanism of Hearing
  152. 152. Mechanism of Hearing  Once stimulated, the hair cells transmit impulses along the cochlear nerve to the auditory cortex
  153. 153. Mechanism of Hearing  Sound usually reaches the two ears at different times, or “in stereo”  This helps us determine the location of sounds
  154. 154. Mechanism of Hearing  We are able to habituate, or adapt, to constant, repetitive sounds
  155. 155. Mechanism of Hearing  Hearing is also the last sense to leave us when we fall asleep and the first to return when we wake up
  156. 156. Hearing and Equilibrium Deficits
  157. 157. Hearing and Equilibrium Deficits  Deafness: hearing loss of any degree  Two main kinds:  1. conduction  2. sensorineural
  158. 158. Hearing and Equilibrium Deficits  Temporary or permanent conduction deafness results when something interferes with the conduction of sound vibrations to the fluids of the inner ear
  159. 159. Hearing and Equilibrium Deficits  Conduction deafness can be caused by  Earwax  Otosclerosis, the fusion of the ossicles  Ruptured eardrum
  160. 160. Hearing and Equilibrium Deficits  Sensorineural deafness occurs when there is degeneration or damage to the receptor cells in the spiral organ of Corti, cochlear nerve or neurons in the auditory cortex
  161. 161. Hearing and Equilibrium Deficits  Hearing aids use the skull bones to conduct sound vibrations to the inner ear  They are generally very successful in helping people with conduction deafness to hear  They are less helpful for people with sensorineural deafness
  162. 162. Hearing and Equilibrium Deficits  Equilibrium problems are usually obvious; nausea, dizziness, and problems in maintaining balance  There are often strange, jerky eye movements
  163. 163. Hearing and Equilibrium Deficits  Meniere’s Syndrome causes progressive deafness of the inner ear  Sufferers become nauseated and often have howling or ringing sounds in their ears and vertigo
  164. 164. Hearing and Equilibrium Deficits  Vertigo: a sense of spinning so severe that they cannot stand up without extreme discomfort
  165. 165. Chemical Senses - Taste and Smell
  166. 166. Taste and Smell  Both senses use chemoreceptors Stimulated by chemicals in solutions Taste has four types of receptors Smell can differentiate a large range of chemicals  Both senses complement each other and respond to many of the same stimuli
  167. 167. Olfaction - Smell  Olfactory receptors are in the roof of the nasal cavity Neurons with long cilia Chemicals must be dissolved in mucus for detection
  168. 168. Olfaction - Smell
  169. 169. Olfaction - Smell  Impulses are transmitted via the olfactory nerve  Interpretation of smells is made in the cortex (olfactory area of temporal lobe)
  170. 170. http://asb.aecom.yu.edu/histology/labs/images/slides/A74_OlfactoryEpith_40X.jpg
  171. 171. Taste  Taste buds house the receptor organs  Location of taste buds Most on the tongue Soft palate Cheeks
  172. 172. Tongue and Taste  The tongue is covered with projections called papillae  Filiform papillae – sharp with no taste buds  Fungiform papillae – rounded with taste buds  Circumvallate papillae – large papillae with taste buds  Taste buds are found on the sides of papillae
  173. 173. http://neuromedia.neurobio.ucla.edu/campbell/oral_cavity/wp_images/96_fungiform.gif
  174. 174. http://www.esg.montana.edu/esg/kla/ta/vallate.jpg
  175. 175. Structure of Taste Buds  Gustatory cells are the receptors Have gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva
  176. 176. Structure of taste buds
  177. 177. Structure of taste buds  Impulses are carried to the gustatory complex (parietal lobe) by several cranial nerves because taste buds are found in different areas Facial nerve Glossopharyngeal nerve Vagus nerve
  178. 178. http://www.biosci.ohiou.edu/introbioslab/Bios171/images/lab6/Tastebuds.JPG
  179. 179. Taste Sensations  Sweet receptors Sugars Saccharine Some amino acids  Sour receptors Acids  Bitter receptors Alkaloids  Salty receptors Metal ions  Umami Glutamate, aspartate (MSG, meats)
  180. 180. Development of the Special Senses  Formed early in embryonic development  Eyes are outgrowths of the brain  All special senses are functional at birth

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