Special senses.pptx

SPECIAL SENSES
Michael Mutisya

3
Objectives:
• List and describe the major forms of special senses.
• Identify the location, the structure, and function of
the special sense organs.
a. Tactile-skin
b. Gustation-taste
c. Olfactory-smell
d. Visual -sight
e. Auditory-hearing

Essentials of Human Anatomy & Physiology
Special Senses

The Senses
 General senses of touch
Temperature
Pressure
Pain
 Special senses
Smell
Taste
Sight
Hearing
Equilibrium

The Eye and Vision
Slide 8.2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
 Vision is the dominant sense in humans
 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

• 40% of the cerebral cortex is involved in
processing visual information
• Diameter 2.5 cm (1 inch)
PETER

Accessory parts of the eye
• Eyebrows
• Eyelashes
• Lacrimal gland
• Muscles of the eyes -6 of them
PETER

Accessory Structures of the Eye
Slide 8.3a
 Eyebrows
 Eyelids
Meets at
medial
and
lateral
canthus
 Eyelashes Figure 8.1b

Slide 8.3b
 Eyelashes
=Meibomian
glands modified
sebacious
glands
produce an
oily secretion
to lubricate
the eye Figure 8.1b

Slide 8.3c
 Ciliary glands –
modified
sweat glands
between the
eyelashes
Figure 8.1b

Slide 8.4a
 Conjunctiva
Membrane that lines the eyelids
Connects to the surface of the eye
Secretes mucus to lubricate the eye

Slide 8.4b
 Lacrimal
apparatus
Glands,
ducts, (eye),
canals, sac,
nasolacrimal
duct
Tears:
antibodies,
lysozymes,
stress?
Figure 8.1a

15
Lacrimal apparatus
• Responsible for tears
– The fluid has mucus,
antibodies and lysozyme
• Lacrimal gland in orbit
superolateral to eye
• Tears pass out through
puncta into canaliculi into
sac into nasolacrimal duct
• Empty into nasal cavity
(sniffles)

Extrinsic Eye Muscles
Slide 8.6
 Muscles attach to the outer surface of
the eye (review cranial nerve No iii, iv,
vi)
 Produce eye movements
Figure 8.2

18
Extraocular (extrinsic) eye muscles: 6 in # “EOMs intact”
means they all work right
• Four are rectus muscles (straight)
– Originate from common tendinous or anular ring,
at posterior point of orbit
• Two are oblique: superior and inferior

19
Extraocular (extrinsic) eye muscles
Cranial nerve innervations:
• Lateral rectus: VI (Abducens n.) – abducts eye outward
• Medial, superior, inferior rectus & inf oblique: III (Oculomotor n.) –
able to look up and in if all work
• Superior oblique: IV (Trochlear n.) – moves eye down and out

When Extrinsic Eye Muscles Contract
Superior oblique- eyes look out and down
Superior rectus- eyes looks up
Lateral rectus- eyes look outward
Medial rectus- eyes look inward
Inferior rectus- eyes looks down
Inferior oblique- eyes look in and up

http://www.esg.montana.edu/esg/kla/ta/eyemusc.jpg

Structure of the Eye
Slide 8.7
 The wall is composed of three
tunics/layers
 Sclera&Cornea
fibrous outside layer
 Choroid –
middle
layer
 Sensory
tunic –
(retina) inside
layer
Figure 8.3a

24
Layers of external wall of eye
1. (outer) Fibrous: dense connective tissue
– Sclera – white of the eye
– Cornea
2. (middle) Vascular: uvea
– Choroid – posterior, pigmented
– Ciliary body
– Iris
3. (inner) Sensory
– Retina -------rods and cones

The Fibrous Tunic
Slide 8.8
 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

Choroid Layer
Slide 8.9
 Blood-rich nutritive tunic
 Pigment prevents light from scattering
 Modified interiorly into two structures
Cilliary body – smooth muscle
Iris
Pigmented layer that gives eye color
Pupil – rounded opening in the iris

http://www.phys.ufl.edu/~avery/course/3400/vision/eye_photo.jpg

Sensory Tunic (Retina)
Slide 8.10
 Contains receptor cells (photoreceptors)
Rods
Cones
 Signals pass from photoreceptors and
leave the retina toward the brain
through the optic nerve

Neurons of the Retina
Slide 8.11
Figure 8.4

Neurons of the Retina and Vision
Slide
 Rods
Most are found towards the edges of the
retina
Allow dim light vision and peripheral vision
Perception is all in gray tones

Neurons of the Retina and Vision
Slide
 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
 No photoreceptor cells are at the
optic disk, or blind spot

33
Photoreceptors: 2 types
• Rod cells
– More sensitive to light - vision permitted in dim
light but only gray and fuzzy
– Only black and white and not sharp
• Cone cells
– High acuity in bright light
– Color vision
– 3 sub-types: blue, red and green light cones
*Know that rods are for B & W and cones are for color

34
One of the Ishihara charts for color blindness
Commonly X-linked recessive: 8% males and 0.4% females

36
Ishihara Color Blindness Test
Normal Color Vision
25 29
45 56
6 8

37
Red-Green Color Blind
25 Spots
Spots 56
Spots spots

38
• normal color vision: 5
revealed in the dot
pattern.
• Red/Green color
blindness: 2 revealed in
the dots.

Lens
Slide 8.14
 Biconvex crystal-like structure
 Held in place by a suspensory ligament
attached to the ciliary body
Figure 8.3a

Internal Eye Chamber Fluids
Slide
 Aqueous humor in Anterior Segment
Watery fluid found in chamber between the
lens and cornea
Similar to blood plasma
Helps maintain intraocular pressure
Provides nutrients for the lens and cornea
Reabsorbed into venous blood
Blocked drainage = glaucoma

Internal Eye Chamber Fluids
Slide
 Vitreous humor in Posterior Segment
Gel-like substance behind the lens
Keeps the eye from collapsing
Lasts a lifetime and is not replaced

42
Visual pathway
• Cornea  aqueous humor  iris & pupil 
lens  vitreous humor  retina  optic
nerve  occipital lobe of brain

43
Visual pathways
Green is area seen by both eyes, and is
the area of stereoscopic vision
At optic chiasm, medial fibers from each eye (which
view lateral fields of vision) cross to opposite side.
Optic tracts (of crossed and uncrossed, sensing
opposite side of visual field of both eyes) synapse with
neurons in lateral geniculate of thalamus. These axons
form the optic radiation and terminate in the primary
visual cortex in the occipital lobe. Left half of visual
field perceived by right cerebral cortex, and vice
versa.

Lens Accommodation
Slide 8.16
 Light must be
focused to a point
on the 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
Figure 8.9

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.

46
Common Refraction Disorders

Astigmatism
• Unequal curvatures in
cornea & lens

51
Eye Disorders
• Myopia – nearsighted
– The eye is long so the image forms in front of the
retina
• Hyperopia – farsighted
– The eye is short so the image forms behind the
retina

52
Eye Disorders
• Cataracts – clouding of the lens, usually due to
aging

53
Eye Disorders
• Glaucoma – excess aqueous humor puts
pressure on the retina, causing damage
(usually caused by aging)
• Strabismus – cross-eyes; eye muscles are not
properly coordinated

CONJUNCTIVITIS
- Inflammation of the conjunctiva
- Caused by bacterial or viral infection
- Highly contagious
http://www.healthseva.com/images/eye/conjunctivitis.jpg

The Ear
Slide 8.20
 Houses two senses
Hearing
Equilibrium (balance)
 Receptors are mechanoreceptors

57
Auditory (Hearing) and Balance

Anatomy of the Ear
Slide 8.21
 The ear is divided into three areas
Outer
(external)
ear
Middle
ear
Inner
ear
Figure 8.12

The External Ear
Slide 8.22
 Involved in
hearing only
 Structures of
the external
ear
Pinna
(auricle)
External
auditory canal Figure 8.12

The External Auditory Canal
Slide 8.23
 Narrow chamber in the temporal bone
 Lined with skin
 Ceruminous (wax) glands are present
 Ends at the tympanic membrane

The Middle Ear or Tympanic Cavity
Slide
 Air-filled cavity within the temporal bone
 Only involved in the sense of hearing

The Middle Ear or Tympanic Cavity
Slide
 Two tubes are associated with the inner
ear
The opening from the auditory canal is
covered by the tympanic membrane
The auditory tube connecting the middle ear
with the throat
 Allows for equalizing pressure during yawning
or swallowing
 This tube is otherwise collapsed

Bones of the Tympanic Cavity
Slide
 Three bones
span the cavity
Malleus
(hammer)
Incus (anvil)
Stapes (stirrip)
Figure 8.12

Bones of the Tympanic Cavity
Slide
 Vibrations from
eardrum move
the malleus
 These bones
transfer sound
to the inner ear
Figure 8.12

Inner Ear or Bony Labyrinth
Slide
 Includes sense organs for hearing and
balance
 Filled with
perilymph
Figure 8.12

Inner Ear or Bony Labrynth
Slide
 A maze of bony chambers within the
temporal bone
Cochlea
Vestibule
Semicircular
canals
Figure 8.12

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

68
Hearing
• Inner ear continued:
– Perilymph – thin liquid in spaces of the inner ear
– Endolymph – thick liquid found in the cochlear
ducts of the inner ear

Organs of Hearing
Slide
Figure 8.13

70
Mechanism of (Hearing)
• Pinna is designed to capture sound vibrations and channel them
into the auditory canal.
• The tympanic membrane transfers the sound vibrations to the
auditory ossicles of the middle ear.
• The auditory ossicles then transfer the vibrations to the round
window of the cochlea.

71
Auditory (Hearing)
• Within the cochlea is the organ of Corti where the hair cells
are located. Each respond to a different frequency of
vibration.
• The cochlea have canals which are filled with fluid, which
surrounds the Organ of Corti.
• When the fluid is stimulated by vibrations from the round
window, the fluid transfers the vibrations to the hair cells,
which then transfers the message to the auditory center of
brain for interpretation through the acoustic nerve

72
Hearing pathway
• Pinna  auditory canal  tympanic
membrane  malleus  incus  stapes 
cochlea  Organ of Corti  auditory nerve 
temporal lobe of brain

Summary mechanisms of Hearing
Slide 8.28
 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

Mechanisms of Hearing
Slide 8.29
Figure 8.14

Organs of Equilibrium
Slide
 Receptor cells are in two structures
Vestibule
Semicircular canals
Figure 8.16a, b

Organs of Equilibrium
Slide
 Equilibrium has two functional parts
Static equilibrium – sense of gravity at rest
Dynamic equilibrium – angular and rotary
head movements
Figure 8.16a, b

Static Equilibrium - Rest
Slide 8.31
 Maculae – receptors in the vestibule
Report on the position of the head
Send information via the vestibular nerve
 Anatomy of the maculae
Hair cells are embedded in the otolithic
membrane
Otoliths (tiny stones) float in a gel around
the hair cells
Movements cause otoliths to bend the hair
cells

Function of Maculae
Slide 8.32
Figure 8.15

Dynamic Equilibrium - Movement
Slide
 Crista ampullaris –
receptors in the
semicircular canals
Tuft of hair cells
Cupula (gelatinous cap)
covers the hair cells
Figure 8.16c

Dynamic Equilibrium
Slide
 Action of angular head
movements
The cupula stimulates the
hair cells
An impulse is sent via the
vestibular nerve to the
cerebellum
Figure 8.16c

81
Quiz :label
the parts
1.
2.
5.
4.
3.
6.
Key Choices
Malleus
Tympanic
membrane
Incus
Pinna
Cochlea
Auditory canal
Eustachian
tube
Semicircular
canals

82
Hearing disorders
• Presbyscusis – deafness with aging, caused by
bones fusing; fusion makes them unable to
transfer vibrations; hearing aids can help
• Vertigo – dizziness, variety of causes
• Meniere’s disease – condition of they
labyrinth (semicircular canals) which causes
marked vertigo and fullness of the ear; may
require bed rest

83
Hearing disorders
• Otitis media – middle ear infection; build up of
fluid caused by bacteria
• Otosclerosis – bones of the ear become
immovable; causes deafness because the
stapes fuses with the bone of the ear and
does not allow sound vibrations to transfer to
the cochlea
• Tinnitus – ringing in the ear; caused by wax
build up, infection, exposure to loud sounds

Chemical Senses – Taste and
Smell
Slide 8.34
 Both senses use chemoreceptors
Stimulated by chemicals in solution
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

Types of tastes
• Sweet and salty- mainly at the tip
• Sour- at the sides of the tongue
• Bitter – at the back of the tongue
NB: a substance is tasted only when it is in a
solution form
Sensory neurons for taste are cranial nerves
VII, IX, and X, which take impulses to taste
area in parietal lobe in cerebrum

Olfaction – The Sense of Smell
Slide 8.35
 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
cortex

Olfactory Epithelium
Slide 8.36
Figure 8.17

88
Olfactory epithelium in roof of nasal cavity
– Pseudostratified columnar epithelium
– Has millions of bipolar neurons = olfactory receptor cells
Only neurons undergoing replacement throughout adult life
Olfactory cilia bind odor molecules
– Mucus captures & dissolves odor molecules
Each receptor cell has an axon - are bundled into “filaments” of olfactory
nerve
– Penetrate cribriform plate of ethmoid bone & enter olfactory bulb
Smell
(olfaction)

89
• Olfactory bulb is in forebrain
• In bulb nerve axons branch and synapse with mitral
cells (neurons in clusters of “glomeruli”)
• Mitral cells send signals via olfactory tract
Olfactory bulb__
_______Olfactory tract
___Filaments of Olfactory nerve (CN I)
*
*

91
• 1000 types of smell receptors (approx.)
• Convergence of many receptor cell signals
onto one glomerulus registers a signature
pattern
• Brain recognizes the pattern: sent to unclus
(olfactory center) and limbic area
Anosmia: absence of the sense of smell
– Trauma
– Colds or allergies producing excessive mucus
– Polyps causing blockage
– 1/3 are from zinc deficiency

The Sense of Taste
Slide 8.37
 Taste buds
house the
receptor
organs
 Location of
taste buds
Most are on
the tongue
Soft palate
Cheeks Figure 8.18a, b

The Tongue and Taste
Slide 8.38
 The tongue is covered with projections
called papillae
Filiform papillae – sharp with no taste buds
Fungifiorm papillae – rounded with taste
buds
Circumvallate papillae – large papillae with
taste buds
 Taste buds are found on the sides of
papillae

Structure of Taste Buds
Slide
 Gustatory cells are the receptors
Have gustatory hairs (long microvilli)
Hairs are stimulated by chemicals
dissolved in saliva

Structure of Taste Buds
Slide
 Impulses are carried to the gustatory
complex by several cranial nerves
because taste buds are found in
different areas
Facial nerve
Glossopharyngeal nerve
Vagus nerve

Anatomy of Taste Buds
Slide 8.40
Figure 8.18

Taste Sensations
Slide 8.41
 Sweet receptors
Sugars
Saccharine
Some amino acids
 Sour receptors
Acids
 Bitter receptors
Alkaloids
 Salty receptors
Metal ions

Taste Sensations
 Umami
 Glutamate,
 aspartate

(MSG, meats)
http://instruct1.cit.cornell.edu/courses/psych431/student2000/mle6/tonguebig.gif

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