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Transcript
The Special Senses
1
Objectives:
• List and describe the major forms of special
senses.
• Identify the location, the structure, and
function of the special sense organs.
a. Tactile
b. Gustation
c. Olfactory
d. Visual
e. Auditory
2
Tactility: Touch
• Specialized nerve receptors are located in the dermal layers of
the skin which are sensitive to pressure associated with touch,
heat, cold, and pain. These are specially modified sensory
neurons called receptors. There are also receptors in muscle
tissue which detect stretching, force of contraction and the
stretching of tendons.
3
Skin Receptors
• Skin:
I. Free nerve endings:
a. Nocireceptors: Temperature, mechanical (pain
itching, tickle, stretching) Dermis
b. Merkel discs: Light pressure, mechanical (discriminative
touch) Dermis
c. Root hair plexus: Hair movement, mechanical dermis
II. Encapsulated Nerve Endings:
a. Meissner’s corpuscle: light pressure mechanical, Located
in hairless areas, palms or hands and soles of feet.
(discriminative touch, vibrations.) Dermis
b. Ruffini’s corpuscle: mechanical, thermal (rough and
persistent touch) Dermis
c. Krauses corpuscle: mechanical, thermal (touch, low
frequency vibrations) Dermis of mucus membranes
d. Pacinian corpuscle: Deep pressure, mechanical (deep
pressure, stretch, and high frequency vibrations) Dermis of
skin and joint capsules
4
Skin Receptors
5
Muscle Receptors
•
Muscle
I. Encapsulated nerve endings
a. Muscle spindles: stretch, mechanical, sense of muscle
length, all skeletal muscle
b. Golgi tendon receptors: stretch mechanical, muscle tension
6
• Taste buds:
Gustation: Taste
– located on the tongue, some are located within other
areas of the mouth
– Papillae: small elevated projections on the tongue
• Fungiform (sweet), circumvallate (bitter), and
foliate (sour) contain taste buds (all taste salty)
• Filiform are sensitive to touch
– Gustatory cells - specialized receptors located on
each taste bud (50-125 per taste bud); have special
hair like projections (sensitive to various chemicals acts as stimuli for various taste sensations)
– gustatory nerves - connected by the cranial nerves to
the medulla oblongata  relays the message to the
thalamus  to the gustatory center of the brain
where the stimulus is interpreted.
– Gustation and olfaction are closely associated to
produce the sensation of taste.
7
Gustation: Taste
8
Olfactory: Smell
• Sensory cells - located in the epithelial lining
of the mucous membrane of the nose
• Olfactory neural chemoreceptors - have
specialized cilia which detect the presence of
specific chemicals within the air we breath
• The neurons connected to the olfactory bulb
when stimulated sends a message to the
olfactory center of the brain where the smell
is interpreted
9
Olfactory Smell
10
Auditory (Hearing) and Balance
• The ear is a duel organ, not only is responsible for
the sense of hearing but also it functions as the
organ of balance.
• The sensation of balance and hearing are both
associated with specialized receptors with hair-like
mechanoreceptors (hair cells).
• The ear is divided into three major regions:
a. External: Pinna or auricle and auditory canal
b. Middle : Tympanic membrane (eardrum) and
auditory ossicles ( malleus (hammer), incus
(anvil) and stapes (stirrup)
c. Inner: Semicircular canals and vestibular
nerve (balance) and the cochlea and round or
oval window and the cochlear nerve (sound)
11
Auditory (Hearing) and Balance
12
Hearing
• Outer ear:
– Pinna – ear flap
• Collects and directs sound waves into the ear
– Auditory canal – channels waves to the ear
drum; houses ceruminous glands
• Ceruminous glands - secrete ear wax (cerumin) to
keep ear drum moist
– Tympanic membrane – ear drum
• Catches vibrations and sends them to the bones of
the inner ear; separates the outer and middle ear
13
Hearing
• Middle ear:
– Eustachian tube – connects the ear to the
throat and equalizes pressure
– Ossicles:
• Hammer (malleus) – outermost bones, receives
vibrations from tympanic membrane
• Anvil (incus) – middle bone
• Stirrup (stapes) – innermost bone, transfers
vibrations to the cochlea
14
Hearing
• Inner Ear:
– Vestibule – space between the cochlea and
semicircular canals
– Cochlea – snail shaped structure; fluid filled with
endolymph and perilymph; contains the organ of corti
– Organ of Corti – tiny hair-like cells that pick up
vibrations and transfer them to the auditory nerve
– Semicircular canals – contain liquid (perilymph) and
tiny hair-like cells that blend with motion to help
maintain equilibrium
– Auditory nerve – carries information from the ear to
the temporal lobe of the brain
15
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
16
Auditory (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.
17
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
18
Hearing pathway
• Pinna  auditory canal  tympanic
membrane  malleus  incus  stapes
 cochlea  Organ of Corti  auditory
nerve  temporal lobe of brain
19
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
20
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
21
Balance
22
Balance
23
Quiz
Key Choices
Malleus
Tympanic
membrane
1.
Incus
Pinna
6.
Cochlea
Auditory canal
5.
Eustachian
tube
Semicircular
canals
3.
4.
2.
24
Vision
• The eye is the organ of vision.
• It converts light energy into electrical nerve
impulses which are then interpreted by the
brain as sight.
• The lens of the eye focus light on the retina.
• The retina contain specialized nerve
receptors sensitive to light intensity (rods)
and wavelengths or colors of light (cones).
• The optic nerve then carries the message to
the brain where it is interpreted as sight in
the visual center of the occipital lobes.
25
Vision
• Conjunctiva – the thin, transparent tissue that
covers the outer surface of the eye
– Secretes oils and mucus that moisten and lubricate
the eye
• Cornea – clear, allows light to enter the eye.
– Most anterior part of the eye.
• Eye lashes – protect the eye from debris
• Eye lid – works to keep the eye moist (blink)
26
Vision
• Sclera – the white of the eye
– Holds the shape and protects the inner eye
• Lens – directs images to the retina; helps focus
on images by changing shape
• Lacrimal gland – produces tears
– Tears cleanse and moisten they eye, kills bacteria
• Pupil – a space in the iris where light enters
• Iris – the colored part of the eye; muscular
– Controls the amount of light entering the eye by
changing the size of the pupil
27
Vision
• Choroid coat – middle of the 3 eye layers;
has dark pigment to keep light from
scattering
• Aqueous humor – watery substance
anterior to the lens; helps maintain shape
of eye ball and refracts light
• Vitreous humor – jelly-like substance
found posterior to the lens inside the
eyeball; helps maintain eyeball shape and
refracts light
28
Vision
• Ciliary body – muscle that controls the
shape of the lens
• Suspensory ligaments – hold the lens in
place
• Retina – interior most layer of the eye
– Rich in nerve cells
• Rods – cells for dim light
• Cones – receptor cells for sensitivity to bright light
(color)
• Macula – center region of the retina; area
for sharp central vision
29
Vision
• Optic Nerve – carries impulse from the
retina to the occipital lobe of the brain
• Optic disk – blind spot; no receptors
therefore no vision
• Fovea centralis – site of cones
• Extrafovial region – area of rods
– Also where peripheral vision occurs
30
Eye Structure
31
Retina Structure
32
Visual pathway
• Cornea  aqueous humor  iris & pupil
 lens  vitreous humor  retina  optic
nerve  occipital lobe of brain
33
Light Refraction
34
Common Refraction Disorders
35
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
36
Eye Disorders
• Cataracts – clouding of the lens, usually
due to aging
37
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
38
Ishihara Color Blindness Test
Normal Color Vision
25
29
45
56
6
8
39
Ishihara Color Blindness Test
Red-Green Color Blind
25
Spots
Spots
Spots
56
spots
40
Ishihara Color Blindness Test
• normal color vision: 5
revealed in the dot
pattern.
• Red/Green color
blindness: 2 revealed
in the dots.
41