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SENSES
• Sensory Receptors - detect environmental
changes and trigger nerve impulses
• - somatic senses (touch, pressure, temp,
pain)
- special senses (smell, taste, vision,
equilibrium)
Receptors and Sensations
1. Chemoreceptors = stimulated by changes in chemical
concentration of substances
2. Pain receptors = respond to tissue damage
3. Thermoreceptors = by changes in temperture
4. Mechanoreceptors = changes in pressure or movement
5. Photoreceptors = by light energy
Sensation = feeling that occurs when a brain interprets a sensory
impulse
Projection = process where the cerebral cortex causes a feeling to
stem from a source (eyes, ears)
Sensory adaptation = sensory receptors stop sending signals when
they are repeatedly stimulated
Somatic Senses
1. Sensory Nerve Fibers - epithelial tissue, pain and
pressure
2. Meissner's corpuscles - hairless areas of skin (lips,
fingertips)
3. Pacinian corpuscles - deep pressure (tendons, joints)
Temperature Senses
(warm and cold receptors)
Sense of Pain
Pain Sensation
• Visceral Pain - occurs in visceral tissues such
as heart, lungs, intestine
• Referred pain - feels as though it is coming
from a different part (heart pain may be felt as
pain in arm or shoulder)
• Acute Pain - originates from skin, usually
stops when stimulus stops (needle prick)
• Chronic Pain - dull aching sensation
Regulation of Pain
• Inhibitors of Pain (natural brain chemicals can
be mimiced by drugs such as morphine)
Enkephalins
Serotonin
Endorphins
10.4 Special Senses
Smell – Olfactory
Taste – Taste Buds (Gustatory )
Hearing & Equilibrium (ears)
Sight
Sense of Smell (Olfactory)
Olfactory organs contain olfactory receptors
Odor Molecule --> olfactory receptor cell --> olfactory bulb -->
olfactory tract --> limbic system
Sense of Taste (Gustatory)
Taste buds = Papillae – Sweet, Sour, Bitter, Salty
Taste Receptors --> cranial nerves --> medulla oblongata
--> Thalamus --> Parietal Lobe of Cerebrum
• What did the right eye say to the
left eye?
• Between you and me, something
smells!
Sense of Hearing
External Ear
Auricle (pinna) - outer ear
External Auditory Meatus
Middle Ear (tympanic cavity)
• Eardrum (tympanum)
• Auditory Ossicles - malleus, incus, stapes transmit vibrations and amplify the signal
• Auditory Tube (eustachian tube) - connects
the middle ear to the throat - helps
maintain air pressure
Inner Ear
• Labyrinth - communicating chambers and tubes
Osseous Labyrinth and Membranous Labyrinth
Perilymph and Endolymph (fluids within the labyrinth)
• Semicircular Canals - sense of equilibrium
• Cochlea - sense or hearing
• Organ of Corti - contains hearing receptors, hair cells
detect vibrations
• Pathway: Nerve cells --> interpreted by the temporal
lobe of the cerebrum
Why do children get tubes put in their ears?
Inner Ear: Cochlea
• Inside the cochlea are special neurons
called HAIR CELLS
• The stapes is attached to the OVAL
WINDOW, and vibrations cause the
perilymph to vibrate; the hair cells here
transmit this vibration.
• Therefore the HAIR CELLS in this region
are receptors for HEARING.
As you age, hair cells become damaged (loud music can speed this
process along). Older people usually can’t hear frequencies that
younger people can hear. Try the hearing test!
Steps in Hearing
1. Sound waves enter external auditory meatus
2. Eardrum vibrates
3. Auditory ossicles (malleus, incus, stapes) amplify vibrations
4. Stapes hits oval window and transmits vibrations to
cochlea
5. Organs of corti contain receptor cells (hair cells) that
deform from vibrations
6. Impulses sent to the vestibulocochlear nerve
7. Auditory cortex of the temporal lobe interprets sensory
impulses
8. (Round window dissipates vibrations within the cochlea)
Cochlear Implants
A cochlear implant receives sound from
the outside environment, processes it,
and sends small electric currents near
the auditory nerve.
These electric currents activate the
nerve, which then sends a signal to the
brain. The brain learns to recognize this
signal and the person experiences this
as "hearing".
The cochlear implant somewhat
simulates natural hearing, where sound
creates an electric current that
stimulates the auditory nerve. However,
the result is not the same as normal
hearing.
How cochlear implants work
(youtube video)
Ear Was Removal
• http://www.youtube.com/watch?v=9ezkN4RId4&feature=relmfu&safety_mode=true&persis
t_safety_mode=1
Ear Tubes Surgery
• http://www.youtube.com/watch?v=TohJhfHTp3s
&feature=related&safety_mode=true&persist_saf
ety_mode=1
Sense of Equilibrium
• Static Equilibrium sense the position of
the head, maintain
stability and posture
• Dynamic Equilibrium
(semicircular canals) balance the head
during sudden
movement
• Cerebellum interprets impulses
from the semicircular
canals and maintains
overall balance and
stability
• The eye is in the orbit of the skull for protection.
• Within the orbit are 6 extrinsic eye muscles, which move
the eye.
• There are 4 cranial nerves: Optic (II),
Occulomotor (III), Trochlear (IV), and Abducens
(VI).
People of Asian descent have an EPICANTHIC FOLD in the
upper eyelid; no functional difference.
Visual Accessory Organs
• Eyelid
• Conjuctiva
• Lacrimal Gland
• Extrinsic Muscles
Eyelid
• Covers and
protects the
eye, thin skin
• Skin will not
protect you
from intense
radiation,
that’s why we
use special
goggles in a
tanning bed
CONJUNCTIVA is like a covering around the
eye and under the eyelids.
• PINK EYE (layman’s term), known as
CONJUNCTIVITIS (from bacteria, very
contagious).
• LACRIMAL GLANDS are
the largest set. They are on
the superior lateral eyelid
and they produce tears,
which drain into the nasal
cavity via the LACRIMAL
DUCT.
• The function is to moisten
and lubricate the eye
surface, and it has
enzymes to kill bacteria
(which thrive in warm, moist
conditions).
Figure 16.5b
Extrinsic Eye Muscles
Moves the eyeball
Outer Tunic
• Cornea - transparent, focuses light
rays
• Sclera – continuation of cornea,
going toward the back of the eye
(white of the eye)
• Optic Nerve – exits at the optic disk
and transmits visual information from
the eye to the brain.
Middle Tunic
Choroid Coat – contains blood
vessels
Ciliary Body – holds the lens
in place
Lens – focusing
Iris – colored portion of the
eye
Aqueous humor – liquid
surrounding the lens
Pupil – opening for light to
enter
Figure 16.9a
Inner Tunic
Retina - visual receptor cells
Fovea Centralis - region of the sharpest
vision (aka, macula)
Optic Disc – where nerve fibers leave the
eye, creating the blind spot
Vitreous Humor – supports internal parts,
fluid
Figure 16.7a
Retina
The retina is made up of PHOTORECEPTORS,
which are sensors for light.
Photoreceptors:
Rods & Cones
Located within
the retina
Figure 16.11
Rods = monochromatic (b&w)
Cones = color vision
Retinal neurons --> form optic nerves --> optic chiasma --> thalamus --> visual
cortex of the occipital lobe
Light
Refraction
The bending of light
around an object.
Images viewed by the
eye are upside down,
our brain interprets
them properly!
Accommodation – the lens changes shape to focus on objects
(ciliary muscles, suspensory ligaments)
R.O.Y.G.B.I.V
Rainbows are
seen after rain
because light is
passing through
water
droplets. This
separates the
white light into
the individual
colors of the
spectrum
We have difficult interpreting images
that are upside down
Which one is the real mona lisa?
• Fun Fact: -When you are looking at someone
you love, your pupils dilate, and they do the
same when you are looking at someone you
hate.
Problems with the Eyes
Clouding of the lens leads to a clinical condition
known as CATARACTS.
Treatment is to remove the lens and replace it with
a plastic one (which is not flexible either).
Cataract
Cataract Vision
Eye FLOATERS
are when a
capillary breaks
and cells break
off.
Floaters don’t
actually move,
the eye just tries
to track them.
Problems with the IRIS and PUPIL
The function is to constrict or dilate the pupil
(opening) to allow light in.
Therefore, it regulates the amount of light
passing to the visual receptors of the eye.
ANIRIDIA = a condition
where a person is born
without an iris
Why are all babies born with
blue eyes?
• Melanin is a brownish
pigment that adds color to
your hair, eyes, and skin. At
the time babies are born,
melanin hasn't yet been
"deposited" in the eyes' iris.
Hence, they appear blue.
• After about six months, eyes
change color depending on
the amount of melanin. If you
have a lot of it, your eyes will
turn dark brown. If you have
little, they'll stay blue. And if
you have no melanin, your
eyes may appear pink
(albino). .
Colorblindness
A genetic trait that affects boys more than girls.
The location of the gene is on the X chromosome
HYPEROPIA (far-sighted)
eyes are too short
MYOPIA (nearsighted)
eyes are too long
ASTIGMATISM
• ASTIGMATISM is when the cornea has an
irregular shape. Part of the field of
view is out of focus.
• The eyeball changes shape until age
24.
Astigmatism Vision
Lasik Surgery
See a real LASIK surgery (not for the
squeamish)
• The region where the optic nerve and blood
vessels goes in and out of the eye has no
photoreceptors = BLIND SPOT.
• Hold your hands out at 45° and that’s the location
of the blind spot.
• You can still see your hands because the other
eye sees it. Close your right eye and look for your
right hand and you’ll find the blind spot.