Download Special Senses

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http://faculty.washington.edu/chudler/chvisi
on.html
I Senses of the body
A. General sensory receptors are found all over
the body.
1. Proprioceptors of muscles and joints.
2. Pressure, pain, touch, and temperature
receptors of the skin.
3. Special senses include the following with
special receptors/organs:
Hearing
Taste
Vision
Smell
Equilibrium
II The eye and vision (70% of all
sensory receptors are in the eye)
A. Structures of the eye
1. Eyelashes – Prevent
debris from entering eye
2. Eyelids – Cover and
protect the eye
3. Conjunctiva – Lines the
eyelid and part of the
surface of the eyeball.
Secretes mucus for
lubrication.
4. Lacrimal Glands secrete the
dilute salt solution with
enzymes and antibodies,
5. Extrinsic eye muscles –
Six muscles attached to
the outer eye surface,
responsible for gross
motor movement of the
eyeball.
6. Meibomian glands –
specialized sebaceous
glands to lubricate eye.
7. Ciliary glands – modified
sweat glands
between
eyelashes for lubrication.
8. Eye ball – hollow sphere made from
3 tunics (coats) and is filled with a
liquid (humors). Divided into two
chambers by the lens.
a. Tunics
i. Sclera – outermost layer, thick
and white with a transparent
center called the cornea (where
light enters the eye).
ii. Choroid – blood rich nutritive tunic with a dark
pigment (prevents light from scattering inside the
eye). Forms the ciliary body and the iris (smooth
muscles). Iris has a rounded opening – pupil –
which regulates the amount of light entering the
eye.
1. Ciliary body – attaches to
the lens to
modify shape
2. Iris – contracts and relaxes to control pupil
size.
iii. Retina – Sensory tunic; location
of cones (detects color) and
rods (low levels of light, grays
and peripheral vision). These
receptor cells lead to sensory
neurons that converge to form
the optic nerve.
1. Blind spot – on the retina
where the optic nerve is
found (no sensory receptors
so no vision at this
point)
2. Fovea centralis – area
lateral to each blind spot
where the highest
concentration of sensory
receptors is located (area of
highest visual
acuity:reading, watching TV,
driving)
-center of the macula)
b. Humors
i. Aqueous humor – in the anterior chamber of the
eye. Helps maintain intraocular pressure and
provides nutrients for lens and cornea (they lack
blood supply).
ii. Vitreous humor – in the posterior chamber of
the eye. Gel like liquid used to prevent collapse of
the eye.
B. Physiology of vision
1. Light waves travel towards the
eye and enter through
the pupil.
2. The movement of the light
waves through the structures
of the eye, bend the light rays
(hopefully to focus directly on
the retina). This is called
refraction.
3. Depending on the distance of
the object you are looking
at,
the lens must change shape (with
contraction of ciliary body) to
focus light waves on the
retina.The ability to change and
focus on objects at different
distances is called
accommodation. The image is
also inverted as the light waves
travel through the lens.
eye animation
Notice that the farther the
image, the smaller the
image on the retina.
4.
5.
6.
Once the receptors have been
stimulated, thereby changing the
shape of pigment proteins in the
cell, this change causes electrical
changes creating the nerve
impulse (Action potential!!).
The optic nerves from both eyes
cross at the optic chiasma, which
results in the left side of the
brain receiving visual information
from the right eye and vice versa.
Once the impulse has reached
the occipital lobe, the visual
information will be interpreted
and understood by known visual
information stored in that area of
the brain. Ex. recognizing
someone you have met before.
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CAN see objects
at close range
but difficulty
with distances
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CAN see things
far away but
not up close
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Lasik Eye surgery
http://www.youtube.com/watch?v=7PJ391MD
tpo
Strabismus animation
http://www.midwesteyecare.com/SubSection/index.php?Se
ctionID=7&SubSectionID=170&ParentID=59
7. Eye muscle fatique – Internal and
External muscles
a. External muscles- responsible
for convergence – reflexive
movement of the eyes medially
(toward the center) when you
view something close.
Strabismus “crossed “ eyes is
caused by unequal pulls by
these muscles. (This is not the
same thing as “lazy eye”, it is
associated with strabismus and
can result in decreased vision
in the affected eye.) The
muscles must be retrained. (If
the eyes cannot be retrained a
patient may choose to have
surgery to realign the eyes)
7. b. Internal muscles –
ciliary body constrict
focusing lens and iris
contracts reducing the
size of the pupil.
c. Over time these
muscles can become
fatigued such as when
you read for long
periods of time. Take a
break and look off in
the distance to relax
those muscles.
Cataracts- clouding of the
lens of the eye
Glaucoma- increased
intraocular pressure
5
6
7
1- fluid
2
3transp
4- muscle
athat is
attcached
to lens
8
9-gel-like fluid
a. Controls the size of the pupil, colored
part of the eye
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10. choroid
11. lens
12. vitreous
humor
13. sclera
14. iris
15. retina
16. aqueous
humor
b. Changes shapes to focus on objects by
bulging when things are up close
c. The outermost tunic or coat of the eye,
is white and protective
d. The nutritive layer of the eye, is darkly
Pigmented to prevent the scattering of light
e. The sensory tunic, contains rods and
cones
f. gel- like fluid that fills the posterior
chamber of the eye
g. The fluid that fills the anterior chamber
of the eye, provides nutrients to cornea
and lens
III
Hearing and Equilibrium
A. Mechanoreceptors are used which respond to physical
forces (movement of liquid) to convey information on
hearing and equilibrium. There are two different systems in
the ear, one for hearing and one for equilibrium.
B. Hearing
1. Anatomy of the ear
a. External ear
i. Pinna or Auricle – external auditory
meatus, gathers sound waves and
directs them down the canal.
ii. External canal – (about 1 inch), conduct
waves through the temporal bone.
iii. Ceruminous glands – secrete wax,
contains antibodies and filters debris,
also a deterrent for mosquitoes
iv. Tympanic membrane – vibrates when
sound waves strike it and transmit
vibrations to middle ear.
b. Middle ear (about the size of a dime)
i. Auditory tube – links middle
ear with throat and helps to
equalize pressure in middle ear.
Typically is closed.
ii. Oval window – connects the
stirrup (stapes) to the inner ear
on cochlea.
iii. Ossicles
1. Hammer / malleus –
transmits vibrations of the
eardrum to the next ossicle.
2. Anvil / incus – second
ossicle, transmits vibrations.
3. Stirrup / stapes –
transmits vibrations to
cochlea.
c. Inner ear (bony
chamber/labyrinth) –just
behind eye orb.
i. Cochlea (contains the
organ of corti) –
location of hair cells
(hearing receptors).
Receives vibrations
from oval window.
Made up of vestibule
and semicircular
canals. Contains a
fluid that transmits
vibrations to auditory
nerves
2. Pathway and mechanism
of hearing – the journey
of the vibration
3. Hearing Deficit Causes
a. Conduction deafness – There is an
obstruction to the conduction of
vibrations on the way to the organ of
corti. Causes include ear infection,
build
up of wax in canal, fusion of
ossicles, and
ruptured eardrum.
Hearing aids can help
by sending the
vibrations via the bone.
b. Sensorineural deafness –
Degeneration or damage to the receptor
cells. Causes include over
exposure to very
loud sounds. No treatment.
C. Equilibrium
1. Monitored by the vestibular apparatus
(includes the vestibule and semicircular canals of
inner ear). Help control balance with the
cerebellum! Where are you in space or deep in the
water?
2. Two different functions:
a. Static equilibrium – receptors in
vestibule monitor the position of the head with
respect to gravity when you are not moving.
(i.e. – sitting in your chair and you turn your
head to the side). When your head moves, the
gel moves and triggers the hair cells sending
the message to the brain via the 8th cranial
nerve (vestibular).
b. Dynamic equilibrium – Receptors are in
semicircular canals and respond to the
circular movements of the head (ex.
twirling on the dance floor, the
movements of your body while on a boat
in rough seas). The endolymph(fluid)
within the semicircular canals moves
opposite the direction that your body is
moving, this motion shifts the cupula (gel
like material) thereby stimulating the
receptor hairs. Once stimulated the
information about the movement of the
head and body is transmitted to the brain
via the vestibular nerve.
IV
Chemical Senses – These receptors respond to specific
chemicals in solution
A. Olfactory (smell)
1. Olfactory receptors are located in the roof of
each nasal cavity, there are 1000’s that each
detect a different chemical odor. These receptors
are at the top of the nasal cavity, which is why
“sniffing” intensified the smell, because more air
is forced to the top of the cavity, stimulating the
receptors.
2. The receptor cells have hairs on them (similar to
equilibrium and hearing). They are bathed in a
thick layer of mucus. As the olfactory chemicals
diffuse through the mucus, they stimulate the
receptors which send the message via the
olfactory filaments to the olfactory nerve (CN I).
3. This pathway goes directly through the limbic
system (emotional center), therefore there tends
to be strong emotional ties to smells. These
receptors, like others, can adapt to stimuli that
are constant, which is why women or men don’t
smell their own cologne or perfume after a
period of time.
V Sense of Taste
A. Receptors are called taste buds and
there are over 10,000 located on the
tongue. Very few are located on your
soft palate and the inside of your
cheek.
1. There are 4 basic taste
sensations:
a. Sweet – respond to sugar,
saccharine, and some amino
acids.
b. Sour – respond to H+ ions
(acids)
c. Bitter – respond to
alkaloids (basic)
d. Salty – respond to metal
ions
2. The regions of the tongue
don’t truly hold true, because the
receptors are pretty well evenly
distributed over the surface of the
tongue.
B. Sense of taste and certain cravings help to
satisfy homeostatic imbalances. When you
crave carbohydrates or orange juice it can be
your body’s way of communicating to your
consciousness to fulfill these deficiencies.