THE SENSES
Sight
Hearing
Taste
Smell
Touching
General Sense Organs
• widely distributed throughout the body
• detect stimuli (pain, touch, temperature,
pressure);
• Ex.: free nerve endings, Meisners & Pacinian
corpuscles
Special Sense Organs
• large and complex grouping of specialized receptors
(eye, ear, tongue, nose)
• types of stimuli include:
Photoreceptors  light
Chemoreceptors  chemicals
Mechanoreceptors  movement
Converting a Stimulus into a Sensation
1. Detect stimulus.
2. Stimulus 
converted to a
nerve impulse.
3. Nerve
impulse 
perceived
as a sensation
in the CNS.
THE EYE (photoreceptors) http://www.youtube.com/watch?v=GMGSw3GDyJQ
http://www.youtube.com/watch?v=RE1MvRmWg7I
CORNEA – transparent part of sclera that covers the Iris
tough outer coat;
the white of the
eye
PUPIL – hole
in center of the Iris
SCLERA
IRIS – colored part
http://www.youtube.com/watch?v=JunCyiGfreo
contains
rods (night
vision)
and cones
(colorvision)
-pigmented layer
that prevents
scattering of light
-nourishes eye
Ciliary muscle – muscles that control the
opening & closing of the eye
fluid in anterior of lens
fluid in
posterior of
lens
directs light rays to retina
no
receptors
To view distant objects: ciliary muscle relaxes & lens flattens
To view near objects: ciliary muscle contracts & lens curves
onjunctiva –
membrane that
lubricates the eye
C
Conjunctivitis – infection
of conjunctiva
Normal focusing: clear, upside down image on retina,
brain rights the image automatically
 Myopia (nearsightedness): eyeball is too long; lens
focuses image in front of retina
 Hyperopia (farsightedness): eyeball is too short; lens
focuses image behind retina
 Astigmatism: irregular curvature of lens / cornea;
ripples or flat spots in image
 Glaucoma: fluid build up
in the eye; damages optic
nerve & restricts blood
flow; can cause blindness
 Colorblindness: color perception problem; 1) lacking
green and/or red cones and/or blue cones or 2) absorbs an
abnormal wavelength of color
THE EAR (mechanoreceptors)
Structure :
1. External ear
or auricle - surrounds external auditory
canal
3 smallest bones in body
2. Middle ear
3. Inner ear
Function:

tympanic
membrane
Hearing: sound vibrations
 Equilibrium and balance: fluid movements
http://www.youtube.com/watch?v=0jyxhozq89g
Tympanic membrane
Normal
Swimmer’s ear (Otitis Media)
sound waves travel
through the canal, strike the
eardrum, and cause it to
vibrate.

http://www.youtube.com/watch?v=ahCbGjasm_E
(function)
- contains hairs
that respond to
ear fluid set in
motion by sound
waves
http://www.blackwellpublishing.com/matthews/ear.html
Eustachian Tube:
connects middle
ear to the throat
TASTE (chemoreceptors)
http://www.youtube.com/watch?v=0hwOL91cjwM
Papillae – contain tastebuds
Taste buds –
chemoreceptor
s for taste
http://www.bbc.co.uk/science/humanbody/body/factfiles/taste/taste_ani_f5.swf
“Primary” taste
sensations:
1. Sweet
2. Sour
3. Bitter
4. Salty
5th Taste: UMAMI ??
chemicals (odors/tastes) must be dissolved in
nasal mucus / saliva in order to be detected; sent
as an impulse to be interpreted
 olfactory receptors (detect odors) are
extremely sensitive but easily fatigued
impulses are closely associated with areas of
the brain important in memory / emotion
 a cold that interferes with olfactory receptors
will dull taste sensations
SMELL (chemoreceptors)
http://education-portal.com/academy/lesson/the-sense-of-smell-olfactory-bulb-and-the-nose.html#lesson
Concept Check #1
1. What are 3 types of receptors that your
special sense organs detect. State the organ that
detects each stimuli.
Photoreceptors – eye
Chemoreceptors–tongue/nose
Mechanoreceptors - ear
2. Explain how a stimulus turns into a sensation.
a) stimulus detected b) converted into an impulse
c) Perceived as a sensation in the CNS
3. Draw a picture of an eye and label the cornea,
sclera, pupil, & iris.
4. What are the 2 layers behind the sclera?
Choroid – prevents scattering of light
Retina – contains rods & cones for night / day vision.
Concept Check #2
5. How does the lens change to view distant and near
objects?
Distant – lens flattens
Near – lens curves
6. What happens during normal focusing?
Clear, upside down image on retina – brain rights it automatically.
7. Name and describe any 3 diseases/disorders
associated with the eye.
Myopia, hyperopia, colorblindness, glaucoma, astigmatism
8. Draw the ear and label the pinna (auricle), external
auditory canal, ossicles, eustachian tube, and
cochlea.
Concept Check #3
9. Why is the ear considered a mechanoreceptor?
Detects fluid movements set in motion by sound waves
10. What must happen 1st before odors and tastes
can be interpreted as stimuli?
dissolved in mucus and/or saliva
11. Draw a picture of the tongue and label the
location of the 4 different taste sensations.