Credits: Ed Cabalang Jr

1. Chapter 7
Sense Organs

2. CHARACTERISTICS OF
SENSATIONS
1. Projection- projecting sensation to source of stimulation
2. After-image- sensation persists in consciousness after
cessation of stimulation
3. Adaptation- continuous stimulus- one gets used to it or
ignores it
4. Local Sign- ability to recognize point of application of
stimulus
5. Contrast- sensation is affected by events which preceded
or accompany it
6. Intensity- dependent on number of receptors stimulated
and rate of transmission

3. Taste
Smell
Vision
Hearing
Balance
General SensesGeneral Senses vs.vs. __ Special SensesSpecial Senses
•Produce the
somatic senses
•Widely
distributed
receptors
•Produce the special
senses
•Grouped in localized
areas

4. Sensory Receptors
• Receptor is any structure specialized to detect a
stimulus (simple nerve ending or sense organ)
• All receptors are transducers converting one form
of energy to another

5. Types of Sensory Receptors
• By modality:
– chemoreceptors, thermoreceptors, nociceptors (pain),
mechanoreceptors and photoreceptors
• By distribution
– general (somesthetic) sense --- widely distributed
– special senses --- limited to head
• By origin of stimuli
– interoceptors = detect internal stimuli
– proprioceptors = sense position & movements of body
– exteroceptors = sense stimuli external to body

6. General Senses
skin, bones, internal organs, joints
Naked nerve endings surrounded
by one or more layers
Pacinian corpuscle
Free nerve endings
Encapsulated NerveEncapsulated Nerve
EndingsEndings
vs
UnencapsulatedUnencapsulated
Nerve EndingsNerve Endings
Deeper tissue, muscles

7. Somatic senses
1. Pain and temperature- receptors are free nerve
endings; respond to a variety of stimuli as
mechanical stretching, extremes in temperature to
produce pain
 characteristics of Heat and Cold sensation:
successive contrast, adaptation, after-image
pain, light touch, and temperature

8. • Free nerve endings include
– warm, cold & pain
• Tactile discs are associated
with cells at base epidermis
• Hair receptors monitor the
movement of hairs

9. 2. Touch and Pressure Receptors-respond to stimuli that
‘deform’ or change their shape and placement and that
more hair
– ruffini corpuscles
• heavy touch, pressure, joint movements
& skin stretching
– tactile (meissner) corpuscles
• light touch & texture
– krause end bulb
• tactile corpuscles in mucous membranes
– lamellated (pacinian) corpuscles
• deep pressure, stretch, tickle, itch &
vibration
Char: adaptation, local sign

10. Muscle Spindles - Skeletal Muscle Stretching
Golgi Tendon Organs - Tendon Stretching
3. Stretch Sensations

11. 4. Organic sensations
• Hunger- projected to stomach
-associated with rhythmic contractions and
weakness, trembling, nausea, headache
- NS is hyperexcitable
• Thirst- projected to pharynx
- due to low water levels
- extreme thirst leads to mental anguish

12. 5. Visceral Sensations
three groups of stimuli
• Dilation/distension
• Spasm/strong contraction
• Chemical irritation
Referred pain occurs because of the common nerve
pathways leading from skin and internal organs.

13. • Referred pain is misinterpreted pain
–Visceral impulse and cutaneous impulse
share the same neurons to brain
–Results in confusion
–ex. Angina pectoris- spasm of smooth
muscle in coronary arteries of heart
– brain “assumes” pain is coming from skin not heart
– Pain in left shoulder and left arm instead of heart
– ex. pneumonia- pain in abdomen

14. Referred Pain-felt on the body
surface

15. The Special Senses
Taste- Gustation
Smell- Olfaction
Vision
Hearing
Balance

16. The Chemical Sense -- Taste
respond to chemicals in an aqueous
solution
food dissolved in saliva
Closely-linked with olfaction and
nutrition
•Taste and smell are involved with specific
receptor cells called chemoreceptors

17. THE TONGUE
• Gustation is the sensation of taste resulting from
the action of chemicals on the taste buds
• Lingual papillae
– filiform (no taste buds)
• most abundant
– foliate (no taste buds)
– fungiform
• at tips & sides of tongue
– circumvallate
• at rear of tongue
• contains 1/2 of taste buds

18. Circumvallate Papilla
Filiform
papilla
Fungiform
papilla
Connective tissue Tongue epithelium
Taste Bud structure

19. • Lemon-shaped groups of 3 kinds of cells
– taste cells, supporting cells, and basal cells
• taste cells with a apical microvilli serving as a receptor surface
• taste cells synapse with sensory nerve fibers at their base

20. Taste Buds
taste
buds
papilla
taste
pores

21. Five Basic Tastes
Salty- metallic ions (NaCl)
Sweet- sugarSweet- sugar
UmamiUmami
Sour- HSour- H++
Bitter- alkaloidsBitter- alkaloids
Why are they important?

22. Physiology of Taste
• To be tasted, molecules must dissolve in
saliva
• 5 primary sensations: salty, sweet, sour, bitter
& umami (taste of amino acids such as MSG)
• Taste is also influenced by food texture,
aroma, temperature, and appearance.
–hot pepper stimulates free nerve endings
(pain)

24. GUSTATION- TASTE
acids cause strong salivary reflex
bad tasting food causes gagging or reflexive
vomiting
taste can change over time
taste is 80% smell-depends heavily on
olfactory receptors
Taste also dependent on thermoreceptors,
nociceptors, mechanoreceptors

25. Projection Pathways for Taste
• Innervation of the taste buds (gustatory cells)
– facial nerve for the anterior 2/3’s of the tongue
– glossopharyngeal nerve for the posterior 1/3
– vagus nerve for palate, pharynx & epiglottis
• Medulla oblongata
• thalamus
• postcentral gyrus of the cerebrum
– conscious sense of taste

27. THE SENSE OF SMELL

28. Smell in man not as good as animals’; however,
some people are wine tasters, perfumers
If you smell a particular odor all day, you won’t
recognize its presence, you become accustomed, ex.
garbage men
Old people lose sense of smell- lots of perfume
Humans can distinguish 10,000 or so chemicals
What we really smell is pain: ex. chili, ammonia,
menthol (cold)
Olfaction-some features

29. The Chemical Sense -- Smell
• Receptor cells for olfaction form
olfactory mucosa
– smell is highly sensitive (more so in
women than men)
– distinguish as many as 10,000 odors
• Characteristics : memory
adaptation
•Stimuli in gaseous form
•Less impt in man than animals

30. 7 PRIMARY ODORS
• Floral- roses
• Musky- perfume/aftershave
• Camphoric- mothballs
• Pepperminty- mint gum
• Ethereal- dry cleaning fluid
• Pungent- vinegar
• Putrid-rotten eggs

31. Physiology of Smell
• Odor molecules bind to a receptor on an olfactory hair
triggering the production of a second messenger
– opens the ion channels & creates a receptor potential
• olfactory nerves in olfactory bulbs
• olfactory tracts
• Olfactory centers in thalamus
– lead to temporal lobe, amygdala, hypothalamus
• emotional responses to odors
• cough, salivate, sneeze or vomit in response to odors
• cerebral cortex sends feedback to bulb cells
• changing quality & significance of odors when hungry

32. Olfactory Epithelial Cells
• Olfactory cells
– neurons with 20 cilia
called olfactory hairs
• binding sites for odor
molecules in thin layer
of mucus
– Live for 60 days
• Supporting cells
• Basal cells divide

33. Olfactory Pathway
olfactory hairs
olfactory
receptor cell
bone
olfactory bulb
Nasal conchae

34. Olfactory Projection Pathways

35. Olfactory auras- prior to epileptic attack
May be genetic or a cold (mucus), allergy, zinc
deficiency, smoking, aging and growth of nasal
polyps
Anosmias- loss of sense of smell
Lose sense of smell→lose taste
Uncinate- olfactory hallucinations; may be
psychological ex. rotting meat smell
From head injuries that destroy olfactory nerves

36. THE SENSE OF HEARING AND
BALANCE

37. SENSE OF HEARING
• the ‘watchdog’ of the senses
•Stimulus- sound waves
•Sound- an audible vibration of molecules
•Receptors- hair cells in Organ of Corti
Molecules collide with
eardrum & make it vibrate.

38. Pitch and Loudness
• The frequency at which parts of the ear vibrate give us
sense of Pitch (high or low pitched sounds)
– hearing range is 20 - 20,000 Hz (cycles/sec)
• Loudness is perception of intensity of sound energy
– how much the air molecules are compressed in decibels
Sounds > 90 dB
can cause damage.

40. Auditory Pathway
auricle External auditory
canal
Tympanic
membrane
Malleus, incus stapes
Cochlear fluid is
disturbed
Ripple disturbs hair
cells in Organ of Corti
Cochlear
nerve
Brain stem
thalamus
Auditory nerve of
temporal lobe

41. Eustachian Tube
• Tympanic cavity filled with air by auditory tube
(Eustachian tube) connected to nasopharynx
– opens during swallowing or yawning to equalize air pressure on
both sides of eardrum

42. Anatomy of Middle Ear
• Middle ear is cavity containing ear ossicles.

43. Inner Ear
• Passageways in temporal bone = bony labyrinth
• Endolymph-filled tubes floating in perilymph
inside the bony labyrinth = membranous
labyrinth vestibular apparatus
cochlea

44. Anatomy of the Cochlea
• Stereocilia of hair cells attached to tectorial membrane.
• Hearing comes from inner hair cells -- outer ones adjust cochlear
responses to different frequencies
2.5 coils
3 fluid-filled
chambers
Organ of Corti

45. Stimulation of Cochlear Hair Cells
• Sound is produced by vibration of ossicles and
then vibration of basilar membrane under hair cells
• Can happen as often as 20,000 time per second

46. Balance and Equilibrium
• Receptors in vestibular apparatus
– semicircular ducts contain crista
– saccule & utricle contain macula
• Static equilibrium is perception of head
orientation when one is not moving
– perceived by macula
• Dynamic equilibrium is perception of motion or
acceleration
– linear acceleration perceived by macula
– angular acceleration perceived by crista

47. The Saccule and Utricle
• Saccule & utricle chambers containing macula
– patch of hair cells in macula embedded in a gelatinous
otolithic membrane weighted with granules called
otoliths ( CaCO3 crystals)
– otoliths add to density & inertia and enhance the sense
of gravity and motion; aka ‘ear stones’
Otoliths

48. Macula Saccule and Macula Utricle
With the head erect, stimulation is minimal, but when the head is
tilted, weight of membrane bends the stereocilia (static equilibrium)
When car begins to move at green light, linear acceleration is
detected since heavy otolith lags behind (one type of dynamic
equilibrium)

49. Crista ampullaris of Semicircular Ducts
• Crista ampullaris consists of hair cells buried in a mound
of gelatinous membrane (one in each duct)
• Orientation of ducts causes different ducts to be stimulated
by rotation in different planes

50. Crista Ampullaris & Head Rotation
• As head turns, the endolymph lags behind
pushing the cupula and stimulating its hair cells

52. • Vision is perception of light emitted or reflected from
objects in the environment
• Stimulus- light waves
VISION
THE SENSE OF SIGHT

53. The Optical Apparatus

54. THE PROCESS OF SEEING
1. Formation of
retinal image
Processes involved:
a. refraction of light
rays- due to cornea,
aqeous
humor, lens, vitreous
humor
b. accomodation of lens

55. Accommodation of Lens

56. SEEING cont.
2. Constriction of pupil-directs light rays to retina
3. Convergence of eyes- eyeballs converge so that
visual axes come together at the object viewed

57. •Neural apparatus includes the retina & optic nerve
•Retina forms as an outgrowth of the brain
attached only at optic disc where optic nerve begins
•Detached retina
blow to head or lack of sufficient vitreous body
blurry areas in field of vision
leads to blindness due to disruption of blood supply

58. Test for Blind Spot
• Optic disk or blind spot is where optic nerve exits
the posterior surface of the eyeball
– no receptor cells are found in optic disk
• Blind spot can be seen using the above illustration
– in the right position, stare at X and red dot disappears
• Visual filling is the brain filling in the green bar
across the blind spot area

59. blind spot macula
The Retina

60. Effects of Corrected Lenses
• Hyperopia is farsighted (eyeball too short)
– correct with convex lenses
• Myopia is nearsighted (eyeball too long)
– correct with concave lenses

61. Retinal Cells
• Posterior layer of retina is pigment epithelium
– purpose is to absorb stray light & prevent
reflections
• Photoreceptors cells are in next layer
• Rod cells (night vision)
-with rhodopsin pigment molecules (light-sensitive)
-w/light= breaks down into opsin and retinal
-sensitive to movement of objects
• Cone cells (color vision in bright light)
– Detail and color
– Less sensitive to light
– Needs brighter light to break down pigments
and generate action potential

62. Details of
the Retina
lightlight
photoreceptive cells
Choroid
Schlera
Ganglion
Amacrine
Bipolar neuron
Horizontal cells