1. SPECIAL
SENSES

2. •General senses – all throughout
the body.
•Special senses – confined in the
head, eyes and ears ( hearing and
balance, sight, taste, smell)
- conveyed by
cranial nerves

3. •TYPES OF RECEPTORS based on Location:
1. SUPERFICIAL
2. DEEP
3. CORTICAL (combination of superficial and deep)
Info: ↓ ↓
Exteroreceptors Proprioceptors
- pain, temp., light
touch, pressure
-from OUTSIDE the
body
-position sense,
kinesthesia,
vibration
-- from inside the
body (muscle
spindle, tendons,
ligaments)

4. •Visceral Sensation – relayed by the autonomic
efferent fibers
- hunger, nausea, visceral pain
- visceral pain receptors are only in
the viscera and respond differently to
stimulation not localized
Referred pain – as if coming from
other parts of the body
Ex: liver and gall bladder problem
may be referred to the right shoulder

5. I. MECHANORECEPTORS
 Respond to mechanical deformation of
receptors
A. CUTANEOUS SENSORY RECEPTORS
Free nerve ending – pain and temp
Merkel’s disk - two-pt discrimination,
localization of touch
Ruffini – warmth (above 25 deg C)
Krause end bulb – cold (100-200 deg C)

6. Meissner’s – discriminative touch (texture
recognition)
Pacinian – deep touch and vibration
B. DEEP/JOINT RECEPTORS
Muscle Spindle – velocity of movement
GTO- monitors tension
Free nerve endings- pain and temp
Pacinian
II. THERMORECEPTORS – for temperature
changes
III. NOCICEPTORS – noxious stimuli ( damage to
tissues)

7. III. ELECTROMAGNETIC RECEPTORS – respond
to light (rods and cones)
IV. CHEMORECEPTORS – respond to chemical
substance
A. Taste- receptors of taste buds
B. Smell - receptors of olfactory nerves in
olfactory epithelium
C. Arterial O2- receptors of Aortic and
carotid bodies
D. Osmolality - neurons of supraoptic
nuclei

8. E. Blood CO2 - receptors in or on surface of
medulla and in aortic and carotid bodies
F. Blood Glucose, amino acid and fatty acids -
receptors in hypothalamus
Projection – the brain projects sensation back
to the source
- person pinpoints region of
stimulation

9. Pathways From Sensation to Perception (Example of an
Apple)

10. •ACUTE PAIN
A-delta fibers
Fast
Sharp pain
Localized
•CHRONIC PAIN
C fibers
Slow
associated with
dull aching pain
diffused (difficult
to pinpoint)
ACUTE PAIN VS. CHRONIC PAIN

11. •OLFACTION - sense of smell, occurs in response
to odors that stimulate sensory
receptors
- receptors located in the extreme
superior region of the nasal cavity,
called the olfactory recess
PATHWAY:
Once olfactory receptors are stimulated, nerve
impulses travel through olfactory nerves →
olfactory bulbs → olfactory tracts →limbic
system (for emotions)  olfactory cortex (for
interpretation)

12. •olfactory receptors undergo sensory
adaptation rapidly
•sense of smell drops by 50% within a second
after stimulation
•Mechanism of olfactory discrimination
- unknown
-wide variety of detectable (4000) smells
actually combinations of a smaller number
of primary odors

13. 7 primary scents
•Camphor
•Musk
•Floral
•Peppermint
•Ether
•Pungent
•Putrid
GUSTATION/Taste
- a chemical sense that requires dissolving
substance before it can be tasted.

14. GUSTATORY RECEPTORS
Located at the taste buds
Can also be found on the soft palate, pharynx
and larynx
Taste buds declines with age
Taste bud
Organs of taste
Location
a. Tongue Papillae
b. Mouth(roof)
c. Cheeks(lining)
d. Pharynx(wall)
e. Lips

15. Taste receptors
•Chemoreceptors
•Taste cells-function as receptors
•Taste hairs- microvilli that protude from taste
cells;sensitive parts of taste cells
4 major types of Papillae according to shape:
1. Vallate- largest; V-shaped
-between anterior and posterior border of
tongue
2. Fungiform-mushroom-shaped
-contains most sensitive to taste buds
-folds on the sides of the tongue

16. -most numerous in CHILDREN
-decreases with age
4.Filiform-filament-shaped
-most numerous
-no taste function

17. Five Primary Sensations
•Sweet- stimulated by carbohydrates
•Sour- stimulated by acids
•Salty- stimulated by salts
•Bitter- stimulated by many organic compounds
•Umami
Spicy foods activate pain receptors
Taste Pathway
Impulses from taste receptors → cranial
nerves97,9,10) →medulla →thalamus
↓
limbi syste,hypothalamus↓
Gustatory cortex

18. Visual System
oComponents
1.Eyes- respond to light and initiate afferent action
potentials.
2. Accessory structures- help protect the eyes from
direct sunlight and damaging particles
-includes:eyebrows, eyelids,
eyelashes, lacrimal apparatus,conjunctiva, extrinsic
eye muscles
3. Optic nerves (II), tracts, and pathways

19. Eyebrows- Protects eyes
1. Perspiration
2. Shade from the sun
 Eyelid(PALPEBRA)-for blinking (protects the eye
from foreign objects)
-Average blinking: 25x/min
 Muscles
a. Orbicularis Oculi- closes
b. Levator Palperbrae Superiosis- opens
• Canthi: angels where the eyelids join at the medial
and lateral margins of the eye
• Caruncle: small reddish, on the medial canthi;
contains modified sabaceous and sweat galnds

20. CONJUNCTIVE-mucous membrane; lines eyelid and
covers portion of eyeball
Conjunctivitis-”pink eye”
-Inflammation caused by infection
or irritation

21. Extrinsic Eye Muscles
Lateral rectus- outward; paralysis of both lateral
will cause eyes to deviate inward (internal strabismus)
Medial rectus- inward; paralysis of both medial will
cause eyes to deviate outward (external strabismus)
Superior rectus- up and in
Inferior rectus- down and in
Superior oblique- down and out
Inferior oblique- up and out
EYELASHES-double or triple row of hairs to the free
edges of the eyelids
-lubricates lids and restrains tears from flowing over
the margin of the eyelids; openings behind the lashes

22. •Lacrimal Apparatus
Lacrimal
•Lateral to eye
•Secretes tears
Canaliculi
•Collect tears
Lacrimal Sac
•Collects from canaliculi
Punctum
•Opening of each lacrimal canaliculis
Nasolacrimal Duct
•Collects from lacrimal sac
•Empties tears into nasal cavity

25. Optical Components:

26. •LAYERS/TUNICS:
1. Outer Fibrous Tunis Sclera
Cornea
2. Middle/Vascular Tunic Choroid
Ciliary Body
Iris
3.Inner Retina
Cornea
Anterior portion
AVASCULAR
Transparent
Light permission

27. Light refraction
One of the first organs transplanted
Central part of the cornea receives oxygen from
the outside air.
soft plastic contact lenses worn for periods must
be permeable to air to reach the cornea.
Sclera
Posterior portion; firm, opaque, white functions:
Protection
Muscle attachment
Shape of the eye
Iris
Anterior portion
pigmented

28. Smooth muscle
Controls light intensity
Pupil is the hole in iris
Dim light stimulates radial muscles and pupil
dilates
Bright light stimulates circular muscles and pupil
constricts
-blue eyes: decreased melanin
-black/brown: increased melanin

30. •Ciliary Body
Anterior portion
Pigmented
Holds lens
Moves lens for focusing
Forms internal ring around front of eye
Ciliary processes-radiating folds
Ciliary muscles-contract and relax to move lens
•Choroid Coat
Provides blood supply
Pigments absorb extra light

31. •Retina
Contains visual receptors
Continuous with optic nerve
Macula lutea- yellowish spot in retina
Fovea centralis-center of macula lutea;produces
sharpest vision
Optic disc-blind spot; contains no visual receptors
Vitreous humor- thick gel that holds retina flat
against choroid coat fluid in anterior cavity of eye
•Aqueous Humor
Fluid in the anterior cavity; provides nutrients
Maintains shape of anterior portion of eye

32. •Lens
Transparent
Biconvex
Lies behind iris
Held in place by suspensory ligaments of ciliary
body

33. Accomodation Changing of lens shape to view
objects

34. •Refraction
Bending of light
Occurs when light waves pass at an oblique angle
into mediums of different densities
Convex lenses cause light waves to converge
Concave lenses cause light waves to diverge

35. •Focusing on retina
 As light enters eye, it is refracted by
 Convex surface of cornea
 Convex surface of lens
 Image focused on retina is upside down and
reversed from left to right

36. Visual Receptors
•Rods
oContain light sensitive pigment called rhodopsin
oMore sensitive to light than cones
oProvide vision in dim light
oProduce colorless vision
oProduce outlines of objects
•Cones
oShort, blunt projections
oProvide vision in bright light
oProduce sharp images
oProduce color vision

37. Clinical Correlation
•Myopia-nearsightedness, too ↑ refraction
•Hyperopia- farsightedness, ↓ refraction
•Astigmatism- curvature of either lens or cornes is
greater in 1 axis or meridian
•Scotomas- abnormal blind spot in visual fields

38. Visual Pathway and Visual field cuts
Lesions:
a.Blindness in one eye
b.Bitemporal Hemianopia
c.Homonymous Hemianopia
d.Quadrantanopsia
e.Homonymous Hemianopsia

39. HEARING AND BALANCE
EAR

40. External ear
•Consists of: auricle and external auditory meatus
•Function: hearing only
Middle Ear/Tympanic Cavity
•Consist of: air-filled CAVITY within the temporal
bone, and auditory ossicles
•Function in both hearing balance
Auricle/Pinna:
•Fleshy part of the external ear on the outside of
the head
•Shape helps to collect sound waves and direct
them toward the external auditory meatus
•Elastic cartilage covered with skin, extrinsic and
intrinsic mm

41. External auditory meatus
•Sinus tube that leads to tympanic cavity
•Isthmus: narrowest potion of meatus
Functions:
1. Conduct sounds waves from auricle to tympanic
membrane
2. Prevents foreign objects from reaching the
delicate eardrum thru the lined hairs and
ceremonous glands, which produce
cerumen(earwax)
o Tympanic Membrane/Eardrum
 Thin, semitransparent, nearly oval
 Separates the external ear from the middle ear.

42. Auditory Ossicles:
1. Malleus: largest; handle is attached to the
center of the eardrum
2. Incus: attached to the other side of malleus
:Whenever malleus moves, incus moves
with it.
3. Stapes: attatched to opposite end of incus
- Lies against the membranous labyrinth in
the opening of oval window where
sound waves are conducted into inner
ear.

43. Middle ear
Chorda tympani
-branch if the facial nerve carrying taste impulses
from the anterior two-thirds of the tongue
-no function in hearing
Inner ear
Bony Labyrinth:
1. Vestibule: for balance
2. Semicircular canals: for balance
3. Cochlea: for hearing
 Membranous labyrinth
1. Utricle
2. Saccule
3.Semilunar ducts
4. Cochlear ducts

44. STEPS IN HEARING
1. The auricle collects sound waves that are then
conducted through the external auditory meatus
to the tympanic membrane, causing it to vibrate.
2. The vibrating tympanic membrane causes the
malleus, incus, and stapes to vibrate.
3. Vibration of the stapes produces vibration in the
perilymph of the scala vestibuli.
4. The vibration of the perilymph produces
simultaneous vibration of the vestibular
membrane and the endolymph causes in the
cochlear duct.
5. Vibration of the endolymph causes the basilar
membrane to vibrate.

45. 6. As the basilar membrane vibrates, the hair cells
attached to the membrane move relative to the
tectorial membrane, which remains stationary.
7. The hair cell microvilli, embedded in the tectorial
membrane, become bent.
8. Bending of the microvilli causes depolarization of
the hair cells.
9. The hair cells induce action potentials in the
cochlear neurons.
10. The action potentials generated in the cochlear
neurons are conducted to the CNS.
11. The action potentials ate translated in the cerebral
cortex and are perceived as sound.

46. Auditory Pathway:
Sensory axons from the cochlear
↓
Ganglion terminate in the cochlear nucleus in the
brainstem
↓
Superior olivary nucleus or to the inferior colliculus
↓
Medial geniculate nucleus of the thalamus
↓
Auditory cortex
↓
Neurons in the superior olivary

47. Neurons in the superior olivary nucleus send axons to
the inferior colliculus, back to the inner ear, or to
motor nuclei in the brainstem that send efferent
fibers to the middle ear muscles.
Clinical correlation:
1. Tinnitus- ringing, buzzing, roaring or “paper
crushing” noises in the ear, frequently an early sign
of peripheral cochlear disease
2. Deafness
a. conduction- impaired conduction through the
external canal and ossicles to endolymph and
tectorial membrane
-cause:external/middle ear diseases

48. b. sensorineural/nerve- interruption of cochlear
nerve fibers from hair cells to BS
-cause: cochlear nerve/ inner nerve
VESTIBULAR SYSTEM
For maintenance of stance and body posture;
coordination of the body, head and eye movements;
and visual fixation
STATIC LABYRITH
-Stuctures involved:
1. Saccule
2. Utricle
-involved in evaluating the position of the head
relative to gravity

49. -responds to linear acceleration deceleration, such
as when a person is in a car that is increasing or
decreasing speed
•Macula of the Utricllie: determines person’s head
position w/ respect to gravitational force when person
is in upright position
•Macula of the saccule: equilibrium in lying down
OTOLITHS/OTOCONIA: small Ca Carbohydrates
crystals in saccule and utricle
-displaces the hair cells and excites the saccule and
utricle in response to Vertical and Horizontal
acceleration

50. •KINETIC LABYRITH
-Detects head rotation: Angular Rotation
-When head begins to rotate-endolymph in S.D.
remain stationary while S.D moves w/ the head
direction-cause flow to flow into ampula, bending
cupula to side
-From hair cells- vestibular nerve to apprise the N.S
of change in the rate of direction
-Pathway For Balance
1. Sensory axons from the vestibular ganglion
pass through the vestibular nerves to the
vestibular nucleus, which also receives input
from several other sources, such as
proprioception from the legs.

51. 2. Vestibular neurons send axons to the
cerebellum, which influences postural muscles,
and to the motor nuclei (oculomotor, trochlear,
andabducents), which control extrinsic eye
muscles.
3. Vestibular neurons also send axons to the
posterior ventral nucleus of the thalamus.
4. Thalamic neurons project to the vestibular area
of the cortex.
 OTOSCLEROSIS
-Is an ear disorder in which spongy bone
grows over the oval window and
immobilizes the stapes, leading to
progressive loss of hearing

52.  TINNITUS
Consists of noises such as ringing, clicking,
whistling, or booming in the ears
MOTION SICKNESS
Consists of nausea, weakness and other
dysfuntions caused by stimulation of the
semicircular canals during motion, such as is boat,
automobile, airplane, swing or amusement park
ride
OTITIS MEDIA
Infections of the middle ear
VERTIGO