3. General Senses
• receptors that are widely distributed throughout the
body
• skin, various organs and joints
Special Senses
• specialized receptors confined to structures in the
head
• eyes and ears
3
4. Chemoreceptors
• respond to changes in chemical concentrations
Pain receptors (Nociceptors)
• respond to tissue damage
Thermoreceptors
• respond to changes in temperature
Mechanoreceptors
• respond to mechanical forces
Photoreceptors
• respond to light
4
5. • stimulation of receptor causes local change in its receptor potential
• a graded electrical current is generated that reflects intensity of stimulation
• if receptor is part of a neuron, the membrane potential may generate an
action potential
• if receptor is not part of a neuron, the receptor potential must be
transferred to a neuron to trigger an action potential
• peripheral nerves transmit impulses to CNS where they are analyzed and
interpreted in the brain
5
6. Projection
process in which the brain projects the sensation
back to the apparent source
it allows a person to pinpoint the region of
stimulation
6
7. • ability to ignore unimportant stimuli (clothes)
• involves a decreased response to a particular stimulus
from the receptors (peripheral adaptations) or along
the CNS pathways leading to the cerebral cortex
(central adaptation)
• sensory impulses become less frequent and may cease
• stronger stimulus is required to trigger impulses
7
8. Free nerve endings Meissner’s corpuscles
• common in epithelial • abundant in hairless portions
tissues of skin; lips
• simplest receptors • detect fine touch; distinguish
• sense itching between two points on the skin
Pacinian corpuscles
• common in deeper subcutaneous
tissues, tendons, and ligaments
• detect heavy pressure and
vibrations
8
10. Warm receptors
• sensitive to temperatures above 25oC (77o F)
• unresponsive to temperature above 45oC (113oF)
Cold receptors
• sensitive to temperature between 10oC (50oF) and 20oC
(68oF)
Pain receptors
• respond to temperatures below 10oC
• respond to temperatures above 45oC
10
11. • free nerve endings
• widely distributed
• nervous tissue of brain lacks pain receptors
• stimulated by tissue damage, chemical, mechanical forces,
or extremes in temperature
• adapt very little, if at all
11
12. • pain receptors are the only receptors in viscera whose
stimulation produces sensations
• pain receptors respond differently to stimulation
• not well localized
• may feel as if coming from some other part of the body
• known as referred pain
12
13. • may occur due to sensory impulses from two regions
following a common nerve pathway to brain
13
14. Acute pain fibers Chronic pain fibers
• A-delta fibers • C fibers
•thin, myelinated •thin, unmyelinated
• conduct impulses • conduct impulses more
rapidly slowly
• associated with • associated with dull,
sharp pain aching pain
• well localized • difficult to pinpoint
14
15. Thalamus
• allows person to be aware
of pain Pain Inhibiting Substances
• enkephalins
Cerebral Cortex • serotonin
• judges intensity of pain • endorphins
• locates source of pain
• produces emotional and
motor responses to pain
15
16. • sensory receptors are within large, complex sensory
organs in the head
• smell in olfactory organs
• taste in taste buds
• hearing and equilibrium in ears
• sight in eyes
16
17. Olfactory Receptors
• chemoreceptors
• respond to chemicals dissolved in liquids
Olfactory Organs
• contain olfactory receptors and supporting epithelial
cells
• cover parts of nasal cavity, superior nasal conchae,
and a portion of the nasal septum
17
19. Once olfactory receptors are stimulated, nerve impulses
travel through
• olfactory nerves olfactory bulbs olfactory
tracts limbic system (for emotions) and
olfactory cortex (for interpretation)
19
20. • olfactory organs located high in the nasal cavity
above the usual pathway of inhaled air
• olfactory receptors undergo sensory adaptation
rapidly
• sense of smell drops by 50% within a second after
stimulation
20
21. Taste Buds
• organs of taste
• located on papillae of tongue, roof of mouth, linings of
cheeks and walls of pharynx
•Each has from 50-150 taste cells.
Taste Receptors
• chemoreceptors
• taste cells – modified epithelial cells that function
as receptors
• taste hairs –microvilli that protrude from taste
cells; sensitive parts of taste cells
21
23. Five Primary Taste Sensations
• sweet – stimulated by carbohydrates
• sour – stimulated by acids
• salty – stimulated by salts
• bitter – stimulated by many organic compounds
•umami- stimulated by certain amino acids
Spicy foods activate pain receptors
23
24. Sensory impulses from taste receptors travel along
• cranial nerves to
• medulla oblongata to
• thalamus to
• gustatory cortex (for interpretation)
24
28. Ear – organ of hearing
Three Sections
• External
• Middle
• Inner
28
29. • auricle
• collects sounds waves
• external auditory meatus
• lined with ceruminous
glands
• carries sound to tympanic
membrane
• terminates with tympanic
membrane
• tympanic membrane
• vibrates in response to sound
waves
29
30. • tympanic cavity
• air-filled space in temporal
bone
• auditory ossicles
• vibrate in response to tympanic
membrane
• malleus, incus, and stapes
• oval window
• opening in wall of tympanic
cavity
• stapes vibrates against it to
move fluids in inner ear
30
31. • eustachian tube
• connects middle ear to
throat
• helps maintain equal
pressure on both sides
of tympanic membrane
• usually closed by
valve-like flaps in
throat
31
32. • complex system of labyrinths
• osseous labyrinth
• bony canal in temporal
bone
• filled with perilymph
• membranous labyrinth
• tube within osseous
labyrinth
• filled with endolymph
32
33. Three Parts of Labyrinths
• cochlea
• functions in hearing
• semicircular canals
• functions in
equilibrium
• vestibule
• functions in
equilibrium
33
34. Scala vestibuli
• upper compartment
• leads from oval window to
apex of spiral
• part of bony labyrinth
Scala tympani
• lower compartment
• extends from apex of the
cochlea to round window
• part of bony labyrinth
34
35. Cochlea
Cochlear duct
• portion of membranous
labyrinth in cochlea
Vestibular membrane
• separates cochlear duct
from scala vestibuli
Basilar membrane
• separates cochlear duct
from scala tympani
35
36. Organ of Corti
• group of hearing receptor cells
(hair cells)
• on upper surface of basilar
membrane
• different frequencies of vibration
move different parts of basilar
membrane
• particular sound frequencies cause
hairs of receptor cells to bend
• nerve impulse generated
36
40. Static Equilibrium Dynamic Equilibrium
• vestibule • semicircular canals
• sense position of • sense rotation and
head when body is movement of head and
not moving body
40
41. • Utricle
• communicates with
saccule and
membranous portion of
semicircular canals
• Saccule
• communicates with
cochlear duct
• Mucula
• hair cells of utricle and
saccule
41
42. • responds to
changes in head
position
• bending of hairs
results in generation
of nerve impulse
42
43. • three canals at right angles
• ampulla
• swelling of membranous
labyrinth that communicates
with the vestibule
• crista ampullaris
• sensory organ of ampulla
• hair cells and supporting
cells
• rapid turns of head or body
stimulate hair cells
43
46. The eye, the organ that contains the visual
receptors, provides vision with the assistance of :
Visual Accessory Organs
• eyelids
• lacrimal apparatus
• extrinsic eye muscles
46
47. They are housed within the orbital cavity,
or orbit of the skull.
Each orbit contains fat, blood vessels,
nerves and connective tissue
47
59. • composed of connective
tissue and smooth muscle
• pupil is hole in iris
• dim light stimulates
radial muscles and pupil
dilates
• bright light stimulates
circular muscles and
pupil constricts
59
60. • fluid in anterior cavity of eye
• secreted by epithelium on inner surface of the ciliary body
• provides nutrients
• maintains shape of anterior portion of eye
• leaves cavity through canal of Schlemm
60
61. • retina
• contains visual receptors
• continuous with optic nerve
• ends just behind margin of the ciliary body
• composed of several layers
• 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
61
62. • contains vitreous humor – thick gel that holds retina
flat against choroid coat
62
63. • receptor cells, bipolar cells, and ganglion cells - provide
pathway for impulses triggered by photoreceptors to reach the
optic nerve
• horizontal cells and amacrine cells – modify impulses
63
65. Refraction
• bending of light
• occurs when light waves pass at an oblique angle into
mediums of different densities
65
66. Convex lenses cause Concave lenses cause
light waves to converge light waves to diverge
66
67. • 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
67
68. Rods Cones
• long, thin projections • short, blunt projections
• contain light sensitive • contain light sensitive
pigment called rhodopsin pigments called
• hundred times more erythrolabe, chlorolabe,
sensitive to light than cones and cyanolabe
• provide vision in dim light • provide vision in bright
• produce colorless vision light
• produce outlines of objects • produce sharp images
• produce color vision
68
70. Rhodopsin Pigments on Cones
• light-sensitive pigment in rods • each set contains different light-
• decomposes in presence of sensitive pigment
light • each set is sensitive to different
• triggers a complex series of wavelengths
reactions that initiate nerve • color perceived depends on
impulses which sets of cones are stimulated
• impulses travel along optic • erythrolabe – responds to red
nerve • chlorolabe – responds to green
• cyanolabe – responds to blue
70
74. Age related hearing loss due to
• damage of hair cells in organ of Corti
• degeneration of nerve pathways to the brain
• tinnitus
Age-related visual problems include
• dry eyes
• floaters (crystals in vitreous humor)
• loss of elasticity of lens
• glaucoma
• cataracts
• macular degeneration
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