1. Sensory Systems General Senses
receptors that are widely distributed throughout the body
skin, various organs and joints
Special Senses
specialized receptors confied to structures in the head
eyes and ears

2. Senses Sensory Receptors
specialized cells or multicellular structures that collect information from the environment
stimulate neurons to send impulses along sensory fibers to the brain
Sensation
a feeling that occurs when brain becomes aware of sensory impulse
Perception
a person’s view of the stimulus; the way the brain interprets the information

3. SENSORY RECEPTION
Sensory receptors convert stimulus energy to action potentials
Sensory receptors
Are specialized cells or neurons that detect stimuli

4. The Adequate Stimulus
A critical concept in sensory processes is the concept of the adequate stimulus. Many sensory receptors will respond to numerous forms of energy. A great example is your retina and your little cousin. When he accidentally sticks his finger in your eye, you see light (stars!), but
pressure is not the adequate stimulus for the retina’s rods and cones. Photon’s are!

5. Sensory transduction is the process of converting energy (environmental) into receptor (neural), also called generator potentials
Which if sufficiently large enough, triggers action potentials that are transmitted to the brain
Sugar molecule (stimulus)
Membrane of sensory receptor cell
Taste pore
Sugar molecule 2
Tongue 1
Taste bud
Sensory receptor cells
Signal transduction pathway
Ion channels
Sensory receptor cell 3  
Sensory neuron
Ion
Receptor potential 4
Neurotransmitter
Sensory neuron
Action potential mV
No sugar
Sugar present 5
Action potentials

6. Action potential frequency
Action potential frequency
Reflects stimulus strength
Sugar
receptor
“Sugar” interneuron
Brain
Taste
bud
“Salt” interneuron
Salt
Sensory
neurons
No sugar
Increasing sweetness
No salt
Increasing saltiness
Figure 29.2B

7. Mechanoreceptors
Respond to mechanical energy such as touch, pressure, and sound
“Hairs” of
receptor cell
Neurotransmitter
at synapse
More
neurotransmitter
Less
neurotransmitter
Sensory
neuron
Action
potentials
Action
potentials 1
Receptor cell at rest 2
Fluid moving in one direction 3
Fluid moving in other direction
Figure 29.3B

8. Repeated stimulus May lead to adaptation, a decrease in sensitivity
Repeated stimulus
May lead to adaptation, a decrease in sensitivity
Habituation is the similar psychological process

9. Specialized sensory receptors detect five categories of stimuli
A section of human skin
Reveals many types of sensory receptors
Heat
Light
touch
Pain
Cold
Hair
Epidermis
Dermis
Nerve
Connective
tissue
movement
Strong
pressure
Figure 29.3A

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

11. Receptor Types 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

12. Sensory Impulses
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

13. Sensations Projection
process in which the brain projects the sensation back to the apparent source
it allows a person to pinpoint the region of stimulation

14. Sensory Adaptation ability to ignore unimportant stimuli
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

15. General Senses
senses associated with skin, muscles, joints, and viscera
three groups
exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain
visceroceptive senses – senses associated with changes in viscera; blood pressure stretching blood vessels, ingesting a meal
proprioceptive senses – senses associated with changes in muscles and tendons

16. Touch and Pressure Senses
Free nerve endings
common in epithelial tissues
simplest receptors
sense itching
Meissner’s corpuscles
abundant in hairless portions of skin; lips
detect fine touch; distinguish between two points on the skin
Pacinian corpuscles
common in deeper subcutaneous tissues, tendons, and ligaments
detect heavy pressure and vibrations

17. Touch and Pressure Receptors

18. Temperature Senses 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

19. Sense of Pain 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

20. Visceral Pain 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

21. Referred Pain
may occur due to sensory impulses from two regions following a common nerve pathway to brain

22. Pain Nerve Pathways Chronic pain fibers Acute pain fibers C fibers
thin, unmyelinated
conduct impulses more slowly
associated with dull, aching pain
difficult to pinpoint
Acute pain fibers
A-delta fibers
thin, myelinated
conduct impulses rapidly
associated with sharp pain
well localized

23. Regulation of Pain Impulses
Thalamus
allows person to be aware of pain
Pain Inhibiting Substances
enkephalins
serotonin
endorphins
Cerebral Cortex
judges intensity of pain
locates source of pain
produces emotional and motor responses to pain

24. Proprioceptors mechanoreceptors
send information to spinal cord and CNS about body position and length and tension of muscles
Main kinds of proprioreceptors
Pacinian corpuscles – in joints
muscle spindles – in skeletal muscles*
Golgi tendon organs – in tendons*
*stretch receptors

25. Stretch Receptors

26. Summary of Receptors of the General Senses

27. Special Senses
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

28. Sense of Smell 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

29. Olfactory Receptors

30. Olfactory Nerve Pathways
Once olfactory receptors are stimulated, nerve impulses travel through
olfactory nerves olfactory bulbs olfactory tracts limbic system (for emotions) and olfactory cortex (for interpretation)

31. Olfactory Stimulation
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
Olfactory Code
hypothesis
odor that is stimulated by a distinct set of receptor cells and its associated receptor proteins

32. Sense of Taste Taste Buds organs of taste
located on papillae of tongue, roof of mouth, linings of cheeks (??) and walls of pharynx.
Taste Receptors
chemoreceptors
taste cells – modified epithelial/hair cells that function as receptors
taste microvilli protrude from taste cells; sensitive parts of taste cells

33. Taste Receptors

34. Taste Sensations Four Primary Taste Sensations
sweet – stimulated by carbohydrates
sour – stimulated by acids
salty – stimulated by salts
bitter – stimulated by many organic compounds
MSG-newly discovered (circa. 1985)
Spicy foods activate pain receptors

35. Taste Nerve Pathways
Sensory impulses from taste receptors travel along
cranial nerves (VII, IX, X) to Solitary Nucleus
in the medulla to
thalamus to
gustatory cortex (for interpretation)

36. Hearing
Ear – organ of hearing
Three Sections
External
Middle
Inner

37. External Ear auricle external auditory meatus tympanic membrane
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

38. Middle Ear 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

39. Auditory Tube 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

40. Inner Ear complex system of labyrinths osseous labyrinth
bony canal in temporal bone
filled with perilymph
membranous labyrinth
tube within osseous labyrinth
filled with endolymph

41. Inner Ear Three Parts of Labyrinths cochlea semicircular canals
functions in hearing
semicircular canals
functions in equilibrium
vestibule

42. Cochlea 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

43. 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

44. 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

45. Organ of Corti

46. Auditory Nerve Pathways

47. Summary of the Generation of Sensory Impulses from the Ear

48. Equilibrium Dynamic Equilibrium Static Equilibrium semicircular canals
sense rotation and movement of head and body
Static Equilibrium
vestibule
sense position of head when body is not moving

49. Vestibule
Utricle
communicates with saccule and membranous portion of semicircular canals
Saccule
communicates with cochlear duct
Mucula
hair cells of utricle and saccule

50. Macula responds to changes in head position
bending of hairs results in generation of nerve impulse

51. Semicircular Canals 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

52. Crista Ampullaris

53. Sight Visual Accessory Organs eyelids lacrimal apparatus
extrinsic eye muscles

54. Eyelid palpebra composed of four layers orbicularis oculi - closes
skin
muscle
connective tissue
conjunctiva
orbicularis oculi - closes
levator palperbrae superioris – opens
tarsal glands – secrete oil onto eyelashes
conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball

55. Lacrimal Apparatus lacrimal gland lateral to eye secretes tears
canaliculi
collect tears
lacrimal sac
collects from canaliculi
nasolacrimal duct
collects from lacrimal sac
empties tears into nasal cavity

56. Extrinsic Eye Muscles Superior rectus rotates eye up and medially
Inferior rectus
rotates eye down and medially
Medial rectus
rotates eye medially

57. Extrinsic Eye Muscles Lateral rectus rotates eye laterally
Superior oblique
rotates eye down and laterally
Inferior oblique
rotates eye up and laterally

59. Structure of the Eye hollow spherical wall has 3 layers
outer fibrous tunic
middle vascular tunic
inner nervous tunic

60. Outer Tunic Cornea anterior portion transparent light transmission
light refraction
Sclera
posterior portion
opaque
protection

61. Middle Tunic Iris anterior portion pigmented controls light intensity
Ciliary body
anterior portion
pigmented
holds lens
moves lens for focusing
Choroid coat
provides blood supply
pigments absorb extra light

63. Anterior Portion of Eye
filled with aqueous humor

64. Lens transparent biconvex lies behind iris
largely composed of lens fibers
elastic
held in place by suspensory ligaments of ciliary body

65. Ciliary Body forms internal ring around front of eye
ciliary processes – radiating folds
ciliary muscles – contract and relax to move lens

66. Accommodation
changing of lens shape to view objects

67. To focus, a lens changes position or shape
To focus, a lens changes position or shape
Focusing
Involves changing the shape of the lens
Ciliary muscle contracted
Ligaments slacken
Choroid
Retina
Lens
Light from a near object
(diverging rays)
Near vision (accommodation)
Ciliary muscle relaxed
Ligaments pull on lens
Light from a distant object
(parallel rays)
Distance vision
Figure 29.6

68. Iris 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

69. Aqueous Humor 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

70. Inner Tunic 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

71. Posterior Cavity
contains vitreous humor – thick gel that holds retina flat against choroid coat

72. Major Groups of Retinal Neurons
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

73. Layers of the Eye

74. Light Refraction Refraction bending of light
occurs when light waves pass at an oblique angle into mediums of different densities

75. Types of Lenses Convex lenses cause light waves to converge
Concave lenses cause
light waves to diverge

76. 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

77. Visual Receptors Rods long, thin projections
contain light sensitive pigment called rhodopsin
hundred times more sensitive to light than cones
provide vision in dim light
produce colorless vision
produce outlines of objects
Cones
short, blunt projections
contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe
provide vision in bright light
produce sharp images
produce color vision

78. Rods and Cones

79. Visual Pigments Rhodopsin light-sensitive pigment in rods
decomposes in presence of light
triggers a complex series of reactions that initiate nerve impulses
impulses travel along optic nerve
Pigments on Cones
each set contains different light-sensitive pigment
each set is sensitive to different wavelengths
color perceived depends on which sets of cones are stimulated
erythrolabe – responds to red
chlorolabe – responds to green
cyanolabe – responds to blue

80. Rod Cells

81. Stereoscopic Vision provides perception of distance and depth
results from formation of two slightly different retinal images

82. Visual Nerve Pathway

83. Life-Span Changes 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

84. Clinical Application Refraction Disorders
concave lens corrects nearsightedness
convex lens corrects farsightedness