1. Somatic and Special Senses
Chapter 12
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2. Chapter 12 Somatic and Special Senses
Sensory Receptors
specialized cells or multicellular structures that collect information
stimulate neurons to send impulses along sensory fibers to the brain
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3. Receptor Types Chemoreceptors
respond to changes in chemical concentrations
Nociceptors (Pain receptors)
respond to tissue damage
Thermoreceptors
respond to changes in temperature
Mechanoreceptors
respond to mechanical forces
Photoreceptors
respond to light
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4. Sensation and Adaptation
feeling that occurs when brain interprets sensory impulse
Sensory Adaptation
adjustment of sensory receptors from continuous stimulation
stronger stimulus required to activate receptors
smell and temperature receptors undergo sensory adaptation
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5. Somatic Senses
senses associated with skin, muscles, joints, and viscera
three groups
exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain
proprioceptive senses – senses associated with changes in muscles and tendons
visceroceptive senses – senses associated with changes in viscera
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6. Touch and Pressure Senses
Free nerve endings
common in epithelial tissues
detect touch and pressure
Meissner’s corpuscles
abundant in hairless portions of skin
detect light touch
detect motion on skin
detect texture
Pacinian corpuscles
common in deeper subcutaneous tissues, tendons, and ligaments
detect heavy pressure
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7. Touch and Pressure Senses
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8. Temperature Senses Warm receptors
sensitive to temperatures between 25oC (77o F) and 45oC (113oF)
Cold receptors
sensitive to temperature between 10oC (50oF) and 20oC (68oF)
In between – brain interprets impulses from both
Pain receptors
respond to temperatures below 10oC (50 F)
respond to temperatures above 45oC (113 F)
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9. 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
do not adapt
Visceral Pain
may exhibit referred pain
not well localized
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10. Referred Pain
may occur due to sensory impulses from two regions following a common nerve pathway to brain
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11. Stretch Receptors proprioceptors
send information to CNS concerning lengths and tensions of muscles
2 main kinds of stretch receptors
muscle spindles – in skeletal muscles
Golgi tendon organs – in tendons
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12. Stretch Receptors
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13. 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 (hair cells)
sight in eyes (rods and cones)
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14. 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
small patch of tissue (12 million cells) on the roof of nasal cavity
smells start as a gas, but must be dissolved in watery fluid that surrounds the cilia of the receptors (each receptor has 10-12) to be detected
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15. Olfactory Receptors
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16. Olfactory Nerve Pathways
Once olfactory receptors are stimulated, nerve impulses travel through
olfactory nerves to
olfactory bulbs to
olfactory tracts to
limbic system (for emotions) and olfactory cortex (for interpretation)
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17. 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 cells that function as receptors
taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells
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18. Taste Receptors
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19. Taste Sensations Four Primary Taste Sensations (or are there five?)
sweet – stimulated by carbohydrates
most plentiful near tip
sour – stimulated by acids
most plentiful at margins
salty – stimulated by salts
most plentiful at tip and upper front
bitter – stimulated by many organic compound
most plentiful at back
may be protective – spit out
umami (?)– stimulated by amino acids (meat, cheese)
Spicy foods activate pain receptors
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20. What does food REALLY Taste like?
Taste is affected by:
Smell
Temperature
Texture
Psychological impacts such as color

21. Taste Nerve Pathways
Sensory impulses from taste receptors travel along
cranial nerves to
medulla oblongata to
thalamus to
gustatory cortex (for interpretation)
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22. Hearing
Ear – organ of hearing
3 Sections
External
Middle
Inner
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23. 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
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24. Middle Ear tympanic cavity air-filled space in temporal bone
auditory ossicles (bones)
vibrate in response to tympanic membrane
malleus, incus, and stapes
oval window
opening in wall of tympanic cavity (cochlea)
stapes vibrates against it to move fluids in inner ear
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25. 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
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26. Inner Ear complex system of labyrinths osseous (bony) labyrinth
bony canal in temporal bone
filled with perilymph
membranous labyrinth
tube within osseous labyrinth
filled with endolymph
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27. Inner Ear 3 Parts of Labyrinths cochlea semicircular canals vestibule
functions in hearing
semicircular canals
functions in equilibrium
vestibule
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28. Cochlea portion of membranous labyrinth in cochlea Scala vestibuli
upper compartment
Scala tympani
lower compartment
Cochlear duct **
portion of membranous labyrinth in cochlea
contains Organ of Corti
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29. 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
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30. Organ of Corti
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31. Auditory Nerve Pathways
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32. Summary of the Generation of Sensory Impulses from the Ear
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33. 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
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34. Vestibule Macula **(sensory organ)
hair cells of utricle and saccule sense static balance
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35. Macula responds to changes in head position
bending of hairs results in generation of nerve impulse
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36. Semicircular Canals three canals at right angles ampulla
swelling of membranous labyrinth
crista ampullaris (in ampulla)
sensory organ of dynamic balance
hair cells and supporting cells
rapid turns of head or body stimulate hair cells
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37. Crista Ampullaris
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38. Sight Visual Accessory Organs eyelids lacrimal apparatus
extrinsic eye muscles
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39. Eyelid palpebra (eyelid) composed of four layers
skin
muscle
connective tissue
conjunctiva
orbicularis oculi - closes
levator palpebrae superioris – opens
tarsal glands – secrete oil onto eyelashes
conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball
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40. Lacrimal Apparatus lacrimal gland lateral to eye secretes tears
canaliculi (superior, inferior)
collect tears
lacrimal sac
collects from canaliculi
nasolacrimal duct
collects from lacrimal sac
empties tears into nasal cavity
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41. Extrinsic Eye Muscles Superior rectus rotates eye up and medially
Inferior rectus
rotates eye down and medially
Medial rectus
rotates eye medially
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42. Extrinsic Eye Muscles Lateral rectus rotates eye laterally
Superior oblique
rotates eye up and laterally
Inferior oblique
rotates eye down and laterally
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43. Structure of the Eye hollow spherical wall has 3 layers
(outer) fibrous tunic
(middle) vascular tunic
(inner) nervous tunic
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44. Outer Tunic Cornea anterior portion transparent light transmission
light refraction
Sclera
posterior portion
opaque
protection
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45. Middle Tunic Iris anterior portion pigmented controls light intensity
Ciliary body (muscle)
anterior portion
pigmented
holds lens
moves lens for focusing
Choroid coat
provides blood supply
pigments absorb extra light
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46. Anterior Portion of Eye
filled with aqueous humor
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47. Lens transparent biconvex lies behind iris
largely composed of lens fibers
elastic
held in place by suspensory ligaments of ciliary body
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48. Accommodation
changing of lens shape to view objects
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49. 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
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50. 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 , center, 1 mm
fovea centralis – center of macula lutea; produces sharpest vision, where lens tries to focus light**
optic disc – blind spot; contains no visual receptors
vitreous humor – thick gel that holds retina flat against choroid coat
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51. 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
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52. 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
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53. Rods and Cones
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54. 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
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55. Stereoscopic Vision provides perception of distance and depth
results from formation of two slightly different retinal images
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56. Visual Pathway
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57. 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
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58. Clinical Application Refraction Disorders
concave lens corrects nearsightedness (myopia) when eye is too long or lens focuses light in front of retina
convex lens corrects farsightedness (presbyopia or hyperopia) when eye is too short or lens focuses light behind retina
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