1. The Sensory System Hearing General Senses
RAD 101
Chapter 10

2. Anatomy of the Ear The ear is divided into three areas
Outer (external) ear
Middle ear
Inner ear
Figure 8.12
Slide 8.21
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3. The External Ear Involved in hearing only
Structures of the external ear
Pinna (auricle)
External auditory canal
Figure 8.12
Slide 8.22
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4. The External Auditory Canal
Narrow chamber in the temporal bone
Lined with skin
Ceruminous (wax) glands are present
Ends at the tympanic membrane
Slide 8.23
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5. The Middle Ear or Tympanic Cavity
Air-filled cavity within the temporal bone
Only involved in the sense of hearing
Slide 8.24a
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6. The Middle Ear or Tympanic Cavity
Two tubes are associated with the inner ear
The opening from the auditory canal is covered by the tympanic membrane
The eustachian (auditory) tube connecting the middle ear with the throat
Allows for equalizing pressure during yawning or swallowing
This tube is otherwise collapsed
Slide 8.24b
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7. Bones of the Tympanic Cavity
Three bones span the cavity
Malleus (hammer)
Incus (anvil)
Stapes (stirrip)
Figure 8.12
Slide 8.25a
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8. Bones of the Tympanic Cavity
Vibrations from eardrum move the ossicles
These bones transfer sound to the inner ear through the oval window
Figure 8.12
Slide 8.25b
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9. Inner Ear or Bony Labyrinth
Includes sense organs for hearing and balance
Filled with perilymph
Figure 8.12
Slide 8.26a
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10. Inner Ear or Bony Labrynth
A maze of bony chambers within the temporal bone
Cochlea
Vestibule
Semicircular canals
Figure 8.12
Slide 8.26b
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11. Organs of Hearing Organ of Corti Located within the cochlea
Receptors = hair cells on the basilar membrane
Gel-like tectorial membrane is capable of bending hair cells
Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe
Slide 8.27a
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12. Organs of Hearing Slide 8.27b Figure 8.13
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13. Mechanisms of Hearing
Vibrations from sound waves move tectorial membrane
Hair cells are bent by the membrane
An action potential starts in the cochlear nerve
Continued stimulation can lead to adaptation
Slide 8.28
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14. Mechanisms of Hearing Slide 8.29 Figure 8.14
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15. Organs of Equilibrium Receptor cells are in two structures Vestibule
Semicircular canals
Figure 8.16a, b
Slide 8.30a
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16. Organs of Equilibrium Equilibrium has two functional parts
Static equilibrium
Dynamic equilibrium
Figure 8.16a, b
Slide 8.30b
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17. Static Equilibrium Maculae – receptors in the vestibule
Report on the position of the head
Send information via the vestibular nerve
Anatomy of the maculae
Hair cells are embedded in the otolithic membrane
Otoliths (tiny stones) float in a gel around the hair cells
Movements cause otoliths to bend the hair cells
Slide 8.31
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18. Function of Maculae Slide 8.32 Figure 8.15
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19. Dynamic Equilibrium Cristae – receptors in the semicircular canals
Function when the body is spinning or moving in different directions
An impulse is sent via the vestibular nerve to the cerebellum
Figure 8.16c
Slide 8.33a
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20. Chemical Senses – Taste and Smell
Both senses use chemoreceptors
Stimulated by chemicals in solution
Taste has four types of receptors
Smell can differentiate a large range of chemicals
Both senses complement each other and respond to many of the same stimuli
Slide 8.34
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21. Olfaction – The Sense of Smell
Olfactory receptors are in the roof of the nasal cavity
Neurons with long cilia
Chemicals must be dissolved in mucus for detection
Impulses are transmitted via the olfactory nerve
Interpretation of smells is made in the cortex
Slide 8.35
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22. Olfactory Epithelium Slide 8.36 Figure 8.17
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23. The Sense of Taste Taste buds house the receptor organs
Location of taste buds
Most are on the tongue
Soft palate
Cheeks
Figure 8.18a, b
Slide 8.37
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24. The Tongue and Taste
The tongue is covered with projections called papillae
Taste buds are found on the sides of papillae
Slide 8.38
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25. Structure of Taste Buds
Gustatory cells are the receptors
Have gustatory hairs (long microvilli)
Hairs are stimulated by chemicals dissolved in saliva
Slide 8.39a
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26. Structure of Taste Buds
Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas
Facial nerve
Glossopharyngeal nerve
Vagus nerve
Slide 8.39b
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27. Taste Sensations Sweet receptors (tip of tongue)
Sugars
Saccharine
Some amino acids
Sour receptors (laterally on the tongue
Acids
Bitter receptors (posterior part of tongue)
Alkaloids
Salty receptors (anterior sides of the tongue)
Metal ions
Slide 8.41
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28. Developmental Aspects of the Special Senses
Formed early in embryonic development
Eyes are outgrowths of the brain
All special senses are functional at birth
Slide 8.42
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29. The General Senses Touch
Tactile receptors found in the dermis of the skin
Sensitivity varies with number of touch receptors
Pressure
Receptors for deep touch located in the subcutaneous tissue
Slide 8.42
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30. Sense of temperature Free nerve endings widely distributed in the skin
Separate receptors for heat and cold
Temperature receptors in the hypothalamus help to adjust body temperature
Slide 8.42
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31. Sense of Position
Proprioreceptors located in muscles, tendons and joints
Relay impulses that help to judge position and changes in location of body parts
Inform the brain of muscle and tendon tension
Aided by equilibrium receptors in the internal ear
Kinesthesia
Sense of body movement
Slide 8.42
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32. Sense of Pain Receptors are widely distributed nerve endings
Two pathways to brain
Sharp acute pain
Slow, chronic pain
Slide 8.42
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33. Pain Relief Analgesic drugs Nonnarcotic analgesics Narcotic
Act locally to reduce inflammation
Non-steroidal antiflammatory drugs (NSAIDS)
Ibuprofen, naproxen
Narcotic
Act on the CNS to alter the reception and response to pain
Anesthetics
Prevent pain during surgery
Used to prevent chronic pain

34. Pain Relief Endorphins Applications of heat and cold
Released naturally from certain areas of the brain
Associated with pain relief
Applications of heat and cold
Relaxation or distraction techniques
Endorphins

35. Sensory Adaptation
When exposed to continuous stimulus, sensory receptors adjust themselves so the sensation becomes less acute