1. Human Anatomy and Physiology
Tenth Edition
Chapter 15 Part D
The Special Senses
Copyright © 2016 Pearson Education, Inc. All Rights Reserved

2. Hearing

3. 15.8 Sound Detection
Hearing is the reception of an air sound wave that is converted to a fluid wave that ultimately stimulates mechanosensitive cochlear hair cells that send impulses to the brain for interpretation
Properties of Sound
Sound is a pressure disturbance (alternating areas of high and low pressure) produced by a vibrating object and propagated by molecules of the medium (air)

4. Properties of Sound (1 of 6)
Sound waves are created when an object moves:
Air molecules that are displaced by object movement are pushed forward into adjacent area, adding to air molecules already there
Creates an area of high pressure due to compression of molecules together
As object returns to original position, the area it leaves now has fewer air molecules
Creates an area of low pressure due to presence of fewer air molecules
Referred to as rarefaction

5. Properties of Sound (2 of 6)
Sound waves are alternating areas (waves) of compressions and rarefactions
Object vibrating causes waves to move outward in all directions as air all around it is compressed and rarefied
Kinetic energy of object is transferred to air molecules, which then transfer it to other air molecules
Wave energy declines with time and distance

6. Properties of Sound (3 of 6)
Illustrated as an S-shaped curve, or sine wave
Compressions shown as crests, rarefactions as troughs

7. Figure 15.28a Sound: Source and Propagation

8. Figure 15.28b Sound: Source and Propagation

9. Properties of Sound (4 of 6)
Sound can be described by two physical properties: frequency and amplitude
Frequency
Number of waves that pass given point in a given time
Pure tone has repeating crests and troughs
Wavelength
Distance between two consecutive crests
Shorter wavelength = higher frequency of sound
Wavelength is consistent for a particular sound

10. Properties of Sound (5 of 6)
​​Frequency
Frequency range of human hearing is 20–20,000 hertz (Hz = waves per second), but most sensitive between 1500 and 4000 Hz
Pitch: perception of different frequencies
Higher the frequency, higher the pitch
Quality: characteristic of sounds
Most sounds are mixtures of different frequencies
Tone: one frequency (ex: tuning fork)
Sound quality provides richness and complexity of sounds (music)

11. Figure 15.29a Frequency and Amplitude of Sound Waves

12. Properties of Sound (6 of 6)
Amplitude
Height of crests
Amplitude perceived as loudness: subjective interpretation of sound intensity
Measured in decibels (dB)
Normal range is 0–120 decibels (dB)
Normal conversation is around 50 dB
Threshold of pain is 120 dB
Severe hearing loss can occur with prolonged exposure above 90 dB
Amplified rock music is 120 dB or more

13. Figure 15.29b Frequency and Amplitude of Sound Waves

14. Transmission of Sound to Internal Ear (1 of 2)
Pathway of sound
​​Tympanic membrane: sound waves enter external acoustic meatus and strike tympanic membrane, causing it to vibrate
The higher the intensity, the more vibration​
​Auditory ossicles: transfer vibration of eardrum to oval window
Tympanic membrane is about 20× larger than oval window, so vibration transferred to oval window is amplified about 20×

15. Transmission of Sound to Internal Ear (2 of 2)
​​Scala vestibuli: stapes rocks back and forth on oval window with each vibration, causing wave motions in perilymph
Wave ends at round window, causing it to bulge outward into middle ear cavity
4a. Helicotrema path: waves with frequencies below threshold of hearing travel through helicotrema and scali tympani to round window
4b. Basilar membrane path: sounds in hearing range go through cochlear duct, vibrating basilar membrane at specific location, according to frequency of sound

16. Figure 15.30 Pathway of Sound Waves (1 of 5)

17. Figure 15.30 Pathway of Sound Waves (2 of 5)

18. Figure 15.30 Pathway of Sound Waves (3 of 5)

19. Figure 15.30 Pathway of Sound Waves (4 of 5)

20. Figure 15.30 Pathway of Sound Waves (5 of 5)

21. Resonance of the Basilar Membrane
Resonance: movement of different areas of basilar membrane in response to a particular frequency
Basilar membrane changes along its length:
Fibers near oval window are short and stiff
Resonate with high-frequency waves
Fibers near cochlear apex are longer, floppier
Resonate with lower-frequency waves
So basilar membrane mechanically processes sound even before signals reach receptors

22. Figure 15.31-1 Basilar Membrane Function

23. Figure 15.31-2 Basilar Membrane Function

24. Sound Transduction (1 of 3)
Excitation of inner hair cells
Movement of basilar membrane deflects hairs of inner hair cells
Cochlear hair cells have microvilli that contain many stereocilia (hairs) that bend at their base
Longest hair cells are connected to shortest hair cells via tip links
Tip links, when pulled on, open ion channels they are connected to
Stereocilia project into K+-rich endolymph, with longest hairs enmeshed in gel-like tectorial membrane

25. Figure 15.27c Anatomy of the Cochlea

26. Sound Transduction (2 of 3)
Excitation of inner hair cells
Bending of stereocilia toward tallest ones pull on tip links, causing
ion channels in shorter stereocilia to open
flow into cell, causing receptor potential that can lead to release of neurotransmitter (glutamate)
Can trigger AP in afferent neurons of cochlear nerve
Bending of stereocilia toward shorter ones causes tip links to relax
Ion channels close, leading to repolarization (and even hyperpolarization)

27. Figure 15.32 Bending of Stereocilia Opens or Closes Mechanically Gated Ion Channels in Hair Cells

28. Sound Transduction (3 of 3)
Role of outer hair cells
Nerve fibers coiled around hair cells of outer row are efferent neurons that convey messages from brain to ear
Outer hair cells can contract and stretch, which changes stiffness of basilar membrane
This ability serves two functions:
Increase “fine-tuning” responsiveness of inner hair cells by amplifying motion of basilar membrane
Protect inner hair cells from loud noises by decreasing motion of basilar membrane

29. 15.9 Auditory Pathways to Brain (1 of 2)
Neural impulses from cochlear bipolar cells reach auditory cortex via following pathway:
Spiral ganglion →
Cochlear nuclei (medulla) →
Superior olivary nucleus (pons-medulla) →
Lateral lemniscus (tract) →
Inferior colliculus (midbrain auditory reflex center →
Medial geniculate nucleus (thalamus) →
Primary auditory cortex

30. 15.9 Auditory Pathways to Brain (2 of 2)
Some fibers cross over, some do not; so both auditory cortices receive input from both ears

31. Figure 15.33 The Auditory Pathway

32. Auditory Processing (1 of 2)
Perception of pitch: impulses from hair cells in different positions along basilar membrane are interpreted by brain as specific pitches
Detection of loudness is determined by brain as an increase in the number of action potentials (frequency) that result when hair cells experience larger deflections

33. Auditory Processing (2 of 2)
Localization of sound depends on relative intensity and relative timing of sound waves reaching both ears
If timing is increased on one side, brain interprets sound as coming from that side

34. Equilibrium

35. 15.10 Maintenance of Equilibrium
Equilibrium is response to various movements of head that rely on input from inner ear, eyes, and stretch receptors
Vestibular apparatus: equilibrium receptors in semicircular canals and vestibule
Vestibular receptors monitor static equilibrium
Semicircular canal receptors monitor dynamic equilibrium

36. Figure 15.24b Structure of the Ear

37. The Maculae (1 of 6)
Maculae: sensory receptor organs that monitor static equilibrium
One organ located in each saccule wall and one in each utricle wall
Monitor the position of head in space
Play a key role in control of posture
Respond to linear acceleration forces, but not rotation

38. Figure 15.26 Membranous Labyrinth of the Internal Ear

39. The Maculae (2 of 6) Anatomy of a macula
Each is a flat epithelium patch containing hair cells with supporting cells
Hair cells have stereocilia and special “true stereocilium” called kinocilium
Located next to tallest stereocilia
Stereocilia are embedded in otolith membrane, jelly- like mass studded with otoliths (tiny CaCO3 stones)
Otoliths increase membrane’s weight and increase its inertia (resistance to changes in motion)

40. The Maculae (3 of 6) Anatomy of a macula
Utricle maculae are horizontal with vertical hairs
Respond to change along a horizontal plane, such as tilting head
Forward/backward movements stimulate utricle
Saccule maculae are vertical with horizontal hairs
Respond to change along a vertical plane
Up/down movements stimulate saccule (Example: acceleration of an elevator)

41. The Maculae (4 of 6) Anatomy of a macula
Hair cells synapse with fibers of vestibular nerve whose cell bodies are located in superior and inferior vestibular ganglia
Part of vestibulocochlear cranial nerve (VIII)

42. Figure 15.34a Structure and Function of a Macula

43. The Maculae (5 of 6) Activating receptors of a macula
Hair cells release neurotransmitter continuously
Acceleration/deceleration causes a change in amount of neurotransmitter released
Leads to change in AP frequency to brain
Density of otolith membrane causes it to lag behind movement of hair cells when head changes positions
Base of stereocilia moves at same rate as head, but tips embedded in otolith are pulled by lagging membrane, causing hair to bend
Ion channels open, and depolarization occurs

44. The Maculae (6 of 6) Activating receptors of a macula
Bending of hairs in direction of kinocilia:
Depolarizes hair cells
Increases amount of neurotransmitter release
More impulses travel up vestibular nerve to brain
Bending of hairs away from kinocilia:
Hyperpolarizes receptors
Less neurotransmitter released
Reduces rate of impulse generation
Thus brain is informed of changing position of head

45. Figure 15.34b Structure and Function of a Macula

46. The Cristae Ampullares (1 of 5)
Receptor for rotational acceleration is crista ampullaris (crista)
Small elevation in ampulla of each semicircular canal
Cristae are excited by acceleration and deceleration of head
Major stimuli are rotational (angular) movements, such as twirling of the body
Semicircular canals are located in all three planes of space, so cristae can pick up on all rotational movements of head

47. The Cristae Ampullares (2 of 5)
Anatomy of a crista ampullaris
Each crista has supporting cells and hair cells that extend into gel-like mass called ampullary cupula
Dendrites of vestibular nerve fibers encircle base of hair cells
Activating receptors of crista ampullaris
Cristae respond to changes in velocity of rotational movements of head
Inertia in ampullary cupula causes endolymph in semicircular ducts to move in direction opposite body’s rotation, causing hair cells to bend

48. Figure 15.35a Location, Structure, and Function of a Crista Ampullaris in the Internal Ear

49. Figure 15.35b Location, Structure, and Function of a Crista Ampullaris in the Internal Ear (1 of 2)

50. The Cristae Ampullares (3 of 5)
Activating receptors of crista ampullaris
Bending hairs in cristae causes depolarization
Rapid impulses reach brain at faster rate
Bending of hairs in opposite direction causes hyperpolarizations
Fewer impulses reach brain
Thus brain is informed of head rotations

51. The Cristae Ampullares (4 of 5)
Activating receptors of crista ampullaris
Axes of hair cells in complementary semicircular ducts are opposite
Depolarization occurs in one ear, while hyperpolarization occurs in other ear
Endolymph will come to rest after a while, so this system detects only changes in movements

52. Figure 15.35b Location, Structure, and Function of a Crista Ampullaris in the Internal Ear (2 of 2)

53. The Cristae Ampullares (5 of 5)
Vestibular nystagmus
Semicircular canal impulses are linked to reflex movements of eyes
Nystagmus is strange eye movements during and immediately after rotation
Often accompanied by vertigo
As rotation begins, eyes drift in direction opposite to rotation; then CNS compensation causes rapid jump toward direction of rotation
As rotation ends, eyes continue in direction of spin, then jerk rapidly in opposite direction

54. Equilibrium Pathway to the Brain
Equilibrium information goes to reflex centers in brain stem
Allows fast, reflexive responses to imbalance so we don’t fall down
Impulses from activated vestibular receptors travel to either vestibular nuclei in brain stem or to cerebellum
Three modes of input for balance and orientation:
Vestibular receptors
Visual receptors
Somatic receptors

55. Figure 15.36 Neural Pathways of the Balance and Orientation System

56. Clinical – Homeostatic Imbalance 15.15 (1 of 2)
Equilibrium problems are usually unpleasant and can cause nausea, dizziness, and loss of balance
Nystagmus in the absence of rotational stimuli may be present

57. Clinical – Homeostatic Imbalance 15.15 (2 of 2)
Motion sickness: sensory inputs are mismatched
Visual input differs from equilibrium input
Conflicting information causes motion sickness
Warning signs are excess salivation, pallor, rapid deep breathing, profuse sweating
Treatment with antimotion drugs that depress vestibular input, such as meclizine and scopolamine

58. 15.11 Homeostatic Imbalances of Hearing (1 of 2)
Deafness
Conduction deafness
Blocked sound conduction to fluids of internal ear
Causes include impacted earwax, perforated eardrum, otitis media, otosclerosis of the ossicles
Sensorineural deafness
Damage to neural structures at any point from cochlear hair cells to auditory cortical cells
Typically from gradual hair cell loss

59. 15.11 Homeostatic Imbalances of Hearing (2 of 2)
Sensorineural deafness research is under way to prod supporting cells to differentiate into hair cells
Cochlear implants that convert sound energy into electrical signals are effective for congenital or age/noise cochlear damage
Inserted into drilled recess in temporal bone
So effective that deaf children can learn to speak

60. Figure 15.37 Boy with a Cochlear Implant

61. Tinnitus
Ringing, buzzing, or clicking sound in ears in absence of auditory stimuli
Due to cochlear nerve degeneration, inflammation of middle or internal ears, side effects of aspirin

62. Ménière’s Syndrome
Labyrinth disorder that affects cochlea and semicircular canals
Causes vertigo, nausea, and vomiting
Treatment: anti–motion sickness drugs in mild cases or surgical removal of labyrinth in severe cases

63. Developmental Aspects of the Special Senses (1 of 7)
Taste and Smell
All special senses are functional at birth
Chemical senses: few problems occur until fourth decade, when these senses begin to decline
Odor and taste detection is poor after 65

64. Developmental Aspects of the Special Senses (2 of 7)
Vision
Optic vesicles protrude from diencephalon during week 4 of development
Vesicles indent to form optic cups
Stalks form optic nerves
Later, lens forms from ectoderm
Vision is not fully functional at birth; babies are hyperopic because eyes are shortened
See only gray tones
Eye movements are uncoordinated
Tearless for about 2 weeks

65. Developmental Aspects of the Special Senses (3 of 7)
Vision
By 5 months of age, infants can follow objects, but acuity is still poor
Depth perception and color vision develop by age 3
Adult eye size reached around 8–9 years of age
Around year 40, lenses start to lose elasticity, resulting in presbyopia

66. Developmental Aspects of the Special Senses (4 of 7)
Vision
With age, lens loses clarity, dilator muscles are less efficient; visual acuity is drastically decreased by age 70
Lacrimal glands less active, so eyes are dry, more prone to infection

67. Developmental Aspects of the Special Senses (5 of 7)
Hearing and Balance
Ear development begins in 3-week embryo
Inner ears develop from thickening of ectoderm called otic placodes, which invaginate into otic pit and otic vesicle
Otic vesicle becomes membranous labyrinth, and surrounding mesenchyme becomes bony labyrinth

68. Developmental Aspects of the Special Senses (6 of 7)
Hearing and Balance
Middle ear structures develop from endodermal pharyngeal pouches, ossicles from neural crest cells, and pharyngeal cleft (branchial groove) develops into outer ear structures
Newborns can hear, but early responses are reflexive in nature
By month 4, infants can turn head toward voices of family members

69. Developmental Aspects of the Special Senses (7 of 7)
Hearing and Balance
Language skills tied to ability to hear well
Few ear problems until 60s, when deterioration of spiral organ becomes noticeable
Hair cell numbers decline with age
Presbycusis: loss of high-pitch perception occurs first
Type of sensorineural deafness

70. Clinical – Homeostatic Imbalance 15.16
Congenital problems of eyes are relatively uncommon, but incidence is increased by certain maternal infections
Rubella (German measles) is dangerous, especially during critical first 3 months of pregnancy
Common problems associated with rubella infections are blindness and cataracts

71. Clinical – Homeostatic Imbalance 15.17
Congenital abnormalities are common
Missing pinnae, closed or absent external acoustic meatuses
Maternal rubella causes sensorineural deafness