1. SENSE OF HEARING
EAR

2. LEARNING OBJECTIVES
Describe components and functions of external, middle &inner ear.
How sound waves are converted into nerve impulses generated in inner hair cells in cochlea.
How the rotational linear acceleration are detected by receptors located in semicircular canals, utricle and saccule.
Know the various type of deafness

3. Ear Consists of 3 parts External ear Middle ear Inner ear
Consists of pinna, external auditory meatus, and tympanum
Transmits airborne sound waves to fluid-filled inner ear
Amplifies sound energy
Middle ear
Transmits airborne sound waves through auditory ossicles to fluid-filled inner ear
Inner ear
Houses 2 different sensory systems
Cochlea
Contains receptors for conversion of sound waves into nerve impulses which makes hearing possible
Vestibular apparatus
Necessary for sense of equilibrium

4. Ear

5. Parts of the ear
Outer (external) ear
Middle ear (ossicles) for hearing)
Inner ear (labyrinth) for hearing & equilibrium

6. The Tympanic Membrane and the Ossicular System
Tympanic membrane functions to transmit vibrations in the air to the cochlea
Amplifies the signal because the area of the tympanic membrane is 17 times larger than the oval window
Tympanic membrane connected to the ossicles
malleus
incus
stapes

7. Attenuation of Sound by Muscle Contraction
two muscles attach to the ossicles
stapedius
tensor tympani
a loud noise initiates reflex contraction after milliseconds
attenuates vibration going to cochlea
serves to protect cochlea and damps low frequency sounds i.e., your own voice

8. Sound in external acoustic meatus hits tympanic membrane (eardrum) – it vibrates
Pressure is equalized by the pharyngotympanic (tube ( eustachian or auditory tube

9. Inner ear = bony “labyrinth” of 3 parts
Cochlea - hearing
Vestibule - equilibrium
Semicircular canals - equilibrium

10. Hearing Neural perception of sound energy Involves 2 aspects
Identification of the sounds (“what”)
Localization of the sounds (“where”)
Sound waves
Traveling vibrations of air
Consist of alternate regions of compression and rarefaction of air molecules

11. Formation of Sound Waves

12. Hearing Pitch (tone) of sound Depends on frequency of air waves
Intensity (loudness)
Depends on amplitude of air waves
Timbre (quality)
Determined by overtones

13. Decibel Is unit of sound
expressed in terms of the logarithm of their intensity
Intensity of sound in bels is the log of ratio of the intensity of
sound and a standard sound
0.1 bel is a decibel
0 decibel=pressure level of dyne/cm2
(just auditory threshold for average human)
0 decibel does not mean absence of sound ,but sound
level of intensity equal to that of standard
Human can hear from 20-20,000 Hz
The greatest sensitivity being between Hz range
0- to 140-dB range from threshold pressure to a pressure potentially damaging to organ of corti

15. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

16. Sound Wave Transmission
Tympanic membrane vibrates when struck by sound waves,
Middle ear transfers vibrations through ossicles (malleus, incus, stapes) to oval window (entrance into fluid-filled cochlea)
Total amplification of sound is about 20 times Waves in cochlear fluid set basilar membrane in motion
Receptive hair cells are bent as basilar membrane is deflected up and down
Mechanical deformation of specific hair cells is transduced into neural signals that are transmitted to auditory cortex in temporal lobe of brain for sound perception

17. Transmission of Sound Waves

20. Organ of Corti receptor organ that generates nerve impulses
lies on the surface of the basilar membrane, contains rows of cells with stereo cilia called hair cells
the tectorial membrane lies above the stereo cilia of the hair cells
movement of the basilar membrane causes the stereo cilia of the hair cells to shear back and forth against the tectorial membrane

22. Bending of Hairs on Deflection of Basilar membrane

23. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

25. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

26. Determination of Sound Frequency and Amplitude
Place principle determines the frequency of sound perceived.
Different frequencies of sound will cause the basilar membrane to oscillate at different positions.
Position along the basilar membrane where hair cells are being stimulated determines the pitch of the sound being perceived.
Amplitude is determined by how much the basilar membrane is displaced.

27. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

28. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

29. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

30. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

31. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

33. Nerve Impulse Origination
The stereo cilia, when bent in one direction cause the hair cells to depolarize, and when bent in the opposite direction hyperpolarize.
this is what begins the neural transduction of the auditory signal
Inner hair cells (HEAR)
Auditory signals are transmitted by the inner hair cells.
outer hair cells are 3-4 times more than inner hair cells
outer hair cells may control the sensitivity of the inner hair cells for different sound pitches

34. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

36. Auditory pathway
Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

37. Determining the Direction of Sound
superior olivary nucleus divided into lateral and medial nuclei
lateral nuclei detects direction by the difference in sound intensities between the 2 ears
medial nuclei detects direction by the time lag between acoustic signals entering the ears

38. Equilibrium Vestibular apparatus In inner ear Consists of
Semicircular canals
Detect rotational acceleration or deceleration in any direction
Utricle and saccule
Detect changes in rate of linear movement in any direction
Provide information important for determining head position in relation to gravity

39. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

40. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

43. Equilibrium
Neural signals generated in response to mechanical deformation of hair cells by specific movement of fluid and related structures
Vestibular input goes to vestibular nuclei in brain stem and to cerebellum for use in maintaining balance and posture, controlling eye movement, perceiving motion and orientation

44. Equilibrium

46. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

47. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

48. Chapter 6 The Peripheral Nervous System: Afferent Division; Special Senses Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

52. Deafness (Hearing impairment/loss)
Is difficulty in hearing
Types of deafness/hearing loss:
Three types of deafness/hearing loss;
1. Conductive deafness/ hearing loss
(impaired sound transmission in external or
middle ear)
2. Sensorineural deafness/hearing loss
(damage to cochlear hair cells or 8th cranial nerve,
rarely ascending aud. pathway or aud. cortex)
3. Mixed hearing loss i.e.
(both conductive & sensorineural hearing loss)
Presbycusis: the gradual hearing loss associated
with aging, affects 1/3rd above 75 yrs of age,
Due to gradual loss of hair cells

54. Conductive Hearing Loss
Sensorineural Hearing Loss
Middle and outer ear infections
Age-related hearing loss
Collection of fluid in the middle ear (glue ear in children)
Noise exposure
Perforated eardrum
Viral infections of the inner ear (e.g. mumps or measles)
Impacted earwax
Diseases e.g. multiple sclerosis
Absence or malformation of the outer ear, ear canal, or middle ear
Infections or inflammation of the brain or brain covering – e.g. meningitis
Presence of a foreign body
Acoustic neuroma, a benign (non-cancerous) tumor affecting the auditory nerve
Otosclerosis (fusion of the bones of the middle ear)
Drugs toxic to the auditory system
Benign (non-cancerous) tumors
A brain tumor

58. Hearing aids:
Helpful in conductive deafness
Increase the intensity of airborne sounds,
Modify sound spectrum
May help particular pattern of hearing loss at
higher/lower frequencies
Cochlear implants are available

59. References
Human physiology by Lauralee Sherwood, seventh/eighth edition
Text book physiology by Guyton &Hall,
12th edition
Text book of physiology by Linda .s contanzo, third edition