1. Hearing and balance

2. Functions of the human ear The human ear has two functions 1.Hearing 2.Balance

3. Hearing Sound is vibrations in the air around us. The ear is the sensory organ that can distinguish sounds

4. Structure of the Ear

5. Outer ear Pinna and auditory canal direct sound waves to the eardrum at the end of the auditory canal

6. Hearing 1.Vibrations enter the ear through the auditory canal, causing vibrations of the ear drum (tympanic membrane) 2.Ear drum vibrations are picked up by ear ossicles: these are three bones 1.Hammer (Malleus) 2.Anvil (Incus) 3.Stirrup (Stapes) Ossicles amplify vibrations as they pass across them. Stapes transmits vibrations to the oval window

8. Hammer (Malleus) Anvil (incus)

9. Hearing 3.The oval window is a membrane covered opening at the end of the cochlea 4.Vibrations of the oval window create pressure on the fluid-filled choclea

10. The Cochlea The organ of corti runs along the whole length of the coiled cochlea The receptor haircells in the organ of corti convert vibrations to nerve impules

13. Cochlea uncoiled for understanding

14. The cochlea The outer fluid-filled canal runs from the oval window, all the way along the top of the cochlea and back to the round window The round window is a membrane covered opening at the end of the cochlea

16. The cochlea Between the two parts of the outer canal (upper and lower part) is a middle chamber, also filled with fluid. The organ of corti is in a membrane between the middle and outer canals Receptor cells in the organ of corti have sensory hairs in a second membrane

20. Hearing 1.Vibrations of the oval window are transmitted to the fluid in the outer canal of the cochlea 2.Sensory hairs of the receptor cells in the organ of corti stretch according to the movement of the fluid in the outer canal 3.The sensory hair cells (Receptor cells) respond by producing nerve impulses that move through receptor neurones where sounds are converted to nerve impulses 4.Round window vibrates with the opposite phase to vibrations entering the inner ear through the oval window. This allows pressure changing between the middle ear and cochlea

22. The round window Round window vibrates with the opposite phase to vibrations entering the inner ear through the oval window. This allows pressure changing between the middle ear and cochlea

23. Sound Frequency

26. Sound Frequency Determination The brain determine the frequency (pitch) of sounds by detecting which hair cells are being stimulated Hair cells at the base of cochlea are sensitive to high frequency sounds Hair cells at the apex are sensitive to low- frequency sound

27. Sound Frequency Highest frequency sounds are detected near the oval window at the base Lowest frequency sounds are detected at the apex

28. Sound Loudness

29. Sound loudness can be determined by the amplitude (size) of vibrations of the hair cells Loud sounds produce high amplitude vibrations, which result in more nerve impulses per sound in the sensory neurones

30. The Eustachian Tube The Eustachian tube connects the middle ear with the throat, and allows the air pressure to be equalized either side of the eardrum

31. Ear Popping in Planes Your ears pop in planes because as the airplane rises, air pressure falls, causing eardrum to bulge outwards When you swallow, the Eustachian tube opens and allows air to pass to the middle ear from your throat, equalizing the pressure The eardrum goes back to its normal position and you feel the pop

32. What is the function of the round window The round window vibrates with the OPPOSITE PHASE to the vibrations entering the inner ear through the oval window. This allows for pressure changes between the middle ear and the cochlea

34. What is the function of the Eustachian Tube The Eustachian tube connects the middle ear with the throat and allows the air pressure to be euqalised on either side of the ear drum

36. Balance Semicircular canals: Three structures of the inner ear that help monitor body position Semicircular canal, along with the saccules and the utriculus are the balancing parts of the ear

38. Balance: ampulla and cupula At the end of the semicircular canals, there are swellings called ampulla. Inside the ampulla are hair cells embedded in a jelly-like mass called cupula Movement of fluid in the semicircular canals causes the cupula to pull on the hair cells, which stimulates them to send nerve impulses to the brain.

41. Balance The semicircular canals are arranged in three planes at right angles to each other, so they detect movement in all directions

42. Balance: Sacculus and Utriculus The sacculus and utriculus also contain hair cells. Their hairs are embedded in the otolith The otolith: a jelly in the sacculus and utriculus containing calcium carbonate crystals. The weight of the otolith pulls on the hairs, stimulating the hair cells to produce nerve impulses, giving information about the position of the head

43. Utriculus and Sacculus have hair cells in otolith Weight of otolith pulls hair cells stimulating them to produce nerve impulses. This gives the brain info on head position

45. Balance in inner ear Semicircular canals to ampulla: cupula in ampulla pulls hair cells Sacculus and utriculus have hair cells in otolith (gel including CaCO3 crystals)

46. Ampulla has cupulla Utriculus and Sacculus have otolith

48. Structure of the ear

49. Loud noise can damage your ears Normally, sounds are at safe levels that do not damage our hearing Loud sounds, especially if long lasting, can be very harmful to ears. They damage the sensitive ear structure NIHL: Noise Induced Hearing Loss: Loss of hearing caused by loud noises that damage the ear structure

50. Loud noises cause eardrum rupture Exposure to very loud noise, such as explosion, can rupture the eardrum or damage the delicate bones of the inner ear: The ear can recover from this

51. Long term exposure to noises Exposure to loud noises for longer periods can cause temporary deafness. It may also cause tinnitus Tinnitus: ringing or buzzing sound in the ear

52. Examples of decibel ratings Humming refrigerator: 45 decibels Normal conversation: 60 decibels Heavy traffic: 85 decibels MP3 player at full volume: 105 decibels Loud fireworks: 150 decibels

54. Prolonged exposure to moderately loud or very loud noises causes permanent hear loss Prolonged exposure to moderately loud or very loud noises causes damage to the ear and permanent hear loss Sounds above 85 decibels cause permanent damage and hearing loss Sounds less than 75 decibels are unlikely to cause damage or hearing loss

55. NIHL NIHL is caused by damaged to the delicate hair cells in the inner ear. It is a gradual process, and may not be noticed at first. Overtime, sounds become distorted or muffled, so the person may struggle to follow a conversation, or may have to turn up the volume on TV

56. Prevent NIHL NIHL is completely preventable: 1.avoid exposure to sounds over 85 decibels. 2.If you have to take part in an activity that involves loud noises, wear earplugs or ear protectors

57. Practical: Investigating the range of frequencies that can be detected by the human ear Signal generator connected to oscilloscope and speaker

58. Signal generator Frequency of sound waves is measured in Hertz (cycles per second) Signal generator produces sound waves from 1 to 100,000 Hertz The human ear detects sound frequencies between 20 and 20,000 Hertz Normal speech is a few hundred hertz

59. Human Hearing

63. It is thought that the range of audible frequencies decreases with age. Describe an investigation you could carry out to test this hypothesis Make sure you include details of the variables you need to control

64. 1.Connect the signal generator to a speaker 2.Examine the hearing of samples of people: Separate the samples to be tested by age groups, Make sure that the number of people per age group is the same. (e.g. five 10- year olds, five 30-year olds, five 60-year olds, five 80-year olds) (age is the dependent variable) 3.Examine the hearing of each group at set frequencies, starting from 20 Htz, then 1000 Htz, then 5000, then 10000, then 15000 then 20000, and examine the hearing of each age group. Record your results in a table (Frequency is the independent variable) 4.Make sure that, during the experiment, the subjects are tested within the same distance from the sound source, and that they do not have hearing problems (e.g. due to work in loud areas). (distance from sound source is a control variable) 5.Make sure that you use the same loudness and amplitude for all subjects on each frequency (loudness is a control variable)