1. Hearing

2. The Ear The ear is a fascinating organ
It is a complex system that involves coordinating both hearing auditory signals and giving information on balance and position
It does an incredible job of relaying information to the brain about the state of the environment

3. The Ear The ear is composed of three major components
The external ear collects and condenses signals from the outside world
The middle ear translate signals and waves of the outside world for the deeper parts of the ear
The inner ear contains sensory organs that make sense of input to create sounds and balance

4. The Ear
However to understand how the ear works we first have to understand how sound works
Sound is just a series of molecule moving waves
These waves cause variances in pressure
Those pressure waves can be picked up by the ear

5. Video
h?v=qNf9nzvnd1k

6. External Ear
The external ear has several different structures and formations
The main section of the external ear is the auricle (aka the pinna)
This is designed to funnel sound from a forward conversation to the interal parts of the ear

7. Demo
This one is brief…
Turn your heads towards a partner and have them speak at a normal conversational volume
Now cup your hands behind your ears during their conversation
Now use your hands to pin your ears back against your head

8. External Ear
The auditory canal (aka the external auditory meatus) is the hollow tube that funnels sound to deeper parts of the ear
This section of the ear is a common site for infection for infants because of its position
It is also a common site for different invaders to attack

9. Video
?t=45s
Yup… this is a thing

10. External Ear
In order to try to prevent this your body uses ceruminous glands to secrete a waxy substance that traps particles and invaders
This wax is designed to not only trap substances, it is designed to make fight off microorganisms
This helps slow the growth of invaders

11. Video http://www.dailymotion.com/vi deo/x2n90cf
Not my favorite video of all time…

12. External Ear
The external ear ends at the outer covering of the tympanic membrane
The tympanic membrane is better known as the ear drum
The tympanic membrane vibrates based on pressure waves that are received from the outside environment

13. Video https://www.youtube.com/watc h?v=osFBNLA7woY
Helps you understand what happens when your ear drum gets a pressure wave
Except this pressure wave is much larger

14. Middle Ear
The middle ear is an air filled chamber separated from the auditory canal by the tympanic membrane
Inside of the tympanic membrane are three small and distinct bones
These bones are called the auditory ossicles

15. Middle Ear
The three bones of the auditory ossicles are called the malleus (hammer), incus (anvil) and stapes (stirrup)
These joints change pressure waves into mechanical energy
These three bones are the smallest bones and synovial joints within the body

16. Middle Ear
This process begins when a sound wave hits the tympanic membrane
The membrane flexes and bends which vibrates the malleus
The malleus then vibrates that incus
Finally the incus causes the stirrup to act like a plunger against the auditory window

17. Middle Ear
Because the tympanic membrane is much larger than the auditory window, there is a very large amplification of sound
Small sounds that barely vibrate the tympanic membrane will create a large amount of vibration in the auditory window

18. Internal Ear
The senses of equilibrium and hearing are provided by the internal ear
The entire shape with all of the contours of the internal ear is consistent with the surrounding temporal bone
This is called the bony labyrinth
A series of fluid filled tubes that follow the bony labyrinth is called the membranous labyrinth

19. Internal Ear The internal ear contains two major structures
The first set of structures are the semicircular canals
The semicircular canals are hollow fluid filled tubes that are stimulated by rotation of the head
They are used to help you keep balance and orientation for the body

20. Internal Ear
The cochlea is a spiral shaped and bony chamber that contains the cochlear duct
Its main job is to provide a sense of sound within the body
Receptors within the cochlea are designed to distinguish sound and perceive pitch

21. Equilibrium
The balance system is commonly referred to as the vestibular system
The vestibular system can detect the speed, amount and length of any change in position
This us a useful tool to be able to locate ourselves in the world
Along with light and gravity it is one of the ways that we orient ourselves in the world
It is one of the only ways that an astronaut can figure out how to move around in space

22. Equilibrium
The semicircular ducts are divided into the anterior, posterior and lateral ducts
These ducts are lined with hair cells that are used to create the sense of motion
The hair cells are located within the ducts in areas called apulla

23. Equilibrium
When you move your head in any direction the liquid inside of the ducts, endolymph, moves structures on the surface of the hair cell
The structures on the hair cells are called sterocillia and kinocilium
As these projections move, the hair cells release neurotransmitters to sensory neurons

24. Video
h?v=dSHnGO9qGsE

25. Equilibrium Sometimes people get a feeling of motion sickness
This often happens when people get conflicting sensory information from the outside world
Examples include when your eyes are focused on a fixed object (book) and your vestibular system is focused on motion (car)

26. Video https://www.youtube.com/watc h?v=GoQ0OXJCbaE
Mature Language Warning

27. Introduction To Sound Hearing is the perception of sound
Sound is the transmission of waves in a medium
This means sounds that we hear are pressure waves in the air or water
We just interpret these waves into sound

28. Introduction To Sound
The wavelength is the distance of the wave’s crest from each other
Frequency is the number of waves in any particular amount of time
This is measured in Hertz
In our hearing, the more frequent a wave, the higher pitched the tone of the sound
Humans can hear between 20Hz and 20,000Hz

29. Demo
Start the recording and it will start a tone that increases in frequency
It starts at 1Hz and will go to 20,000Hz
Remember 20Hz to 20,000Hz is the range of perfect human hearing
hearingtest.html

30. Introduction To Sound
The energy that is in each wave is related to the amplitude of each wave
The amplitude of each wave is related to its sound intensity
This creates a sound that is higher in volume to your ear
This is measured in Decibels

31. Introduction To Sound
The increase in Decibels creates a smaller or louder noise
Humans can hear things that are just above zero Decibels
They also experience pain from exposures above 120 Decibels
Long term damage can happen from greater than 80 Decibels for extended periods of time

32. Demo So lets test your ability to perceive sound
hearing-test
com/us/

33. Introduction To Sound
The common ailment that is perceived when exposed to high volumes over long times is tinnitus
This presents most often as a high pitched ringing in the ears
This presents most commonly in people that have job that require high sound thresholds

34. Pathway of Sound
The receptors of the cochlear duct provide a sense of hearing
Remember…
1) The tympanic membrane will vibrate based on the pressure waves from the environment
2) Then the auditory ossicles will collide with each other to push the stapes into the auditory window of the cochlea

35. Pathway of Sound
3) Movement of the stapes causes the inside of the cochlea to have pressure waves
The inner fluids of the cochlea are will have pressure waves due to the stapes plunger action
These pressure waves are carried on the inner fluid called perilymph

36. Pathway of Sound 4) The pressure waves distort the basilar membrane
The basilar membrane is a structure that is inside of the cochlea
Its structure mimics the inner folds and bends of the cochlea
Different frequencies of sound will vibrate different sections of the basilar membrane

37. Pathway of Sound
5) The vibration of the basilar membrane stimulates hair cells
Vibrations of the different sections of the basilar membrane stimulate different sections of hair cells
These cells will move based on the vibration of the basilar membrane

38. Pathway of Sound 6) The sound is carried along nerves to the CNS
The sounds that are interpreted are carried to the brain through pathways of nerves
Information is sent to the midbrain
From there reflexes are acted upon or it is relayed to the auditory cortex

39. Video
h?v=2HUsoISnW_c

40. Video https://www.youtube.com/watc h?v=zeg4qTnYOpw
We can now fix a cochlea that does not work
?t=2m34s
Really Cute