1. Hearing and the Ears

2. The Anatomy of the Ear
The ear consists of 3 different sections 1. The External Ear 2. The Middle Ear - The Auditory Ossicles 3. The Inner Ear

3. Anatomy of the Ear Vestibulocochlear nerve (VIII) EXTERNAL EAR
MIDDLE EAR
INNER EAR
Auricle
Auditory ossicles
Semicircular
canals
Petrous part
of temporal bone
Facial nerve
(VII)
Bony labyrinth
of inner ear
To pharynx
Tympanic
membrane
Cartilage
External
acoustic
canal
Cochlea
Vestibule
Round window
Oval window
Auditory tube

4. The External Ear

5. The External Ear
Made up of fleshy and cartilaginous auricle, which surrounds the external acoustic canal
Sounds coming from the back of the head are blocked by auricle, and sounds coming from the sides of the head are collected and channeled into the external acoustic canal.
The external acoustic canal ends where the tympanic membrane is located.

6. The External Ear Tympanic Membrane
- separates the external ear from the middle ear
-is very delicate, and is protected by external acoustic canal and the auricle
Foreign objects are denied access by the ceruminous glands which secrete a waxy secretion, cerumen.

7. The Middle Ear

8. The Middle Ear Air filled chamber
Communicates with the nasopharynx through the auditory tube and mastoid air cells
The auditory tube permits the equalization of pressures on either side of the tympanic membrane
-On the down side, the auditory tube can also let in microorganisms causing an unpleasant middle ear infection, aka otitis media.

9. Video!!!!!! http://www.youtube.com/watch?v=M3znkf_OEt8
*Warning*real ear endoscopy! Don’t get grossed out!

10. The Auditory Ossicles

11. The Auditory Ossicles
The collection of the three tiny bones in the middle ear. The malleus, the incus, and the stapes
Stapedius
muscle
Malleus
attached to
tympanic
membrane
Inner
surface of
Stapes
(b)
(a)
External
acoustic
canal
Tympanic
Auditory tube
Tensor
tympani
Footplate of
stapes in
oval window
Incus
Branch of
cranial
nerve VII
(cut)
Round
window
Connections
to mastoid
air cells
Temporal
bone
Tendon of tensor
tympani muscle
Footplate
of stapes at
Vibration of the tympanic membrane converts arriving sound waves into mechanical movements, the auditory ossicles acts as a lever for these vibrations to arrive to the inner ear.

12. The Auditory Ossicles
There are two muscles located in the middle ear that protect the tympanic membrane and ossicles from violent movements under noisy conditions.
Tensor tympani muscle, stiffens the tympanic membrane, this increased stiffness reduces the amount of movement possible.
Stapedius muscle, contraction of the stapedius pulls the stapes, reducing movement of the stapes at the oval window

13. The Inner Ear

14. The Inner Ear Provides senses of equilibrium and hearing
The superficial contours are made up of a dense bone layer called the bony labyrinth, which can be subdivided into the vestibule, three semicircular canals and the cochlea.

15. The Inner Ear The Vestibule
Consists of two membranous sacs: the uricle and the saccule
The receptors in the uricle and the saccule provide sensations of gravity and linear acceleration

16. The Inner Ear Semicircular canals Enclose semicircular ducts
Are stimulated by the rotation of the head
The cochlea
Senses within the cochlear duct provide the sense of hearing
Looks like a snail shell

17. The Inner Ear KEY Lateral Semicircular canal Cristae within ampullae
Maculae
Endolymphatic sac
Cochlea
Vestibular duct
Cochlear duct
Organ of
Corti
Tympanic
duct
Posterior
(a)
(b)
Anterior
Semicircular
ducts
Vestibule
Saccule
Utricle
Endolymph
Perilymph
Membranous
labyrinth
Bony labyrinth

18. The state of physical balance
Equilibrium
The state of physical balance

19. Equilibrium
Equilibrium sensations are provided by receptors of the vestibular complex
Semicircular ducts convey information about rotational movements of the head
The saccule and utricle convey information about your position with respect to gravity, this also stimulated by rapid acceleration

20. Equilibrium
The anterior, posterior, and lateral semicircular ducts are continuous with the utricle
Each semicircular duct contains
an ampulla: the expanded region that contains the receptors
Crista: area where receptors are located in the ampulla. Each crista is bound to a cupula
A cupula being a gelantinous structure that extends the entire ampulla
Semicircular Ducts:
Contain sensory receptors and hair cells
Active during movement
Are quite when motionless

21. Vestibular branch (VIII)
Endolymphatic
duct
sac
Vestibular branch (VIII)
Semicircular
ducts
Utricle
Ampulla
Saccule
Maculae
(a) Right semicircular ducts, anterior view
Direction of
duct rotation
relative
endolymph
movement
At rest
(c)
Hair cells
Crista
Cupula
Supporting cells
Sensory nerve
(b) Cross section through the ampulla
Stereocilia
Kinocilium
Hair cell
ending
(d) Hair cell
Displacement in this
direction stimulates
hair cell
Displacement in
this direction
inhibits hair cell
Supporting cell
Anterior
Posterior
Lateral
Cochlea

22. Introduction to Sound

23. Introduction to Sound
The sound we hear consists of pressure waves through the air
Each pressure wave consists of a certain wavelength and each wavelength has a certain frequency (# of waves that pass a fixed reference point in given time)

24. Sound Sound is measures in hertz (Hz)
Amplitude of sounds determines how loud something seems to be.
Greater the energy = Greater the amplitude

25. Sound
When sounds waves strike an object, their energy is a physical pressure
For you to be able to hear any sound, your thin tympanic membrane must vibrate in resonance
Resonance is the phenomenon that with the right combination of frequencies and amplitudes, objects will vibrate at the same frequency.

26. The Hearing Process

27. The Hearing Process Sound waves arrive at the tympanic membrane
Sound waves have direct access to the tympanic membrane on the side of the head they enter

28. The Hearing Process
2. Movement of the tympanic membrane causes displacement of the auditory ossicles
the tympanic membrane provides a surface to collect sound
It vibrates in resonance to sound waves with frequencies between 20 and 20,000 Hz

29. The Hearing Process
Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular ducts
When the stapes moves inward, the round window bulges outward into the middle ear
Stapes move in and out, vibrating at the frequency of sound arriving at the tympanic membrane
This creates pressure waves within the perilymph

30. The Hearing Process
The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct
The louder the sound = the more the basilar membrane moves

31. The Hearing Process
Vibration of basilar membrane causes vibration of hair cells against the tectorial membrane
Movement of hair cells causes there to be a rush of ions to be sent to neurotransmitters causing the simulation of neurons
More intense sound= hair cells become more active
Hair cells are located on the organ of Corti

32. The Hearing Process
6. Information about the region and intensity of stimulation is relayed to the CNS over the cochlear branch of the vestibulocochlear nerve (VIII)
bipolar sensory neurons that monitor cochlear hair cells are located at the center of the bony cochlea, the spiral ganglion
From there information is carried to the cochlear nuclei of the medulla oblongata for distribution to other centers of the brain

33. The Hearing Process External acoustic canal Movement of sound waves
Malleus
Incus
Stapes
Oval window
Cochlear branch
of cranial nerve VIII
Vestibular duct
(perilymph)
Cochlear duct
(endolymph)
Tympanic duct
Round
window
Tympanic
membrane
Vestibular membrane
Basilar membrane 1 2 3 4 5 6
Sound waves
arrive at tympanic
membrane.
Movement of
tympanic membrane
causes displacement
of the auditory
ossicles.
Movement of the
stapes at the oval
window establishes
pressure waves in
the perilymph of
the vestibular duct.
The pressure waves
distort the basilar
membrane on their
way to the round
window of the
tympanic duct.
Vibration of the
basilar membrane
causes vibration of
hair cells against
the tectorial
Information about the
region and the intensity
of stimulation is relayed
to the CNS over the
cochlear branch of
cranial nerve VIII.

34. Professions Audiologist- Help people with hearing or balance problems
Otolaryngologists (ENT)- treat anything wrong with the ears, nose, or throat
Pediatrician- treat children with ear infections. Children are more likely to contract an ear infection

35. Diseases
Middle Ear Infection- In the pocket of air behind the eardrum, if germs get into the middle ear, it fills with germ-fighting fluid called pus. The build up this fluid is what causes pain.

36. Diseases
Nystagmus- The inner part of the ear senses movement and position helps control eye movements, if injured it can cause eyes to shake. If the shaking is so bad, then it can prevent the person from having 20/20 vision.

37. Diseases
Deafness- occurs when sound vibrations don't go from the air around a person to the moving bones of the inner ear as well as they should. Causes: hereditary disorders, genetic disorders, prenatal exposure to disease, prolonged exposure to loud noises, trauma
Swimmers Ear- Germs get into the outer part of the ear and cause an outer ear infection. Can often be brought on by water sitting in the outer ear, allowing for bacteria to grow.