1. CHAPTER 9- Auditory System
ANATOMY OF HEARING
CHAPTER 9- Auditory System

2. STRUCTURES OF HEARING Audition- the process associated with hearing
Essential element of verbal communication
Energy Transducer- converts acoustic energy into electrochemical energy

3. The Ear
The three parts of the ear- Outer, Middle and Inner

4. OUTER EAR
THREE BASIC COMPONENTS
Pinna or Auricle- It serves as a collector of sound to be processed at deeper levels. It is primarily made of a cartilagenous framework
External Auditory Meatus- ear canal. It is approximately 7 mm in diameter and 2.5 cm long.
Tympanic Membrane- most medial portion of the EAM

5. Look at the person next to you and examine- find all of these parts
Helix forms the curled margin of the pinna- most distal border (outer lobe)
Antihelix- immediately anterior to the helix (inside lobe)
Bifucates superiorly which is the crura anthelix
Triangular fossa- space between helix and crus of helix
Scaphoid fossa- posterior space between the helix and antihelix
Concha Cava- entrance to the ear canal/External Auditory Meatus
Tragus- a flap of epithelium covered cartilage
Antitragus- posterior and inferior to tragus
Lobule- Below the antitragus

6. PARTS OF EXTERNAL AUDITORY MEATUS
Outer 1/3 is lined with hairs and has cerumen- traps insects and dirt which protects the medial most point of the outer ear, the Tympanic Membrane
Osseus Meatus- medial 2/3 of the canal surrounded by the temporal bone
Isthmus- junction of the cartilaginous and bony framework of the ear canal .

7. The lateral third of the canal is comprised of cartilage and the medial two-thirds is the bony meatus of the temporal bone. At the end of the EAM is the Tympanic Membrane which is the structure separating the outer and middle ear.

8. Look at the shape of the Outer ear- external auditory meatus

9. Tympanic Membrane Tympanic Membrane- thin 3 layer sheet of tissue
Fibrocartilaginous ring that fits into the tympanic sulcus, a groove in the temporal bone.
The epithelial cover of the pinna continues into the EAM and is the outer layer of the TM
Middle layer is fibrous tissue that provides structure
Inner layer is the lining of the middle ear
TM is slightly concave oval structure with Umbo the most depressed portion of this concavity

10. Outer to Middle Ear
Pay attention to the shape and how the middle ear ossicles are attached

11. Tympanic Membrane

12. MIDDLE EAR Occupied by three of the smallest bones of the body
Ossicles- The bones of the ear
Malleus
Incus
Stapes
Tympanic Muscles
Stapedius
Tensor Tympani
Landmarks of the Middle Ear
Medial Wall
Anterior Wall
Posterior Wall and Floor

13. Middle ear or tympanic cavity is a box
Superior wall or “roof” is thin plate of bone separating the tympanic cavity from the cranium
Inferior wall or “floor” is a thin bone that separates the tympanic cavity from the internal jugular vein. Tympanic nerve, branch of the glossopharyngeal nerve pass through the floor
Lateral wall (membranous) is the tympanic membrane
Medial wall (laryrinthine) is the oval window, round window, chorda tympani nerve (facial nerve),

14. Middle Ear

15. Ossicles of Middle Ear
Let’s talk about the individual bones of the middle ear
Malleus
Handle or Manubrium is the long process, thin neck and a head
Anterior and lateral processes provide points of attachment for the ligaments
Stapes
Head (Caput) of the stapes articulates with the lenticular process of the incus
Neck of the stapes bifurcates to become an arch of the anterior and posterior crura which attach to the footplate
The footplate of the stapes rests in the oval window of the temporal bone held in place by the annular ligament
Incus
The long process of the incus is nearly parallel with the manubrium of the malleus
The short process projects posteriorly
The end of the long process bends medially forming the lenticular process

16. Tympanic Membrane
Umbo- most distal point of attachment of the inner TM to the malleus bone in middle ear
The handle/manubrium attaches to the TM along its length, terminating with the lateral process.
This attachment of the lateral process with the TM forms the anterior and posterior malleolar folds and the pars flaccida

17. Malleus
Largest of the 3 bones- attaches to the TM

18. Malleus

19. Incus Shaped like an anvil
Intermediate communicating link of the ossicular chain
The body of the incus articulates with the head of the malleus by means of the malleolar facet- saddle joint
Malleus and Incus move as a unit upon movement of the TM

21. Stapes Shaped like a stirrup
Incus/Stapes articulation is a ball and socket joint

22. Stapes

23. Ligaments in Middle Ear
Strategically placed ligaments suspend the ossicles from the walls of the middle ear cavity
Anterior ligament of the malleus
Superior ligament of the malleus
Lateral ligament of the malleus
Superior ligament of the incus
Posterior ligament of the incus
Annular ligament

24. Middle Ear Ligaments
Superior ligament of the malleus- holds the head of the malleus within the epitympanic recess
Anterior ligament of the malleus binds the neck of the malleus to the anterior wall of the middle ear
Lateral ligament of the malleus attaches the head of the malleus to the lateral wall
Posterior ligament of the incus suspends the incus by means of its short process
Superior ligament of the incus binds the incus to the epitympanic recess
Annular ligament attaches the footplate of the stapes to the oval window of the cochlea

25. Middle Ear Muscles Stapedial Smallest striated muscle in the body
Originates from the posterior wall
Inserts into the posterior surface of the stapes
Innervated by the facial nerve
Contraction rotates the stapes posteriorly
Stiffens the middle ear ossicles
Reduces strength of the signal reaching the cochlea- protects from loud sounds

26. Middle Ear Muscles Tensor Tympani
Originates from the anterior wall just superior to the eustachian tube Inserts into the upper manubrium malli
Contraction pulls the malleus anteromedially
Innervated by trigeminal nerve
Stiffens the middle ear ossicles
Reduces strength of the signal reaching the cochlea- protects from loud sounds

27. Tympanic Muscles Stapedius muscle
Embedded in the bone of the posterior wall of the middle ear
Inserts into the posterior neck of the stapes
Upon contraction the stapes is rotated posteriorly
Innervation of the stapedius is by means of the stapedial branch of the VII facial nerve
Tensor Tympani
Housed in bone
Originates from the cartilaginous part of the Eustachian tube and greater wing of the sphenoid and inserts into the upper manubrium malli
Contraction pulls the malleus anteromedially and stiffens ossicular chain
Innervation by the V trigeminal nerve

28. Medial Wall Middle ear or tympanic cavity is a box- Air filled cavity
Lateral wall (membranous) is the tympanic membrane
Medial wall (laryrinthine) is the oval window, round window, chorda tympani nerve (facial nerve),
Promontory of the cochlea
Promontory of the semicircular canal
Looking from the tympanic membrane into the inner ear (medial wall)
Fenestra vestibuli or fenestra ovalis: Oval window is where the footplate of the stapes is embedded
Fenestra cochlea; fenestra rottunda: Round window which is sealed by the secondary tympanic membrane and marks the entrance into the scala tympani of the cochlea
Promontory- between the two above- created by the basal turn of the cochlea.
The prominence of the lateral semicircular canal can be seen above the oval window
The prominence of the facial nerve can be seen in between the oval window and the lateral semicircular canal

29. Anterior Wall Separates the tympanic cavity from the carotid artery
Entrance to the Eustachian tube
Internal carotid artery courses
Canal for the tensor tympani arises from this wall

30. Posterior Wall and Floor
Mastoid Antrum- sinus cavity that opens to the mastoid air cells
Prominence of the stapedial pyramid where the tendon of the stapedius arises before attaching to the neck of the stapes
Chorda Tympani and VII Facial nerve may be seen to continue to the medial wall
Beneath the floor of the middle ear cavity lies the jugular bulb and Mastoid air cells
Floor is thin bone that separates the tympanic cavity from the internal jugular vein- Glossopharyngeal nerve passes through the floor of the tympanic cavity

31. Eustachian Tube
Extends downward, forward and medially from the tympanic cavity to the nasopharynx
Lateral part is bony (osseous)
Medial part is cartilage and connective tissue
It is normally closed to protect the middle ear
It opens during yawning and swallowing
Equalizes pressure between the middle ear and external pressure
Drains the middle ear cavity

32. Eustachian Tube

33. Eustachian Tube

34. Eustachian Tube

35. INNER EAR Houses the vestibular system – needed for balance
Houses the cochlea- needed for hearing
Osseous-Bony Labyrinth
Outer system
Membranous Labyrinth
Internal system

36. Osseous “Bony” Labyrinth
A series of ducts and cavities
Lie within the petrous portion of the Temporal bone
Vestibule
Semicircular Canals
Coiled Cochlea

37. Osseous Vestibule
Oval window is within the lateral wall of the vestibule
Vestibular Aqueduct is in the medial wall
Vestibule is the space between the entrance to the cochlea and the semicircular canals
It houses 3 prominent recesses
Spherical- vestibular nerve passes through
Cochlear- communicates between the vestibule and the basal end of the cochlear duct
Elliptical-communicates between the utricle and the ampullae

38. Vestibule

39. Osseous Semicircular Canals
House the sense organs for the movement of the body in space
Near the opening to the vestibule in each canal is an enlargement that houses the ampulla
A series of three rings attached to a ball ( the vestibule)
Anterior (anterior, vertical, superior)
Posterior (posterior vertical)
Horizontal (lateral)

40. Semicircular Canals

41. SEMICIRCULAR CANALS Anterior Vertical Canal Posterior Vertical Canal
Senses movement of your head as it moves toward your shoulder
Posterior Vertical Canal
Sense movement if you move your head to nod “yes”
Lateral horizontal Canal
Helps your brain differentiate rotatory movement toward the left vs. right- shaking your head “no”

42. Inner Ear Utricle and Saccule
Mediating the sense of acceleration of your head in space, such as in sudden movement or falling

43. Utricle and Saccule

44. OSSEOUS COCHLEAR LABYRINTH
Looks like a coiled snail shell
Modiolus- core of the labyrinth which is a finely perforated bone
Fibers of the VIII vestibulocochlear nerve pass through these perforations

46. Cochlear Duct- Scala Media houses the sensory organ for hearing
Divided into two incomplete chambers by the Osseous spiral lamina which is an incomplete bony shelf protruding from the modiolus
Scala vestibuli
Scala Tympani

48. OSSEOUS COCHLEAR LABYRINTH
Osseous spiral lamina becomes progressively smaller approaching the apex
Space between it and the opposite wall of the labyrinth increases
The apex where the two chambers formed by the incomplete lamina become hooklike which forms the helicotrema which is the region where the scala tympani and scala vestibuli will communicate

49. Inner Ear
2 ¾ turns from the base to the apex around a central core of a bone called the modiolus
Small perforations in the modiolus and the spiral lamina shelf allow passage of the auditory nerve fibers

50. Round Window provides communication between the scala tympani and the middle ear space
Oval window permits communication between the scala vestibuli and the middle ear space
Perilymph fluid fills the scala vestibuli and the scala tympani

52. MEMBRANOUS LABYRINTH
A fluid-filled sac that rests within the cavity of the osseous labyrinth- filled with endolymph fluid
Vestibular system- Houses the vestibular organ
Membranous labyrinth is in each ampulla, saccule and utricle
Parallels the bony labyrinth

54. Membranous Vestibular System
Each ampulla houses a crista ampularis which is the sense organ for movement
Houses the vestibular organ
Ampulla- expanded region of the semicircular canals
Utricle and Saccule- houses the otolithic organs of the vestibular system
Communicate via the endolymphatic duct

56. Membranous Cochlear Duct
Cochlear duct forms a small portion of the membranous labyrinth
Fluid in cochlear duct is endolymph
Cochlear Duct- membranous labyrinth within the Cochlea
Called the Scala Media-Resides between the scala vestibuli and scala tympani
Houses the sensory apparatus for hearing

57. Membranes of the Organ of Corti
Reissner’s Membrane
Divides the Scala vestibuli from the Scala Media
Ceiling of the Organ of Corti
Basilar Membrane
Divides the Scala Media from the Scala tmpani
Organ of Corti sits on it
Floor of the Organ of Corti
Tectorial Membrane
Semitransparent and gelatinous-like
Overlays hair cells- outer hair cells are embedded

59. MEMBRANOUS LABYRINTH Cochlear Duct
Organ of Corti has four rows of hair cells resting on a bed of Deiters’ cells for support
Tunnel of Corti- separates 3 rows of outer hair cells from the single row of inner hair cells

60. Hair Cells Outer Hair Cells Inner Hair Cells
Three rows- approximately 12,000
Broadens to four rows at the apical end
At the surface of each hair cell, forms a “W” or “V” pattern
Shaped like a test tube
Inner Hair Cells
Modiolar side of the tunnel of Corti
3500 Hair cells
Form a single row stretching from base to apex
Upper surface of each hair cell forms a slight “U” pattern
Shaped like a test tube or gourd

61. Hair Cell Innervation
Each inner hair cell is connected to as many as 10 VIII vestibulocochlear nerve fibers referred to as “many-to-one” innervation
Each outer hair cell shares its innervation with 10 other outer hair cells, all being innervated by the same VIII nerve fiber (one to many

62. Cochlea

63. Cochlea