The document summarizes the anatomy and embryology of the ear and related structures. It is divided into four main parts: outer, middle and inner ear, as well as pharynx. The outer ear collects and directs sound waves. The middle ear contains ossicles that amplify vibrations through the tympanic membrane. The inner ear converts these vibrations into neural signals via hair cells in the cochlea. The pharynx is divided into naso, oro, and hypopharynx and contains structures like the tonsils, epiglottis and vocal cords. Embryologically, the structures develop from pharyngeal arches which contribute muscles, nerves and skeletal components to the head

1. Main Components of the Hearing
Mechanism:
Divided into 4 parts (by function):
• Outer Ear
• Middle Ear
• Inner Ear
• Central Auditory Nervous System

2. Major Divisions of the Ear
Peripheral Mechanism Central Mechanism
Outer
Ear
Middle
Ear
Inner
Ear
VIII
Cranial
Nerve
Brain

3. Embryology.
• The most typical feature in development of
the head and neck is formed by the
pharyngeal or branchial arches.
• These arches appear in the fourth and fifth
weeks of development and contribute to the
characteristic external appearance of the
embryo

4. Embryology of the pharyngeal arches
- From the arches are derived muscle and
nerves of the head and neck which are
involved in speech.
• The first 8 weeks constitutes the period of
greatest embryonic development of the head
and neck. There are 5 arches named
pharyngeal or branchial arches.

5. • Between these arches are the grooves or
clefts externally and the pouches internally.
• The derivatives of arches are usually of
mesoderm origin. The original mesoderm of
the arches gives rise to the musculature of the
face and neck.
• The groove is lined by outside surface
ectoderm while the pouch is lined by inside
endoderm.

7. • Each arch has an artery, nerve, and cartilage bar.
• The core of each arch receives substantial
numbers of neural crest cells, which migrate into
the arches to contribute to skeletal components
of the face.
• The muscular components of each arch have
their own cranial nerve, and wherever the
muscle cells migrate, they carry their nerve
component with them

9. C L I N I C A L C O R R E L A T E S
Deafness and External Ear Abnormalities
 Congenital deafness, may be caused by abnormal development of the
membranous and bony labyrinths or by malformations of the auditory
ossicles and eardrum. In the most extreme cases the tympanic cavity and
external meatus are absent.
 Most forms of congenital deafness are caused by genetic factors, but
environmental Factors may also interfere with normal development of the
internal and middle ear. Rubella virus, affecting the embryo in the seventh
or 8th wk, may cause severe damage to the organ of Corti. It has also been
suggested that poliomyelitis, diabetes, hypothyroidism, and toxoplasmosis
can cause congenital deafness.

10. • External ear defects are common; they
include minor and severe abnormalities often
associated with other malformations.
• Congenital microtia occurs about 1:20.000
births.

11. • The auricle is formed early. Therefore,
malformation of the auricle implies
malformation of the middle ear, On the other
hand, a normal auricle with canal atresia
indicates development in the 28th week, by
which time ossicles and middle ear are
already formed.
• Improper fusion of the first and second
branchial arches results in a preauricular.

12. Malformation of first branchial arch and
groove results in:
a. Auricle abnormality (first and second arches)
b. Bony meatus atresia (first groove)
c. Abnormal incus and malleus (first and second
arches)
Anotia and microtia often combined with EAC
stenosis.
Rubella embrypopathy- middle ear dysplasia.

13. Outer Ear
Pinna
External
Auditory
Meatus
Pinna/lobe
Preauricular Tags
Preauricular Pits
EAM
Cerumen
Q-tips/ ear
buds
Microtia
Anotia
Atresia
Function
EAM resonance

14. Structures of the Outer Ear
1. Auricle (Pinna)
Functions
- Collects sound
- Helps in sound
localization
-Directing sounds to
the
eardrum.
- Cosmesis

15. 2. External Auditory Canal
• Approx. 26 millimeters (mm) in length and 7
mm in diameter in adult ear. “S” shaped
• Size and shape vary among individuals.
• Outer 1/3 - cartilage; inner 2/3 - mastoid
bone
• Cerumenous glands moisten/soften skin
• Presence of some cerumen is normal

16. Functions
• Warms air before it reaches the TM.
• Protects TM from physical damage.
• Resonator so as to amplify sound.

17. Cerumen
• The purpose of wax:
– Repel water
– Trap dust, sand particles, micro-organisms, and
other debris
– Moisturize epithelium in ear canal
– Odor discourages insects
– Antibiotic, antibacterial, antifungal properties
– Cleanse ear canal

18. Outer Ear Hearing Disorders
Outer ear
CHARGE syndrome
Down Syndrome
◦ Ears small and low set
Fetal Alcohol
Syndrome
◦ Deformed ears
DiGeorge syndrome
◦ Low set ears

19. Middle Ear
Tympanic Cavity
Tympanic Mastoid
Eustachian Tube
Function Membrane
Ossicles
Middle Ear Muscles
Eustachian Tube
Mastoid
Middle Ear Cavity
Ossicles
Middle Ear Muscles
Amplifier
Temporal bone fractures
Otitis Media
vent tubes

20. Ossicles
• Malleus
(hammer)
• Incus (anvil)
• Stapes
(stirrup)
smallest
bone of the
body

21. Function of Middle Ear
 Conduction
◦ Conduct sound from the outer ear to the inner ear
 Protection
◦ Creates a barrier that protects the middle and inner
areas from foreign objects
◦ Middle ear muscles may provide protection from
loud sounds
 Transducer
◦ Converts acoustic energy to mechanical energy
◦ Converts mechanical energy to hydraulic energy
 Amplifier
◦ Transformer action of the middle ear

22. Tympanic Membrane
• The eardrum separates the outer ear from the
middle ear
• Creates a barrier that protects the middle and
inner areas from foreign objects
• Cone-shaped in appearance
– about 17.5 mm in diameter
• The eardrum vibrates in response to sound
pressure waves.
• The membrane movement is incredibly small
– as little as one-billionth of a centimeter

23. TM

24. Eustachian Tube
The eustachian tube connects the front wall of
the middle ear with the nasopharynx .
The eustachian tube also operates like a valve,
which opens during swallowing and yawning
◦ This equalizes the pressure on either side of the
eardrum, which is necessary for optimal hearing.
◦ Without this function, a difference between the
static pressure in the middle ear and the outside
pressure may develop, causing the eardrum to
displace inward or outward
 This reduces the efficiency of the middle ear and less acoustic energy
will be transmitted to the inner ear.

25. Mastoid Process of Temporal Bone
Bony ridge behind the auricle
Hardest bone in body, protects cochlea and
vestibular system
Provides support to the external ear and
posterior wall of the middle ear cavity
Contains air cavities which can be reservoir for
infection

26. Middle Ear Disorders
• Middle Ear disorders
– Acute otitis media
– Disarticulation
– Mastoiditis
– Tympanosclerosis
– OME
– TM Perforation
• Down’s Syndrome

27. Inner Ear
Auditory
Vestibular
Vestibule
- semicircular
canals
- utricle and
saccule
Cochlea

28. Vestibule and cochlear.

29. Function of Inner Ear
• Convert mechanical
sound waves to neural
impulses that can be
recognized by the brain
for Hearing
• Balance
– Linear motion (vestibule)
– Rotary motion (canals)

30. Cochlea
The cochlea
resembles a snail shell
and spirals for about 2
3/4 turns around a
bony column

31. • 8th Cranial Nerve or “Auditory Nerve” carries
signals from cochlea to brain
• Fibers of the auditory nerve are present in the
hair cells of the inner ear
• Auditory Cortex: Temporal lobe of the brain
where sound is perceived and analyzed.

32. Inner Ear Etiologies
• Genetic
– Connexin 26
• Excessive Noise
• Head Trauma
• Metabolic
– Diabetes, thyroid dysfunction
• Ototoxic
– Gentamycin, neomycin, cisplatin, quinine, Aspirin,
streptomycin, nitrofurantoin etc.
• Disease ( DM

33. Nonorganic Hearing Loss
• Sometimes referred to as functional, feigning,
etc.
• No physical evidence of hearing loss
• Conscious and unconscious
• Adults: medical/legal reasons
• Children: attention, psychological, reward,
etc.

34. Summary of hearing physiology.
Acoustic energy, in the form of sound waves, is
channeled into the ear canal by the pinna. Sound waves
hit the tympanic membrane and cause it to vibrate, like
a drum, changing it into mechanical energy. The
malleus, which is attached to the tympanic membrane,
starts the ossicles into motion. The stapes moves in and
out of the oval window of the cochlea creating a fluid
motion, or hydraulic energy. The fluid movement
causes membranes in the Organ of Corti to shear
against the hair cells. This creates an electrical signal
which is sent up the Auditory Nerve to the brain. The
brain interprets it as sound!

35. QUESTIONS?

36. Clinically.
 History
◦ Otalgia (Otitis externa- swimmers ear, trauma O.media with
effusion, refered, shingles)
◦ Otorrhoea ( O.E, O.M - acute with perforation, chronic,
blood)
◦ Hearing loss
◦ Tinnitus( HTN, inner ear- age, drugs)
◦ Trauma( noise, FB- children, ear buds)
◦ FHx( cong . H.Loss)
◦ Vertigo ( spinning differs from dizziness)
◦ Aural fullness

37. Associated complaints
• Throat pain.
• Tooth ache.
• Nasal blockage
• Sinus disease
• Upper respiratory infection.
• Allergies ( skin, nasal)
• fever

38. Otoscopy.
• Inspection ( site/ position, red, swollen,
abnormalities- pits/sinuses, tags,)
• Palpation (tender, flactuant)
• Ear speculum- otoscope
• Tuning fork, audiogram- hearing tests.

39. Common problems.
• Wax impaction- soften then syringe 3-5 days.
• O. externa- topical antibiotic, antifungal,
steriod.
• O. Media- Rx URTI
• O. M with perforation, chronic- topical
opthalmic topical antibiotics.
For all water precaution.

40. Requires referal
• >7-10days.
• Persistence of symptoms/signs or progressing
• TM perforation.
• Mastoiditis
• Unilateral H.Loss, tinnitus

41. Nose
• Divided into external nose and nasal cavity
• External nose
– made up of bone above
– nasal bones, frontal processes of maxilla, and
nasal process of frontal bone
– cartilage below
– upper and lower lateral cartilages, septal cartilage

43. Nasal cavity
• Extends from nares anteriorly (singular: naris) to
choanae posteriorly
• Medial wall - nasal septum (cartilage, perpendicular
plate ethmoid, vomer)
• Lateral wall - three turbinates (superior, middle,
inferior)
• Roof - cribriform plate - leads to anterior cranial fossa
• Floor - hard palate

45. Lateral wall nose
• Middle meatus lies under middle turbinate -
opening called hiatus semilunaris into which
the maxillary, frontal, and ethmoid sinuses
drain
• Inferior meatus lies under inferior turbinate -
receives the opening of the nasolacrimal duct

47. Roof nose
• The mucosa in the superior part of the nose
contains nerve endings from the olfactory
nerve which come through the cribriform
plate (called olfactory mucosa)
• Function of the nose:
– warm, humidify air
– filter out particulate matter from air
– mucociliary blanket

49. Sinuses
• Maxillary
• Ethmoid
• Frontal
• Sphenoid

50. Maxillary sinuses
• Located in body of maxilla
• Roof is floor of orbit, medial wall is lateral wall
of nose, floor is hard palate (teeth can erupt
into sinus)
• Opens into middle meatus through hiatus
semilunaris

52. Frontal sinus
• Contained in frontal bone, anterior to anterior
cranial foss (infections can thus spread into
brain and cause meningitis or abscess)
• Bony septum divides two sides
• Opens into middle meatus via frontonasal
duct

54. Sphenoid sinus
• Lies within body of sphenoid bone
• Opens into sphenoethmoidal recess above
superior turbinate
• Septum separates into two sides
• Lateral wall contains cavernous sinus with
internal carotid artery and nerves
• Optic nerve runs along lateral roof

56. Ethmoid sinuses
• Contained within ethmoid bone, between
nose and orbit
• Separated from orbit by thin layer of bone
(lamina papyracea, allows spread of sinus
infection into orbit)
• Drain mostly into middle meatus
• A series of small cells

59. Pharynx
• Divided into nasopharynx, oropharynx, and
hypopharynx
• Nasopharynx -
– behind nose
– Eustachian tube orifices
– adenoids

61. Pharynx
• Oropharynx
– soft palate to upper border epiglottis
– base of tongue (with lingual tonsils)
– palatine tonsils
– median/lateral glossoepiglottic folds
– vallecula is area just lateral to median GEF
– two folds of mucus membrane near tonsil (anterior and
posterior tonsillar pillar aka palatoglossal and
palatopharyngeal arch)

63. Hypopharynx
• Behind and lateral to larynx
• lower border is cricoid cartilage (opening into
esophagus)
• Epiglottis is anterior fold of mucosa and
cartilage, flops down over larynx to prevent
aspiration during swallowing
• Aryepiglottic folds, pharygoepiglottic folds
• Piriform sinuses are lateral to larynx

65. Vocal cords
• True vocal cords - nonkeratinizing squamous
epithelium, over muscles that can move and
tense cord
• False vocal cords - aka vestibular folds - above
true vocal cords
• Ventricle is between the two
• Vocal cords attached to thyroid cartilage
anterior, arytenoid cartilage posterior