1. Anatomy of the ear
Dr. Mohammed Abuelnor

2. Objectives
At the end of the lecture, the students should be able to:
List the parts of the ear: External, Middle (tympanic cavity) and Internal (labyrinth).
Describe the parts of the external ear: the auricle and the external auditory meatus.
Identify the walls of the middle ear : roof, floor and four walls (anterior, posterior, medial and lateral).
Define the contents of the tympanic cavity:
Ear ossicles,: (malleus, incus and stapes)
Muscles, (tensor tympani and stapedius).
Nerves (branches of facial and glossopharyngeal).
List the parts of the inner ear, bony part filled with perilymph (Cochlea, vestibule and semicircular canals), in which is suspended the membranous part that filled with endolymph).
List the organs of hearing and equilibrium

3. The ear is the organ of hearing and balance. It has three parts :
Regions of the Ear
The ear is the organ of hearing and balance. It has three parts :
the external ear consisting of the part attached to the lateral aspect of the head. 3

4. Regions of the Ear
the middle ear-a cavity in the petrous part of the temporal bone bounded laterally to the external ear. 4

5. Regions of the Ear
the internal ear consisting of cavities within the temporal bone between the middle ear laterally and the internal acoustic meatus medially. 5

6. External Ear 1. Auricle
Formed of elastic cartilage , Gives attached to the extrinsic muscles of the auricle, the anterior, superior, and posterior auricular muscles.,
Auricle

7. External Ear 2. External acoustic meatus
The lateral one-third is formed from cartilaginous and the medial two-thirds is a bony tunnel in the temporal bone.
• Its outer 1/3 is lined by skin with hair, sebacous and wax secreting glands.
• Its internal 2/3 are lined with sensitive hairless skin.
External acoustic meatus

8. External Ear External acoustic meatus
passes upward in an anterior direction, then turns posteriorly still passing upward, and finally, turns again in an anterior direction with a slight descent.
For examination purposes, observation of the external acoustic meatus and tympanic membrane can be improved by pulling the ear superiorly, posteriorly, and slightly laterally.
External acoustic meatus

9. Sensory innervation of the auricle

10. THE MIDDLE EAR Tympanic membrane (Eardrum)-
is a cone-shaped piece of skin about 10mm wide.
it is very sensitive
even the slightest pressure variation will cause it to vibrate.
separates the outer ear from the middle ear

11. Tympanic membrane sensory innervation
The skin on the outer surface of the tympanic membrane is supply by the auriculotemporal nerve, with additional branches of vagus, facial & glossopharyngeal.
Sensory innervation of the mucous membrane on the inner surface of the tympanic membrane is carried entirely by the glossopharyngeal [IX] n.
Tympanic membrane. A. Diagram. B. Otoscopic view.
Otitis Media 11

12. Middle ear
The middle ear is, mucous membrane-lined space in the temporal bone.
It is consisting of two parts:
the tympanic cavity
the epitympanic recess superiorly.
The middle ear communicates with the mastoid area posteriorly .
the nasopharynx (via the pharyngotympanic tube) anteriorly.
Parts of the middle ear

13. Boundaries of the middle ear
Roof = tegman tympani
separates it from the middle cranial fossa
Floor = Jugular wall
separates it from the internal jugular vein.
Lateral = Membranous wall
Medial = Labyrinthine:
promontory
oval window
round window
prominence of facial canal
prominence of lateral
semicircular canal.
Boundaries of the middle ear

14. Boundaries of the middle ear
Posterior = Mastoid wall
aditus to the mastoid antrum
the pyramidal eminence
(for tendon of the stapedius).
opening for chorda tympani n.
Anterior = Carotid wall
separates it from the internal carotid artery.
Boundaries of the middle ear

15. Pharyngotympanic tube
It connects the middle ear with the nasopharynx .
It equalizes pressure on both sides of the tympanic membrane.
It consists of:
- a bony part (the one-third nearest the middle ear);
-a cartilaginous part (the remaining two-thirds).
Pharyngotympanic tube

16. Auditory ossicles Auditory ossicles. A. Malleus. B. Incus. C. Stapes.16

17. Muscles associated with the auditory Ossicles

18. Muscles associated with the auditory ossicles

19. Innervation of the middle ear
The tympanic plexus innervates the mucous membrane lining the walls and contents of the middle ear.
It is formed by the tympanic nerve, a branch of the glossopharyngeal nerve [IX], and from branches of the internal carotid plexus.

20. Internal ear
The internal ear consists of a series of bony cavities (the bony labyrinth) and
membranous ducts and sacs (the membranous labyrinth) within these cavities.
The bony labyrinth consists of the vestibule, three semicircular canals, and the cochlea.
Membranous labyrinth, consists of the semicircular ducts, the cochlear duct, and two sacs (the utricle and the saccule). the cochlear duct is the organ of hearing; the semicircular ducts, utricle, and saccule are the organs of balance.
Location of the internal ear in temporal bone
Internal ear

21. Bony Labyrinth The vestibule:
which contains the oval window in its lateral wall, is the central part of the bony Labyrinth.
Semicircular canals:
anterior, posterior, and lateral semicircular canals.

22. Cochlea
is a bony structure that twists on itself two and one-half times around the modiolus.
The cochlear duct, which is a component of the membranous labyrinth is encircling around the modiolus.
The cochlear duct creates two canals:
the scala vestibuli and the scala tympani, which extend throughout the cochlea and are continuous with each other at the apex through a narrow slit (the helicotrema).
Cochlea

23. Membranous labyrinth Consisting of two sacs (the utricle and the saccule) and four ducts (the three semicircular ducts and the cochlear duct). The membranous labyrinth has unique functions related to balance and hearing: * The utricle, saccule, and three semicircular ducts are part of the vestibular apparatus (i.e., organs of balance) * The cochlear duct is the organ of hearing.
Membranous labyrinth

24. Sensory receptors in the organs of balance
Detection of Rotational Movement
The sense organ is the macula of utricle, the macula of saccule, and in the ampulla of each of the three semicircular ducts it is the crista.
The utricle responds to centrifugal and vertical acceleration,
The saccule responds to linear acceleration.
The three semicircular ducts respond to movement in any direction.
When head moves, the attached semicircular ducts and hair cells move with it.
Nerve signals to the brain are generated indicating which direction the head has been rotated.

25. Stapes pushes on fluid of scala vestibuli at oval window.
Transmission of sound
Stapes pushes on fluid of scala vestibuli at oval window.
At helicotrema, vibration moves into scala tympani.
Fluid vibration dissipated at round window which bulges.
The central structure is vibrated (cochlear duct).

26. Two parts of the Vestibulocochlear nerve:
7/16/2019
Two parts of the Vestibulocochlear nerve:
Vestibular nerve has receptors in:
semicircular ducts (ampulla), utricle & saccule.
Cochlear nerve has receptors in:
spiral organ (organ of Corti).
Cochlear branch has spiral ganglion in bony modiolus.
Deafness
Nerve deafness
Damage to hair cells from antibiotics, high pitched sounds, anticancer drugs.
Conduction deafness
Perforated eardrum & Otosclerosis 26 26

27. References: Gray's Anatomy for Students- Second edition
Netter’s Clinical Anatomy, Second edition