1. The Ear
Anatomy:
The ear is an organ responsible for hearing &balance sensation composed of 3 main parts :
1-The external ear: Consists of three parts:
A-The auricle
B-The external ear canal (external
meatus).
C-Tympanic membrane (ear drum).
2-The middle ear:It contains the auditory ossicles &it communicates with the Eustachian tube &the mastoid air cells.
3-The inner ear:Consists of 2 parts:
I-Bony labyrinth: Localized in the temporal bone &consists of the semicircular canal &the cochlea.
II-Membranous labyrinth: consists of sacs of endolymph & perilymph.

3. The External Ear
I-The auricle:
It is also called the pinna ,it is attached to the lateral surface of the head &consists of elastic cartilage covered by perichondrium &skin.
The lobular part of the auricle is free of cartilage&consists of skin &fibrous tissue.
II-The External auditory Canal (EAC):
It extends from the auricle laterally to the tympanic membrane medialy,its length is(24mm) it is not a straight tube &consists of 2 parts:
1-Cartilagenous part: It represents the outer 1\3 which is directed upward & backward covered by skin which contains hair & sebaceous wax secreting glands which is bacteriocidal &containing various amino acids ,lysosmes ,fatty acids & immunoglobulins
2-Bony part:It is located deep in petrous bone & represents the inner 2\3 which is directed downward & forward ,the skin here is thin ,loose & easily damaged there is no hair & no wax secreting glands.

4. The middle Ear (ME):
It is nearly box shaped cavity (biconcave medially & laterally )&also called the tympanic cavity or middle ear cleft which includes the mastoid air cells & Eustachian tube ,it is situated in the temporal bone between the EAC &the inner ear structures.
The middle ear cavity is larger than the tympanic membrane
It has superior, inferior, lateral, medial, anterior &posterior walls with the following dimensions:
Length (15mm), height (15mm) &width (3.5mm)
It divides into 3 parts:
1-Epitympanum:It lies above the tympanic membrane.
2-mesotympanum:It lies opposite to the tympanic membrane.
3-Hypotympanum:It lies below the tympanic membrane.

5. The contents of the middle ear cleft are:
1-Chorda tympani nerve: which is a branch of the facial n.that supplies special sensation to anterior 2\3 of the tongue.
2-Two small muscles:
A-Tensor tympani m.:Which is attached to the
neck of malleus.
B-Stapedius m. Which is attached to the neck
of stapes.
3-The auditory ossicles:which are three bones attached to each other:
a-Malleus:the handle is firmly attached to the middle layer of the tympanic membrane (the fibrous layer)&its head articulates with the body of incus
b-Incus:it has 2 processes:
1-Short process-attached to the tip of the aditus.
2-lomg process-attached to the head of stapes.
c-Stapes-resembles stirrup & its footplate occupies the oval window.

7. Walls of the middle ear
1- The lateral wall:It is formed by the tympanic membrane that separates the EAM from the middle ear.
2-The medial wall: It separates the middle ear from the inner ear &formed mainly by the bony cochlea & 2 openings, the oval & round windows, these windows are not opened but are covered by membrane and are important in conducting sound waves to the inner ear
The oval window is above the promontory (the bony cochlea) while the round window lies below the promontory, the facial n. run horizontally above the promontory &is covered by thin layer of bone.
3-The superior wall: Separates the middle ear from the middle cranial fossa.
4-The inferior wall:it separates the middle ear from the bulb of the internal jugular vein.

8. 5-The anterior wall: it separates the middle ear from the internal carotid artery ,in the lower part of the wall there is an opening for the Eustachian tube (which connects the middle ear to the nasopharynx ,tensor tympani m, enters this wall through a canal lies above the Eustachian tube opening.
6-The posterior wall:It has the opening into the aditus which connects the mastoid antrum to the middle ear.

10. The tympanic membrane
It separates the EAM from the ME, its oval in shape, semitransperant pearly gray in color like a finger nail; its longitudinal diameter is larger than the transverse diameter &concave laterally toward the EAM.
Structurally it is divided into 2 unequal parts the larger of which is the pars tensa which consists of 3 layers, single epithelial layer laterally, fibrous layer in the middle &mucous layer medially.
The other part is called pars flaccida which is smaller than the pars tensa & similar to it except that it lacks the fibrous layer in the middle.
The tympanic membrane also has a bright surface which reflects light located in the antero-inferior part of the tympanic membrane & ends up in a depression called umbo this surface is triangular in shape & called cone of light.

12. The Communications of the ME:
The ME communicates with nasopharynx through the Eustachian tube &with the mastoid antrum through the aditus .
Eustachian Tube:
It is a tube connecting the middle ear with the pharynx, it is (36mm) in length &directed downward medially &forward. In children the tube is shorter, wider & more horizontal than the adults.
It is composed of 2 parts: the bony part (lateral 1\3) & the cartilaginous part (medial 2\3)
The whole tube is lined by mucous membrane that contains goblet cells; physiologically the tube is closed at rest &opens during swallowing & yawing by the contraction of the tensor palati m. which is attached to its wall.

13. Mastoid Air Cells:
It's located in the mastoid process which appears as projection behind the auricle & gives origin to the sternomastoid m. & considered as a part of the temporal bone.
The mastoid air cells are communicating cells, their size & numbers are variable between different individuals ,sometimes they are absent & here they are called sclerotic type ,normally they are absent at birth & appears as a process at the age of 2 years.
The function of the air cells is as a reservoir of air in the normal atmospheric pressure, but during pressure changes & infections it may be filled by blood, fluid or pus.

14. The Inner Ear
It is called the labyrinth & it is an important part of the ear located in the petrous part of the temporal bone between the ME & internal acoustic meatus( IAM)
It measures 20 mm in length & consists of 2 parts:
1- The Bony Labyrinth: Consists of the bony cochlea, vestibule &the semicircular canals.
2-The Membranous Labyrinth: Consists of the cochlear duct, saccule, utricle & semicircular ducts.

16. The cochlea:
It is a snail like structure two & a half turn ,it contains the organ of Cotri which is responsible for hearing sensation by its neuroepithilium located on the basilar membrane loss of its function leads to deafness .
When sound waves reaches the external ear it moves the tympanic membrane causing vibration of the ossicles which transmits the vibration to the oval window then the fluid in the cochlea & movement of the tectorial membrane that stimulates the auditory cells (neuroepithelium) which converts the mechanical stimulation to electrical impulses conducted through the 8th cranial n. in to the auditory nucleus in the higher center in the brain.

18. The vestibule & the Semicircular canals:
They are responsible for balance & equilibrium & affected by movement & body posture &loss of this function leads to vertigo.
The vestibule contains the saccule & the utricle & the semicircular canals contain the semicircular ducts which are the anterior, posterior & the horizontal (lateral) ducts.
The stimulation of this system causes vibration of the fluid in the sacs & the ducts leading to the movement of the copula (gelatinous material) causing stimulation of the hair cells that converts the mechanical stimulation to a nerve impulses transmitted in the vestibular part of the 8th cranial n. to the brain.