Ear Anatomy

Functions of Ear The ear is the organ of hearing. plays an important role in maintaining the balance (equilibrium) of the body

Subdivisions 3 parts:- 1. External ear. 2. Middle ear. 3. Internal ear

The external ear 1- Auricle or pinna. 2- External auditory meatus. 3- Tympanic membrane (ear drum).

Middle Ear (Tympanic Cavity) Small air-filled space within the petrous part of the temporal bone. It contains the auditory ossicles. It communicates with the nasopharynx through auditory tube & mastoid process by aditus to mastoid. By its medial wall; it communicates with the internal ear (via oval or round windows).

The internal (Labyrinth)ear It consists of:- 1- bony labyrinth:- a complicated space in the petrous part of the temporal bone. 2- fluid-filled membranous labyrinth. The membranous labyrinth contains sensory receptors for hearing and balancing.

EXTERNAL EAR The external ear consists of:- (a) pinna or auricle. (b) external auditory meatus. It is concerned with collection and transmission of sound waves to the tympanic membrane.

AURICLE/PINNA Overview The auricle is undulating projection on the side of the head The entire pinna except its lobule is made up of a single piece of yellow elastic cartilage The lobule of pinna is made of fibro-fatty tissue covered with skin

The External Auditory canal It is a curved tube (S-shape) that leads from the auricle to the tympanic membrane. It has two components:- 1- Outer 1/3 is 1- cartilaginous 2- is provided with hairs and sebaceous and ceruminous glands (wax-producing glands).

The External Auditory canal 2- Inner 2/3 is :- 1- bony 2- contains no appendages or hair The sensory nerve supply of the lining skin is derived from 1- the auriculotemporal nerve (roof & ant.wall) 2- the auricular branch of vagus n.(floor & post.wall) The lymph drainage:- 1- Superficial parotid 2- Mastoid and 3- Superficial cervical lymph nodes.

Middle Ear (Tympanic Cavity) It is an air-containing cavity in the petrous part of temporal bone It is lined with mucous membrane. It contains the auditory ossicles & muscles. It communicates in front through the auditory tube with the nasopharynx and behind with the mastoid antrum. .

The tympanic membrane It is a thin fibrous structure covered 1-Externally with a thin layer of stratified squamous epith. 2- and internally lined with low columnar epith. 3- The framework consists of collagen fibres.

Tympanic membrane

General features of TM It is circular, 1 cm in diameter. It lies obliquely at 55 ْwith external auditory meatus. It is concave towards the meatus. At the depth of the concavity is a small depression, the umbo The handle of the malleus is firmly attached to the inner surface of the membrane.

Tympanic membrane From the lateral process of the malleus two thickened fibrous folds (mallear folds) diverge up to the margins of the tympanic bone; Between them the small upper segment of the membrane is lax (pars flaccida). The rest of TM is pars tensa

Tympanic membrane Nerve supply:- 1- Auriculotemporal nerve. 2- Vagus nerve. Both lateral surface; while glossopharyngeal nerve (medial surface)

Walls of Middle Ear 6 walls;- 1- lateral wall (tympanic):- tympanic membrane 2- medial wall (Labyrinthine):- lat. wall of inner ear 3- Anterior wall (carotid);- two openings:- a- canal for tensor tympani b- Eustachian tube 4- Posterior wall (mastoid). 5- Superior wall (roof) Tegmen tympani 6- floor (inferior wall) jugular

Compartments of ME 1- Epitympanum:- the part above the TM containing the head of malleus; body & short process of incus. 2- mesotympanum:- the part opposite the TM containing handle of malleus, long process of incus & stapes. 3- hypotympanum:- the part below the tympanic membrane

Auditory Ossicles 1- The malleus:- is the largest ossicle and possesses a head, a neck, a long process or handle, an anterior process, and a lateral process. 2- Incus:- it has a large body and two processes 3- The stapes:- smallest bone that has head, neck & two limbs

Auditory ossicles 3 ossicles

Auditory Ossicles

Auditory muscles Two muscles 1- Tensor tympani muscle. 2- Stapedius muscle. T T= tensor tympani ET= eustachian tube Nerve supply Action insertion Origin Muscle Mandibular n. Slow down vibration of TM (dampening effect) Neck of malleus Wall of 1- canal for T T. 2- wall for ET Tensor tympani Facial nerve Neck of stapes Pyramid Stapedius

Tympanic cavity Tympanic cavity

Inner Ear (Labyrinth) The labyrinth is situated in the petrous part of the temporal bone, medial to the middle ear It consists of The bony labyrinth, comprising a series of cavities within the bone. The membranous labyrinth, comprising a series of membranous sacs and ducts contained within the bony labyrinth.

Bony labyrinth It consists of three parts:- 1- Cochlea:- anteriorly; it resembles snail shell 2- Vestibule:- central part 3- Semicircular canals:- posteriorly They are lined by endosteum and contain a clear fluid, the perilymph, in which is suspended the membranous labyrinth.

Membranous labyrinth

Membranous Labyrinth It is lodged within the bony labyrinth. It is filled with endolymph and surrounded by perilymph. It consists of the utricle and saccule, which are lodged in the bony vestibule; the three semicircular ducts, which lie within the bony semicircular canals; And the duct of the cochlea, which lies within the bony cochlea.

The scala media ( Cochlear duct) It is a blind tube that divides the bony cochlear canal into two passages The upper chamber called scala vestibuli The lower passage known as scala tympani. The two passages communicate with each other at a narrow opening called the helicotrema.

Scala media It is triangular in cross section. It is stretched between the Reissner’s membrane & basilar membrane. It contains the sensory organ of hearing (i.e. organ of corti) which contains the hair cells as the receptors of hearing; These cells are embedded in the thick gelatinous tectorial membrane.

Organ of Corti Scala media is located between Reissner’s membrane & basilar membrane. Organ of corti is the sense organ of hearing and lies on the basilar membrane It is overlaid by the gelatinous tectorial membrane.

Organ of Corti