GROSS ANATOMY OF THE ‘EAR’

EAR

Parts:• It has 3 parts; 1st part ……………external ear 2nd part….................middle ear 3rd part……………..inner ear • The external and middle ear are mainly concerned with the

transference of sound to the internal ear• internal ear is for hearing and balancing (equilibrum)

External ear• has 2 parts; The Auricle (pinna) which projects from the lateral side of the head the External acoustic meatus (ear canal) which is a canal leading

inwards

AURICLE

Auricle (pinna)• is on the side of the head and assists in capturing sound• It consists of cartilage covered with skin and arranged in a pattern of

various elevations and depressions • The large outside rim of the auricle is the helix• It ends inferiorly at the fleshy lobule (ear lobe)• The lobule is the only part of the auricle not supported by cartilage• It is consists of fibrous tissue, fat, and blood vessels• It is easily pierced for taking small blood samples and inserting

earrings• The hollow center of the auricle is the concha of auricle• at the depth of the concha is the opening of the external acoustic

meatus• Just anterior to the opening of the external acoustic meatus, in front

of the concha, is an elevation called the tragus

• Opposite the tragus, and above the fleshy lobule, is another elevation (the antitragus)

• A smaller curved rim, parallel and anterior to the helix is the antihelix

• The antihelix divides above into 2 legs or crura• In between these crura is a depression called the triangular fossa• A curved depression lies between the helix and antihelix and it is

called the scapha/scaphoid fossa

Muscles

Include; Intrinsic muscles Extrinsic muscle

intrinsic muscles• pass between the cartilaginous parts of the auricle and may change

the shape of the auricle

They include:• Helicis major• Helicis minor• Tragicus• Antitragicus• Transverse muscle• Oblique muscle

extrinsic muscles• pass from the scalp or skull to the auricle and may also play a role in positioning

of the auricle• anterior auricular muscle • Superior auricular muscle • posterior auricular muscle

Both groups of muscles are innervated by the facial nerve [VII]

Arterial supply • posterior auricular artery • superficial temporal artery

Venous drainage • through vessels following the arteries

Innervation

superficial surfaces supplied by;• great auricular nerve

• auriculotemporal branch of the mandibular nerve [V3] (anterior superior portion)

• lesser occipital nerve (posterior superior portion)

deeper parts are supplied by;• facial nerve [VII]• vagus nerve [X] (the auricular branch)

Lymphatic drainage : drain• anteriorly into parotid nodes • posteriorly into mastoid nodes• possibly into the upper deep cervical nodes

External acoustic meatus• extends from the deepest part of the concha to the tympanic

membrane (eardrum)• a distance of approximately 1 inch (2.5 cm)• Its walls consist of cartilage and bone• The lateral 1/3 is formed from cartilaginous extensions from some

of the auricular cartilages • the medial 2/3 is a bony tunnel in the temporal bone• Throughout its length the external acoustic meatus is covered with

skin• some of this skin contains hairs and modified sweat glands

producing cerumen (earwax)• cerumen protects the skin of the ear canal, assists in cleaning and

lubrication, and also provides some protection from bacteria, fungi, insects and water

Clinical anatomy• Excess production of cerumen can press against the eardrum and/or

occlude (block) the external auditory canal or hearing aids, potentially hindering hearing

Tympanic membrane (ear drum)• is a membrane that separates the external acoustic meatus from the

middle ear • is a thin, oval semi-transparent membrane• approximately 1 cm in diameter• it is covered with thin skin externally and with mucous membrane of

the middle ear internally• When viewed through an otoscope, the tympanic membrane appears

concave toward the external acoustic meatus with a shallow, cone-like central depression

• the peak of this cone like depression is called the umbo of the tympanic membrane

• The lower end of the handle of malleus is attached to the umbo of tympanic membrane

• Superior to the handle of the malleus is a small elevation called the lateral process of the malleus

• the part of the tympanic membrane superior to the lateral process of the malleus is thin and is called the flaccid part /pars flaccida

• the remaining part of the membrane is thick and is called the tense part /pars tensa

• The pars flaccida lacks the radial and circular fibers present in the remaining part of the membrane

• in the anterior-inferior quadrant of the membrane is a bright triangular reflection of light called the cone of light

• This region is usually visible when examining the tympanic membrane with an otoscope

innervation• external surface of the tympanic membrane is supplied; the auriculotemporal nerve (a branch of CN V3 ) {main contribution}

a small auricular branch of the vagus (CN X)• The internal surface of the tympanic membrane is supplied by the

glossopharyngeal nerve (CN IX)

Clinical anatomy

External Ear Injury• Bleeding within the auricle resulting from trauma may produce an

auricular hematoma

Acute Otitis Externa• Otitis externa is an inflammation of the external acoustic meatus• The infection often develops in swimmers who do not dry their meatus

after swimming and/or use ear drops• it may also be the result of a bacterial infection of the skin lining the

meatus

Middle Ear• is the narrow air-filled chamber in the petrous part of the temporal

bone• It has a cavity called tympanic cavity

parts• The cavity has 2 parts: tympanic cavity proper epitympanic recess Tympanic cavity proper is the space directly internal to the tympanic

membrane while the space superior to the membrane is called the epitympanic

recess The middle ear communicates with the mastoid area/ mastoid antrum

posteriorly It communicates anteriorly with the nasopharynx via the

pharyngotympanic tube

contents of the middle ear: Auditory ossicles (malleus, incus, and stapes) Stapedius and tensor tympani muscles Chorda tympani nerve, a branch of CN VII Tympanic plexus of nerves

Walls of the Tympanic Cavity• The middle ear is shaped like a narrow box with concave sides• It has 6 walls, which include;

I. Tegmental wall (roof)

II. Jugular wall (floor)

III. membranous wall (lateral wall)

IV. labyrinthine wall (medial wall)

V. carotid wall (anterior wall)

VI. Mastoid wall (posterior wall)

Tegmental wall (roof):• is formed by a thin plate of bone called the tegmen tympani• This bone separates the tympanic cavity from the middle cranial fossa

jugular wall (floor)• is formed by a layer of bone that separates the tympanic cavity from

the internal jugular vein• Near the medial border of the floor is a small aperture, through which

the tympanic branch from the glossopharyngeal nerve [IX] enters the middle ear

Membranous wall (lateral wall) • is formed mostly by the tympanic membrane and superiorly by the

bony wall of the epitympanic recess

labyrinthine wall (medial wall)• separates the tympanic cavity from the internal ear• also the lateral wall of the internal ear

• features on this wall include; promontory of the labyrinthine wall: a round bulge produced by the

basal coil of the cochlea Oval window Round window

carotid wall (anterior wall):• separates the tympanic cavity from the carotid canal• superiorly, it has the opening of the ; pharyngotympanic tube canal for the tensor tympani

mastoid (posterior) wall •  has an opening called the aditus to the mastoid antrum• The aditus to the mastoid antrum connects the tympanic cavity

(epitympanic recess) to the mastoid air cells (sinus)

Note: The mastoid antrum is a cavity continuous with collections of air-filled spaces (the mastoid cells), throughout the mastoid part of the temporal bone

Other features on the mastoid wall are: the pyramidal eminence, a small elevation through which the

tendon of the stapedius muscle enters the middle ear the opening through which the chorda tympani nerve, a branch of

the facial nerve [VII], enters the middle ear

Clinical anatomy

Mastoiditis:

Infection within the mastoid antrum and mastoid cells