SURG3LEC ME: L4.1 - Ear Anatomy

Otitis externa

inflammation of the vertical or horizontal ear canal or both.  

Otitis media

 inflammation of the tympanic cavity and membrane

Otitis interna

 inflammation of the inner ear that causes vestibular disease in dogs

Presbycuses

term used to describe age-related hearing loss

1. inner ear

2. middle ear 

3. external ear 

The ear is composed of three parts

inner ear

• consists of a membranous and bony labyrinth 

• functions for hearing and balance.

middle ear 

• which is formed by the tympanic cavity and 

• connects to the pharynx via the auditory tube (eustachian tube).

external ear

which is formed by the auditory meatus and a short canal.

osseous labyrinth

The inner ear is located within the __ __ of the petrous part of the temporal bone

tympanic membrane

The middle and external ears are separated by the __ __

external acoustic meatus

the opening of the horizontal canal into the middle ear is known as the __ __ __

tympanic cavity

The __ __ is air-filled and in dogs is composed of 

1. a small dorsal epitympanic recess and 

2. a large ventral tympanic bulla.

15

In medium-sized dogs, the long axis of the tympanic cavity is about __ mm.

bony septum

The feline tympanic cavity is divided into two compartments by a thin, __ __ that arises along the cranial aspect of the bulla and curves to attach to the midpoint of the lateral wall.

tympanic bulla

The larger ventromedial compartment is an air-filled __ __. For complete drainage of the middle ear of cats, this bony septum often needs to be perforated.

fissure

Most of the lateral wall of the smaller craniolateral compartment is formed by the tympanic membrane. These compartments communicate through a narrow __ located dorsally near the cochlear window.

promontory

Near this fissure, the postganglionic sympathetic nerves form a plexus on a structure known as the __.

Horner’s syndrome

Because of their vulnerable location, these nerves are often traumatized during surgical curettage of the feline middle ear, causing __ __.

tympanic membrane

normally is thin and semitransparent but may thicken or rupture when diseased.

facial nerve

The __ __ exits the stylomastoid foramen caudal to the ear and courses ventral to the horizontal canal close to the middle ear.

auditory ossicles

The __ __ are found in the middle portion of the tympanic cavity. 

stapes, malleus, and incus

3 auditory ossicles

Vibrations

__ of the tympanic membrane are transmitted through the chain of these auditory ossicles to perilymph fluid within the vestibule.  

auditory tube

The middle ear also connects to the nasopharynx via the __ __

eustachian tube

auditory tube aka

Nasopharyngeal polyps

may extend from the nasopharynx into the tympanic cavity and can extrude into the external ear canal.

external ear

The __ __ varies in size and shape among dog breeds.  

auricular cartilage

The __ __ determines the appearance of the canine pinna.

1. Tragus  

2. Lateral crus of the helix  

3. Pretragic incisure  

4. Intertragic incisure 

The base of the ear is composed of several ridges that are important landmarks for ear surgery.  Includes these 4:  

external auditory meatus

The external opening of the vertical canal is known as the __ __ __. Numerous muscles attach to the cartilage of the ear, allowing it to move to localize sound.  

1. vertical

2. horizontal

The external ear canal consists of 

1. an initial __ part and 

2. a shorter __ canal that runs medially.

cartilaginous

The vertical part and most of the horizontal part of the canal are ___

osseous

the deepest part (near the tympanic membrane) is __.

parotid salivary gland

The __ __ __ overlies the auricular cartilage, forming the vertical canal.