External Ear

What are the Parts of Ear?

The ear consists of following three parts:

External ear

It consists of auricle (pinna) and external acoustic meatus(EAM). The auricle collects the sound waves and EAM conducts them to the tympanic membrane. External ear is separated from the middle ear by tympanic membrane.

Middle ear

It is an air-filled cavity which is separated from internal ear by a bony wall. It communicates anteriorly with the nasopharynx through the auditory tube (Eustachian tube).

Internal ear

Internal ear contains bony labyrinth (cochlea, vestibule and semicircular canals) within which lies membranous labyrinth containing receptors for sound and maintenance of equilibrium. Vetsibulocochlear nerve reaches internal ear through the internal acoustic meatus.

Parts of ear

Draw a Labelled Diagram to Show Gross Features of Auricle.

auricle - gross features

Cymba conchae of auricle corresponds to the suprameatal triangle. For aspiration of pus from mastoid antrum, the needle is inserted 2mm deep in infants and about 12 mm in adults (as the thickness of bony wall at suprameatal triangle increases by 1mm till 12 years of age).

Name the Sensory nerves Supplying Auricle.

Sensory innervation of auricle: The following nerves supply the skin of auricle:

Great auricular nerve (ventral rami of C2,C3): supplies lower 1/3 of the auricle/pinna on lateral and medial surfaces of auricle.
Auriculotemporal nerve (branch of posterior division of mandibular nerve): supplies upper 2/3^rd of the lateral surface of auricle.
Lesser occipital (ventral ramus of C2): supplies upper 2/3^rd of the medial/cranial surface of auricle.
Auricular branch of vagus: supplies the root of auricle (near external acoustic meatus).

sensory innervation of auricle

Few fibers of facial nerve accompany the auricular branch of vagus nerve. Therefore, vesicular eruption appear on auricule or external acoustic meatus in case of herpes zoster infection of geniculate ganglion of facial nerve.

What are the Parts of External Acoustic Meatus?

The external acoustic/auditory meatus (EAM):

Extends from concha to tympanic membrane.
It is approx. 24-25 mm long.
It has two parts-
- Outer cartilaginous part: it is 8 mm long. Its wall contains elastic cartilage.
- Inner bony part: it is 16 mm long. Tympanic plate of temporal bone forms its anterior, inferior and posterior walls. Posterosuperior wall is formed by squamous part of temporal bone.
At the medial end of the bony canal is tympanic membrane.
EAM has two constrictions:
- First is at the junction of cartilaginous and bony part.
- Second called isthmus is its narrowest part, which is located 6 mm lateral to tympanic membrane.
It is lined with skin and has numerous ceruminous gland which secret ear wax.

bony and cartilaginous parts of external auditory meatus

Shape and Direction: It is S-shaped and has two curves.

Outer part is directed upwards, forwards and medially.
Middle part is directed upwards, backwards and medially.
Inner part is directed downwards, forwards and medially

Name the Sensory Nerves That Supply External Acoustic Meatus.

Sensory innervation of EAM is by following nerves:

Auriculotemporal nerve– supplies roof and anterior wall.
Auricular branch of vagus– supplies floor and posterior wall.

Applied Aspects

During examination of ear, the auricle is pulled upwards, backwards, outwards

As external auditory meatus is ‘S’ shaped, therefore, during examination of ear, the auricle is pulled upwards, backwards, outwards in adults, to straighten the ear canal to a certain extent and provide a better view in examination.

Syringing of external auditory meatus to remove wax may stimulate auricular branch of vagus

Skin over the concha of external ear is supplied by auricular branch of vagus and therefore, syringing of external auditory meatus to remove wax may stimulate auricular branch of vagus and result in:

reflex coughing
vomiting
may result in cardiac arrest also.