The ear

د. سعد يونس سليمان

الدكتور سعد يونس سليمان

The ear can be divided into three parts :

The external ear The middle ear The inner ear.
Transmission of sound
Organ of hearing Part of the balance system of the body.

The auricle (pinna). The external canal (external auditory meatus).

The External Ear

Auricle Emberyology

The auricle skeleton and skin
Helix
Tragus
Lobule
Concha

The external canal

Outer one third(8 mm) Cartilaginous skeleton Thick skin contain adnexial structures (sebaceous glands, hair follicles and ceruminous glands) The skin is tightly adherent to the underlying cartilage, therefore inflammation e.g. boil is extremely painful.

Inner two thirds(16mm) Bony skeleton Thin skin devoid of adnexial structures. The thin skin is tightly adherent to the underlying bone and is easily traumatized

Nerve Supply of External Ear

5th, 9th and 10th cranial nerves. great auricular nerve (C2 and C3) lesser occipital nerve (C2).

Relations of external auditorymeatus;

Anteriorly; temporomandibular joint. Posteriorly; mastoid antrum and mastoid air cells. Superiorly; the middle cranial fossa. Inferiorly and anteriorly; the parotid gland.

The tympanic membrane (drumhead or eardrum);

Separate the external meatus from the middle ear. consist of three layers; Outer epithelial layer Middle layer of fibrous tissue Inner layer of mucous membrane

The drum membrane is divided into two parts:

Pars Flaccida
Pars Tensa

Difference between pars tensa and pars flaccida

Pars tensa Lower portion of the tympanic membrane Larger (2/3 ) Thicker In the middle layer there is fibrous tissue.
Pars flaccida Upper portion Smaller (1/3) Thinner Deficient of fibrous tissue.

Landmarks of the eardrum;

Landmarks of the eardrum;
Malleus
Umbo
Incus
Cone of Light
Pars Flaccida
Pars Tensa

The middle ear (tympanic cavity)

lies between the tympanic membrane laterally and the cochlea medially


The middle ear (tympanic cavity)
Epitympanum (Attic)
Mesotympanum
Hypotympanum

Posterior

Anterior
tegmen tympani
bulb of internal jugular vein
Internal carotid artery
Eustachian tube
aditus
pyramid
The promontory
Ov.W
RW
Facial nerve
Roof
canal for tensor tympani muscle


Contents of middle ear;
Air. Ossicles; Malleus Incus Stapes Muscles Tensor tympani Stapedius Nerves; Chorda tympani Tympanic plexus

The Eustachian tube

Tympanic cavity the nasopharynx About 36mm in length. In infant is shorter ,wider and more horizontal.

The Eustachian tube

It is lined by columnar ciliated epithelium. It has 2 parts: 1) Pharyngeal cartilaginous part (2/3 of its length) 2) Tympanic bony portion. Opened by swallowing or yawning( tensor palati) and thus equality of air pressure is maintained on both sides of the tympanic membrane

The Inner Ear

The inner ear, or labyrinth, consists of: Bony capsule (otic capsule) Membranous labyrinth

Bony capsule (otic capsule)

Membranous labyrinth

There are two types of fluid in the inner ear;

Very similar to the ECF and CSF (has low k+ and high Na+ concentration).
Similar to the ICF (has high K+ and low Na+ concentration)


The Otic Capsule (bony labyrinth)
Cochlea
Vestibule
Semicircular canals
Anterior
Posterior

The Membranous Labyrinth

Membranous cochlear duct (scala media) Saccule and utricle Membranous semicircular ducts
1
2
3

The membranous cochlear duct or scala media 

Cochlear duct

Basilar membrane

Scala media
Scala tympani
Scala vestibuli
Organ of Corti

Cochlea cross-section

Saccule and utricle
They lie in the bony vestibule stimulated by linear acceleration. joined by Y – shaped endolymphatic duct which extends to the endolymphatic sac that is probably concerned with absorption of endolymph.

The membranous semicircular ducts

occupy , but not filing the lumen of the corresponding bony canal set at right angles to each other stimulated by angular acceleration.

Semicircular canal containing

Perilymph
Semicircular duct containing
Endolymph


The ampullary, utricular and saccular nerves unite to form the vestibular nerve. The vestibular and cochlear nerves together constitute the 8th cranial nerve.

Facial Nerve

Pons
C P A
Temp.b
G.g

Physiology of Hearing

Sound travels in air at 340 m/sec at 20C ͦ and atmospheric pressure. Sound has two subjective physical properties; frequency (pitch) and intensity (loudness). The frequency is measured by hertz (Hz) [Hz = Cycle/sec], whereas the decibel (dB) is the unit of intensity.

How Sound Travels?

Physiology of the Vestibular Apparatus
The balance of the body is maintained by coordination of information from three systems: Proprioception, i.e. sensation from muscles, joints, tendons and ligaments. The eyes. The vestibular system.

The vestibular system consists of:

The semicircular canals respond to angular (rotatory) acceleration and gives rise to: sensation of rotation reflex movement of the eyes and body to counter the movement. The utricle and the saccule. respond to linear acceleration: the position of the head in space initiate reflexes which tend to keep the head in upright position.

Symptoms of ear disease

Hearing loss; Is defined as subjective impairment of hearing. Three types; * conductive * sensorineural * mixed


CHL
SNHL

Conductive Hearing Loss

Sensorineural Hearing Loss
1.
Sound appears quieter but it is not distorted.
Sound appears quieter and distorted.
2.
Sounds are well heard when amplified.
Sounds` distortion limits the benefit of amplification.
3.
Paracusis Willisii positive.
Paracusis Willisii negative.
4.
The quality of speech is well maintained.
In severe cases the speech becomes indistinct and expressionless because the patient does not hear his own voice.


2. Discharge; Serous or purulent discharge; Otitis externa. Mucopurulent discharge; Otitis media. Watery discharge; CSF otorrhea following head injury or aural surgery. It occurs as a result of damage to tegmen tympani. Bloody discharge; due to granulation tissue in chronic suppurative otitis media or due to malignant disease.


3. Pain (Otalgia); 1. Within the ear (otogenic or primary) 2. Out side the ear (non- otogenic or referred otalgia).

Earache/ear pain or otalgia

Otogenic or Primary
Non- otogenic or Referred otalgia
2nd +3rd cervical spine nerves
IX (Jacobson) + X (Arnold) nerves
V cranial nerve
from lesions of related Structures whose nerve supply also send branches to the ear

4. Itching: Otitis externa. Wax.

5. Tinnitus:Is a subjective sensation of sound in the ear or head in the absence of any relevant external signals. (Occasionally it is objective e.g. in palatal myoclonus and glomus tumors). sign of irritation of the cochlea… ear disease …symptom of some general diseases (renal disease, cardiac disease, intracranial tumors and anaemia, and certain drugs, such as quinine, the salicylates and ototoxic antibiotics. )

6. Vertigo: Is defined as hallucination of movement or subjective sense of imbalance. It can be due to CVS disease, CNS disease or ear disease. Vertigo is considered as a symptom of irritation of the vestibular apparatus.

Assessment of hearing

While assessing the auditory function it is important to find out: Type of hearing loss ( CHL, SNHL or mixed ) Degree of hearing loss. Site of lesion. Cause of hearing loss.


Hearing Tests
A) Clinical tests of hearing: Finger friction test; rubbing the thumb and finger close to the ear.2) Watch test;.. by clicking watch …..3) Speech ( voice ) test;… conversation voice ,,,,distance of 6 meters.4) Tuning fork tests

Tuning fork tests The tuning fork (TF) used should have a frequency of 512 Hz. The note of the higher frequency forks tends to decay quickly where as the lower frequency forks induce perception by vibration sensation.

Rinne`s test

The TF is struck against resilient surface and then held so that the acoustic axis is in line with the EAM. In this way the sound of the TF is heard by air conduction (AC). Bone conduction (BC) is heard by holding the TF with its base placed firmly against the mastoid bone. Here the sound is transmitted through the bones of the skull to the cochlea.

Rinne`s test

Normal subject = AC > BC (Rinne +ve) CHL = BC > AC (Rinne -ve) SNHL = AC > BC(Rinne +ve) and often the BC is not heard.

Weber test;

In normal subjects the sound is heard in the midline or in both ears equally. In CHL the sound is heard in the affected ear (absence of environmental noise). In SNHL the sound is heard in the non-affected ears.

False negative Rinne

In unilateral severe SNHL, Rinne`s test will appear to give a negative result, i.e., AC is absent but BC may be good because the sound is transmitted to the opposite cochlea through the skull. In this situation Weber test is important (if it is CHL, the TF should be heard in the deaf ear).


This condition can be overcome by applying a Barany`s noise box to the non-test ear. It is a clock work device which emits noise and raises the threshold of hearing in the non –test ear to such a level that the TF can not be heard in that ear by cross hearing. It will then be found that the patient is unable to hear the TF by either AC or BC.


B) Audiometric tests:
1. Pure Tone Audiometry (PTA); 2. Speech Audiometry 3. Impedance Audiometry; a. Tympanometry b. Acoustic reflex measurement

Pure Tone Audiometry (PTA)

Pure Tone Audiometry (PTA)

Speech Audiometry

the patient ability to hear and understand speech is measured.

Impedance Audiometry

Particularly useful in children and consists of; (1) Tympanometry; is based on a simple principle, i.e. when a sound strikes tympanic membrane, some of the sound energy is absorbed while the rest is reflected. A stiff tympanic membrane would reflect more of sound energy than a compliant one.

Assessment of vestibular function

Clinical tests: Spontaneous Nystagmus Fistula Test Romberg Test Gait Hallpike Maneuver

(B) Laboratory test of vestibular function

1. Rotation test ;It is done by a rotating chair and has a disadvantage of stimulating both sides simultaneously. 2. Electronystagmography; is used to detect nystagmus which is not seen with the naked eye by placing electrodes at suitable places round the eyes. 3. Caloric test; Syringing the ear with hot or cold water induces convection currents within the lateral SCC and therefore stimulates them with resulting vertigo and nystagmus.


Rotation test

Electronystagmography

Caloric test
The ears are irrigated in turn with water at 30 C then at 44 C (7 C above and below body temperature). This situation causes nystagmus with its quick component away from the ear on the cold testing and towards the ear on hot caloric testing (COWS). This nystagmus commonly lasted for about 2 minutes from the beginning of stimulation.

Canal paresis is present if the duration of nystagmus is reduced equally for both hot and cold tests. Canal paresis is suggestive of a lesion in the peripheral vestibular apparatus e.g. vestibule or vestibular nerve.