Ear eBook

Question 1

The ear has two functions:

Answer 1

1. Facilitation of hearing

2. Facilitation of balance

Question 2

The ear consists of three regions:

Answer 2

1. External ear – channels sound
2. Middle ear ‐ hearing
3. Inner ear ‐ balance

Question 3

External Ear

Answer 3

The external ear channels collected sound waves through to the middle and inner ear. The pinna (also known as the auricle) is the visible external structure and is made of elastic cartilage. The external auditory canal is approximately 2.5cm long in adults and terminates in the tympanic membrane (the ear drum). Ceruminous glands are found near the outer opening which secrete cerumen (ear wax). The cerumen is responsible for moving shed cells and other debris away from the tympanic membrane but overproduction of this cerumen may lead to impaction. The main symptom of cerumen impaction is muffled hearing as the tympanic membrane cannot vibrate fully.

Question 4

Middle ear

Answer 4

The middle ear is an air filled cavity, completely sealed off from the external auditory canal. It contains the bones of hearing – the ossicles, the smallest bones in the body – which consist of:
 Malleus (hammer)
 Incus (anvil)
 Stapes (stirrup)
The tensor tympani and the stapedius muscles are responsible for controlling the response to loud or violent sounds. The tensor tympani limits the movement of the tympanic membrane, thus reducing vibration and the stapedius dampens large vibrations of the stapes. The auditory (Eustachian) tube opens into the back of the throat and is responsible for equalising air pressure within the ear. If the auditory tube is inflamed (for example if the patient has a viral upper respiratory tract infection) this equalisation function may be impaired and so the patient’s hearing may become muffled.

Question 5

Definitions

volume and pitch

Answer 5

 Volume = amplitude of soundwaves
o Measuredindecibels(dB)
o Decibels are a log scale and so an increase of 1dB means that the sound is 10x louder.
 Pitch = frequency of soundwaves
o Measuredinhertz(Hz)
“Middle C” has the frequency of 260 Hz

Question 6

Sound and hearing

Answer 6

The human hearing range for pitch is typically between 20 and 20000 Hz. Sounds between 500 and 5000 Hz are the easiest to hear. The threshold for human hearing is 0 dB at 1000 Hz. Human speech is typically 100 – 3000 Hz and 60 dB. Sound becomes uncomfortable at approximately 120 dB and painful at approximately 140 dB. Sustained exposure to sounds louder than 90 – 95 dB can lead to permanent hearing loss. Short term exposure to sounds louder than 140 dB will result in permanent hearing loss.

Exposure to sustained sound levels above 90 dB (for example at a rock concert or with some in‐ car audio systems) can lead to a “temporary threshold shift”. This is where hearing becomes temporarily impaired (this is the muffling effect that you may experience if you have been in a particularly loud environment such as a rock concert, nightclub or a car with the sound system seriously jacked up). In situations where the person has control of the sound system, the temptation is to turn up the volume even further and so a spiral of permanent hearing loss may be set in motion.

Question 7

typical volume levels.

Answer 7

 Whisper – 30 dB
 Telephone dial tone (land line) – 80 dB
 Chain saw at 1m distance – 110 dB
 In‐car entertainment systems (particularly with large subwoofers) – 90 dB
 Loud rock concert – 115 dB
 Jet engine at 30m distance – 140 dB

Question 8

Hearing

Answer 8

Hearing occurs when transmitted sound waves are collected by the auricle and funnelled down the external auditory tract, through the tympanic membrane and into the cochlea via the ossicles. Sound waves must have sufficient amplitude to vibrate the tympanic membrane in order to be “heard”.

Question 9

The mechanism of hearing

Answer 9

1. Sound waves are directed into the external auditory canal
2. The tympanic membrane vibrates
3. The malleus vibrates & the vibrations are transmitted to the incus and stapes
4. The oval window vibrates
5. This causes pressure waves in the perilymph in the scala vestibuli
6. The pressure waves are transmitted to the scala tympani and back to the round window (number 9 on the above diagram)
7. The walls of the scala vestibule and scala tympani deform, deforming the vestibular membrane in turn
8. Pressure waves in the cochlear duct cause the basilar membrane to vibrate and move the hair cells of the spiral organ (the organ of Corti). These transmit impulses along the vestibulocochlear (VIII) nerve to the medulla oblongata.

Question 10

Inner Ear (Labyrinth)

Answer 10

The outer bony labyrinth is lined with periosteum and contains perilymph. This encloses the inner membranous labyrinth which contains endolymph. The inner ear consists of three areas:

                                                    1. Semicircular canals  2. Vestibule 3. Cochlea

Question 11

The physiology of equilibrium (balance)

Answer 11

The utricle and saccule are responsible for maintaining static equilibrium whilst the three semicircular canals are responsible for maintaining dynamic equilibrium.

Question 12

Static equilibrium

Answer 12

This is the detection of movement of the head in either a forward or backward direction – linear acceleration or deceleration. The utricle and saccule are perpendicular to one another within the inner ear and each contains a strip of macula.

Macula is made up of a series of hair cells each of which has a hair bundle attached. The hair cells are surrounded by supporting cells. The supporting cells secrete a glycoprotein which forms the otolithic membrane. This membrane in turn supports the otoliths which are calcium carbonate crystals.

Question 13

When the head is tilted forward or backward the following sequence of events occurs:

Answer 13

1. The otolithic membrane (weighted down by the otoliths) slides in the direction of the tilt of the head.
2. The sliding of the membrane bends the hair bundles which stimulates the hair cells.
3. The hair cells send messages along the vestibular nerve conveying a sense of the position of the head in a linear direction (i.e. up / down) and also a sense of acceleration / deceleration.

Question 14

Dynamic equilibirium

Answer 14

The three semicircular canals are arranged so that movement can be detected in any plane of motion. Each of the semicircular canals (and the internal semicircular ducts) terminates in an ampulla. Within each ampulla is found a structure known as the crista ampullaris.

This is similar in structure to the macula found in the utricle and saccule but it does not support a layer of otoliths. The supporting cells secrete a slightly different glycoprotein forming the cupula which floats on the endolymph within the semicircular ducts. Rotation of the head causes inertia which moves the endolymph within the semicircular ducts in the opposite direction of the head movement. The endolymph drags at the cupula which stimulates the hair cells to send messages along the vestibular nerve. When the rotation stops the inertia generated causes the cupula to move in the direction of the original rotation. These two activities give a sense of change of direction and a rate of movement.

Question 15

Equilibrium (balance)

Answer 15

mpulses from the inner ear travel along the vestibular branch of the vestibulocochlear (VIII) nerve. These terminate in the vestibular nuclei in the medulla oblongata and pons which also receive signals from the eyes and the proprioreceptors in the neck muscles. To maintain balance commands are sent from the vestibular nuclei to:

1. The muscles of the head and neck to maintain visual focus and head position.
2. The skeletal muscles to maintain balance.
3. The parietal lobe of the cerebral cortex to give a sense of movement and position of the body.

Question 16

Ear pathology

The most commonly encountered ear conditions include:

Answer 16

 Over‐production of cerumen (ear wax)

 Otitis media  Otosclerosis  Labyrinthitis

Question 17

Causes of muffled hearing/deafness

Answer 17

Patients often ascribe muffled hearing to excess wax but there are many possible causes of muffled hearing and so this diagnosis should not be assumed.

1. Cerumen impaction
2. Perforated ear drum
3. Temporary threshold shift following exposure to loud noise
4. Foreign object obstruction
5. Otitis media (acute and chronic)
6. Eustachian catarrh (glue ear)
7. Barotrauma
8. Otosclerosis

Question 18

Ear drops should not be recommended to patients until

Answer 18

Ear drops should not be recommended to patients until it can be confirmed that the tympanic membrane is intact. Physically this can only be done by viewing the tympanic membrane with an otoscope. With very careful questioning it is possible to determine whether the tympanic membrane is intact but if there is any doubt at all, the patient should be referred to an appropriate practitioner.

Question 19

Management of common ear pathologies

Cerumen impaction

Answer 19

If the ear drum cannot be visualised because of a build up of ear wax, a careful history must be taken from the patient to determine the likelihood of ear drum perforation. The following is a (not exhaustive) list of questions that can be asked to help rule out a perforated ear drum.
Has the patient:
1. Had an ear infection recently?
2. Suffered from a perforated ear drum before?
3. Experienced any discomfort or pain in the ear? This may be following swimming, diving,
other water sports or air travel.
4. Any chronic discharge from the ear?

If the answer to any of these questions is yes, then the patient should be treated as if the ear drum is perforated.
If the ear drum is intact then the preferred method of treating cerumen impaction is syringing by an appropriately qualified professional. Prior to syringing the patient may be recommended to use a cerumenolytic to soften, loosen or partially dissolve any excess wax.
There are many proprietary products available for the treatment of ear wax. These may be aqueous or oil based solvents or products that generate oxygen to allow water to penetrate the wax plug. There is very little evidence for difference in efficacy between products and some evidence to show that warm water or sodium chloride applied just before syringing is as efficacious. The BNF (section 12.1) recommends olive oil, almond oil or sodium bicarbonate drops to be used before syringing.

Question 20

Management of common ear pathologies

Otitis media – acute

Answer 20

This most commonly occurs in children as the internal auditory tube is almost horizontal whereas in adults it is at a much sharper angle (see diagram on page x). Because of the horizontal nature of the internal auditory tube, drainage into the throat is poor and pathogens from the nasopharynx can track into the middle ear, usually following a cold. These pathogens may be viral or bacterial with the most common being Haemophilus influenzae, Streptococcus pneumonia and Maraxella catarrhalis.
The symptoms of acute otitis media include:  Pain
 Fever
 Loss of hearing
Otitis media is generally self‐limiting lasting for approximately 4 days. Severe pain should be referred to an appropriate practitioner to eliminate a perforated ear drum or chronic suppurative otitis media.
NICE CG69 (Respiratory tract infections) recommends that no antibiotics should be prescribed for cases of acute otitis media. A delayed prescription for antibiotics may be offered to patients or their parent/carer with instructions that it should be used if the patient does not improve within 72 ‐ 96 hours. Immediate antibiotics should be offered to children younger than 2 years with bilateral otitis media or any patient who is significantly systemically ill.
Pain is one of the most common symptoms of acute otitis media and is a useful diagnostic indicator as it is rare with other common ear pathologies.
It is important to remember that teething in young babies can present with similar symptoms to acute otitis media.

Question 21

Management of common ear pathologies

Otitis media – chronic

Answer 21

The most common pathogens which cause chronic otitis media are Pseudomona aeruginosa, Staphylococcus aureus and several species of fungi. Chronic otitis media is a much more serious condition as it can lead to penetration of the cranial vault causing abscesses or meningitis. Suspected cases should be referred to an appropriate practitioner for treatment.

Question 22

Management of common ear pathologies

Barotrauma

Answer 22

This usually occurs during the (fairly rapid) descent of an aircraft, particularly if the patient is suffering from a cold or Eustachian catarrh. An oral decongestant (e.g. pseudoephedrine) taken one hour before coming in to land, or a topical decongestant (e.g. xylometazoline, ephedrine) taken just before descent begins can be useful. If decongestants are contra‐indicated for the patient then sucking on a boiled sweet, swallowing, the use of ear plugs or Valsalva’s manoeuvre can all be useful. Valsalva’s manoeuvre involves pinching the nose closed, closing the mouth and then breathing out forcefully. All of these techniques are designed to equalise the pressure in the middle ear.

Question 23

Management of common ear pathologies

Otosclerosis

Answer 23

This is the main cause of conduction deafness (problems with the bones of the middle ear). Extra bone forms around the oval window which then overgrows the footplate of the stapes and the rim of the oval window. Because of this overgrowth the footplate of the stapes becomes anchored to the oval window meaning that the stapes can no longer oscillate and transmit sound waves into the cochlea.

Question 24

Management of common ear pathologies

Labyrinthitis

Answer 24

This is inflammation of the inner ear leading to problems with the movement of endolymph within the semicircular canals. Patients will present most commonly with dizziness and they may also suffer from nausea and, in extreme cases, vomiting.

Question 25

Management of common ear pathologies

Meniérè’s disease

Answer 25

This is caused by excess endolymph production in the cochlea. As a result the basilar membrane bulges unevenly causing the cupula to drag at the hair cells in the ampulla despite little or no movement of the head. The presenting symptoms can include vertigo (dizziness, nausea and vomiting) and patients may also complain of deafness or tinnitus.

Question 26

Management of common ear pathologies

Otitis Externa

Answer 26

This is inflammation of the external auditory canal which may or may not also include the pinna.
Acute otitis externa is usually either infective or reactive. Bacteria are the most common infective cause and are usually of traumatic origin. Reactive otitis externa is most commonly seen as an acute reaction to nickel in earrings. Reactive otitis externa will appear as red, dry and possibly scally skin and the reaction may track back to the ear canal. It can be treated with 1% hydrocortisone or with emollients (but not aqueous cream). Occasionally reactive otitis externa may become infected through scratching.
In the community pharmacy situation, aluminium acetate 13% ear drops can be recommended for reactive otitis externa within the external ear canal. This has antibacterial, hygroscopic and anti‐inflammatory activity. Acetic acid 2% spray can be recommended for superficial infections of the auditory canal but if there is no improvement after 48 hours, the patient must seek help from an appropriate practitioner.