Session 6 - Anatomy and Function Of The Ear

Question 0

Label the parts of the external ear:

Answer 0

PICTURE here

Question 1

What are the features of the external ear?

Answer 1

Pinna
External auditory canal
Tympanic membrane

Question 2

What is a Pinna Haematoma?

Answer 2

When there is haematoma between the cartilage and the perichondrium. This is usually caused by force to the ear. This prevents the cartilage from being oxygenated by the perichondrium so unless the haematoma is drained avascular necrosis develops. This is seen as the physical deformity cauliflower ear.

Question 3

What is the Pinna made from?

Answer 3

Elastic cartilage

Question 4

What are some of the congenital deformities that can affect the external ear?

Answer 4

Antihelix deformity
Pinna malformation
Pre-auricular pit
Pre-auricular skin tag

Question 5

How is the external ear innervated?

Answer 5

Greater auricular nerve
Lesser occipital nerve
Branches of the facial and vagus nerve.

Question 6

Describe the external auditory canal:

Answer 6

Approximately 5.5cm long, sigmoidal in shape
Lateral third is made of cartilage and the medial two thirds is made of bone.
The canal ends in the tympanic membrane.

Question 7

What forms earwax?

Answer 7

Cerumen glands in the external auditory canal secrete oil which is wafted along the canal to the exterior by epithelial cells. This is added to by dead epithelial cells.

Question 8

Describe the tympanic membrane:

Answer 8

A membrane with two layers of epithelia separated by a collagen membrane. It is at a 55 degree angle and on the medial side is attached to the malleolus.
Pars flacida - collagen has haphazard fibres which means the area is loose
Pars tensa - collagen is arranged radially which means membrane is tense and taunt.
Light reflex - reflection of light of the tympanic membrane should point towards patient feet.
Annulus - edge of thickened epithelium around the edge of the tympanic membrane
Can see the indentation of the malleolus, lateral process, handle and umbro.

Question 9

What is the function of the tympanic membrane?

Answer 9

To transmit sound from the external ear to the middle ear.

Question 10

What is otitis externa?

How can you treat it?

Answer 10

Infection of the external ear - cellulitis type disease
Causes swelling and can lead to closure of the auditory canal.
Treatment includes clearing any debris and giving ear drops. Oral antibiotics are not very effective.

Question 11

What are causes of tympanic perforation?

What signs are seen?

Answer 11

Can get sub-total or total perforation
This can be due to trauma or secondary to infection.
Pressure or pus can block the Eustachian tube - pressure must be released one way so the tympanic membrane perforates.

Question 12

What does the middle ear consist of?

Answer 12

Ossicles
Eustachian tube
Muscles
Mastoid air cells

Question 13

Name the ossicles and describe them:

Answer 13

Malleolus - head, lateral process, umbo - in contact with tympanic membrane.
Stapedius - anterior and posterior stapes cura, stapes footplate - which is in contact with oval window
Incus - short process, body and long process

Question 14

Where are the ossicles found?

Answer 14

Epitympanic recess

Question 15

What features of the middle ear allow for pressure to be equalised between the middle ear and external environment?

Answer 15

Eustachian tube connects the middle ear to the nasopharynx.

The mastoid airs cells in the mastoid bone.

Question 16

What muscles are in the middle ear and what is their function?

Answer 16

Stapedius - CNVII - connects to the stapes bone and is to prevent excessive vibration due to loud noises this is a protective mechanism.
Tensor tympani - CNV - attached to malleolus and again protects the middle ear from loud noises.

Question 17

Describe the structure of the Eustachian tube:

Answer 17

Outer part of the tube is bony

The inner part of the tube is cartilaginous.

Question 18

Why are infants more susceptible to middle ear infections?

Answer 18

The Eustachian tube is shorter, wider and more horizontal in children.
This is because the cartilage hasn’t developed fully yet.

Question 19

What is tympanic retraction?

Answer 19

Can see outline of the malleolus bone in the membrane.

Caused by negative pressure in the ear.

Question 20

What is otitis media?

Answer 20

Middle ear infection
Usually caused by resp organisms spreading from the nasopharynx e.g. Organism such as Haemophilus, streptococcus, pneumococcus.
Painful, building eardrum with pus in the middle ear.
This can lead to perforation and discharge.
Again more common in children due to Eustachian tube structure and immature immune system.

Question 21

What is glue ear?

Answer 21

Otitis media with effusion.
This is caused by a chronic infection - prolonged negative pressure forms an exudate. This causes water to move into the channel by osmosis and this does not conduct sound well so you get conductive hearing loss.

Question 22

What are grommets?

Answer 22

Small tubes that are surgically inserted into the tympanic membrane to allow fluid to move into the external auditory canal and release pressure.
They fall out naturally.

Question 23

What are some of the complications of otitis media?

Answer 23

Facial muscle paralysis - as facial nerve runs through middle ear
Loss of taste on anterior two thirds of tongue - damage to chordi tympani nerve
?Loss is salivation - loss of innervation to sublingual and submandibular glands.
Mastoiditis - back pressure means infection can spread into mastoid air cells. The infected bone can cause the Pinna to stick out of the side of the head. There is also risk of intracranial infection and death.
Cholesteatoma

Question 24

What is a cholesteatoma?

Answer 24

When prolonged negative pressure cause retraction pockets to be formed.
Dead skin remains trapped in these pockets.
A necrotic mass forms (mainly keratin) which is called a cholesteatoma.
The skin releases lytic enzyme which can degrade bone and middle ear structures. This can lead to hearing loss.

Question 25

Describe the structures of the inner ear?

Answer 25

Cochlear - responsible for hearing

Vestibule - responsible for balance

Question 26

Describe the vestibular labyrinth:

Answer 26

2 sacs of fluid
3 cylinders of fluid.

The two sacs give information about vertical and horizontal direction.
The 3 cylinders of fluid are at 90 degree angles to each other and give information about other directions.

Question 27

What is responsible for balance?

Answer 27

Interplay between vestibular end organ
Vision
Sensation

Question 28

What are some of the causes of vertigo?

Answer 28

Benign positional paroxysmal vertigo - only occurs for a few seconds some otoliths are displaced and carry on moving even after a person has stopped giving the feeling of vertigo.
Ménière’s disease - vertigo that lasts several minutes or hours - is due to high pressure in the sacs of the vestibular labyrinth due to excessive endolymph - the fluid that is fills the sacs/cylinders.

Question 29

Describe the cochlear:

Answer 29

A snail shaped organ that has two and half turns.
It contains three sacs filled with fluid.
The scalar tympani
Basilar membrane
Scalar vestibular

Question 30

How does the cochlear allow hearing?

Answer 30

The stapes bone connects to the top sac the scale tympani and transmits the vibrations. The vibrations are transmitted through the fluid in the sac and this causes the movement of tiny. Hairs in hey he basilar membrane. This generates an electrical signal which is sent to the brain. The vibrations are dissipated by the scalar vestibular which is connected to the oval window which joins to the middle ear.