W2: Ear

Question 1

What is external ear composed of?

Answer 1

Auricle/pinna and external auditory meatus

Question 2

Where does external ear end?

Answer 2

Tympanic membrane

Question 3

What is auricle formed from?

Answer 3

Elastic cartilage + skin

Question 4

What supplies skin of auricle anterior to external auditory meatus?

Answer 4

Auriculotemporal nerve, from mandibular branch of trigeminal

Question 5

What supplies back surface of ear + helix, antihelix and lobule?

Answer 5

Great auricular nerve - arises from cervical plexus - C2/3

Question 6

Label external ear

Answer 6

Helix - outer edge
Lobule - lobe
Tragus - medial bumpy bit

Question 7

Discuss external auditory canal - what makes it up?

Answer 7

The outer third of the canal is cartilaginous and lined with skin that is continuous with the skin of the pinna.The medial 2/3rds is bony and lined with thin skin, which is continuous with the external surface of the tympanic membrane

Question 8

What produced cerumen?

Answer 8

ceruminous and sebaceous glands of the cartilaginous part

Question 9

What is the external auditory meatus innervated by?

Answer 9

Auriculotemporal (V3) and vagus

Question 10

Otoscopy

Answer 10

On otoscopy, the handle and the lateral process of the malleus can be seen through the membrane, which aids orientation – the lateral process always points to the anterior of the patient.This means the lateral process is seen on the right side of the membrane in the right ear, and vice versa for the left ear. The centre of the tympanic membrane, at the level of the top of the malleus, is known as the umbo, which is the most retracted point of the structure.

Incus in within the malleus

Above malleus = pars flaccida

Question 11

What nerve is the external surface of typanic membrane supplied by? What about the inner?

Answer 11

Auriculotemporal nerve - V3, although some innervation is provided by the auricular branch of theVagus nerve.

Glossopharyngeal

Question 12

Where is middle ear? What does it include?

Answer 12

Petrous temporal bone

ossicles, stapedius and tensor tympani muscles and the chorda tympani nerve

Question 13

What is chorda tympani?

Answer 13

Facial nerve branch carrying afferent special sensation from the anterior two-thirds of the tongue via the lingual nerve, as well as efferent parasympathetic secretomotor innervation to the submandibular and sublingual glands.

Question 14

Discuss ossicle chain

Answer 14

The auditory ossicles form a chain of three articulating bones, linked by synovial joints, which transmit vibrations from the tympanic membrane to the oval window of the inner ear.

Ossciles are malleus, incus and stapes

As the base plate of the stapes vibrates on the oval window, the round window of the inner ear vibrates in opposite phase into the middle ear.

Question 15

Discuss malleus

Answer 15

The malleus is the largest and most lateral of the ear bones, attaching to the tympanic membrane, via the handle of malleus. The head of the malleus lies in the epitympanic recess, where it articulates with the next auditory ossicle, the incus.

Question 16

Discuss incus

Answer 16

The next bone – the incus – consists of a body and two limbs. The body articulates with the malleus, the short limb attaches to the posterior wall of the middle, and the long limb joins the last of the ossicles; the stapes.

Question 17

Discuss stapes

Answer 17

The stapes is the smallest bone in the human body. It joins the incus to the oval window of the inner ear. It is stirrup-shaped, with a head, two limbs, and a base. The head articulates with the incus, and the base joins the oval window.

Question 18

What are mastoid air cells?

Answer 18

are a collection of air-filled spaces in the mastoid process of the temporal bone. The air cells are contained within a cavity called the mastoid antrum. The mastoid antrum communicates with the middle ear via the aditus to mastoid antrum.

The mastoid air cells act as a ‘buffer system‘ of air – releasing air into the tympanic cavity when the pressure is too low.

Question 19

Discuss pharyngotympanic tube

Answer 19

Aka Eustachian tube, connects to pharynx

The auditory tube (eustachian tube) is a cartilaginous and bony tube that connects the middle ear to the nasopharynx. It acts to equalise the pressure of the middle ear to that of the external auditory meatus.

It extends from the anterior wall of the middle ear, in an anterior, medioinferior direction, opening onto the lateral wall of the nasopharynx. In joining the two structures, it is a pathway by which an upper respiratory infection can spread into the middle ear.

The tube is shorter and straighter in children, therefore middle ear infections tend to be more common in children than adults.

Question 20

Otitis media

Answer 20

Also known as a middle ear infection, otitis media is extremely common in childhood and may be caused by either bacterial or viral infection. Most children experience a self-limiting illness and complain of ear- ache, tiredness and fever. On examination, the eardrum may appear bulging and red.Acute otitis media can usually be treated with pain relief and good hydration, as the infection resolves on its own after a few days.

In some cases, slow resolution results in chronic inflammation with the accumulation of a glue-like fluid behind an intact tympanic membrane (so called “glue-ear” or otitis media with effusion), which is probably due to Eustachian tube dysfunction.The main symptom is dulled hearing.The fluid often drains away grad- ually over time, but repeated bouts may require the insertion of grommets into the tympanic membrane to allow drainage.

Grommets = tiny tubes inserted into the eardrum

Question 21

Otosclerosis

Answer 21

A genetic condition affecting the auditory ossicles, resulting in sclerosis of the stapes baseplate in the oval window. The condition results in a slowly progressive conductive hearing loss, as sound waves are less effectively conducted from the tympanic membrane to the inner ear. Hearing loss can be improved using bilateral hearing aids, whilst surgical stapedectomy can result in significant improvements to hearing.

Abnormal growth on stapes

Stapedectomy = removal of stapes

Question 22

Round window

Answer 22

The inner ear has two openings into the middle ear, both covered by membranes. The oval window lies between the middle ear and the vestibule, whilst the round window separates the middle ear from the scala tympani (part of the cochlear duct).

Question 23

Conduction Deafness

Answer 23

Results from blockage or damage to the conducting mechanisms of the external or middle ear: may be due to wax, otosclerosis or damage to the ossicles.

This is in contrast to sensorineural deafness, which involves damage to the cochlea or its innervation.

Question 24

Muscles in inner ear

Answer 24

There are two muscles which serve a protective function in the middle ear; the tensor tympani and stapedius. They contract in response to loud noise, inhibiting the vibrations of the malleus, incus and stapes, and reducing the transmission of sound to the inner ear. This action is known as the acoustic reflex.

The tensor tympani originates from the auditory tube and attaches to the handle of malleus, pulling it medially when contracting. It is innervated by the tensor tympani nerve, a branch of the mandibular nerve. The stapedius muscle attaches to the stapes, and is innervated by the facial nerve.