L16 - Outer ear

Question 1

The three parts of the ear: what are they, what are their components, and what do they do?

Answer 1

Outer ear:
* Pinna (auricle)
* External auditory meatus
* Tympanic membrane
- Conducts sound to middle ear

Middle ear:
* Tympanic cavity
* Ossicles (malleus, incus and stapes)
- Conducts sound to the inner ear

Inner ear:
* Cochlear and vestibular system
* Vestibulocochlear nerve
- Hearing and equilibrium (balance)

Question 2

Pinna: what are its components, where are they located, and what do they do?

Answer 2

Helix
Crura of antihelix
Triangular fossa of antihelix
Scapha
Antihelix
Concha (composed of cymba and cavity)
Tragus
Antitragus
Intertragic notch

All of the above funnel/direct sound waves to the external acoustic meatus

Lobule - keeping the ears warm and maintaining balance
Opening of external acoustic meatus - passage allowing sound waves to travel to the middle ear

Question 3

Auricle: what is its other name, what is its blood supply, and what is its lymph drainage?

Answer 3

Pinna

Posterior auricular and superficial temporal
arteries

Lymph drains to the superficial parotid, superficial cervical, deep cervical and mastoid lymph nodes

Question 4

Pinna innervation

Answer 4

Medial and posterior - Great auricular and lesser occipital nerves (C2 & C3)

Skin anterior to the external auditory meatus - auriculotemporal nerve (a branch of V3)

Concha near E.A.M. – Auricular branch of the facial (VII)

Question 5

EAM: what does it stand for, what is it, what are its key features, what is its innervation, and what is the skin continuous with?

Answer 5

External auditory meatus

Canal that conducts sound to the tympanic membrane (located at the distal end of EAM)

• 2 – 3 cm long
• Supported by cartilage - cartilaginous lateral third
• Medial two-thirds in tympanic part of temporal bone
• Has a slight S-bend - needs to be straightened to use an otoscope
• Sebaceous and ceruminous glands produce earwax (cerumen)

Mandibular branch of trigeminal nerve (V3 (auriculotemporal)) and vagus nerve X (auricular branch)

Skin continuous with the skin of the pinna (keratinised stratified squamous)

Question 6

looking into eam: the process

Answer 6

Adults: move the ear up, back, out

Children: down, back

Question 7

Earwax: what is its main use?

Answer 7

Trap dust/foreign debris (invertebrates too)

Question 8

Where does the carotid artery enter the skull?

Answer 8

Carotid canal

Question 9

Tympanic membrane: what is it, what does it do, what is it covered with, what key features does it have, what parts are there to it, what do they do, and what is its innervation?

Answer 9

Oval, thin and semitransparent membrane

Separates the external ear (EAM) from the middle ear (tympanic cavity) and conducts sound waves to auditory ossicles - eardrum

Covered with skin externally (stratified squamous epithelium) and the mucous membrane internally (columnar epithelium)

• About 1 cm in diameter
• Laterally concave
• Central umbo – formed by handle of malleus

Tense part inferior to lateral handle of malleus - contains radial and circular fibres
Flaccid part superior to handle of malleus - thin and lacks fibres

Externally by auriculotemporal nerve (a branch of V3) and auricular branch of the vagus nerve (X) (same as EAM)
Internally by the glossopharyngeal nerve (IX)

Question 10

MLF: what is it, where is it located, and what does it do?

Answer 10

Middle lacerate foramen

Between sphenoid & petrosal bones – cartilage

Allows passage of Eustachian tube and some minor nerves and vessels

Question 10

ICA: where does it pass and what covers it in both animals and humans?

Answer 10

ICA primitively passes over inferior surface of braincase and enters it near the MLF

In many mammals ICA is covered by the tympanic
In humans - carotid canal

Question 11

Stylomastoid foramen

Answer 11

Transmits the main motor
branch of the facial nerve

Question 12

Petrosquamous fissure

Answer 12

Transmits the chorda tympani