ENT

Question 1

What is the outer ear and what is its function?

Answer 1

Includes the auricle on the outside and the external auditory meatus, leads all the way to the tympanic membrane
- collects and localises sound

Question 2

Describe the external auditory meatus

Answer 2

• lateral cartilaginous part and medial bony part

- lined by hairy skin and cerumen glands –> prevent maceration of skin with water

Question 3

What is the nerve supply to the posteroinferior wall of the EAM?

Answer 3

Vagus

Question 4

What is the nerve supply to the anterior and superior wall of the EAM and the external surface of the tympanic membrane?

Answer 4

Auriculotemporal nerve (branch of V3 from trigeminal)

Question 5

What is the tympanic membrane and its function?

Answer 5

A membrane that produces a complete seal around the EAM

• allows pressure waves from sound to produce vibration
• concave outwards and convex inwards
• when shine a light should see it in the anterior-inferior quadrant

Question 6

What is the middle ear?

Answer 6

Space between the tympanic membrane and the inner ear

- consists of two parts: tympanic cavity proper, and the epitympanic recess (communicates to mastoid air cells)

Question 7

What is the function of the auditory tube and what are some complications?

Answer 7

Gives a communication between the atmosphere and the nasal cavity - allows equalisation of pressure across the membrane

• projects anteroinferiorly into the nasopharynx
• easy for infections to drain down
• gradient is much more horizontal in children –> drainage of middle ear is much more difficult

Question 8

What are the ossicles?

Answer 8

3 bones that connect the tympanic membrane with sensory receptors in the inner ear

• stapes (sits directly over the oval window)
• incus (articulates with stapes in the middle)
• malleus (attached directly to the medial surface of the membrane)

Question 9

What are the two muscles in the middle ear?

Answer 9

Tensor tympani and stapedius

• both work to pull on the ossicles and dampen the amplitude of vibration –> protection from loud sounds, under reflex control
• tensor tympani innervated by the trigeminal nerve
• stapedius innervated by the facial nerve

Question 10

What is the organisation around the promontory and what is it?

Answer 10

Swelling formed by the basal turn of the cochlea

• oval window is above and posterior to it
• round window is inferior and posterior to it

Question 11

Describe the inner ear

Answer 11

Embedded into the petrous part of the temporal bone

• bony labyrinth filled with perilymph
• suspended inside the bony labyrinth is the membranous labyrinth, which contains endolymph

Question 12

What is the organisation of the cochlea?

Answer 12

Contains part of the membranous labyrinth which contains the receptors for hearing

• semicircular canals - bony (ducts, membranous) - 3 oriented in anterior, posterior and horizontal planes –> dynamic equilibrium
• vestibule - bony (utricle and saccule, membranous) –> sensory receptors which code for static equilibrium (also the part that communicates with the middle ear)

Question 13

What is the organisation of sound in the cochlea?

Answer 13

Sensory receptors at the base of the cochlea best respond to high frequency sounds and those at the apex best respond to low frequency sounds