Ear

Question 1

Outer ear function

comprises (3)

Answer 1

Channels sound to ear drum

1. Auricle/Pinna
2. External Auditory meatus
3. Eardrum

Question 2

Middle ear function

Comprises (3)

Answer 2

Transformer

1. Maleus
2. Incus
3. Stapes

Question 3

Outer ear function

Comprises (7)

Answer 3

Special sense for hearing, balance, movement and bodily orientation.

1. Semi-circular canals
2. External
3. Posterior
4. Anterior
5. Vestibuli
6. Cochlea
7. CN8

Question 4

Ear Development during growth

Answer 4

The External auditory meatus elongates during childhood.

Question 5

The middle and inner ears are enclosed in

Answer 5

The petrous part of the temporal bone.

Question 6

The inner ear has a mucous membrane

Autonomics supplied by:

Answer 6

CN7 and CN9 parasympathetics

Sympathetics from internal carotid plexus

Question 7

The Lateral wall of the inner ear is formed

Answer 7

mostly by the eardrum / Tympanic Membrane

Question 8

The tensor tympani muscle runs inside the petrous temporal bone alongside

Answer 8

The auditory tube runs alongside the Tensor tympani

Question 9

The auditory tube runs alongside the Tensor tympani

Answer 9

The tensor tympani muscle runs inside the petrous temporal bone alongside

Question 10

Auditory Ossicles

4

Answer 10

1. The Maleus is attatched to the incus which is attached to the stapes.
2. The Hndle of the maleus is attached to the tympanic membrane
3. The tensor tympani is attached nearer to the head of the maleus. It is innervated by the mandibular nerve.
4. Because the Stapedius is derived from the 2nd arch, its tensor muscle, the stapedius, is derived from the facial nerve.

Question 11

Auditory ossicles evolutionary significance

Answer 11

The Synovial joint Between the maleus and the incus corresponds to the original jaw joint for early synapsids

The malleus then corresponds to the articular

The Incus corresponds to the quadrate.

Menkels cartilage maintains the maleus in continuity with the lower jaw via the sphenomandibular ligament

Question 12

The ear of the foetus

Answer 12

The Foetal Jaw is suspended from the roof of the middle ear by the ligament of the incus

Meantime, the sphenomandibular ligament carries on to the jaw.

Question 13

The Medial wall of the middle ear contains

5

Answer 13

1. The promontory (caused by the cochlea bukging in) It is covered in a plexus formed by the lesser petrosal nerve and the the tympanic nerve.
2. It also has the fenestra vestibuli
3. Fenestra rotundum (inferior to fenestra vestibuli)
4. The prominence formed by the passing facial nerve
5. The chorda tympani branches off the facial nerve and passes between the tensor tympani and the maleus-incus joint. It is not involved in the ear either.

Question 14

The Ossicle chain functions as

Answer 14

A transformer. The large surface area of the tympanic membrane is transferred to small the foramen vestibuli,

This compensated for the lower sonic pressure exerted by vibrating air as the sound is vibrated by fluid.

The Hydraulic ratio is around 14x

There is also a lever effect: the handle of the maleus is longer than the crus of the incus. Torque is increased by 1.3

In all sound pressure is increased by 18.3 times.

Question 15

Nerves associated with the middle ear

Answer 15

1. The facial nerve turns off the internal auditory meatus at the geniculate ganglion.
2. Then in proceeds through the facial canal to the stylomastoid foramen.
3. The Chorda tympani that branches off and hitchhikes on a branch of CN5. It recieves afferents from the anterior 2/3 of the tongue and sends parasympathetics to the mandibular and sublingual glands.
4. The Greater petrosal nerve sends some parasympathetics to the Pterygopalatine/sphenopalatine “hay fever” ganglion. It sends Postganglionic fibers to lacrimal and mucous glands in the nose.

Question 16

Inner ear histology

(2)

Answer 16

1. the Membranous part of the vestibular apparatus contains endolymph,
2. but the space between the membrane and surounding bone is filled with perilymph.

Question 17

Inner ear organisation and function

Main parts: (4)

Answer 17

The Endolymphatic duct supplies the utricle and the saccule

The hair cells in the utricle and saccule respond to otoliths, registering the head’s orientation at rest.

The utricle is intimately commected to the Semi-circular canals contain hair cells which when disturbed register movemento n a particular plane.

The saccule is connected to the cochlea by the ductus reuniens. The cochlea contains the long organ of corti.

Question 18

How hearing happens

7

Answer 18

1. Auditory ossicles transfer tympanic membrane movement to the oval window (fenestra vestibula)
2. Pulses pass through the perilymph around the organ of corti .
3. The first half is in the Scala vestibuli, moving the vestibular membrane of the cochlear duct.
4. On the other side of the tectoral membrane is the basilar membrane and the scala tympani.
5. Pressure changes are offset by the round window.
6. The apex of the organ of corti has a resonanc for higher frequencies than the more proximal region.
7. The population of hair cells lining the sensor typmani send afferents down the cochlear nerve. Those hair cells on the basilar membrane send inputs for the modulation of the tension of the ossicles.