Topic 10 Ear, hearing and balance

Question 1

What two membranes make up the roof and the floor of the scala media?

Answer 1

Roof - Vestibular/Reissner’s membrane

Floor - Basilar membrane

Question 2

Describe how the vibrations from the stapes against the oval window are transferred to the spiral organ of Corti.

Answer 2

• The vibrations from the stapes against the oval window causes displacement of the perilymph in the Scala vestibuli (ascending part of cochlea)
• This causes the Vestibular/Reissner’s membrane to vibrate
• The vibrations then travel through the endolymph of the Scala media and down to the basilar membrane
• Movement of the basilar membrane displaces hair cells in the spiral organ of Corti.

Question 3

What is the name of the structure labelled 4 in the diagram?

Answer 3

Cochclea

Question 4

How is dynamic movement of the head communicated to the brain?

Answer 4

• The semicircular canals also contain hair cells that are embedded in a gel-like membrane (cupula) which is surrounded by endolymph.
• Movement of the endolymph in the canal pushes on the cupula, bending the hairs of the hair cells.
• Depending on the plane of movement, the hair cells in the relevant canal will bend (no otoliths as no relative to graviity)
• The mechanical action activates an electrical potential that is transferred to the dendritic nerve endings.
• They then transmit the signal a short distance to the cell bodies in the Vestibular ganglion.
• The impulse then travels along their axons, forming the Vestibular nerve.
• The Vestibular nerve combines with the Cochlear nerve carrying hearing information, to form the vestibulocochlear nerve (CNVIII).

Question 5

Describe how vibration of the basilar membrane is turned into an electrical potential in the hair cells of the spiral organ of Corti.

Answer 5

• movement of the basilar membrane displaces hair cells in spiral organ of Corti
• Vibration of the hairs on the hair cells causes them to bend (becuase they are attached to the tectorial membrane)
• This mechanical action causes ions to flow from the endolymph into the cell body of the hair cell - causing an electrical potential

Question 6

Idenitfy the structure labelled A

Answer 6

epitympanic recess

Question 7

What is the round window? What is its function?

Answer 7

• The round window is small opening to the inner ear, inferior to the oval window.
• it is covered by a flexible membrane (secondary tympatic membrane)
• Allows for perilymph displacement in the inner ear so that the stapes can transfer vibrations.
• Relieves pressure induced by sound waves in the inner ear.

Question 8

What are the names and functions of the two muscles in the ear?

Answer 8

1. Tensor tympani
2. Stapedius

• muscles contract when a sudden loud sound occurs
• stiffens the ossicles and reduces the vibration transfer from the tympanic membrane to the inner ear (called sound attenuation reflex)

Question 9

What is the bony labyrinth of the inner ear? What are its three main parts?

Answer 9

• The bony labyrinth is a series of tunnels and chambers in the petrous part of the temporal lobe (filled with fluid called perilymph)
• It consists of 3 parts:

1. semicircular canals
2. vestibule
3. cochlea

Question 10

What is the difference between the function of the utricle and the saccule?

Answer 10

• the utricle detects forward and backwards movement in relation to gravity (driving a car)
• the saccule detects up and down movement in relation to gravity (going up and down in an elevator)

Question 11

Where is the Scala media (cochlear duct) located?

Answer 11

Between the Scala tympani and the Scala vestibuli in the Cochlea.

Question 12

What are the middle ear ossicles, and where are they located?

Answer 12

The 3 ossicles are:

1. Malleus
2. Incus
3. Stapes

• Located in the tympatic cavity of the middle ear

Question 13

What is the spiral organ of Corti, and where is it located?

Answer 13

The spiral organ of Corti is a region on the floor of the Scala media comprised of hair cells that rest on the surface of the basilar membrane.

Question 14

What are the two systems in the in the inner ear that regulate balance?

Answer 14

1. Static system (utricle and saccule)
   * detects movement when head is stationary in relation to gravity (e.g. elevator, driving a car)
2. Dynamic balance (3 semicircular canals)
   * detects movement of head in all 3 planes

Question 15

Describe how sound waves initially reach the tympanic membrane.

Answer 15

• Sound waves are funnelled into the external ear by the auricle
• They pass down the External Auditory Meatus (ear canal) of the temporal bone.
• Reaching the end of the ear canal, the sound waves cause vibration of the tympanic membrane.

Question 16

How do the utricle and saccule communicate static movement to the brain?

Answer 16

• the utricle and saccule also contain hair cells.
• When static position changes, there is movement of the gelatinous matrix, which sits on top of the hair cells, aided by the otoliths (crystal like structures that move in responce to gravity).
• This causes bending of the hair on the hair cells in relation to the cell body.
• The mechanical action activates an electrical potential that is transferred to the dendritic nerve endings.
• They then transmit the signal a short distance to the cell bodies in the Vestibular ganglion.
• The impulse then travels along their axons, forming the Vestibular nerve.
• The Vestibular nerve combines with the Cochlear nerve carrying hearing information, to form the Vestibulocochlear nerve (CNVIII) before exiting the temporal bone through the Internal Auditory Meatus.

Question 17

What fluid contains a specialised ion concentration to aid nerve potential activation?

Answer 17

Endolymph

Question 18

What happens to excess sound waves so that they don’t damage the cochlea?

Answer 18

The travel back down the perilymph of the Scala tympani to the round window where they are absorbed.

Question 19

Identify the structure labelled C

Answer 19

tympanic cavity

Question 20

What is the name of the structure labelled 10 in the diagram?

Answer 20

Incus (anvil)

Question 21

What is a macula?

What is the difference between the utricular macula and the saccular macula?

Answer 21

• A macula is a specielised patch of cells containing hair cells, supporting cells and a gelatinous matrix.
• The utricular macula’s hair cells are positioned at right angles to the base of the skull (vertical) so only move with forward/backward motion
• The saccula macula’s hair cells are positioned parallel to the base of the skull (horizontal) so only move with up/down motion.

Question 22

What is the name of the structure labelled 2 in the diagram?

Answer 22

Auditory tube/

Pharyngotympanic tube/

Eustachian tube

Question 23

Identify the structure labelled D

Answer 23

pharygotympanic/auditory tube

Question 24

What is the name of the structure labelled 17 in the diagram?

Answer 24

Semicircular canals

Question 25

What is the name of the structure labelled **18** in the diagram?

Answer 25

**Stapes** (stirrup)

Question 26

What are the **3 parts of the ear,** and what are there *general* functions?

Answer 26

1. **Outer ear** - captures sound waves 2. **Middle ear** - delivers sound vibrates to the inner ear 3. **Inner ear** - converts vibrations into neural impulses

Question 27

What is the name of the structure labelled **6** in the diagram?

Answer 27

**External acoustic meatus** (ear canal)

Question 28

What are the **two chambers** of the **bony labyrinth?**

Answer 28

1. **Scala vestibuli** - assending part 2. **Scala tympani** - descending part

Question 29

Identify the structure labelled **B**

Answer 29

**Incus**

Question 30

What is the **pharygotympanic tube,** and what is its function?

Answer 30

* **canal between the middle ear and the nasopharynx** * allows **air pressure in the middle ear to be equilised** (with atmospheric pressure) by allowing air to enter and leave the tympanic cavity. * this important to allow the **tympanic membrane to move freely** (no suction)

Question 31

Describe how vibrations of the tympanic membrane are transferred to the inner ear.

Answer 31

* The three **Auditory Ossicles** in the middle ear transfer the vibrations from the **Malleus** (connected to **umbo** (cone) of tympanic membrane)-\> **Incus** -\> footplate of the **Stapes** * The footplate of the **stapes** vibrates againsts the **oval window**, causing displacement of the **perilymph** in the **Scala vestibuli** (ascending part of cochlear)

Question 32

What is the name of the structure labelled **22** in the diagram?

Answer 32

**Tympanic membrane** (ear drum)

Question 33

What is the name of the structure labelled **8** in the diagram?

Answer 33

**Ganglia of the vestibular nerve** (one for vestibule, one for semicircular canals)

Question 34

Describe how the electrical potential occuring in the hair cell of the spiral organ of Corti **reaches the brain**.

Answer 34

* The electrical signal created in the hair cell is transferred directly to **dendritic nerve endings** that are attached to its base. * The signal travels a short distance to the cell bodies in the **Cochlear (spiral) ganglion.** * The axons from these nerves combine to form the **Cochlear nerve.** * The Cochlear nerve combines with the Vestibular nerve to form the **Vestibulocochlear nerve (CNXIII)** which then travels through the **internal auditory meatus** to the brain stem. * A second neuron directs the signal to the **thalamus**, and a third neuron to the **primary auditory cortex** in the temporal lobe.

Question 35

What is the **membranous labyrinth** of the inner ear? What are its **three sections** and their **general function**?

Answer 35

The **membranous labyrinth** is a **series of fluid filled sacs and ducts** suspended within the bony labyrinth (filled with **endolymph**) _It has 3 sections:_ 1. **utricle and saccule of the Vestibule** - static balance (gravity) 2. **three semicircular ducts** - dynamic balance (head) 3. **cochlear duct** (scala media) - hearing

Question 36

What is the name of the structure labelled **13** in the diagram?

Answer 36

**Lobule/lobe** (of the auricle - outer ear)

Question 37

Which **three muscles** are used to equilise air pressure in the middle ear?

Answer 37

1. **tensor veli palatini** 2. **levator veli palatini** 3. **salpingopharyngeus** All connected to pharyngotympatic/Eustachian tube Connected to palate -\> swallowing and yawning facilitates equilisation

Question 38

What is the name of the structure labelled **14** in the diagram?

Answer 38

**Malleus** (hammer)