Inner Ear

Question 1

What are the parts of the inner ear?

Answer 1

Cochlea - Hearing
Semi-circular canals - balance
Vestibule - posture

Question 2

What is the outer layer of the labyrinth made up of?

Answer 2

Outer layer of labyrinth is bone, sitting within ‘petrous’ has the cavities for the cochlea and semi circular canals.

Oval window is in the vestibule not the cochlea

Question 3

Describe the Cochlea?

Answer 3

Whole inner ear has a membrane layer underneath bony layer, filled with fluid.

Cochlea
- conical bony structure
- L 36mm, 10mm x 5mm
- spiral 2.75 turns around modiolus (centre part)
- membranous lining

Question 4

Labels for cross section of cochlea? (12)

Answer 4

Stria

Cross section of inner ear

Question 5

What fluid is in the middle ear?

Answer 5

Perilympth
- Scala vestibuli
- Scala tympani

Endolympth
- Scala media

Question 6

Organ of corti labels? (6)

Answer 6

Question 7

Characteristics of perilympth?

Answer 7

Extracellular fluid located in Scala tympani & Scala vestibuli

Rich I. Sodium chloride ions poor in potassium ions

Carries very little electrical charge (if any)

Question 8

Characteristics of endolympth?

Answer 8

Rich in potassium ions

Production involves cells of the tria vascularis

Circulates through membranous labyrinth from the endolymthatic sac

Carries a relatively high electrical charge

Filled with endolympth

Question 9

Characteristics of Scala media?

Answer 9

Membranous tube runs along outer wall of cochlea

Floor comprises of Ossetian lamina and basilar membrane

Roof comprises reissnres membrane

Forms a triangle duct the Scala media

Question 10

What are the characteristics of basilar membrane?

Answer 10

• Apex or Apical end is wider and more flaccid, deals with the lowest frequencies
• the Basel end or entrance is narrow and taut, deals with the higher frequencies
• properties of basilar membrane mean it responds differently to different frequencies
• oval window pushes the Scala vestibuli
• round window is pushed by the Scala tympani

Question 11

Inner hair cell properties?

Answer 11

3500 per cochlea
Single row
Pear / flanked shape
50 / 60 sterocillia
Afferent
Involved with sensorineural HL
Sensory

Question 12

Outer hair cell properties?

Answer 12

12,500 per cochlea
3 rows
Test tube shaped
100 sterocillia in v or w shapes
Efferent
Impact sensitivity of cochlea
Motor (mechanical)

Question 13

What does afferent mean?

Answer 13

Taking signal from ear to brain

Question 14

What does efferent mean?

Answer 14

Carry information from the brain

Question 15

How do sterocillia work?

Answer 15

When resting no gaps
Vibration a correct frequency
Touch basilar membrane
Gap appears

Potassium from endolympth flows into hair cell (high concentration to low)

Potassium in hair cell changes the charge

Calcium enters hair cell increasing charge

Triggers release of neurotransmitters
These travel to brain

Question 16

What is the physiology of the inner ear?

Answer 16

Changes in sound into electricity, for transmission to the brain via the acoustic nerve.

Frequency analyser

Functions
-Transmission
-Transduction
-Frequency resolution

Question 17

What are the functions of the inner ear?

Answer 17

Transmission- transfers sound from oval window to organ of corti

Transduction- converting mechanical energy to electro-chemical energy (inner hair cells)

Frequency resolution - breaking up sounds into component frequencies (basilar membrane)

Question 18

What is temporal resolution?

Answer 18

A pattern of firing nerve fibres that in some way analogous to the sound stimulus

Eg at a frequency of 1k a pattern of nerve impulses that repeats 1,000 times per second will travel to the brain

Question 19

What are the electrical potentials of the cochlea?

Answer 19

Resting
Endolympth potential = +80mv
Hair cell potential = -40 to -70mv
Perilymph 0mv
*Difference is 140 mv

Cochlea microphonic
Louder the sound the more charge changes

Summering potential
Long intensive sound can’t be maintained as no potassium left

Question 20

What is the role of the outer hair cell?

Answer 20

Amplification
Fine tuning
Limiter

Amplification
- quiet signals (<50dBSPL) wouldn’t normally cause inner hair cells to create impulse.
- when detected outer hair cells contract
- pulling the tectorial membrane downwards forcing the IHC’s to shear and create the impulse

Fine tuning
- electromotility of outer hair hair cells act on the basilar membrane causing the wave to focus on smaller group of inner hair cells
- creates sharper hearing

Limiter
When loud sounds efferent signals received from brain, ohc’s push tectorial upwards limiting response of IHC’s