Inner Ear

Question 1

What is the inner ear?

Answer 1

• Cavity within the petrous temporal bone filled with fluid-perilymph
• Within cavity is membranous labyrinth

Question 2

What is the membranous labyrinth?

Answer 2

Epithelial sac filled with fluid- endolymph within inner ear

Question 3

What are the types of sensory receptors in the walls of the membranous labyrinth?

Answer 3

• Maculae= vestibular receptors
• Christae Ampullaris= vestibular receptors
• Spiral organ of Corti= auditory receptors

Question 4

In which region of the membranous labyrinth are the maculae located? What type of sensory information do they pick up?

Answer 4

Utricle & Saccule- balance
U= Centrifugal & vertical acceleration
S= Linear acceleration

Question 5

In which region of the membranous labyrinth is the christie ampullaris located? What type of sensory information do they pick up?

Answer 5

Semicircularis canal

Dynamic equilibrium related to angular acceleration

Question 6

Define vertigo & nystagmus and what type of injury can lead to them

Answer 6

-Injury to peripheral vestibular system
N= Continuous, involuntary movement of the eyes
V= Person/surroundings are spinning

Question 7

What is the Organ of Corti?

Answer 7

-Specialised region in wall of cochlear duct

Question 8

Describe the structure of the bony cochlear

Answer 8

• Encloses cochlear duct
• Duct spirals around central axis of bone
• Central region encloses spiral ganglion made up of cell bodies of first order auditory neurons

Question 9

How does fluid in the inner ear move?

Answer 9

Vibration of basilar membrane caused by sound waves

Question 10

How does vibration of basilar membrane lead action potentials in sensory nerves?

Answer 10

1) Causes hairs (steroecilia) to deform against overlying gelatinous tectorial membrane
2) Leading to depolarisiation/hyperpolarisation of sensory hair cells
3) Generates action potentials in sensory nerve fibres synapsing at the base of the cells

Question 11

Which region of the basilar membrane vibrates maximally with:

• High frequency
• Low frequency

Answer 11

• High= Vibrates near base, stiff, deep part of Heschl’s

- Low= Vibrates near apex, more flexible, anterolateral Heschl’s

Question 12

What is sensorineural & conduction deafness?

Answer 12

S= Damage to hair cells within cochlear/ neural pathway of hearing
C= Problem conducting sound waves along the route of the ear

Question 13

What is the location of the inner ear?

Answer 13

Petrous part of temporal bone

Question 14

What are the cavities? What do they contain

Answer 14

• Vestibule
• SSC
• Cochlea
• All contain perilymph

Question 15

What are perilymph & endolymph made up of? Why is this important?

Answer 15

P= High Na & Low K conc
E= Low Na & High K conc
Important as creates electrical potential across membrane

Question 16

What is the cochlea made up of?

Answer 16

• Cochlea duct
• Scala tympani
• Scala vestibuli

Question 17

What is the Scala Vestibule continuous with?

Answer 17

Scala tympani

Question 18

What is the function of the round window?

Answer 18

Outlet to allow fluid movement

Question 19

How is the cochlea duct distorted?

Answer 19

Perilymph pushes round scala vestibuli and against cochlea duct (fluid filled so distorted)

Question 20

What happens when hair cells move?

Answer 20

• Cilia move opening ion channels
• Depolarisation of cells
• Fibres run down through cochlea nerve

Question 21

How does sound reach the thalamus?

Answer 21

• From inner ear neurons carry impulse to auditory centres in the brainstem
• This is sent superiorly to the superior olivary nucleus
• Next sent to the inferior colliculi via the lateral lemniscus
• To (inferior brachium) medial geniculate nucleus of thalamus
• Finally to Heschl’s gyrus at temporal gyrus

Question 22

What is the function of Stapedius & Tensor tympani?

Answer 22

Dampen down sound to prevent damage to hair cells of specific frequency (inability to hear certain frequencies)

Question 23

What do motor fibres of the auditory pathway project to and where?

Answer 23

• Inferior colliculus= Reflex head &eye movement, CN 3, 4,6
• Superior olivary= to stapedius (CN7), tensor tympani (CN v3)
• Cochlea nuclei= cochlea