2nd Half of Quarter

Question 1

What are the three parts of the tri-laminar embryo?

Answer 1

Ectoderm (neuroectoderm)
mesoderm
Endoderm

Question 2

Ectoderm

Answer 2

• once the tri-laminar embryo folds inward this is on the outside
• surface ectoderm is skin, hair, nails, cutaneous, etc.
• INNER EAR
• Membranous Labyrinth
• Neuroectoderm: forms the brain, sensory system, these start on the outside, obviously on the inside now

Question 3

Mesoderm

Answer 3

• in the middle of the three layers

- skull, muscles, connective tissue, cartilage, skeleton

Question 4

Endoderm

Answer 4

• bottom layer, when it all folds in this is on the inside
• epithelia, mostly the gut, lungs, middle ear, eustachian tube, what begins on the inside, stays insides
• continuos with the meatal skin, skin of the ear canal

Question 5

Otic Placode

Answer 5

• thickening of the surface ectoderm, you see developing hindbrain, it used to be part of the ectoderm, now folded into the mesoderm
• folding in from surface ectoderm, closer to form the neural tube, this will become the central nervous systems
• tube after folding in separates from the surface, becomes a tube, head becomes a brain the part that continues down is the spinal column
• humans 22 days

Question 6

Otic Pit

Answer 6

• otic placode becomes this
• start of the membranous labyrinth (eventually will become this)
• surrounded by mesoderm in which it is folding in to
• mesoderm is going to form the osseous labyrinth around the membranous labryrinth

Question 7

Otocyst

Answer 7

-otic pit then becomes this, also inside of mesoderm, begins to elongate and form two regions
- by only 8 weeks it looks pretty adult like
- this growing is due to the proliferation of cells
- the other process that happens during development, absorption - how do you take a sphere -> the shape it is at adulthood
– folding and programmed cell death
folds into two separate divisions - utricular and saccular division.

Question 8

Utricular division

Answer 8

further divides into the semi-circular canals, utricle, endolymphatic duct & sac

Question 9

Saccular division

Answer 9

further divides into saccule and cochlear duct

Question 10

branchial arches

Answer 10

• two bumps on the side of the head during development
• mandibular (1st Branchial) Arch
• hyoid (2nd) Arch
• directly between these is the 1st branchial groove

Question 11

branchial groove

Answer 11

• where the ear canal forms

- meatal plug - thickening of ectoderm, inside the branchial groove, eventually eroded

Question 12

auricular hillocks

Answer 12

• bumps on the 1st and 2nd arches, this forms into the pinna
• surface of the developing embryo is ectoderm, what gives the auricle its structure is the cartilage underneath (mesoderm), this is what gives the pinna its stricter plus the skin on top that conforms to it

Question 13

Membranous labyrinth is surrounded by…

Answer 13

• mesoderm, this part is going to eventually become the osseous labyrinth
• stria vascularis is in the process of development and the region that is goin to become the organ of corti

Question 14

Inner ridge

Answer 14

• closer to the modiolas, greater epithelial ridge
• develops into:
• • spiral limbus
• • inner sulcus
• • inner hair cells
• • inner pillar cells

Question 15

Outer ridge

Answer 15

• lesser epithelial ridge, this is closer to the developing stria vascularis
• tectoral membrane is going to form on top of these
• outer pillar cells
• dieters’ cells
• hensen cells
• outer hair cells

Question 16

What is the primitive organ of corti called?

Answer 16

The kollicker’s organ

Question 17

Which portion of the basilar membrane develops first?

Answer 17

Base develops before apex

Question 18

Stiffness gradient

Answer 18

• changes in width and stiffness of the basilar membrane
• more narrow but thick (height), (size of the canal is bigger int he base) in the base and (size of the canal is smaller in the apex) thin (height) & wide at the apex
• gradient goes up from apex to base in stiffness 1-100/1000x more stiff at the base depending on the species

Question 19

Type 1 spiral ganglion cells

Answer 19

• radial afferents

- divergent, means many of these come in contact with same hair cell

Question 20

What is the driving force through a hair cell?

Answer 20

• chemical force between endolymph and perilymph, more potassium in scala media (endolymph) and more sodium in the scala vestibuli & scala tympani (perilymph)
• HC has ion channels, path of least resistance

Question 21

What is the driving force to transduction?

Answer 21

Concentration ratio and voltage differences

Question 22

What are the two resistors to hair cell transduction?

Answer 22

• 1 (variable) transduction apparatus, depends on deflecting the hair cell bundle, changes with deflection