04 Flashcards
DEVELOPMENT
Which neural stalk is first to bud? Around how many days into development?
optic stalk - ~20 days
Which eye structures are first to be formed? Which come later?
lens/cornea early on (when optic stalk touches epi/ectoderm)
-RPE/neural retina later (when optic cup infolds into a ball - an embryological vesicle)
Name three PRE-NATAL developments in a developing neuron
stem cells multiply, migrate to their destiny, and differentiate into the TYPE of neuron they’ll be.
Which five phases of neuron development occur mostly POST-natal? What’s the potential issue with this?
- neuron growth
- sending out of axons/dendrites
- synapse formation
- neurox substance formation
- establishing functional circuits
-all are subject to ENVIRONMENTAL factors, may be affected by environment
What term defines when TOO MANY neurons/dendrites/axons w/ broad distribution are being developed?
What term defines the planned apoptosis of these excess axons etc?
sprouting = EXCESS
pruning back = APOPTOSIS
-trims back axons to innervate smaller areas with MORE synaptic endings
What two conditions/types of cells trigger embryological apoptosis?
1) trailblazer/guide cells: lead the way, then try but fail to differentiate (MASS die-off)
2) required formation of synaptic connections for remaining cells to target dendrites/somas - if not, they die - this continues well after birth (EXTENDED die-off)
T/F: formation of the ganglion cell layer occurs across the entire retina (PP to periphery) at the same time.
–what are the first cells to start moving in retinal development?
FALSE - PP ganglion cells form 5-6wks BEFORE the far peripheral ganglion cells
-GANGLION CELLS - first to start moving. Fibers guide pre-ganglion cells to proper layer
What are the first three cell types that start forming in retinal development?
-What’s the LAST cell type to form?
GANGLION - first, then horizontal, then cones.
RODS are last
-amacrine, muller, bipolar - somewhere in the middle
Compared to the cat, are humans or cats generally more developed at birth? What still needs to happen after birth for proper development?
HUMANS - by far. At 8 months gestation, lots of development (including PRs) - this only happens @ 4 wks old in cats
-still need to form much more synapses and increase length of outer segments
T/F: at birth, ERG has a very long latency
True - improves quickly after first exposure to light, over 100 days
A quantitative change continues in the development of the FOVEA until at least __ yrs of age
Give some observations seen:
- at 6 months?
- 13-15 months?
- 3.8 years?
4 Y/O
- 6 mo: no pit, but a HILL (pigpile of cells)
- 13-15 mos: Gang/bip/ama layer still across fovea, cone density only about 1/4 of adults, OS still shorter than in periphery
3. 8 yrs: fovea is mature, cone packing still in development (until about 6-7 yrs)
What happens to the inner and outer segments of cones after birth?
inner segments: get THINNER (allow tighter packing)
outer segments: get LONGER (increase in photopic/scotopic sensitivity d/t increased photopigment)
T/F: the foveal pit diameter in an infant is larger than in an adult
TRUE - about 2x the adult size - it’s spread over a wider range - narrows to about 2/3mm by the time it’s mature
What is the approximate cone density in an adult? (____cones/mm2)
160,000 cones/mm2
-increases to ~6-7Y/O, adult levels by 13-14Y/O
Number of cones in the foveola: 76,000. Because there were only 37K in the fetus, and the area is smaller in adults, what does this suggest?
-Which test explains increased VA based PURELY on this phenomenon?
enormous PACKING increase of the cones
VEP!! - based PURELY on increased PACKING of the cones
