Development of the NS Flashcards
pre embryonic stage
conception to day 14
zygote begins cells division
7-10 days: embryonic disk (ectoderm, mesoderm, and endoderm)
day 2: 4 cells in a clump
day 4: solid sphere of cells
day 5: 3 cell masses and egg attaches to uterus
embryonic stage
day 15 to week 8
formation of organs
germ layer derivatives
ectoderm: NS, sensory organs, and epidermis
mesoderm: muscle, skeleton, circulatory system, and dermis
endoderm: endocrine glands, lungs, digestive tract, and liver
fetal stage
week 9 to birth
NS continues to develop
myelination begins in the PNS at around week 11
- PNS myelination begins in the motor neurons then sensory
CNS myelination begins around 2 months b4 brith in the sensory neurons then motor
which occurs first: neural tube formation or brain formation?
neural tube formation
neural tube formation (neurulation)
day 18-26 (embryonic)
3rd gestational week: neural plate and neural tube
- 3 visible primary germ layers
- neural plate in middle with depression-neural groove
- neural crest on edge of neural plate
- notochordal plate (from mesoderm) creates the midline and defines where the groove and tube is going to be
–> hallmark sign of immature NS
4th gestational week: neural tube closure
- begins in cervical region then zips up and down with superior neural pore closing first
- day 24-superior neural pore closure and 3 vesicles (prosencephalon, mesencephalon, and rhombencephalon)
- day 26: inferior neural pore closure
what happens when the superior neural pore doesn’t close?
anencephaly
what happens when the inferior neural pore doesn’t close?
spina bifida
is the inner layer of the neural tube gray or white matter?
gray
association plate (AP)
dorsal half
develops into dorsal horn of SC
interneurons
input from sensory neurons
basal (motor) plate
motor neurons
becomes ventral horn
neurons innervate myotome
what is the sulcus limitans?
divides the AP and BP
what develops into the peripheral sensory neurons?
neural crest
what neurons innervate the dermatome?
neurons from the neural crest
- DRG
- pseudounipolar
- somas outside SC/neural tube
- projection onto dorsal horn and dermatome
ectoderm neurons
sensory, motor, an d interneurons
what are the 3 vesicles and what do they become?
prosencephalon: forebrain
- telencephalon–> cerebral hemispheres, cerebral cortex, basal ganglia, and lateral ventricle
- diencephalon–> thalamus, hypothalamus, and 3rd ventricle
mesencephalon: midbrain
- stays same
- becomes midbrain
- has cephalic flexure
rhombencephalon: hindbrain
- metencephalon–> pons, cerebellum, and cerebral aqueduct
–> has pontine flexure
- myelencephalon–> medulla and 4th ventricle
- has cervical flexure separating rhombencephalon and SC
what is the pontine flexure? where is it? why is it important?
in the metencephalon
bends posteriorly while the other bend anteriorly
makes the AP move lateral of the BP and creates the 4th ventricle
when do the gyri and sulcus form?
6-9 months
what is differentiation in the developing NS?
neuroepithelial cells are undifferentiated cells in the NS that become neurons and glial cells
what is neural migration?
neuroepithelial cells find the right target
axon guidance from growth cone projections out of the axon
filopodia at the ends of growth cones test the environment for targets:
- post molecules-guide growth in that direction (anterograde transport)
- neg molecules-retracted (retrograde transport)
what is synaptogenesis?
creation of new synapes decided by the filopodia
dendritic spines-site for synapse formation and determine the number of synapses that can form
determination of muscle fiber types
size principle: smalll recruited first
innervated by large neuron-type 2B
innervated by medium neruon-type 2A
innervated by small neuron-type 1
what is synaptic pruning?
axon retraction or neuronal apoptosis
what is neuronal apoptosis?
programmed death of neurons
what is polyneuronal innervation?
muscles fibers innervate 2 neurons
hallmark of immature NS
