Development and Regeneration Flashcards
what germ layer is the neural plate, crest, and placode made from?
ectoderm
what is neurulation?
the neural plate folds dorsally until the borders touch to form a hollow tube (neural tube)
where do neural crest cells migrate?
laterally and ventrally
what do neural crest cells form?
most of the peripheral nervous system including sensory and autonomic ganglia
what part of the peripheral nervous system is not formed from the neural crest cells?
neurogenic placodes
what are neurogenic placodes associated with?
cranial sensory systems
what cranial sensory systems are associated with neurogenic placodes?
trigeminal, otic, geniculate, petrosal, nodose
what are the openings of the neural tube?
cranial and caudal neuropore
what does the neural tube form?
the CNS
what are the 3 initial vesicles of the CNS
prosencephalon, mesenchephalon, rhombencephalon
what are the 5 initial vesicles of the CNS
telencephalon, diencephalon, mesencephalon, metenchephalon, myelencephalon
what is anencephaly
defect that occurs when cranial neuropore does not close
what is spina bifida
defect that occurs when caudal neuropore does not close
what reduces defects of the neuropores?
folic acid
during the 4th week, what does the neural tube differentiate into?
dorsal and ventral portions
what is the dorsal portion of the neural tube?
alar plates, sensory
what are the alar plates crucial for?
reflexes
what is the ventral portion of the neural tube?
basal plate, motor
what is the dorsal root ganglion from?
neural crest cells
what is holoprosencephaly?
failure of the forebrain to separate into distinct hemispheres
where do holoprosencephaly facial deformities affect?
the eyes, nose, and upper lip
what are causes of holoprosencephaly?
teratogens and/or genetics
trisomy 13
where can cell bodies migrate?
radially or tangentially
what direction is radial migration?
from ventricles toward pial surface (built from the inside to out)
what direction is tangential migration?
parallel with ventricular system
when is radial migration not toward the pial surface?
in the cerebellum (pia to ventricle)
what is lissencephaly?
failure of neuronal migration, appears as a smooth brain
often accompanied by microcephaly
what are causes of lissencephaly?
viral infections or genetic mutations
what are the three Seddon classifications of injury?
neurapraxia, axonotmesis, neurotmesis
neurapraxia
transient loss of function with minimal myelin damage
axonotmesis
longer term loss of function with damage to axons while the epineurium remains intact
neurotmesis
complete disruption of a nerve as well as coverings
what is Sunderland’s 1st degree of injury?
neurapraxia
heals in minutes to weeks
what is Sunderland’s 2nd degree of injury?
damage of axon with intact CT
heals 1mm/day by following existing CT
what is Sunderland’s 3rd degree of injury?
damage of axon and endoneurium
possible surgery, usually incomplete healing
what is Sunderland’s 4th degree of injury?
damage of axon, endoneurium, and perineurium
surgery needed, poor recovery
what is Sunderland’s 5th degree of injury?
damage of all layers
recovery is unlikely
what do growth cones do in axons?
send guidance cues as to where they should grow
adhesive cues
found on surfaces or extracellular matrix
tropic cues
attractants or repellants that cause intracellular changes in cytoskeleton growth
modulatory cues
change the sensitivity of the growth cones
can the CNS regenerate?
mostly no
olfactory epithelium regeneration
allows for regrowth of neurons which attach to CNS
subventricular zone regeneration
regenerates new cells that migrate to the olfactory bulb
subgranular zone of the hippocampus regeneration
contains stem cells that regenerate into part of the hippocampal circuitry
anterograde nerve degeneration
affects the axon away from the cell body
retrograde nerve degeneration
affects the axon toward the cell body
what happens when the nerve is damaged
axonal skeleton disintegrates, membrane breaks, macrophages infiltrate myelin sheath to clear the debris
how does PNS regeneration occur?
Schwann cells accompany macrophages and create a tube that produces growth factor
proximal portion of PNS regeneration
develops a growth cone and will regrow about 1mm/day
