1/17 Development & Regeneration Of The Nervous System Flashcards
What embryologic layer contributes most to the brain/spinal cord?
Ectoderm
What does ectoderm become?
Neural plate (folds dorsally until borders touch to make:)
Neural crest (borders)
Neural placode
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
(excluding derivatives of neurogenic placodes)
What are neurogenic placodes associated with?
Cranial sensory systems:
Olfactory
Lens
Trigeminal
Otic
Geniculate
Petrosal
Nodose
What does the olfactory placode form?
Not neurogenic
Olfactory epithelium
What does the lens placode form?
Not neurogenic
Lens of the eye
What does the trigeminal neurogenic placode form?
Trigeminal ganglion
What does the otic neurogenic placode form?
Cochlear and vestibular
What does the geniculate neurogenic placode form?
Geniculate ganglion & distal CN VII
What does the petrosal neurogenic placode form?
Inferior glossopharyngeal ganglion & distal CN IX
What does the nodose neurogenic placode form?
Nodose ganglion & distal CN X
What does the neural tube separate from?
Separates from ectoderm
What are the openings in the neural tube?
Cranial neuropore
Caudal neuropore
What does the neural tube form?
The central nervous system
What does the neural tube initially have, what happens to these?
Initially has 3 vesicles which separate into 5 vesicles
What are the 3 vesicles of the neural tube?
Forebrain (prosencephalon)
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)
What are the 5 vesicles of the neural tube?
Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon
What does the forebrain of the 3 vesicle stage become in the 5 vesicle stage?
Telencephalon
Diencephalon
What does the midbrain of the 3 vesicle stage become in the 5 vesicle stage?
Mesencephalon
What does the hindbrain of the 3 vesicle stage become in the 5 vesicle stage?
Metencephalon
Myelencephalon
What does the telencephalon become in an adult?
Cerebrum
What does the Diencephalon become in an adult?
Thalamus, hypothalamus, epithalamus, and retina
What does the mesencephalon become in an adult?
Midbrain
What does the metencephalon become in an adult?
Pons and cerebrum
What does the myelencephalon become in an adult?
Medulla oblongata
What are the types of neural tube defects?
Anencephaly
Spina bifida
What happens in anencephaly?
Cranial neuropore does not close
What happens in spina bifida?
Caudal neuropore does not close
What reduces neural tube defects?
Folic acid
What happens to the neural tube in the 4th week?
differentiates into dorsal (alar plates) and ventral (basal plates) portions
What are the dorsal and ventral portions the neural tube differentiates into? What do they do?
Alar plates – Dorsal – Sensory
Basal plates – Ventral – Motor
Where is the dorsal root ganglion come from?
The neural crest cells
What is holoprosencephaly?
Failure of the forebrain to separate into distinct hemispheres. (regionalization)
What is the severity of holoprosencephaly?
Varying levels of severity
Most severe cases will not support life.
What is the appearance of a person with holoprosencephaly?
Facial deformities primarily affect the eyes, nose and upper lip
What are the causes of holoprosencephaly?
Causes are teratogens (i.e. alcohol) and/or genetic (loss of function mutations)
Trisomy 13 is a common cause.
What are the ways in which cell bodies of neuron migrate?
Radially or tangentially
What is radial migration of neurons
from ventricles toward pial surface.
• Except for cerebellum (pia to ventricle)
• Layers of cerebral cortex build from inside to out
What is tangential migration of neurons?
Involves interneurons
What is lissencephaly?
Failure of neuronal migration
Appears as a smooth brain
Leads to intellectually disability
Often accompanied by microencephaly
What is the cause of lissenephaly?
Viral infections or genetic mutations
What are the types of classifications of injury of peripheral neurons?
Seddon vs sunderland
What are the classifications of neuronal injury according to seddon?
Neurapraxia, axonotmesis, neurotmesis
What is neurapraxia?
Transient loss of function with minimal myelin damage
What is axonotmesis?
Longer term loss of function with damage to axons while the epineurium remains intact
What is neurotmesis?
Complete disruption of a nerve
What are the classifications of neuronal injury according to sunderland?
1st degree-5th degree
What is the 1st degree of neuronal damage?
Neurapraxia
What is the 2nd degree of neuronal damage?
Damage of axon with intact connective tissue
What is the 3rd degree of neuronal damage?
Damage of axon and endoneurium
What is the 4th degree of neuronal damage?
Damage of axon, endoneurium, and perineurium
What is the 5th degree of neuronal damage?
Neurotmesis
Damage of all layers
Can the 1st degree of neuronal injury heal?
Heals in minutes to weeks without additional care
Can the 2nd degree of neuronal injury heal?
Heals at a rate of 1mm/day by following the existing connective tissue
Can the 3rd degree of neuronal injury heal?
Possible surgery.
Maybe heal at a rate of 1mm/day by following the existing connective tissue (usually incomplete)
Can the 4th degree of neuronal injury heal?
Surgery will be needed. Recovery is poor and slow.
Can the 5th degree of neuronal injury heal?
Surgery may be attempted. Recovery is unlikely.
How do axons grow?
growth cones that sense guidance cues as to where they should grow
What are the types of cues for axonal growth?
Adhesive, tropic, modulary
What are adhesive cues?
found on surfaces or extracellular matrix (toward target cell)
What are tropic cues?
attractants or repellants that cause intracellular changes in cytoskeleton growth
What are modulatory cues?
change the sensitivity of the growth cones
Can the CNS regenerate?
majority of the CNS will not regenerate if damaged
Olfactory epithelium, subventricular zone, and subgranular zone can regenerate
Increased by excercise
How does the olfactory epithelium regenerate?
allows for the regrowth of neurons which reattach to the CNS
How does the subventricular zone regenerate?
regenerates new cells that migrate to the olfactory bulb
How does the subgranular zone regenerate?
contains stem cells that regenerate into part of the hippocampal circuitry
What are the types of nerve damage?
Anterograde (Wallerian) degeneration affects the axon away from the cell body.
Retrograde degeneration affects toward the cell body
Axonal skeleton disintegrates and the membrane breaks apart
Macrophages infiltrate the myelin sheath to clear the debris
How does PNS regeneration occur?
Schwann cells accompany the macrophages and create a tube that produces growth factors.
Within 4 days the nerve send out new growth
The proximal portion develops a growth cone and will regrow at about 1mm per day.
