Embryology 6 - Neurulation Flashcards
Central nervous system (CNS)
includes ______ & ______
Brain
& Spinal cord
Peripheral nervous system (PNS)
includes ____ & _____
Sensory-somatic nervous system
Autonomic nervous system
What are the 3 germ layers?
- Endoderm (innermost-yellow)
- Mesoderm (middle-red)
- Enctoderm (outermost-blue)
What does the endoderm give rise to?
- GI tract (inner lining)
- GI-linked organs (liver, pancreas)
What does the mesoderm give rise to?
- Anything between ecto & endo
- e.g. muscle, bone, blood, kidney
What does the ectoderm give rise to?
* Skin (epidermis) Nervous system (neuron, glia)
During the 3rd week of development,
the ectoderm cranial to the node becomes
_________________
Neural plate
The neural plate gives rise to
____ & ____
Neural tube
&
Neural crest
The neural crest detaches & migrates/scatters
from edge of neural plate to become _____
the PNS
(green-neural crest)
The neural tube gives rise to _____
the CNS
(Brain & spinal cord)
The mesoderm surrounds the neural tube
& forms ______
Vertebrae
(mesoderm in red)
Neural Tube Defect (NTD)
is caused by _______
failure in neural tube and/or vertebra closure
- Common birth defects (1 in 1,000)
Normal closure of both neural tube (NT) & Sclerotome shown in pic
Two types of Neural Tube Defects (NTD)
- Closed NTD
- Open NTD
Spina bifida occulta
(Closed NTD)
- Vertebra fail to fuse (NT still in place)
- Mostly asymptomatic
- Typically at L5-S1 levels
- **Often marked by patch of hair over affected area
Spina bifida cystica
(Closed NTD)
- NT herniates from unclosed vertebra
- Causes neurological deficits
Two types of Spina bifida cystica
- Meningocele
- Meningomyelocele (more severe)
Open NTD
- Neural plate fails to close
- Neurons exposed to amniotic fluid –> Necrosis
Anencephaly
- Due to anterior neuropore closure (future forebrain) failure
- May be born alive (brain stem still intact)
Intake of _______ can prevent NTD
Folic acid
- Daily intake of FA by mothers reduces NTD by ~70%
- 400 mcg/day recommended for women of reproductive age
- Mechanisms not fully understood
Neuroepithelial cell generates _____ & _____
neuron & glia
Layers of Neural Tube (NT)
- Marginal layer
- Mantle layer
- Neuroepithelial layer
White matter vs. Gray matter
White matter - most cell axons located here
Gray matter - most cell bodies located here
Dorsal-ventral differentiation of NT
Dorsal –> Alar plate –> Sensory input
Ventral –> Basal plate –> Motor output
Spinal nerve contains both
____ & ____ neurons
Sensory & motor
Dorsal root ganglia
(neural crest)
Receives sensory signals from peripheral/neural tube
Intervetebral opening
Where the spinal nerve exits away from the CNS
_____ of spinal cord shifts relative to vertebra
Terminal end
________ grows much faster than spinal cord
Vetebral column (and dura)
Intervetebral opening CAN or CAN’T
change location?
CAN’T change location.
BUT, the length of the spinal nerves can increase/change.
Lower part of spinal cord has longer axon extensions that extend lower down vetebral column.
End of spinal cord at birth?
L3
Cauda equina
L4-S4
(Where lumbar puncture occurs to avoid damaging neural tissue)
Tethered cord syndrome
Abnormal attachment of spinal cord to vetebra
Results in downward stretch of spinal cord
(Often caused by spina bifida)
Neurological symptoms: weakness in legs, low back pain, incontinence
Brain is derived from ______ end of neural tube
Cranial
Telencephalon
- Most cranial
- Precursor to cerebral hemisphere
- Enlarges the most, covers entire brain
Diencephalon
Protrudes into retina
Holoprosencephaly (HPE)
Brain & face abnormalities due to loss of midline structures
Causes:
- Mutation in Sonic Hedgehog (SHH) gene
- Defective cholesterol biosynthesis (Smith-Lemli-Opitz syndrome)
Sonic Hedgehog (SHH) signaling
Signal-sending cell –> SHH protein combines with cholesterol –> SHH receptors on Signal-receiving cell (PTCH/SMO) –> activates transcription factor for turning on/off genes
Neural crest –> _____
PNS
(e.g. Melanocytes, enteric ganglia, Meninges, Schwann cells, Chromaffin cells)
Neural crest from cranial region –> _______
Facial bones
Middle ear bones
Parafollicular cells of thyroid
Dermis of skin
Connective tissues around eyes, muscles of iris, cornea
Dermis, bones, connective tissues, muscle in the trunk are from _____
MESODERM
Neurocristopathy
Disease arising from abnormal development of neural crest
Hirschsprung’s Disease
(Aganglionic megacolon)
Cause: Deficiency of enteric ganglia (neural crest derivatives)
Pathophys: Blockage of colon due to impaired peristalsis
Signs/symptoms: Constipation, vomiting, abdonminal swelling, growth retardation
(Observed 1-2 days after birth.. unable to poop!)
Treatment: surgical removal of affected region of colon
DiGeorge Syndrome
(Velocardiofacial syndrome, 22q11.2 deletion syndrome)
Hearing loss, heart defects, cleft palate, craniofacial anomalies, and learning problems
How do you know which tissues came from neural crest?
Classic experiments: Chick-qual chimera (1970s)
Implanted part of neural crest of quail into chick embryo & observed development.
Quail cells stain differently from chick cells
