Neuroscience Week 2: Development of the CNS & PNS Flashcards
Neurulation overview
Notochord induces overlying ectoderm to develop the neural plate
The neural plate folds into the neural tube and the neural crests are pinched off
the neural tube derives the CNS
the Neural crests derive the PNS + select other cells (e.g. melanocytes)

Notochord
Forms the embryonic central axis
Induces neural plate formation
Establishes central column of spine: degenerates to nucleus pulposus

Neurulation day 17
early regression of primitive streak and the development of the neural plate

Neurulation Day 18
neural plate invaginates to form neural groove that dips centrally
and
the neural folds that peak laterally
and the neural crests are located at the tips of the neural folds
and
somite development in the mesoderm

somites derived from?
Paraxial Mesoderm
Somites become
- Sclerotome
- Myotome
- Dermatome
Sclerotome becomes
bone and cartilage
Myotome becomes
skeletal muscle
Dermatome becomes
dermis
Neurulation Day 21
primitive streak nearly completely regressed
neural groove starts to fully fold to form the neural tube which enters the mesoderm
it closes off in the center first
neural tube is closed and resides in the mesoderm

Neurulation Day 23
Much more of the neural tube is closed
the anterior cranial neuropore closes ~ day 24
The posterior caudal neuropore closes ~ day 26
somites form ridges under the ectoderm
neural crest cells above the neural tube (neural crest produce BMP and WNT) signal the neural tube to form the roof plate and bilateral allar plates
the floor plate of the neural tube is signaled by the notochord to form by SHH and signalled to form the bilateral basal plates as well

Gastrulation overview

Germ layer derivatives

Neurulation Summary

Fate map of the early neural plate


Fatemap of the early neural tube overview

Fate of the notochord

Brain vesicle formation Overview

Brain Vesicle formation
The neural tube differentiates into brain vesicles
The primary brain vesicles have developed by 4 weeks
secondary brain vesicles have developed by 5 weeks
Identify


Primary brain vesicles
Prosencephalon
Mesencephalon
Rhombencephalon
Neural tube
Secondary brain vesicles

Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelecephalon
Neural tube

Identify


Flexures
Cephalic flexure
Cervical flexure
Pontine flexure

Flexure for 4th ventricle
Pontine flexure is 4th ventrical floor

Optic vesicle becomes
Optic cup
Optic Stalk
Optic cup becomes
Retina
Optic Stalk becomes
Optic nerve
brain vesicle formation at 6 months

Insula remains exposed

Cerebral cortex derived from
Telencephalon
Thalamic Areas Derived from
Diencephalon
Midbrain derived from
Mesencephalon
Pons + Cerebellum derived from
Metencephalon
Medulla Oblongata derived from
Myelencephalon
Spinal cord derived from
Neural tube
Regional specification

Continued regional specification

Neural tube defects
anomalies of neural tube folding
2nd is most common cause of congenital anomaly (2nd to cardiac)
Mainstay of neural tube defect prevention
Folic acid supplementation up to 4 mg per day
Important diagnostic marker of neural tube defects
Alpha-fetoprotein (AFP) is an important diagnostic marker because it escapes into the amniotic cavity
Valproic acid
neural tube teratogen (anti-epileptic drug)
Neural Tube Defects: Anencephaly
- acrania (absence of skull)
- failure of cerebral hemispheres to develop (forebrain)
- angiomatous stroma (undifferentiated neural tissue that mimics appearance of brain is present above the orbits and skull base and is exposed to the environment
- infants survive just a few hours and never achieve consciousness
Neural Tube Defects:: Encephalocele
herniation of meninges and brain matter
associated with hydrocephalus and microcephaly
occipital encephalocele a key feature of Meckel-Gruber syndrome
Merkel-Gruber Syndrome
autosomal recessive disorder
cystic renal dysplasia
polydactyly
occipital encephalocele
cephalocele
herniation of the meninges only without brain matter
Neural Tube Defects: Rachischisis , spinal dysraphism
spinal defects
Neural Tube Defects: Rachischisis
Spina bifida w/ myeloschisis
a failure of spinal cord development
spinal cord is flattened along the dorsum of the bodies surface (no neural root plate present)
Not a survivable defect
Spina Bifida w/ myeloschisis AKA
Myelocele
Spina Bifida w/ myeloschisis
Form called rachischisis
not survivable

Spina Bifida w/ Meningocele AKA
Spina Bifida Cystica

Spina Bifida Cystica w/ Meningocele
cyst like meningeal sac protruding through vertebral arch defect
neural structures intact and in the right location
can experience functional deficits similar to meningomyelocele

Spina Bifida w/ Meningomyelocele AKA
Spina Bifida Cystica
Spina Bifida w/ Meningomyelocele
displaced meningeal and neural structures
often results in paralysis below the lesion
allow the spinal cord folds appropriately the displacement results in severe functional deficits

Associated syndromes with Spina Bifida Manifesta
Chiari type II malformation - Lumbar meningomyelocele
Dandy walker - Spina Bifida
Spina Bifida Occulta
no meningeal protrusion but a failure of vertebral arch fusion that is covered in skin
can have hairy patch, dimple or birthmark
can be a harbinger of a tethered cord syndrome

Tethered Cord syndromes
traction damage to the caudal spinal cord e.g. filum terminale thickening or lipoma which commonly cause bladder incontinence

Lumbar punctures

Neural tube internal organization
Basal plates and alar plates fate
Alar plates - Dorsal sensory horns nerve roots
Basal plates - ventral motor horns nerve roots

Dermatome
axial dermis
Myotome
paraspinal and abdominal musculature
Sclerotome
spine and posterior basal skull
Neural tube zones
- Ventricular
- Intermediate
- Marginal zone

Ventricular zone produces
Ependymal layer
Intermediate zone produces
Gray Matter (neurons)
Intermediate zone AKA
Mantle zone
Marginal Zone Produces
White Matter
Glioblasts (Glia)
Alar plate and Basal plate
Alar - dorsal horn
Basal - Ventral horn

Dorsal nerve root ganglion
cluster of pseudounipolar neurons and grows centrally into the alar plate

Ventral Nerve Root
grows from the basal plate is a motor root
Overview of Development of spinal cord and Nerve Roots

Spinal nerve roots

Spinal cord inducing centers

Forebrain Signaling Centers

Neural Crest Cell Differentiation Overview
10 listed

Neural Crest Derivatives
- PNS = Glial Cells + Schwann Cells
- Meninges: Pia and Arachnoid
- Melanocytes
- Enteric Nervous System
Cranial
- Pharyngeal Arch Components
- Musculoskeletal Structures
- Cranial nerves
Trunk and Lumbosacral
- Dorsal Root Ganglia
- Sympathetic chain ganglia
- Adrenal Medullary Cells
- Prevertebral ganglia
Neural Crest Cell Migration

Neural Crest cells as the 4th germ layer

Neural Crest cells and dorsal root and autonomic ganglia

Abnormal Development of CNS / PNS

Prevention of Neural Tube Defects

Failures of anterior Neuropore Closure
2 listed
Anencephaly
Encephalocele
Anencephaly

Encephalocele

Caudal Neural Tube Defects

Failure of posterior neuropore closure
Spina Bifida Occulta
Spina Bifida Cystica (meningocele and meningomyelocele)
Spina Bifida w/ myeloschisis
Spina Bifida Occulta

Spina Bifida Cystica

Non-communicating hydrocephalus

Chiari Malformations

Hydromelia & Syringomyelia

Dandy-Walker Syndrome

Holoprosencephaly HPE Spectrum

Holoprosencephaly Summary

Detection and treatment of NTDs

Maturation of primary brain divisions

Lissencephaly

Ulegyria

Developmental Reflexes

Pyrimidal Tract and myelination

APGAR Scoring system for newborns

Germinal Matrix Hemorrhage

Summary of CNS Developmental Defects/Injuries

Neurocutaneous Disorders

Neurofibromatosis Type I

Neurofibromatosis Type I findings

Neurofibromatosis Type II

Sturge-Weber Disorder

Sturge-Weber Syndrome Findings

Tuberous Sclerosis

Tuberous Sclerosis Findings

Von Hippel-Lindau Syndrome

Von Hippel-Lindau Syndrome Findings

Summary of Neurocutaneous Disorders

dura mater derivative of
mesoderm derivative
holoprosencephaly
mainly week 5 failure of midline structures to segregate
elevated alfa-feto protein can indicate?
& causes of false positives
neural tube defect
- miscalculation of gestational age
- twins
- maternal tumor or liver disease
high levels of AchE in Amniotic fluid
can indicate NTD
When does the rostral neuropore close?
day 24/25
When does the caudal neuropore close?
Day 26/27