Neuroscience Week 2: Development of the CNS & PNS Flashcards by Jay Sandoval

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)

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Notochord

Forms the embryonic central axis

Induces neural plate formation

Establishes central column of spine: degenerates to nucleus pulposus

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Neurulation day 17

early regression of primitive streak and the development of the neural plate

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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

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somites derived from?

Paraxial Mesoderm

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Somites become

Sclerotome
Myotome
Dermatome

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Sclerotome becomes

bone and cartilage

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Myotome becomes

skeletal muscle

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Dermatome becomes

dermis

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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

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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

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Gastrulation overview

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Germ layer derivatives

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Neurulation Summary

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Fate map of the early neural plate

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Fatemap of the early neural tube overview

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Fate of the notochord

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Brain vesicle formation Overview

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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

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Identify

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Primary brain vesicles

Prosencephalon

Mesencephalon

Rhombencephalon

Neural tube

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Secondary brain vesicles

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelecephalon

Neural tube

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Identify

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Flexures

Cephalic flexure

Cervical flexure

Pontine flexure

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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