Development Of The Nervous System Flashcards
What are the germ layers?
Ectoderm
Endoderm
Mesoderm
What dies the endoderm develop into?
GI tract, liver lungs
What does the mesoderm develop into?
Urogenital system, CV system, muscles, bone
What parts of the nervous system develop from
Surface ectoderm: anterior pituitary, lens, cornea
Neural tube: posterior pituitary, retina, optic nerve, brain, spinal cord
Neural crest cells: adrenal medulla, autonomic and sensory nerves
How does the 3rd week significant to neural development?
3rd week development
-Notochord induces the cells of the overlying ectoderm to differentiate into neuroectoderm
- Neuroectoderm contains neural plate and neural groove
- Neural Tube develops and neural crest cells migrate
The neural tube differentiates into the CNS
The neural crest gives rise to cells that form most of the PNS & ANS
Explain neurulation
- By the end of the 3rd week the neural plate consists of a wide cranial portion—> future brain and a narrow caudal portion —> future spinal cord
- As somites continue to develop and be added at the trunk region the future spinal cord region of the neural plate is forced to lengthen
- eventually the neural folds aapproximate and begin to fuse closing the neural groove
- Starts on day 22 at the occipital and cervical region
- As the tube fuses the neuroectodermal cells along the crest of the measurable folds separate
- Neural crest cells from the junction of surface ectoderm and neuroectoderm pinch off and come to lie along the sides of the neural tube
- A narrow canal canal is now present which gets smaller as the cells in the wall of neural tube proliferate
- During neurulation, the ends of tube initially remain open to the amniotic cavity- these openings are the rostral and caudal neuropores
What are the primary brain vesicles?
- Forebrain or prosencephalon
- Midbrain or Mesencephalon
- Hindbrain or Rhombeephalon
What are the secondary brain vesicles?
- telencephalon
- diencephalon
- mesencephalon
- metencephalon
- myelencephalon
Summarize the initiation of the spinal cord development
Initially, wall of the Neural tube is lined by a thick layer of NEUROEPITHELIUM which forms the ventricular zone(gives rise to all the neurons and macroglia of the spinal cord)
- Marginal zone forms superficial to ventricular zone
- cells in the ventricular zone multiply and newly formed cells migrate to form the intermediate zone (mantle layer) between the ventricular zone and the marginal zone
- Cells in the intermediate zone differentiate into neuroblasts which will form nucleus
In spinal cord development, what regions does the intermediate zone/mantle thicken?
The intermediate /mantle zone thickens in 4 regions
Pair of altar plates dorsally (dorsal horns)and dorsal gray columns
Pair of basal plates ventrally (ventral somatic motor and lateral horns)
- Ventral somatic motor - Lateral visceromotor
The sulcus limitans separates the altar and basal plates
Describe development of gray and white matter of the spinal cord
- Intermediates (mantle) layer forms spinal gray matter
- Marginal layer forms white matter
- Cavity of neural tube forms the central canal
- ventricular zone forms the ependymal lining if the central canal
What are the neural tube derivatives?
CNS- brain, brain stem, spinal cord
PNS- Somatic motor system, preganglionic visceral motor portion
What are the neural crest derivatives?
- Ganglion cells of the PNS
- Sensiry ganglia of cranial nerves
- DRG of spinal nerves
- Sympathetic ganglion cells
- Parasympathetic ganglion cells
- Schwann cells (myelin in PNS)
- Leptomeninges (pia-arachnoid)
Outline formation of microglia cells
Mesenchymal of neural tube—> Mesenchymal cell—> microglia cell
Outline development of of a neuron
Neuroepithelium—> a polar neuroblast—> bipolar neuroblast —> unipolar neuroblast—> neuron
Outline astricyte development
Neuroepithelium—>glioblast (spongioblast)—> astroblast—> protoplasmic astcyte and fibrous astrocytes
Outline the development of the oligodendrocyte
Neuroepithelium —> glioblast(spongioblast)—> oligodendroblast—> oligodendrocyte
Outline the development of of the ependymal and choroid plexus epithelium
Neuroepithelium—> ependyma and epithelium of choroid plexus
The cells of the CNS are derived from two sources…
Mesenchyme
Microglia cell
Neural crest diagrams
Come back to do this diagram
How are meninges formed?
Adjacent mesenchyme condenses to form a primordial meninx with two layers
- Inner—> derived from neural crest—> leptomeninges( Pia & arachnoid mater)
- Outer—> derived from mesoderm —> dura mater
Summarize veterbra development to a sentence
Each vertebra develops from mesenchyme of the pair of Sclerotomes which surround the neural tube and the notochord at each level
What are the regions of the Sclerotome?
- Caudally placed, densely packed cells—> forms intervertebral disc and part of vertebral body
- Cranially placed, loosely packed cells—> forms vertebral body together with rest of dense tissue
Intervertebral disc develops from the caudal dense part of the Sclerotome
It forms the annulus fibrosus of the disc
-Hemi-vertebra occurs if one of the pairs of Sclerotome fail to develop
Summarize the formation of the vertebral column
The remnants of the Sclerotome form the mesenchymal primordium of the vertebra
-Appears at the 5th week begins to convert to cartilage and later bone by the end of the 7th week when when the first primary ossification centers appear
Three ossification centers:
- Centrum —> body and
- Two neural arch centers
The neural arch (future vertebral arch) is first to ossify
What are neural tube defects? What causes them?
Genetic and environmental factors are thought to be involved in the production of NTDs. Some medications like anticonvulsants and valproic acid May also cause NTDs
Prophylaxis with folic acid is recommended for all women of reproductive age
What is spina bifida?
Varying degrees of failure of neural tube formation involving the caudal neurophore with accompanying defects in formation of meninges and neural arch of vertebrae
What are the defects of Spina Bifida?
- Most defects results from failure of fusion of one or more neural arches of the developing vertebrae during the 4th week
- Defects involving the embryonic neural arches are refferred to as spina bifida; subtypes of this defect are based on the degree and pattern of the NTD. The term spina bifida denotes non-fusion of the halves of the embryonic neural arches, wh8ch is common to all types of spina bifida
What are the types of spina bifida?
Occulta
Cystia with meningocele
Cystia with meningomyelocele
Cystia with myeloschisis
Summarize spina bifida-occulta
- No bulge over the bony Defect
- No neurological defects
- A tuft of hairs or skin dimple may be present(most common lumbosacral area)
Summarize spina bifida-cystia with meningocele
- Bulge is seen over the defect
- Contains meninges & CSF in the subarachnoid space
Summarize spina bifida with cystia with meningomyelocele
- bulge is seen over the defect
- contains meninges, cord & nerves
Summarize spina bifida- cystia with myeloschisis
-Skin and bony defect with “open” spinal cord”, seen as mass of neural tissue
Outline in detail spina bifida- cystia with meningocele
Lumbar presentations are most common
The cyst usually contains dura and arachnoid mater and CSF
Neurological deficits relatively uncommon
Explain in detail spina bifida - cystia with meningomyelocele
- Membranous sac can be observed which is filled with CSF
- Remnants of neural tissue can also be observed
- Sac contains dysplastic spinal cord, nerve roots, meninges, and vertebral bodies
- Severe neurological deficits are common ranging from paralysis, sensory loss, bladder dysfunction
What Is macroceohaly?
(Image looks like the bottle juice guy)
- Failure of rostral neuropore to close
- Absence of a large part of brain and skull
- Usually embryo ps will not make it to full term (miscarriage), if born they do not live for long (days)
- Exact cause unknown-environmental toxins, lack of folic acid
What is hirschprung disease?
Rare condition where stool becomes stuck in the bowels.
Mainly affects babies and young children.
This causes the large intestines to increased in size
