Embryology of nervous system Flashcards
What is invagination
Epiblast cells migrate towards primitive streak
Detach from the epiblast and slip beneath it by passing through the primitive streak
What is the notochordal plate
Prenotochordal cells that become a part of the hypopblast layer
What causes the development of the notochord
The pre-notochordal cells migrated cranially until they reached the prenatochordal plate
What shape does ectoderm have after gastrulation
Disc shape
Broader at cephalic end
Narrower at the caudal end
What is the neural plate
Develops in midline of the ectoderm due to notochord
Lateral edges elevate to form neural folds
Mid region of the neural plate forms the neural groove
The neural folds fuse in midline to form neural tube
What is the neuropore
Opening of the neural tube
Cranial end = cranial neuropore and vice verca
communicate with amniotic cavity
When do the neuropores close
Cranial neuropore should close about 25 days
Caudal neuropore should close about 28 days
When is neurulation finished
Once neuropores have clsoed
What is anencephaly
Neural tube fails to close in the cranial region
Most of brain fails to form
Lethal
Brain is underdeveloped/absent
What is spine bifida
Neural tube fails to close in caudal region
Spinal cord/nerves exposed
Usually in lumbosacral region
What is spina bifida occulata
defect in vertebral arch
No bony protection to the spinal cord
Often marked with a patch of hair
Usually in the sacral region
What is meningocele and myelomeningeocele
Severe defect Neural tissue and/or meninges protrude through a defect in the vertebral arch and skin Form cyst-like sacs Mostly in lumbosacral region Result in neurological deficits
What parts of the neural tube become the brain and spinal cord respectively
Cranial end of neural tube = brain
Rest of the neural tube = spinal cord
What are the two halves of the neural tube
Basal plate (ventral) Alar plate (dorsal)
What do neuroblasts form
Mantle layer around lumen of neural tube forming grey matter
Later emerge into marginal layer and become myelinated forming white matter of spinal cord
What forms the senory areas and motor areas
Basal plates form motor areas
Alar plates form the sensory areas
WHat seperates the two plates of the spinal cord
Sulcus limitans
When do motor nerve fibres begin to appear
and how do they arise
4th week
Arise from nerve cell bodies in basal plates of spinal cord
Fibres collect into bundles known as ventral nerve roots
Grow out of the spinal cord though the ventral horn
Where do sensory nerve fibres originate
Originate from nerve cells bodies positioned outside of the spinal cord in dorsal root ganglia
Proximal processes from these ganglia form bundle that grow into the dorsal horns of the spinal cord
Distal processes join ventral nerve roots to form spinal nerve
What does dorsal rami innervate
Dorsal muscles, vertebral joints and skin of the back
What does ventral rami innervate
Limbs and ventral body wall
What are neural crest cells
Appear during eleavtion of neural folds
Extend lenght of neural tube
Once the neural tube has formed from the fusion of the neural folds, the neural crest cells migrate laterally
Give rise to sensory ganglia
What happens by the 3rd month of development in relation to the spinal cord
Spinal cord extends the lenght of the embryo
Spinal nerves pass thorugh the intervertebral foramina at level of origin
Where does spinal cord termination shift to by birth
L3
