Development of the nervous system Flashcards
what are the 3 distinct layers that form the nervous system?
ectoderm
mesoderm
endoderm
which layer forms the neural plate?
ectoderm (most exterior/distal layer)
how is the neural canal formed?
when the neural plate folds up and the sides fuse dorsally
what forms the CNS?
neural tube (the wall, i.e. neuroepithelium) neural tube layers: 1) neuroepithelium 2) mantle--> grey matter 3) marginal--> white matter
what forms the PNS?
neural crest
neural crest gives rise to PNS cells like schwann cells
what are the 3 types of cells that differentiate from the neuroepithelium?
1) neuroblasts
2) glioblasts (become astrocytes, oligodendrocytes, microglial)
3) ependymal (lines the central canal of spinal cord)
what are neuroblasts?
all neurones with cell bodies within the CNS
what do glioblasts become?
that become neuroglia
astrocytes and oligodendrocytes
what do ependymal cells line?
line the ventricles and central canal
what are the 4 cells that differentiate from neural crests cells?
1) sensory neurones of the dorsal root ganglia and cranial ganglia
2) post ganglionic autonomic neurones
3) Schwann cells (PNS)
4) non-neuronal derivatives e.g. melanocytes
Neural crest (from the ectoderm)–> PNS
what do the the 3 layers of cells within the neuroepithelium contain?
neuroepithelium aka neuroectoderm surrounds the neural tube; considered the stem cells of the neural tube
the stem cells become radial glial cells
the radial glial cells become neurones and glia
[the most inner undergo mitosis (ependymal layer)
next up the cells contain the cell bodies (grey matter) and the outermost contain the axons (white matter)
the outer cells develop into neuroblasts]
grey means soma
white means axon
what do glioblasts develop instead of axons?
do not develop axons but develop processes
what are the neural tube layers?
o Inner – Ependymal layer – germinal layer.
o Middle – Grey matter – mantle layer.
o Outer – White matter – marginal layer.
what controls differentiation at the neural tube?
signalling molecules secreted by surrounding tissues that bind with receptors on neuroblasts
control of migration and axonal growth by attraction and repulsion
what does differentiation depend on?
concentration gradient and timing
how is the grey matter split in the developing spinal cord?
1) alar plate–> dorsal sensory horn
2) basal plate –> ventral motor horn with some interneurones and motor neurones
this is split by the sulcus limitans
intermediate horns are only found from T1-T12, L1-L2 containing the sympathetic portion of the ANS
what features of the early spinal cord become features of the mature spinal cord?
neural canal–> central canal with CSF
alar plate–> dorsal horns
basal plate–> ventral horns
spinal cord becomes surrounded by thick white matter
what is the notochord?
- found below the basal plate
- produces signalling molecules
- established the conc gradient as the highest concentration is present near here.
what is the result of signalling molecules being produced at the notochord on the neural tube cells nearby?
the cells of the neural tube closest to the notochord are induced to become motor neurones
what other feature produces signalling molecules?
ectoderm
however it tends to inhibit the differentiation of neural tube cells into motor neurones
what part of the neural tube develops into the brain
the anterior region
what are the future forebrain, midbrain and hindbrain
the primary vesicles
prosencephalon
mesencephalon
rhombencephalon
respectively
how many secondary vesicles and how are they created (week 5)
from 3 primary vesicles they become 5
the superior prosencephalon divides into two and the inferior rhombencephalon divides into two
what becomes the cerebral hemispheres at 5 weeks?
the telencephalon
what does the lower region of the forebrain become?
the diencephalon made of the thalamus, hypothalamus, epithalamus and sub thalamus
what does the hindbrain divide into at 5 weeks?
pons and medulla
what does the neural canal become at 8 weeks?
it becomes smaller relative to wall and becomes the ventricular system
what also happens at 8 weeks?
the cerebellum begins to develop from the back of the pons
what are the 3 flexures that divide the crooked vesicles?
cephalic (most anterior)
pontine
cervical
these flexures become more exaggerated during development
what is the first thing to happen in the development of the brainstem
the development of the 4th ventricle
what are the positions of cranial nerve nuclei in the brainstem
medial- motor
lateral- sensory
in-between - autonomic
what are the matters of the brain?
inner- white matter
outer- grey matter
(vice versa for spinal cord)
where do the nuclei in the grey matter originate from ?
inner membrane of the neural tube
where do neuroblasts proliferate?
inner membrane of neural tube
some stay in the middle and form basal ganglia
some migrate to the outer membrane using radial glial cells which have long processes towards the outer membrane
in what pattern does the proliferation and migration of neuroblasts in the cortex occur?
in waves up the 6 layers
name examples of neuro-developmental disorders
schizophrenia- malfunction in development
spina bifida- folic acid deficiency
what is regenerational neurobiology?
replacing lost neurones involves regulating stem cell differentiation
inducing CNS regeneration involves guidance mechanisms for axons
what does the prosencephalon become?
forebrain: telencephalon and diencephalon
what does the mesencephalon become?
midbrain
what does the rhombencephalon become?
metencephalon (pons and cerebellum)
myelencephalon (medulla)
what is the cephalic flexure?
- first to form
- between midbrain and hindbrain
what is the cervical flexure?
between the brainstem and spinal cord
what is the pontine flexure?
between the metencephalon (pons and cerebellum) and the myelencephalon (medulla)
