Development of the nervous system Flashcards
Name the three primary germ layers / embryonic layers
Endoderm
Mesoderm
Ectoderm => nervous system
In terms of nerve tissue, what do neural tube/neuroepithelium and neural crest cells differentiate into?
Wall of neural tube => CNS
Neural crest => PNS, melanocytes
Briefly outline the process of neurulation
- Neurulation begins with the formation of a neural plate, a thickening of the ectoderm caused when cuboidal epithelial cells become columnar
- Changes in cell shape and cell adhesion cause the edges of the plate fold and rise, meeting in the midline to form a tube
- The cells at the tips of the neural folds come to lie between the neural tube and the overlying epidermis - neural crest cells
What regulates the proper location and formation of the neural tube?
Notochord cells
What do neuroblasts differentiate into?
All neurons with cell bodies in the CNS
What do glioblasts differentiate into?
Astrocytes (e.g. help to form B-B barrier, scaffold for other cells, removal and degradation of neurotransmitters etc.)
Oligodendrocytes (Myelin forming cells of the CNS)
What do ependymal cells differentiate into?
Cells lining ventricles and central canal
Neural crest cells differentiate into what kinds of cells?
- Sensory neurons of dorsal root ganglia
- Postganglionic autonomic neurons
- Schwann cells
- Non-neuronal derivatives e.g. melanocytes
Are motor neurons produced from neuroepithelium?
Yes – although most of their axons are outside the CNS, their cell bodies are within the spinal cord
Describe the differentiation of the neuroepithelium
- Cells withdraw from the outer membrane and undergo mitosis near the inner membrane => mass proliferation
- One daughter cell stays attached to the inner membrane and the other daughter cell will move away from the inner membrane and become a neuroblast
- The neuroblast will develop processes and one will become the axon which is directed away from the inner membrane
Note that the membranes are basal laminae
What are the three layers formed by the differentiation of the neuroepithelium?
Ependymal (germinal layer) Grey matter (mantle layer) White matter (marginal layer)
Glioblasts show a similar pattern of differentiation to neuroblasts. State one difference.
Glioblasts can migrate into the white matter
What controls migration and differentiation?
Signalling molecules which interact with receptors on neuroblasts
Which factors are important with regards to signalling molecules?
Their concentration gradient and timing
What can the grey matter of the neural tube be divided into?
Alar plates (located dorsally; => dorsal horns) Basal plates (located ventrally; => ventral horns)
Cells in the alar and basal plates become which types of neurones?
Alar plate – interneurons
Basal plate – interneurons and motor neurons
What are the neural pores and when do they close?
The developing tube zips of rostrally and caudally, leaving only the top and bottom ends open - anterior and posterior neuropores.
Supposed to close at the end of the fourth week.
The wall of the anterior neural tube differentiates to form three primary vesicles. Name these primary vesicles and state when this occurs.
Prosencephalon (future forebrain)
Mesencephalon (future midbrain)
Rhombencephalon (future hindbrain)
- From approx. 4th week
Describe the changes that occur to these three vesicles in the week or so following their formation
The prosencephalon divides into two new vesicles - telencephalon (from alar plate) and diencephalon (from basal plate).
The rhombencephalon similarly divides into the pons and medulla
What important tightly folded structure begins to appear quite late in development, where does it appear from and when?
Cerebellum
Appears as an out pouching from the back of the pons
Around 8 weeks
What also occurs at approx. 8 weeks
Neural tube centre develops to become the ventricular system - two lateral ventricles (fore), midline third ventricle (fore), aqueduct (mid), and fourth ventricle below cerebellum (hind)
Initially the three primary vesicles are separated by 3 flexures. Name them (rostral to caudal)
Cephalic
Pontine
Cervical
How do neuroblasts migrate from the inner membrane to the outer membrane in the brain?
They attach themselves to radial glial cells and climb up them towards the outer membrane
Radial glial cells have their cell bodies anchored to the inner membrane and have a single long process to the outer membrane
What happens to neuroblasts that undergo short migration?
They become the basal ganglia
How many cell layers are there in the cerebral neocortex?
SIX
A deficiency in what can lead to neural tube defects?
Folic acid
Give a summary for each of the different main neural tube defects
- Anencephaly = anterior neuropore not closing
- Encephalocele = herniation if the meninges
- Iniencephaly = Occipital and spine defects with extreme retroflexion of the head
- Spina bifida = posterior neuropore not closing
- Closed spinal dysraphism = deficiency of at least two vertebral arches
- Meningocele = Protrusion of meninges (CSF filled)
- Myelomeningocele = open spinal cord
