Development of the Nervous System Flashcards
Over what time frame does the nervous system undergo development?
It is the first system to begin development, and the last to complete development
What does the early development of the nervous system reflect?
The fact that its formation is a priority for the embryo
What is meant by the nervous system being a very plastic system?
It is changing all the time, even after birth
What is the clinical relevance of the length of time it takes the nervous system to develop?
It is most susceptible to insult during pre-natal development
What effect does alcohol have on the developing nervous system?
It disrupts communication between developing neurones
What is the notocord?
A solid cord of cells
What is the notocord formed by?
Prenotocordal cells migrating through the primitive pit
What does the definitive notocord serve as?
The baseline for the midline, axial skeleton, and neural tube
What does the notocord release?
Lots of diffusion limited signalling molecules
What can the signalling molecules released by the notocord act on?
Only cells that are close, and have the right receptor
What is the result of interaction between the notocord and ectoderm?
Formation of neuroectoderm
What does the formation of neuroectoderm cause?
The induction of the neural plate
What happens to the neural plate in development?
The lateral edges of the neural plate elevate, and the depressed midregion becomes the neural groove
What happens to the neural folds during development?
They gradually approach each other in the midline and fuse
Where does fusion of the neural folds begin?
In the future cervical region (in the middle), and then proceeds in both cranial and caudal directions
What is produced by fusion of the neural folds?
The neural tube
By what stage in development is the neural tube completely closed?
Day 28-32
What do neural tube defects result from?
The failure of the neural tube to close
What happens if failure of the neural tube to close occurs caudally?
Gives spina bifida
Where in the spinal cord does spina bifida occur?
Can occur anywhere along the length, but most common in the lumbosacral region
What occurs with spina bifida?
- Neurological defects
- Hydrocephalus nearly always
Are the neurological defects in spina bifida associated with cognitive delay?
No
What is hydrocephalus?
Accumulation of the CSF within the ventricular system
What can hydrocephalus lead to?
- Brain impairments
- Congitive delay
What happens if failure of the neural tube to close occurs cranially?
Anencephaly
What is anencephaly?
Failure of formation of the head structures, including brain
What is the prognosis of anencephaly?
It is incompatible with life
What is the most severe form of anencephaly?
Rachischisis
What is rachischisis?
Failure of neural fold elevation
How can neural tube defects be deteted?
- Raised maternal serum alpha-fetoprotein
- USS
What causes neural tube defects?
Multi-factoral aetiology
What can reduce the incidence of neural tube defects?
Folic acid pre-conceptually (3 months) and in the first trimester
By how much does folic acid reduce the incidence of neural tube defects?
70%
When is dose of folic acid to prevent neural tube defects increased?
When there is a known increased risk, e.g. past pregnancies or family history
What does the lumen of the neuroectoderm tube become?
The ventricular system
What is the ventricular system comprised of in the adult?
Interconnected ‘reservoirs’ filled by CSF, produced by cells of the ventricular lining
What is the role of the CSF in the ventricular system?
Cushion the brain and spinal cird within their body cases
When can hydrocephalus occur?
When there is any blockage of the ventricular system, e.g. tumour or infection
When is hydrocephalus most common?
In newborns suffering from spina bifida
How is hydrocephalus treated?
By the use of a shunt, which shunts fluid into the jugulovenous system or the peritoneum
What forms cranially after neural tube closure in the 4th week?
3 dilations
What do the dilations that form after neural tube closure become?
The primary brain vesicles; forebrain, midbrain, and hindbrain
What happens after the formation of the primary brain vesicles?
At 5 weeks of development, 5 secondary brain vesicles are formed
What secondary brain vesicles are formed from the forebrain?
- Telencephalon
- Diencephalon
What does the telencephalon form?
Cerebral hemispheres
What does the diencephalon form?
Thalamus
What secondary brain vesicles form from the midbrain?
Mesencephalon
What does the mesencephalon form?
The midbrain
What secondary brain vesicles form from the hindbrain?
- Metencephalon
- Myelecephalon
What does the metencephalon form?
The pons and cerebellum
What does the myelecephlon form?
Medulla oblongata
What does most of the length of the neural tube give rise to?
The spinal cord
How does the length of the spinal cord compare to that of the vertebral column during embryological development?
At the 3rd month, the spinal cord is the same length as the vertebral column, but thereafter, the vertebral column grows faster, as the trunk of the fetus grows more rapidly
What is the result of the vertebral column growing faster than the spinal cord after the 3rd month of embryological development?
Spinal roots must elonagate, because they still exit at their intervertebral foramen
What does the elongation of the spinal roots during embryological development form?
The cauda equina
What do the anatomical divisons of the brain and spinal cord undergo?
Patterning and organisation
What layers are present in the early organisation of the neural tube?
- Neuroepithelial layer on inside
- Intermediate (mantle) layer
- Marginal layer on outside
What does the neuroepithelial layer of the neural tube produce?
CSF
What does the intermediate layer of the neural tube produce?
Neuroblasts
What do the roof and floor plates of the neural tube regulate?
Dorsal and ventral patterning
What does the alar plate of the neural tube form?
Sensory structures
What does the basal plate of the neural tube form?
Motor structures
What happens as the neuroectodermal tube grows?
It runs out of space, causing it to bend
What is produced from the bending of the neuroectoderm tube?
It produces flexures
What flexures are produced from the bending of the neuroectoderm tube?
- Cervical flexure
- Cephalic flexure
Where does the cervical flexure form?
Spinal cord-hindbrain junction
Where does the cephalic flexure form?
In the midbrain region
What is the result of the flexures on the neuroaxis?
Means it does not remain straight
What happens to cells of the lateral border of the neuroectoderm?
They become displaced, and enter the mesoderm, undergoing epithelial to mesenchymal transition to become neural crest cells
What does the neural crest give rise to?
- Dorsal root ganglion
- Sympathetic ganglion
Suprarenal gland and chromatic cells - Preaortic ganglia
- Enteric ganglia
What are the adult nervous system derivatives of the neural crest cells?
- Cranial nerve ganglia
- Spinal root ganglia
- Sympathetic ganglia
- Parasympathetic ganglia
- Schwann cells
- Glial cells
- Leptomeninges
What are the adult head, neck, and midline derivatives of the neural crest cells?
- Connective tissue and bones of the face and skull
- Odontoblasts
- Dermis of the face and neck
- C cells of the thyroid gland
What are the adult derivatives of the neural crest cells?
- Nervous system components
- Head, neck, and midline components
- Conotruncal septum of heart
- Melanocytes
- Adrenal medulla
What is the clinical relevance of the complex migratory pattern of neural crest cells?
They are extremely vulnerable to environmental insult
Do defects in neural crest migration affect a single component, or multiple components?
Can be either
Give an example of where neural crest cell migration defects affect a single component
Hirschsprungs disease
What happens in Hirschsprungs disease?
Ganglia of enteric nervous system doesn’t form
Give three examples of where defects in neural crest migration affect multiple components
- DiGeorge syndrome
- Cardiac defects
- Abnormal facies
