Development of Nervous System Flashcards
What do the following germ layers give rise to?
A) ectoderm
B) mesoderm
C) endoderm
A) skin and NS
B) muscle and CT, skeletal tissue
C) internal linings and internal organs
What happens at 18 days following conception?
The germ disc forms
- 3 layers of cells (endoderm, mesoderm and ectoderm)
- Thickening of the ectoderm as the neural plate develops
When does the neural groove develop and what does it consist of?
Day 20, has neural folds which create a neural groove
Name the five phases of brain development, which germ layer gives rise to it?
Ectoderm gives rise to the neural plate
- Neural plate induction
- Neural proliferation
- Migration and aggregation
- Axon growth and synapse formation
- Apoptosis and synapse rearrangement
Which structures form during the neural plate induction stage of brain development?
- Primitive node
- Notochord
- Primitive streak
- NEURAL PLATE
What is neurulation, which stage of brain development is it associated with and when does it begin?
The process of folding/transforming the neural plate into the neural tube, associated with the third stage migration and aggregation when the neural crest cells develop and migrate.
Begins in the 3rd week
How is the ectoderm able to give rise to different things?
The ectoderm will develop into skin exposed to BMP-4 (body morphogenetic protein)
The primitive node secretes BMP-4 antagonists to allow a region of the ectoderm to develop into nerve tissue!
Name three examples of BMP-4 antagonists
Noggin, chordin and follistatin
What happens during the neural proliferation stage of brain development?
Something
What happens during neurulation to produce the final neural tube? What does the lumen form?
As the neural plate wall thickens (due to increased cell population), the thickenings become apparent on the external surface and are called the ‘vesicles’ or ‘primary swelling’s. The brain will develop from the cranial part of the tube and the spine from the caudal part and will give rise to neurones and glial cells
The lumen forms the ventricular system and the central canal
Which somites develop into the future brain and which develop into the future spinal cord?
Future brain: cranial 2/3 of somites (up to the 4th pair)
Future spinal cord: caudal 1/3 of somites (distal to 4th pair)
What are the cranial and caudal neuropores and what sign indicates =that they have failed to develop properly?
The lateral edges of the neural plate touch in the midline and join together, leaving openings at the cranial and caudal end
If neuropores fail to close alpha feto protein increases in the maternal amniotic fluid
When should the cranial and caudal neuropores close?
Cranial: closure at 25th day
Caudal: closer at 27th day
Name the three primary vesicles at the cephalic end of the neural tube
- Prosencephalon = forebrain
- Mesencephalon = midbrain
- Rhombencephalon = hindbrain
What does the prosencephalon differentiate into and which ‘wall structures’ do they give rise to?
Telencephalon - cerebral hemisphere
Diencephalon - thalamus, hypothalamus, epithalamus
What does the rhombencephalon differentiate into and which ‘wall structures’ do they give rise to?
Metencephalon - pons and cerebellum
Myelencephalon - medulla oblongata
What are the two brain flexures in the neural tube? Where are they and when do they begin to differentiate?
4th week
- Cephalic flexure in the mesencephalon (midbrain) region
- Cervical flexure: at the junction of the rhombencephalon (hindbrain) and spinal cord
List the five secondary vesicles that the three primary vesicles give rise to from “cranial-caudal”, when are they complete?
Completed by the 5th week
- Telencephalon
- Diencephalon
- Mesencephalon
- Fourth ventricle
- Rhombencephalon
Name the five adult cavities that derive from each of the five secondary vesicles (including which corresponds with which!)
Telencephalon: lateral ventricles
Diencephalon: third ventricle
Midbrain/Mesencephalon: aqueduct
The rhomboencephalon derivatives give rise to the fourth ventricle:
Metencephalon: upper part of fourth ventricle
Myelencephalon: lower part of fourth ventricle
What is the cerebral aqueduct (formed by the mesencephalon)?
Narrow 15 mm conduit that allows CSF to flow between the third and fourth ventricle
What happens to the neural tube by day 26?
The tube differentiates into two concentric rings; the mantle layer (grey matter; inner) and the marginal layer (white matter; outer)
Describe the three waves that form the two concentric rings in the migration and aggregation stage of brain development
1st wave: neurones migrate to form mantle (Grey) layer
2nd wave: glioblasts (forerunners for glial cells) give rise to oligodendrocytes (myelination) and astrocytes (transport nutrients and waste across BBB)
3rd wave: forms ependymal cells
What do glial cells do?
They are non-neuronal cells in the CNS and PNS (don’t produce electric impulses) but support and protect neurones by produce myelin and maintain homeostasis
Other than the neural tube, where else do the neural crest cells migrate to form? What stage of brain development does this occur?
3rd stage: migration and aggregation
The neural crest cells migrate into
- Pharyngeal arches - which gives rise to structures of the head and neck
- Facial region
Generally, what do the neural crest cells form?
Most of the PNS and CNS; cranial, spinal and autonomic ganglia
What are autonomic ganglia?
Peripheral sites where preganglionic neurons arising from the brain stem and spinal cord form connections with postganglionic neurons
Where do somatic motor axons emerge from in the fourth stage of brain development?
The ventral spinal cord
What is axon guidance and the growth cone?
The growth cone is a highly motile actin-based structure found at the growing end of the axon. They facilitate axon growth by bundling and extending actin filaments (into structures known as filopodia and microspikes- which creates actin filament assembly and cytoskeleton remodelling, growing the neurone towards its target)
What are neurotrophins? Name three things that they do!
Neurotrophins: proteins inducing the survival development and function of neurones
- Promote growth and survival
- Guide axon
- Stimulate synaptogenesis
What do BMPs of the skin express after the neural tube closes?
They express BMPs in the roof plate which “largely patterns the alar plate”?
What do the alar and basal plates inevitably develop into and do?
Alar plate: develops into the dorsal horn and sends sensory projection to the brain
Basal plate: develops into the ventral horn and is responsible for motor neuron development
Where is the roof plate found and what is its role both during and after development?
It is a signalling centre found on the dorsal side of the central canal that secretes BMPs and Wnts
In the cranial ventricles: the roof plate gives rise to the choroid plexus
What is the role of Wnts in brain development?
They regulate the anatomy of the cytoskeleton, the differentiation of synapses in the cerebellum and regulate apoptosis
May also participate in degenerative processes leading to cell death in the aging breath
Where do the neuroblasts of the alar plate and basal plate migrate and form?
Alar plate: migrates towards the roof/dorsal part of the midbrain called the tectum which gives rise to the superior and inferior colliculi
Basal plate: migrates towards the ventral part of the midbrain called the tegmentum and gives rise to the
- efferent nuclei
- red and reticular nuclei
- substantia Nigra
- crus cerebri
What is the rhombencephalon similar to in its early stages?
The “rostral” (front side) myencephalon
What does the pons allow for?
A passageway for fibres from the cerebral and cerebellar cortices to the spinal cord
Compare the length of the spinal cord and vertebral column at and after the 12 week mark
At 12 weeks: same length
After 12 weeks: vertebrae grow and vertebral column length increases to exceed the length of the spinal cord
What level of the vertebral column does the spinal cord end in adults Vs children and why is there a difference?
Children: L3/4
Adults: L1 due to the caudal portion of the spinal cord regressing
Name ALL the structures that a lumbar puncture would penetrate from superficial-deep
SSTSIEDAS
Stop smelling the stinky icky ED again
- Skin
- Superficial fascia
- Thoracolumbar fascia
- Supraspinous ligament
- Interspinous ligament
- Epidural fat
- Dura mater
- Arachnoid mater
- Subarachnoid space
Where is the epidural space?
Between the dura mater and vertebral wall of the spine
Which vertebral levels are the usual site for a lumbar puncture?
L4/5
Name three examples of neural tube defects and briefly describe each
- Spina bifida: spinal defect due to failure for the neural tube to close
- Hydrocephalus: excessive CSF
Name and briefly describe one example of a condition where ONE structure is affected due to abnormal neural cell migration
Hirschprung’s disease, aganglionic megacolon (missing nerve cells in the muscle’s of the colon), which causes problems passing stool
How does folic acid affect the rate of developmental disorders occurring in the nervous system?
Can reduce the risk of incidences boy 70% if taken pre-conceptually in the first trimester
Which women are at a higher risk of giving birth to a baby with a nervous system disorder?
Women with: diabetes, malabsorption and birth defects in previous children or personally
Name one example of a maternal serum marker that may be raised in the presence of a NS developmental disorder
Alpha-fetoprotein
What is cerebral palsy? Is it curable?
A motor disability caused by a permanent and non-progressive brain lesion as a result of brain injury or malformation (aka congenital or acquired)
Not curable
Name three examples of cephalic neural tube defects and briefly describe each
- Anencephaly: caused by failure of the cephalic end of the neurally tube to close (usually between the 23rd and 26th day), resulting in the absence of a large chunk of the skull and the cerebral hemispheres. The remaining brain tissue is exposed
- Arnold-chiari deformity: the inferior cerebellum and medulla (lower part of brain) elongate and push down into the spinal canal
- Ventricular defects such as hydrocephalus (excessive CSF)
Name two examples of spinal neural tube defects and briefly describe each
- Spina bifida: spinal defect due to failure for the neural tube to
- Neural tube defects where the neural tube stays open or closed ? (Completely closed?)
With anencephaly in mind, describe the following conditions..
A) Encephalocele
B) Iniencephaly
A) Encephalocele: herniation of the meninges and brain
B) Iniencephaly: occipital skull and spine defects with extreme retroflexion of the head
How can spina bifida be treated?
With a shunt; small hollow tube that drains CSF
What can cause spina bifida?
Overproduction of CSF due to infection
Congenital
Acquired blockage of ventricular system (i.e tumour, bleed)
What is myeloschisis?
Failure of the caudal neural folds to close
*MOST severe of defects
What is holoprosencephaly?
Failure of the prosencephalon to divide into two cerebral hemispheres
What deformities are often associated with the following conditions; myeloschisis, Arnold Chiara deformity and holoprosencephaly
Facial deformities:
- Single orbit with two eyes, one eye or no eyes
- Proboscis-type nose located above the eye
- Cleft lip and palate
What deformities are associated with Arnold-Chiari deformity? *not what it is
Hydrocephalus, medulla and pons are small, malformation of lower cranial nerves
Compare spina bifida occulta and spina bifida cystica, is spinal cord function normal?
Occulta: failure of the vertebral arches in the caudal area to develop and so inferior neuropores don’t close. Spinal cord function is usually normal
Cystica: a cyst emerges at the caudal end of the spine where the spinal cord and/or meninges may be found inside. Spinal cord function may be impaired
What dysfunctions may accompany spina cystica?
Lower extremity dysfunction and bladder/bowel dysfunction
Which region of the spinal cord is most commonly affected by spina bifida?
Lumbosacral region
Which conditions are associated with neurological deficits (not mental retardation)
- Spina bifida occulta
- Meningocele
- Meningomyelocele
Name and compare the two types of Spina bifida cystica *including the signs/symptoms of each
Meningocele: a sac of only meninges pushes through a gap in the spine, spinal cord function may be impaired and signs and symptoms vary with location and severity. Still much more mild than…
Meningomyelocele: an opening in the back where both the meninges and spinal cord protrude out in a sac, there is ALWAYS abnormal growth of the spinal cord and associations with
-lower extremity paralysis, bladder/bowel dysfunction and loss of sensation to the lower limbs
Name and briefly describe one example of a condition where MULTIPLE structures are affected due to abnormal neural cell migration
Di George Syndrome; linked with thyroid deficiency, immunodeficiency secondary to a defective thymus, cardiac defects and abnormal facies (facial expression)
*also thought to be causative for some forms of epilepsy
When is the zygote considered an embryo and a fetus?
Embryo: first 8 weeks
Fetus: 8 weeks - birth
What structure induces the folding of the neural plate?
The notochord
What structure is responsible for cranial/caudal linear elongation of the primitive streak and the widening of the neural plate?
The primitive node; an aggregation of cells
Where do glial cells in the PNS and CNS arise from?
CNS: glial cells develop from the ventricular zone of the neural tube
PNS: glia derive from the neural crest
