Neurodevelopment Flashcards
What week does the neural plate begin to form
3rd
How does the neural plate form
Ectoderm thickens in the mid-line
How does the neural groove form
Neural plate undergoes differential mitosis to form the neural groove
How does the neural tube
The neural groove deepens and eventually detaches from the overlying ectoderm to form the neural tube
Where do the neural crest cells lie
Lateral to the neural plate
Run dorsolaterally along the neural groove
What do neural crest cells form
Sensory ganglia, Schwann cells, adrenal medulla, meninges and dermis
Which week does the prosencephalon, mesencephalon and rhombencephalon develop
By week 5
What has happened by week 5
The prosencephalon, mesencephalon and rhombencephalon have developed
By what week have the secondary brain vesicles developed
7
What do the secondary brain vesicles give rise to
The mature brain
Timeline of brain development
Week 3- ectoderm —>neural plate —> neural groove —> neural tube
Week 5- prosencephalon, mesencephalon and rhombencephalon develop
Week 7- secondary brain vesicles develop
Primary brain vesicles
prosencephalon, mesencephalon and rhombencephalon
Secondary brain vesicles
Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon
What are the secondary brain vesicles of the prosencephalon
Telencephalon
Diencephalon
What secondary vesicles are part of the rhombencephalon
Metencephalon
Myelencephalon
Derivative in mature brain of prosencephalon
Cerebral hemispheres
Lateral ventricles
Thalamus
Hypothalamus
3rd ventricle
Derivative in mature brain of mesencephalon
Midbrain
Aqueduct
Derivative in mature brain of rhombencephalon
Cerebellum
Pons
Upper 4th ventricle
Medulla oblongata
What week does eye formation begin
3
Developmental milestones: cerebral expansion and commissures
10 weeks
Developmental milestones: basic structures
3 months
Developmental milestones: eye formation
3 weeks
Developmental milestones: myelination has begun
5 months
Developmental milestones: lobes and cerebrum have formed
7 months
Developmental milestones: gyri and sulci have formed
9 months
What are CNS abnormalities dependent on
Time of infection
Week 6 infection causes
Eye malformations
Week 9 infections cause
Deafness
Week 5-10 infections cause
Cardiac malformation
When do CNS abnormalities typically occur
2nd trimester
When does the risk of CNS disorders fall
After 16 weeks as most structures have developed by this point
When is the dermal skin innervated
28 weeks
When do the dorsal root ganglia connect to the spinal cord
8 week
Non-noxious development of sensation
Dorsal root connect to the spinal cord from 8 weeks
When does C-fibre connection occur
19 weeks
Noxious development of sensation
C-fibre connection occurring in week 19
When does the organised thalamus occur
Week 8
When does retinal input arrive
14-16 weeks
When does myelination occur
Week 25
When does the connection from the thalamus to the cortex occur
24 weeks
Eye malformation
Week 6 infection
Deafness
Week 9 infections
Cardiac malformations
Weeks 5-10 infections
Development of sensation timeline
Week 8: dorsal root ganglia connect to spinal cord (non-noxious) and organised thalamus
Week 14-16: retinal inputs arrive
Week 19: C-fibre connection occurs (noxious)
Week 24: connection from the thalamus to the cortex
Week 25: myelination occurs
Week 28: dermal skin is innervated
When does the blood-brain barrier begin to form
Week 8
What is the blood-brain barrier formed by
Endothelial cells
Pericytes
Astrocytes
(Endothelial tight junctions and continuous basement membrane)
Which parts of the brain lack a blood-brain barrier
Circumventricular organs
I.e. posterior pituitary needs to be connect with blood as has a sensory role
At what week should the neural tube be closed
Week 4
Spina bifida
Failure of the closing of the spinal cord by week 4
Anencephalus
Failure of the neural tube closing in the Cephalic region
Detection of brain activity
Increased neural activity results in increased release of neurotransmitters and their breakdown products
More neurally active regions require more oxygen and blood
EEG (electroencephalogram)
Indication of regional brain activity
electroencephalogram (EEG) is a test that measures electrical activity in the brain using small, metal discs (electrodes) attached to the scalp
Useful for detecting signs of epilepsy
Over-excitation of neurons can lead to cell death
Modern imaging techniques monitor haemodynamuc changes
More neurally active regions require more oxygen and blood
CSF lumbar puncture
Increased neural activity results in increased release of neurotransmitters and their break down products
Ways to detect brain activity
Lumbar puncture
Monitoring haemodynamic changes
EEG (electroencephalogram)
What percentage of the brain is fat
60%
At what age are you ambidextrous until
3 years
Primitive reflexes
Rooting Reflex: turn head and mouth in direction of stroking of cheek
Sucking Reflex: babies will suck object that touches the lips
Moro (Startle) Reflex: back arches, legs and arms are flung out and then brought back toward chest into a hugging motion
Grasping (Palmar) Reflex: babies grasp objects pressed against palms
Stepping Reflex: babies will mimic walking when help upright
Babinski Reflex: infant fans toes when feet are stroked
Tonic-Neck Reflex: infant turns head to one side, extending arm and leg
How far away are objects from the eyes when seen best
7-9 inches
Vision when born
Lack peripheral vision
Able to track movement within 1 day of birth
Convergence does not occur until 7/8 weeks
Cones less developed than rods at birth, but at 3 months can see most visible colours
Hearing when born
Middle and inner ear mature in shape and size. So hear remarkably well
Show preference for mothers’ voice
Smell at birth
Smell well developed at birth
Demonstrate facial expressions to different odours
Aversion for noxious and preference for pleasant odours
Recognize familiar odours
Learned preference for mother
Taste at birth
Tastes sensitive at birth
Discriminate between salty, sour, and bitter tastes
Prefers sweet – works as an analgesic
Developmental progress
Cranial to caudal
Proximal to distal
Simple to complex
Left hemisphere responsible for
Verbal, Speaking, Reading, Thinking, Reasoning, Processes information sequentially, One piece of information at a time
Right hemisphere responsible for
Nonverbal, Spatial relationships, Patterns/Drawing recognition, Music, Emotional expression, Processes information holistically
Red flags of development
Syndromic children/Dysmorphisms
History of brain injury
Any loss of skills at any age
Visually not fixing or following an object
Hearing loss
Low or High muscle tone
Squint after 3 to 4 months (6th nerve)
Cannot hold object placed in hand at 5 months
Can’t sit unsupported by 12 months
Boys not walking by 18 months
Girls not walking by 2 years
Persistent toe walking
No speech by 18 months
Can’t point at object to share interest with others by 2 years
Handedness before 3 years old
Folic acid (B9) supplementation
Reduces the risk of spina bifida and anancephaly
Lissencephaly disorder
Smooth brain
Neuronal migration
Unreactive neonate
Fetal alcohol syndrome
No safe level
Bingeing is worse but as little as 2 units per day can affect a fetus
Low nasal bridge, short nose and flat midface, small forehead (microcephaly), thin upper lip
Cystic periventricular leukomalacia
Death of oligodendrocytes
Around 5% of babies less than 32 weeks
When does eye convergence occur
7/8 weeks
By what age can babies see most visible colours
3 months
Ventricular haemorrhage
Around 80% of babies less than
32 weeks have a normal scan
Around 14% have small bleeds
Around 6% of babies less than
32 weeks have scans like these
Neonatal brains display significant plasticity
What layer of the primitive streak forms the nervous system
Ectoderm
The ectoderm forms
Skin
Nervous sustem
The endoderm forms
Epithelial lining of gut and respiratory system
Liver
Oancreas
The mesoderm forms
Notochord
Muscular system
When does Gastrulation occur
Week 3
Formation of spinal cord
Ectoderm thickens in midline to form the neural plate
Formation of neural tube
- Notochord forms the mesoderm cells soon after Gastrulation is complete
- Signals from notochord cause inward folding of ectoderm at the neural plate
- Ends of the neural plate fuse and disconnect to form an autonomous neural tube
Where do the presumptive neural crest cells lie
Lateral to the neural groove
What do the spinal ganglion give rise to
Dorsal root ganglio
Where do the spinal ganglion lie
Either side of the neural tube
What do the neural crest cells give rise to
Schwann cells
Adrenal medulla
Bony skull
Meninges
Sensory dorsal root ganglia of spinal cord and V/VII/IX/X
What do the mesoderm give rise to
Osteoblasts
Osteoclasts
Adipocytes
Chondrocytes
What do the ectoderm cells give rise to
Melanocytes
Schwann cells
Neurons
When does the neural tube close
End of 4th week
Anencephaly
Failure to close Cephalic region of neural tube
Spina bifida
Failure to close spinal region of neural tube
Environmental factors of spina bifida
Folic acid
Maternal diabetes
Brain development - week 4
Prosencephalon – cerebral hemispheres and thalamic structures
Mesencephalon – midbrain
Rhombencephalon – medulla, pons and cerebellum
Microcephaly
Reduced head circumference
Macrocephaly
Increased head circumference
Periventricular nodular heterotopia
Abnormal migration of neurons
Meningocele
Protrusion of the meninges
Myelomeningocele
Protrusion and opened spinal cord
Hydrocephalus
Accumulation of CSF with increased intracranial pressure
Can cause macrocephaly in children (therefore always scan increasing head size)
Obstructive (non-communicating): e.g. tumour, haemorrhage.
Non-obstructive (communicating): e.g. increased CSF production
When are most spinal cord defects detected
20 week scan
Brain development- week 6
Telencephalon
Diencephalon
Mesencephalon
Rhombencephalon
Fourth ventricle
Brainstem
What does the prosencephalon give rise to
Cerebral hemispheres
Thalamic structures
What does the mesencephalon give rise to
Midbrain
What does the rhombencephalon give rise to
Medulla
Pons
Cerebellum
Is microcephaly or macrocephaly more likely to be indicative of pathology
Microcephaly- stem cells have not divided properly (eg teratogens )
For example alcohol fetal syndrome
Neural crest cells don’t form…
Astrocytes
Developmental milestones: week 3
Eye formation
Developmental milestones: week 10
Cerebral expansion and commissures
Developmental milestones: 3 months
Basic structures
Developmental milestones: 5 months
Myelination has begun
Developmental milestones: 7 months
Lobes and cerebrum have formed
Developmental milestones: 9 months
Gyri and sulci have formed
The nervous system begins to form in week 3 after fertilisation.Which of the following statements about the embryology of the spinal cord is true- formed from?
Ectoderm
Which embryological structure is the precursor to the developing pons and cerebellum?
Metencephalon
