Development of the Neural System and Clinical Paediatric Correlations Flashcards
When does human brain development begin?
In the 3rd week post-conception and continues well into adolescence and beyond
What do genes determine in relation to the brain?
- Correct sequence and evolution of the brain from conception to neuronal proliferation, migration and reorganisation
- Development of dendritic and axonal interconnections
- Development of synapses, receptors and neurotransmitters
Factors in the intra-uterine environment that affect brain development?
Maternal health and disease (maternal PKU)
Insults which may be continuous/episodic throughout pregnancy, e.g: alcohol exposure
Placental function and foetal nutrition
Factors in the extra-uterine environment that affect brain development?
Physical factors, e.g: nutrition, environmental toxins
Emotional and social factors, e.g: neglect and lack of stimulation
Progression of brain development?
- Embryonic period (conception to gestational week 8)
- Foetal development (week 9 to 40/42)
- Post-natal development
Structure of the embryo at the beginning of the embryonic period?
2 layered embryo consists of epiblast (goes onto form the child) and hypoblast (forms placenta, etc)
There is primitive streak and primitive node
Describe migration of cells during the embryonic period?
Migration of cells through streak and then rostral-caudal signalling; this is determined by nodal signalling
What occurs during gastrulation?
Results in development of a 3-layered embryo:
• Ectoderm forms the skin, nails, hair and neural issue
• Mesoderm forms the muscle, bone, cartilage and vascular system
• Endoderm forms the gut and respiratory system
What is the neural tube?
1st well-defined neural structure to form (at around days 20-27)
Neural progenitor cells forms the neural plate with a groove and then there folding and neural tube formation
What is the ventricular zone?
Neural progenitors line the inside of the neural tube
Which part of the neural tube becomes the central channel of the spinal cord?
Hollow centre of the tube becomes the ventricular system and central channel of the spinal cord
Which part of the neural tube becomes the brain?
Anterior/rostral tube
Which part of the neural tube becomes the spinal cord?
Caudal tube
What sets the in the embryonic period for later development?
Neural patterning emerging in the embryonic period
There is complex and continuous refinement, e.g: the neocortex
Signalling molecules in the mature neocortex?
Emx2 and Pax6:
• High conc. of Pax6 with low conc. of Emx2 induces progenitor to differentiate into motor neurons
• Low conc. of Pax6 and high conc. of Emx2 induces visual cortical neurons
When does the foetal period take place?
Week 9 to term
Changes of the brain during the foetal period?
Brain is initially smooth in contour and gradually develops its characteristic folded appearance (sulcal and gyral pattern); this is required to accomodate proliferating neuronal populations
Sequence in which the sulci develop?`
Weeks 8-26:
• Primary sulci
Weeks 30-35:
• Secondary sulci
Weeks 36 and into the post-natal period and early infancy:
• Tertiary sulci
When do neurons develop processes?
i.e: axons and dendrites - this occurs once neurones reach their target cortical regions
Function of axons?
Transmit signals from neurons
Function of dendrities?
Gather information and transmit to neurons
Occurrence of programmed neuronal cell death?
Part of normal brain development, e.g: 50% of neurons will die (apoptosis), mostly pre-natally, and 50% of connections will be eliminated, post-natally and throughout life
Events that occur as part of post-natal brain development?
- Post-natal proliferation and migration
2. Myelination - increase axonal conduction rates
What are OPCs?
Oligodendrocyte progenitor cells - develop processes that wrap around axons, i.e: myelin sheaths
Why is early experience of the post-natal brain essential?
E.g: enrichement, as opposed to deprivation
For the emergence of normal neocortical patterns; when input is lacking, brain areas develop differently
Describe what happens when there is monocular visual deprivation in early post-natal life
Alters patterns of recognition within the primary visual cortex; when both eyes are stimulated, pathways known as ocular dominance columns develop equally
Consequences in the 1st few of life?
Usually not compatible with life
Consequences of the neural tube not closing?
Anencephaly
Spina bifida
Consequences of failure of brain vesicle formation?
Holoprosencephaly - forebrain of the embryo fails to develop into two hemispheres; it varies in severity, i.e: lobar, semi-lobar and alobar
3 types of disorders of myelination?
- Hypomyelination
- Dysmyelination
- Demyelination
What is Pelizaeus-Merzbacher disease?
Most severe form that occurs with PLP1 gene (located on the X-chromosome) disorders that affects the growth of myelin sheaths
Consequences of Pelizaeus-Merzbacher disease?
Progresses to severe spasticity and ataxia and a shortened lifespan
Consequences of malnutrition?
Impact on:
• Brain growth and volume
• Myelination
There is a lack of energy, so there is also a lack of post-natal stimulation and experiences
Development that occurs in adolescence?
Develop relations, identity, independence, self-confidence and self-control
But there is also profound emotional development, so it is a “risk-taking” period
