CNS Development Flashcards
when does human brain development occur?
in the 3rd post conception week and continues well into late adolescence/early adulthood and beyond
how do genes influence the brain?
determine
- 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
what can affect the intrauterine environment?
maternal health and disease (e.g maternal PKU) insults during pregnancy (continuous/episodic) placental function and fetal nutrition
what can affect the extra-uterine environment?
physical factors - nutrition, environmental toxins
emotional and social factors (neglect etc)
exposure to drugs, alcohol etc
what are the stages in brain development?
embryonic period (conception - week 9)
fetal development (week 9 - 40/42)
post natal development adolescent brain
describe 5 features of the embryonic period?
2 layered embryo
epiblast and hypoblast
primitive streak and primitive node
migration of cells through streak then rostral-caudal migration
determined by nodal signalling
what does the ectoderm develop into during gastrulation?
skin hair nails neural tissue
what does the mesoderm develop into?
muscle bone cartilage vascular system
what does the endoderm develop into?
gut and respiratory system
how does the neural tube develop?
first neural structure to develop occurs at 20-27 days
first neural progenitor cells form the neural plate then becomes neural groove then becomes neural tube then becomes neural crest
what does the neural tube develop into?
neural progenitors line the inside of the neural tube (called the ventricular zone)
the hollow centre of the tube will become ventricular system and central channel of the spinal cord
anterior/rostral tube will become the brain caudal tube will become the spinal cord
what are the 3 primary brain vesicles from top to bottom?
prosencephalon (forebrain) mesencephalon (midbrain) rhombencephalon (hindbrain)
what are the 5 secondary brain references?
telencephalon (from forebrain)
diencephalon (from forebrain)
mesencephalon (from midbrain)
metencephalon (from hindbrain)
mylencephalon (from hindbrain)
what is the hypoblast?
lateral to developing endoderm will eventually be taken over by endoderm as it spreads
what is the epiblast?
will become ectoderm
how many layers in the embryonic period?
2
how many layers in gastrulation?
3 - ectoderm - mesoderm - endoderm
when do the primary brain vesicles develop?
3-4 weeks
when do the secondary brain vesicles develop?
5 weeks
what is neural patterning?
the biological process by which cells in the developing nervous system acquire distinct identities according to their specific spatial positions occurs in embryonic period sets stage for later development
give an example of neural patterning?
neocortical patterning neocortex has distinct functional and structural areas
- anterior/rostral
- posterior/caudal
what are the 2 signalling molecules in the neocortex and how are they significant?
Emx2 and Pax6
- high concentration of Pax6 and low Emx2 which induces progenitor cells to differentiate into motor neurons at the posterior/caudal area
- low Pax6 and high Emx2 which induces visual and cortical neurons development at the anterior/caudal area
what happens during the fetal period?
smooth brain (lissencephalic) develops its characteristic folded appearance (sulci and gyrus) happens from week 9 to term
when do the primary, secondary and tertiary sulci develop in the brain?
primary = 8-26 weeks
secondary = 30-35 weeks
tertiary = week 36 onwards into early infancy
what happens to the neuronal progenitor cells during the fetal period?
initially cells divide symmetrically (one progenitor provides 2 progenitor cells) at days 25-42 of the fetal period cells then divide asymmetrically to produce one progenitor and one neuron
what two cell types make up the ventricular zone and what happens to these cells during the fetal period?
progenitor cells and neurons progenitor cells stay where they are and make more cells neurons migrate to the developing neocortex
via what 3 methods can neuronal migration occur?
somal translocation
radial glial guides
tangential migration and signalling pathways
what happens to neurons once they reach their target region (e.g neocortex)?
they develop processes which allow them to communicate and transmit information
- axons (transmit info from neuron)
- dendrites (transmit info to neuron)
describe programmed neuronal cell death
part of normal brain development
50% of neurons will die (mostly prenatally)
50% of connections will be eliminated (postnatally and ongoing throughout life)
what 2 processes occur in the brain postnatally?
postnatal proliferation and migration
myelination
describe postnatal proliferation and migration?
limited neuronal proliferation from ventricular zone
olfactory bulb develops
dentate gyrus of hippocampus develops
glial progenitors become oligodendrocytes (OPC’s) and astrocytes
describe post natal myelination
OPCs develop processes which wrap around axons forming myelin sheaths
occurs from bottom to top and back to front of brain
mainly in first 2 years but continues into twenties
what are the 2 functions of myelin sheaths?
increase axonal conduction rate
maintain axonal integrity and size
how is experience involved in brain development?
involved in mature organisation of the brain
early experience essential for normal neocortical patterns
brain areas develop differently when input is lacking
what are the 7 developmental tasks of adolescence in the brain?
establish nurturing and intimate relationships
development of identity
future perspectives
independence
self-confidence
self control
social skills
what are the risks in adolescence?
time to take risks > elevated risk to health (trauma and substance abuse related deaths and head injuries) and extreme emotions
describe the new dogma surrounding when brain development occurs
significant reorganisation of the brain occurs in adolescence as well as prenatal period and first 5 years of life
what anatomical changes occur in the adolescent brain which are associated with profound emotional and cognitive change?
maturation of grey matter (ongoing through life)
- occurs with synaptic pruning and is experientially determined
concomitant increase in white matter volume
elimination of synapses
changes in neurotransmitter systems
all happens from back to front of brain (sensorimotor cortex > frontal and prefrontal brain)
what hormonal changes occur in adolescence?
rising gonadal hormone concentrations
brain is full of steroid receptors
pubertal hormones affect brain restructuring > permanent reorganisation
how do hormonal effects differ in males and females during puberty?
oestrogens make females more prone to stress
androgens make males more resilient to stress (apparently)
how does monocular visual deprivation in the early post natal period affect development?
altered patterns of organisation within the primary visual cortex
how does stimulation of both eyes in the early post natal period affect development?
development of ocular dominance columns
how does blockage of one eye in the early post natal period affect development?
the bands or columns representing the blocked eye shrink to thin stripes and the inputs from the active eye invade and subsume territory in the Primary visual cortex normally occupied by the blocked eye
name 2 disorders which result from neural tube problems
anencephaly
spina bifida
which disorder results from failure of brain vesicles to develop?
holoprosencephaly
name 3 disorders of myelination
hypomyelination
dysmyelination
demyelination
what is the PLP1 gene responsible for?
gene on X chromosome which encodes a transmembrane proteolipid protein (the main myelin protein in the CNS)
responsible for
- compaction, stabilisation and maintenance of myelin sheaths
- oligodendrocyte development - axonal survival
what is pelizaeus-merzbacher?
disorder causes by mutation of PLP1 gene
how does pelizaeus-merzbacher present?
nystagmus, hypotonia and cognitive impairment in infancy/early childhood
progresses to severe spasticity and ataxia
shortened life span
how can malnutrition affect development?
impact on brain growth and volume
impact on myelination
lack of energy and deprivation > lack of post natal stimulation and experiences
disease and debilitation
