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Samenvatting Humane Ontwikkeling Deel 3
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Samenvatting Humane Ontwikkeling Deel 3 in Nederlands/Engels.
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Aantekeningen HO Deel 319. Neuronal development and the human brain I
Early brain development: all behavioural development has to do with the brain, brain
development is dependent upon both experience and genetcs, brain has a greater deal of
plastcity and can recover over tme.
Brain organizaton: diferent parts of brain control diferent functons, brain cells are nerve
and glial cells, info from outside body is stored into neurons and their communicaton to one
another, reacton to this info requires networks of communicatng neurons, neural
communicaton is infuenced by glial cells ‘enwrapping neurons (against Neuron-Dogma..
- Neuron-Dogma: people thought the neurons were the only and most important cells in
the brain, but with more studies about glial cells they found that these cells support the
neurons and help with the immune system.
- Defnitons:
Cortex = neurons, grey mater.
White mater = axons.
Longitudinal fssure = crest between the two hemispheres.
Ventricles = cavites in brain where cerebrospinal fuid is produced.
Sulci = minor grooves.
Fissures = deep grooves.
Gyri = rims.
Brain’s compositon:
- Three main areas:
Hind brain, rhombencephalon: cerebellum+pons (= metencephalon. and medulla
oblongata (=myelencephalon., integraton of info.
Midbrains, mesencephalon: tectum+tegmetum (= subst nigra., sensing and moving.
Forebrain, prosencephalon: diencephalon and telencephalon (=cerebrum/cortex.,
personality.
Prenatal brain development:
- Begin of brain: human central nervous system begins to form when embryo is -2 weeks
old, dorsal surface thickens forming a neural tube surrounding a fuid flled cavity, the
forward end enlarges and diferentates into hindbrain/midbrain/ forebrain, rest of
neural tube becomes spinal cord; during week 3-4 the neural tube forms, zone ectoderm
thickens on dorsal surface embryo and neural tssue rolls and forms neural tube (brain
and CNS., cells migrate from inner part (ventricular zone. to outside of neural tube to
form brain regions; the neural tube becomes central nervous system and the neural crest
becomes the peripheral nervous system, the somites become spinal vertebrae.
- Brain formaton: from three-vesicle (forebrain, midbrain, hindbrain. to fve-vesicle
(telencephalon with two hemispheres and diencephalon, mesencephalon,
metencephalon and myelencephalon. stage.
- General over months: at 7 weeks the neurons are forming rapidly (1000 s per minute.,
at 14 weeks the division of the halves of brain are visible, at 6 months the nerve cell
generaton is complete and the cortex is beginning to wrinkle and also the myelinizaton
starts, at 9 weeks the cortex folds and the gyri and sulci form.
1
,- Over tme of foetal brain development the gyri and sulci gradually emerge, this is called
the cephalizaton.
Development at 9 months: telencephalon lies on top of diencephalon (as later., as
telencephalon develops it connects both with itself and with diencephalon, telencephalon
has a thin layer of cells covering both hemispheres; the cortcal development begins
prenatally and contnues into late adolescence.
Nervous system:
- Neurons: message transmitng cells, many subtypes depending on neurotransmiter
they make and release, synapse is part of NT release and is composed of presynaptc
(release. and postsynaptc (receiving. side, type of message depends on type of
receptors; the neurons are unable to divide but can make new connectons.
- Glial cells: astrocytes and oligondendrocytes, responsible for maintaining neurons and
communicaton.
Astrocytes: star shaped glial cells, support endothelial cells that form blood-brain
barrier, provide nutrients to nervous tssue.
Oligondendrocytes: later are Schwann cells in PNS (stll called oligondendrocytes in
CNS., they produce myelin surrounding axon and increases speed of electrical
transmission.
Brain facts postnatal: at birth human brain weighs -350 grams and by frst year -1000 grams,
the adult brain weighs 1200-1400 grams; the number of neurons in cortex is 20 billion (NL
miljard., and number of synapses is 60 trillion (NL biljoen.; rate early neuron growth is the
fastest in frst half of pregnancy, it is 200.000/minute.
Eight phases in embryonic and foetal development at cellular level: the eight stages are
sequental for given neuron but all are occurring simultaneously throughout foetal
development, so they all have to go through same order; the cells come from epithelial layer
to diferentaton of CNS cells, the neuroepithelial layer gives rise to neuroblast and they
give rise to neurons and gliablasts,
1. Mitosis/proliferaton: occurs in ventricular zone (inside of neural tube., rate can be
250.000 neurons/min, afer mitosis daughter cells become fxed post-mitotc; at early
stages a stem cell generates neuroblasts and later it undergoes a specifc asymmetric
division (“switch point”. at which it changes from making neurons to making glia.
2. Migraton: radial glial cells act as guide wires for migraton of neurons; growth cones
crawl forward dragging the extending axons behind them, their extension is controlled
by cues in their outside environment that direct them toward their appropriate targets;
these cues are chemical signals form outside or proteins to detect signals made by cell;
diferentaton is during migraton.
3. Differentaton: neurons become fxed post mitotc and specialized, they develop
processes (axons, dendrites., they develop neurotransmiter making ability, and they
develop electrical conducton and receptors; diferentate according to their cell fate and
this is determined by their positon in the gradient of factors
4. Aggregaton: the neurons form organized layers, in cortcal zone frst the botom of layer
with less complex neurons and the upper part has more complex neurons.
Cortcal migraton defects: this has large efect on the working of the brain.
2
, 5. Synaptogenesis: axons (with growth cones. form synapse with other neurons or tssue
(like muscle., takes place as dendrites and axons grow, involves linking together of
billions of neurons of brain, one neuron can make up to 1000 synapses with other
neurons, neurotransmiters and receptors are required; axo-dendritc, axo-somatc, axo-
axonic.
Process: frst contact mediated by adhesion molecules, specifcity of synapses
generated by diversity of proteins through alternatve splicing.
6. Neuron death: between 40-75% of all neurons born in embryonic and foetal
development doe not survive, they fail to make optmal synapses; neuron death can lead
to synapse rearrangement, so the functon of a death neuron can be taken over by a
diferent one.
7. Synapse rearrangement: actve synapses likely take up neurotrophic factor that
maintains synapse, inactve synapses get too litle trophic factor to remain stable, this
could happen in presence or absence of neuronal death; when a neuron is not used you
lose it.
8. Myelinaton: glial cells wrap themselves around axons, increases speed of neural
conducton (saltatory conducton., begins before birth in primary motor and sensory
areas but contnues into adolescence in certain brain regions (like frontal lobes..
Piaget’s object permanence task: an infant sees a toy and they an investgator places a
barrier in front of they toy, the infants younger that about 9 months old fail to reach for the
hidden toy; tasks that require a response to a stmulus that is no longer present depend on
the prefrontal cortex and this matures slowly.
20. Neuronal development and the human brain II
Cerebrospinal fuid (CSF.: made by choroid plexuses in both hemispheres in lateral
ventricles, this fuid is taken up by arachnoid granulatons for entering bloodstream.
- Cerebral aqueduct: this connects 3rd ventricle and 4th ventricle and contains
cerebrospinal fuid; when this is too small it can obstruct the fow of CSS and cause
hydrocephaly, the fuid accumulates in skull.
Development overview:
- Telencephalon -> cerebral hemispheres (lateral ventricles..
- Diencephalon (3rd ventricle. -> thalamus, hypothalamus, pituitary.
3
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