7. Brain Development from Infancy to Adolescence Flashcards
what is the nervous system with regard to neuroplasticity?
The nervous system is not a static network of interconnected elements; rather it is a plastic (changeable), living organ that grows and changes continuously in response to its genetic programs and its interactions with the environment
what are the 2 main cells in the human nervous system?
Neurons and Glial cells
what are neurons?
basic functional units of the nervous system (NS). They take in information form other neurons (reception), integrate those signals (conduction), and pass signals to other neurons (transmission).
what are glial cells?
nourish, protect, and physically support neurons and are thought to be particularly critical in brain development. One type of glial cell, the oligodendrocyte, covers the axons of nervous with myelin, a substance critical to the effective functioning of the brain
what are other words for a synaptic gap?
synaptic clef, synapse
what is the synaptic gap?
the cap between neurons
what is the first step of an action potential
The sodium channels open and sodium ions enter, reversing membrane potential
what is the second step of an action potential
Potassium channels open; potassium ions leave, restoring membrane potential
what is the third step of an action potential?
Ion transporters pump sodium and potassium ions back to their original locations
what is an action potential?
the exchange of positive and negative ions at several points of the axon
how is the speed of propagation of the action potential determined?
by the diameter of the axon (Bigger=faster) and the presence or absence of a myelin sheath
what occurs with a myelinated axon?
depolarisation happens only in the gaps, hence quicker propagation of the axon
what is the myelin sheath?
a fatty layer that surrounds the axon
In the development of an embryonic nervous syste - what happens at 18 days post conception?
an embryo consists of 3 layers of cells: Endoderm, mesoderm and ectoderm. The Ectoderm thickens to form the neutral plate
what will the cell in the ectoderm plate become?
the cell in the ectoderm become specialised tissue that will form the brain and the spinal cord
what is the neural plate?
the specialised tissue formed from the ectoderm that will be the brain and the spinal cord
what will the neural crest develop into?
the peripheral nervous system
what do the neural tubes form 18 days after conception?
discrete enlargements vesicles that will develop the major regions of the brain
what major regions of the brain will the embryonic vesicles that formed from the neural tube be formed?
forebrain, midbrain and hindbrain
what is neurogenesis?
the mitotic division of non-neuronal cells to produce neuroblasts. The production of nerve cells.
what are neuroblasts?
Immature neurons produced via mitosis
what is the mitotic division (mitosis)?
The process in cell division by which the nucleus divides, typically consisting of four stages, prophase, metaphase, anaphase, and telophase, and normally resulting in two new nuclei, each of which contains a complete copy of the parental chromosomes
What is cell migration?
the massive movements of nerve cells or their precursors to establish distinctive nerve cell populations (nuclei in the CNS, layers of the cerebral cortex, etc)
what is differentiation?
the differentiation of cells into distinctive types of neurons or glia.
what is synaptogenesis?
the establishment of synaptic connections as axons and dendrites grow
what is neuronal cell death?
the selective death of many nerves cells
what is synapse rearrangement?
the loss of some synapses and development of others to refine synaptic connections
what is the process of neurogenesis?
the cells that will give rise to neurons begin as a single layer along the inner surface of the neural tube. These cells divide in a process called mitosis and gradually form a closely packed layer of cells.
what is the maturity of cells during cell migration?
immature - no axons or dendrites
what direction do cells migrate?
outwards, so innermost cell layer is oldest
when does differentiation occur?
Once immature neurons have completed their migration and have reached the embryonic region where they become functional units of the nervous system, differentiation takes place
what does differentiation of cells allow?
allows the cell to acquire the distinctive appearance of neurons characteristics of that particular region (i.e. cells become distinct types of neurons or glia as processes are formed)
what are the two influences on cell differentiation?
intrinsic self-organisation, neural environment
what differentiation is involved in the intrinsic self-organisation of a cell influence?
cell-autonomous differentiation
what is cell-autonomous differentiation?
when cells use information contained within itself (e.g. the cell transcribes a particular subset of genes to make the particular proteins it needs)
what differentiation is involved in the neural environment influence?
induction-based differentiation
what is induction-based differentiation?
cells use information from neighbouring cells
What do the tips of axons and dendrites contain?
growth cones
what is filopodia?
fine outgrowths
what is lamelliposia
sheet like outgrowths
what does filopodia and lamelliposia follow?
extracellular environment
how does filopodia and lamelliposia occur?
the growth cone is pulled along extending the axon or dendrite in that direction
what is the growth pathway during synaptogenesis guided by?
a chemical released from the target cell.
what are the chemicals that guide the pathway of growth for axons and dendrites?
chemoattractants and chemorepellants
what do chemoattractants and chemorepellants act on?
they act on specific growth cones.
what are synaptic connections in synaptogenesis affected by?
experience
what stage of brain development is neuronal cell death crucial for?
brain development during prenatal stages
what is the physiological process of eliminating differentiating neurons important for?
the correct design of regions and circuitry in the nervous system
what os apoptisis?
naturally occurring cell death
what are the characteristics of selective death of nerve cells?
it is sculpting and refining
how many nerve cells in a given region will die?
between 20-80%
when do many neurons die?
during normal Early development
what is the basic principle of selective cell death?
The basic principal of selective cell death is that neurons must establish synaptic contacts with other neurons (or neuromuscular plates with muscles) in order to survive: those immature neurons that do not establish functional connections are eliminated
what do cells compete for?
Cells compete not just for synaptic sites, but for a chemical that the target structure makes and releases. Such target-derived chemicals are called neurotrophic factors
what is synapse rearrangement?
the final stage of neuronic development. The process that allows the synaptic connections between the remaining cells to be recognised
what occurs to active synapses in synaptic rearrangement?
they are maintained
what occurs to inactive synapses in synaptic rearrangement?
they are retracted
what occurs to new synapses in synaptic rearrangement?
they are formed
what are the intrinsic factors that influence the development of the brain?
genes
what are the extrinsic factors that influence the development of the brain?
Nutrients, drugs and toxins, cell to cell interactions, neural activity (post-natal sensory input - experience)
what is sensory-driven neural activity?
experience
what is experience critical for?
brain development (an extrinsic factor of brain development)
what are the three ways in which experience modulates neural development?
alteration in the creation of synapses; maintenance of synapses; the elimination of existing neurons and synapses
what are two types of structural brain changes?
cortical changes and white matter changes
With regard to structural brain changes, what is infancy and early childhood characterised by?
a dramatic period of synaptogenesis, following an adaptive process of cell death and pruning. There is another surge of synapse growth just before puberty
what is the strengthening or elimination of synapses dependent on?
environmental demands or experience. Those that more more often used are strengthened and those that are rarely used are eliminated
what is grey matter of a brain?
neuronal cell bodies, dendrites and glial cells
what does the development of the grey matter in a brain follow?
an inverted-U pattern of growth, first thickening in volume, peaking and then thinning
what is the pattern of white matter changes during childhood?
white matter increases in a roughly linear pattern throughout childhood, adolescence and into early adulthood
what are myelogentic cycles?
how different brain structures myelinate at different times
when do sensory/motor pathways myelenate?
early
when do regions mediating higher-order functions myelenate?
late
when does synaptic density reach adult levels?
in adolescence
when is myelination thought to be completed?
in the early 20
what is involved in the development of the prefrontal cortex?
synaptic density and myelination
what does the completion of synaptic density and myelination say about the development of the prefrontal cortex?
the maturation of the prefrontal cortex is relative late
what are the functions of the prefrontal cortex?
- Executive functions
- working memory
- planning and organisation
- inhibitory control
- self-monitoring
- insight and judgement
- cognitive flexibility
- selective and sustained attention
