4. Life-Span Development of the Brain and Behavior Flashcards
The mature human brain has over _______ neurons and _______ synaptic connections
80 billion, 100 trillion
The developing nervous system relies on:
genetic info, experience, and environment
Zygote
Fertilized egg (egg + sperm)
Human embryo develops 3 cell layers
Process of gastrulation:
Endoderm
Mesoderm
Ectoderm
Ectoderm
Outer layer, becomes the nervous system
As it thickens, grown into a flat neural plate
Neural groove
Uneven rates of cell division form the neural groove, which will become the midline
Neural tube
Forms from the neural ridges, which will become the CNS
Neural crest cells
Form the PNS
3 subdivisions of the anterior part of the neural tube
Forebrain, midbrain, hindbrain
Interior of neural tube becomes the ________
cerebral ventricles
Genotype
Sum of all the genetic info that we inherit
Phenotype
Sum of physical characteristics that make up an individual
Most cells are influenced by:
intrinsic factors (internal) AND extrinsic factors (environmental)
Phenylketonuria (PKU)
Recessive genetic disorder where individual cannot metabolize phenylalanine, an amino acid present in a variety of food types
If the individual consumes these things, brain can be damaged from buildup of phenylalanine
How to live with PKU
If you reduce the amount of phenylalanine in their diet, you can save the brain from damaging effects
Change the outcome of genes by influencing their experiences
Example of genes and experience having different outcomes
Phenylketonuria (PKU)
Development of the nervous system can be divided into 6 stages
Neurogenesis
Cell migration
Differentiation
Synaptogenesis
Neuronal cell death
Synapse rearrangement
Neurogenesis
Mitotic production of neurons from neuronal cells
Cell migration
Movement of cells to establish distinct populations
Differentiation
Transformation of precursor cells into distinctive neurons or glial cells
Synaptogenesis
Establishment of synaptic connections
Neuronal cell death
Selective death of many nerve cells
Synapse rearrangement
Loss or development of synapses to refine synaptic connections
Process of neurogenesis
Cells divide through mitosis and form the ventricular zone
Many more cells are born than will be needed
Example of cell fate determined ONLY by intrinsic factors
Mitotic lineage: In the nematode, C. elegans, researchers can follow the development of every neuron
Development in vertebrates
Development is shaped by cell-cell interactions
Extrinsic factor; less predetermined
Adds much more flexibility– if a cell is missing during development, other cells can take its place
Process of cell migration
Cells move away from ventricular layer
In cerebral cortex, radial glial cells act as guides for cells to migrate along to make cortical columns
Inside-out development
Cells establish themselves close to the ventricular layer, and as new cells are born, they move over the existing cells
Cell adhesion molecules (CAMs)
Proteins on cell surfaces that guide migration when cells migrate further distances
Important for populating cerebral cortex and guiding neurons that have to move outward (tangentially)
Migrating cells have _____ that respond to chemicals in the environment and those released by target cells
growth cones
Chemoattractants
Chemical signals that attract certain growth cones
Chemorepellents
Repel growth cones
Filopodia
Outgrowths of growth cones and important for detecting and processing environmental signals (also important for movement)
They adhere to CAMs in the environment and pull the growth cone in a particular direction
Process of cell differetiation
In vertebrates, young neural cells have the capacity to become many varieties of neurons
The type of cell it will become can be limited as it travels based on extracellular factors it comes into contact with
When cells reach their destinations, they express specific genes to make the proteins they need for their cell type
What is the purpose of cell differentiation?
Allows a cell to acquire its specific appearance and function for its final destination
The use of extrinsic factors to guide differentiation offers more flexibility than using intrinsic factors
Process of synaptogenesis
Biggest change in brain cells after birth is growth of axons and dendrites– development of synapses (synaptogenesis)
Extensions emerge from growth cones at the tips of axons and dendrites, and synapses form rapidly on dendrites and dendritic spines
The most intense phase of myelination occurs shortly after birth, extending into young adulthood
Process of cell death
Also called apoptosis
Many more cells are born than the brain needs
So that you only undergo neurogenesis once, easier to make extra than to not have enough
Cells that undergo apoptosis aren’t damaged – they’re just not needed
Cells have death genes that are expressed only during
apoptosis, and this process is highly regulated
Caspases
a family of proteases that cut up proteins and DNA; these are turned on to begin apoptosis
Neurotrophic factors
Neurons compete for chemicals that target cells make, called neurotrophic factors
Without enough, they die
Nerve growth factor (NGF)
A neurotrophic protein essential for the survival of nerve neurons during development
Brain-derived neurotrophic factor (BDNF)
A protein in the brain and spinal cord that helps nerve cells survive, grow, and mature
Process of synapse rearrangement
Synapse rearrangement, or synaptic modeling, refines synaptic connections
This stage continues throughout our lifetime
Thinning of gray matter in cortex as brain develops from back to front
fragile X syndrome
Normal pruning of synapses after birth is blocked, resulting in mental impairment
Environmental factors can limit brain development
Ex: hypoxia– lack of oxygen during birth that affects the brain
Ex: undernourished mothers –> underweight children w brain abnormalities due to lack of nutrients
Ex: drug and alcohol use
Behavioral teratology
studies pathological effects of early exposure to toxic substances
Fetal alcohol syndrome
Abnormal smallness of cerebral cortex
No corpus callosum connecting the two hemispheres
