construction of neural circuits Flashcards
ventricular zone
lining of neural stem cells surrounding the ventricles
neural stem cell
a self-renewing multipotential cell that gives rise to neurons and glia
progenitor cell
precursor cell derived from a stem cell; it migrates and produces a neuron of glial cell
neuroblast
product of a progenitor cell that gives rise to different types of neurons
glioblast
product of a progenitor cell that gives rise to different types of glial cells
how do stem cell know what to become
chemical signal -> turns genes on -> specific proteins are made -> specific cells
7 stages of brain development
- cell birth (neurogenesis; gliogenesis)
- cell migration
- cell differentiation
- cell maturation (dendrite and axon growth)
- synaptogenesis (formation of synapses)
- cell death and synaptic pruning
- myelogenous (formation of myelin)
step 1: cell birth
- 250 000/minute
- a chemical compound acts to support growth and differentiation in developing neurons; begins about 7 weeks after conception
- largely complete by 20 weeks
- brain can more easily cope with injury during this time (first 5 months of gestation)
step 2 and 3: migration and differentiation
- begins approx 8 weeks after conception
- completed by 29 weeks
- damage during this time has more serious consequences
radial glial cell
path-making cell that a migrating neuron follows to tis appropriate destination
step 4: neural maturation
- begins about week 20 and continues long after birth
- dendritic growth: arborization (branching), growth of dendritic spines (where most synapses occur), slower than axonal growth
- axonal growth: growth cone (growing tip of an axon), filopod (process at end of a developing axon that reaches out to search for a potential target or to sample the intercellular environment), filopodia grow by polymerization of actin, tropic molecule (signaling molecule that attracts or repels growth cones
step 5: synaptic development
- combination of genetic programming and environment cues and signals
- 5th gestational month: simple synaptic contacts
- 7th gestational month: synaptic development of deep cortical neurons
- after birth: synaptic development increases rapidly during the first year of life and then continues throughout life
step 6: death and pruning
- we are born with an overabundance of neurons and synaptic connections
- neural darwinism: hypothesis that cell death and synaptic pruning are, like natural selection in species, the outcome of competition among neurons for connections and metabolic resources in a neural environment
- apoptosis: genetically programmed cell death
- synaptic connections that are not part of a functional network are pruned away in an experience-dependent manner
step 7: glial development
- oligodendria form myelin in CNS
- myelination provides a useful rough index of cerebral maturation
- myelination of cortex begins after birth and continues till mid 20s
- some areas are myelinated earlier (those that perform simpler functions) than others (that perform more complex functions)
rats raised in enriched environments have
- larger and more synapses
- larger and more astrocytes
