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
critical period
time window during development in which an animal must receive experience of a certain type
if the experience is absent, the organism fails to develop the appropriate behavior such as: language, vision, imprinting, many others
language development
7 months - babbling
1 year - a few words
2 years - sentences
3+ - language explosion; continues to develop until about puberty
vision development
experience with visual stimuli early in life determines how the visual cortex develops
depth perception
innervations from each eye are needed for binocular vision
hebb’s postualte
coordinated activity btw a presynaptic terminal and a postsynaptic neuron strengthens the connection
