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Ball of cells
Ovum+Sperm
Conception-Two weeks |
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Weeks 3-8
At the end of two weeks, zygote embeds itself in the uterus lining
Critical: buds for all body parts begin development
Heart beats by the end of this stage |
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"Monster maker"
Anything that adversely effects prenatal development
i.e.- Cigarette smoking, alcohol consumption |
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Term
| Five Phases of Neurodevelopment |
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Definition
1)Induction of the Neural Plate
2)Neural Proliferation
3)Migration and Aggregation
4)Axon Growth and Synapse Formation
5)Neuron Death and Synapse Rearrangement |
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Term
Phase One:
Induction of the Neural Plate |
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Definition
Occurs three weeks after conception
Neural Plate: a small patch of ectodermal tissue on the dorsal surface of the developing embryo
-Ectoderm is the outermost layer of bryonic cells
-Development induced by chemical signals from an area of the mesoderm layer
--Mesoderm layer: "Organizer"
The earliest human embryo cells are totipotent, they have the ability to develop into any type of cell in the body if transported to the appropriate site
-As the neural plate develop, cells lose this ability and become multipotent, capable of developing into a limited number of types of mature body cells
Stem Cells
As the neural tube develops, some of its cells become specified as future glial cells of various types, and others as future neurons of various types
-Glial and neural stem cells
Neural plate folds to form the neural groove, then the lips of the neural groove fuse to form the neural tube
-The inside of the neural tube eventually becomes the cerebral ventricles and spinal canal
-Folic Acid
After 40 days, three swellings are visible at the anterior end of the human neural tube, which will eventually become the forebrain, midbrain, and hindbrain |
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Definition
| Seemingly have an unlimited capacity for self-renewal and they have the ability to develop into different types of mature cells |
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Phase Two:
Neural Proliferation |
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Definition
The cells of the neural tube begin to proliferate (increase greatly in number)
Neural proliferation does not occur simultaneously or equally in all parts of the tube
-Most occurs in the ventricular zone, the region adjacent to the ventricle
-Controlled by two organizer areas in the neural tube
--The Floor PLate: runs along te midline of the anterior surface of the tube
--The Roof PLate: runs along the midline of the dorsal surface of the tube |
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Term
Phase Three:
Migration and Aggregation |
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Definition
Migration: once cells divide, they move to their appropriate sites while still in an immature form, laking processes (axons and dendrites)
-Two types of migration:
--Radial Migration
--Tangential Migration
-Two methods of Migration:
--Somal Translocation
--Glia-Mediated Migration
-Timing is everything: neurons of each of the six layers of the cortex migrate at different times, and develop layer-specific anatomical and functional characteristics
-Inside-out Pattern: The pattern of cortical development in which orderly wavs of tangential migrations progress systematically from deeper to more superficial layers.
-Neural Crest
Aggregation: Process of developing neurons aligning themselves with others to form the structures of the nervous system
-Mediated by cell-adhesion molecules (CAMs), which are located on the surface of neurons and others cells (Migration also mediated by CAMs)
-Gap junctions: point of connection between adjacent neurons that aren't as wide as synapses, and are bridged by narrow tubes called connexins
Mostly complete at birth |
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Term
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Definition
A structure situated just dorsal to the neural tube formed from cells that break off from the neural tube as it is being formed
Cells develop into the PNS neurons and glial cells |
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Definition
| Movement of cells in the developing neural tube from the ventricular-zone in a straight line outward toward the tube's outer wall |
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| Movement of cells in a direction parallel to the tube's walls |
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Definition
| An extension grows from the developing cell in the general direction of the migration and draws the cell body up into it |
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Definition
| Immature neurons move out from the central canal along radial glial cells |
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Term
Phase Four:
Axon Growth and Synapse Formation |
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Definition
Axon Growth
-Growth cones on axon and dendrite tips extend out and retracts fingerlike cytoplasmic extensions called filapodia as if searching for the right route for the appropriate target
--Sperry's Frog Experiments
--Chemoaffinity Hypothesis
--Pioneer Growth Cones
--Topographic Gradient Hypothesis
Synapse Formation
-Synaptogensis- the formation of new synapses
--Requires coordinated activity in at least two neurons
--Depends on the presence of glial cells
---Astrocytes
--Needs high levels of cholesterol (provided by astrocytes) |
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Definition
Growing axons are attracted to the correct targets by different chemicals released by the target sites
-Now thought to be series of signals |
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Definition
The first growth cones to travel along a particular route in a developing nervous system, are presented to follow the correct trail by interacting with guidance molecules along the route
-Paves a path for subsequent growth cones
-Called fasciculation |
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| Topographic Gradient Hypothesis |
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Definition
Axons growing from one topographic surface to another are guided to specific targets that are arranged on the terminal surface in the same way as the axon cells are arranged on the original surface
-Guided by two intersecting signal gradients (an anterior-posterior gradient and a medial-lateral gradient)
--Ephrins |
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Term
Phase Five:
Neuron Death and Synapse Rearrangement |
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Definition
Neuron Death
-Survival of the fittest
--About 50% extra neurons produced
---~2x the number of neurons we have as adults during the 6th-8th prenatal month
--Failure to compete for life-perserving chemicals
-Neurotrophins: most prominent life-perserving chemicals
--Nerve Growth Factor (NGF)
--Promote growth and survival of neurons, function as axon guidance molecules, and stimulate synaptogensis
--"Fertilizer"
-Necrosis
-Apoptosis
Synapse Rearrangement
-Increase in transmission selectivity
-Increase in complexity of neural connections
Neurogensis: new neurons created in the adult brain in the hippocampus and olfactory bulb |
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Term
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Definition
Passive Cell Death
Dangerous: contents spill out into extracellular fluid, might cause harmful inflammation |
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Definition
Active Cell Death
More frequent, safer, and cleaner than necrosis
No inflammation
If genetic programs for apoptosis are blocked, this could mean cancer; if they're not properly activated, it could mean neurodegenerative disease |
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| Postnatal Neurodevelopment |
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Definition
Brain volume quadruples between birth and adulthood
-Only Olfactory bulb and Hippocampus develop new neurons.
-Three types of growth: synaptogenesis, myelination of axons, and increased branching of dendrites
Synaptogenesis: general increase shortly after birth, but it differs for different cortical regions
Myelination: increases the speed of axonal conduction; myelination reflects functional development
Dendritic branching: Progresses from deeper to more superficial layers |
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Term
| Development of the Prefrontal Cortex |
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Definition
Prefrontal Cortex plays a role in:
-Working Memory: keeping relevant information accessible for short periods of time while a task is being completed
-Planning and carrying out sequences
-Inhibiting responses that are inappropriate in the current context, but not in others
-Following rules for behavior
Piaget's Cognitive Stages: Sesorimotor, preoperational, concrete operational, formal operational.
Perseveration is the tendency to continue making a formerly correct response when it is currently incorrect
Four times more activity in the prefrontal cortex of babies than adults, because adult brains are more efficient. |
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| Those that are necessary for information in genetic programs to be manifested |
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Definition
| Those that contribute to the direction of development |
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| Those that contribute to the direction of development |
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| If it is absolutely essential for an experience to occur within a particular interval to influence development |
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Definition
If an experience has a great effect on development when it occurs during a particular interval but can still have weak effects outside the interval.
Vast majority |
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| Deprivation and Enrichment |
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Definition
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| Competitive Nature of Experience |
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Definition
Ocular Dominance Columns
Kitten studies |
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Definition
Three Core Symptoms:
1)A reduced ability to interpret the emotions and intentions of others
2)A reduced capacity for social interaction and communication
3)A preoccupation with a single subject or activity
80% Male
60% Suffer from mental retardation
35% Suffer from epilepsy
Risk rises with age of the father
Autism is apparent by age 3
Typical Signs: delayed onset of language ability and delayed onset of social interaction.
Cannot live alone
Intense Behavioral Therapy
Savants- 50% have autism
Twin studies: 60% chance
Autism triggered 20-24 days after conception
Hoxa 1 and neurexin 1 gene
Cerebellum/brain stem and Frontal Lobe |
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