Chapter 9 - Development of the Nervous System Flashcards
The Case of Genie
Genie’s developmental issues were apparently the result of the severe abuse she experienced. This case study suggests the important role that experience plays in neurodevelopment.
Totipotent
A fertilized egg; can develop into any class of cell in the body
Pluripotent
ability to develop into many, but not all, classes
of body cells
Multipotent
cells are more specialized and can only develop into one class of cells (ex. different kinds of blood cells).
Unipotent
can only develop into one class of cells (ex. red blood cells).
Zygote
single cell formed by the result of the combination of an ovum and a sperm; divides into two daughter cells, continues dividing until a mature organism is produced
Cell Differentiation
- Cells must differentiate; some become muscle cells, multipolar neurons, etc…
- Cells must migrate to their appropriate site and align with other cells around them to form particular structures.
- Cells must establish appropriate functional relations with other cells.
The Five Stages of Early Neurodevelopment
- Induction of the neural plate.
- Neural proliferation.
- Migration and aggregation.
- Axon growth and synapse formation.
- Neuron death and synapse rearrangement.
Embryonic Stem cells
cells that can divide and are unspecialized but have the potential to become specialized cells; totipotent, pluripotent and multipotent are all stem cells.
- Almost unlimited capacity for self-renewal if maintained in an appropriate cell culture. Product of asymmetric cell division: stem cell produces one differentiated cell and one stem cell.
- Critical role in the development of the nervous system as it has the ability for each stem cell to develop into many different kinds of cells.
Neural Plate
a small patch of ectodermal tissue on the dorsal surface of the developing embryo
Three Layers of Embryonic Cells
Ectoderm: outermost layer.
Mesoderm: referred to as the organizer, induces the neural plate with chemical signals.
Endoderm: inner layer.
Induction of the Neural Plate
The neural plate grows to form the neural groove, then forms the neural tube; and eventually becomes the cerebral ventricles and spinal cord.
Neural Proliferation
the rapid increase in the number of neurons that follows the formation of the neural tube; occurs in the ventricular zone and subventricular zone.
Two organizers areas in the neural tube
the floor plate (runs along the midline of the ventral surface of the tube), and the roof plate (runs along the midline of the dorsal surface of the tube).
Radial Glial Cells
cells whose cell bodies lie either in the ventricular zone or subventricular zone and have a long process that extends to the outermost part of the developing neural tube.
Stem cells created in the developing neural tube are always radial glial cells
Migration
once cells have been created through cell division in the ventricular zone of the neural tube, they migrate to the appropriate target location; during this, the cells are still in an immature form (lacking the processes, ex. axons and dendrites) that characterize mature neurons.
Time and location are two major factors that govern migration in the developing neural tube.
Two Types of Cell Migration
Radial migration: proceeds from the ventricular zone in a straight line outward toward the outer wall of the tube.
Tangential migration: occurs at the right angle to radial migration.
Two Mechanisms of Cell Migration Development
Somal translocation: developing cells have a process that extends from their cell body the explores the immediate environment; movement is guided by numerous chemicals through attracting and repelling cells.
Radial-glia-mediated migration: developing cell uses the long process that extends from each radial-glia cell as a sort of rope along which pulls itself up away from the ventricular zone; only allowing the cell to migrate radially (spreads from central point).
Inside-out Pattern
waves of cortical cells migrating through already formed lower layers of cortex before reaching their destination
Neural crest
structure situated dorsal to the neural tube; formed by cells that break off from the neural tube as it is being formed. These cells develop into the neurons and glial cells of the PNS
Aggregation
once developing neurons have migrated, they align themselves with other developing neurons that have migrated to the same structures of the nervous system
Cell-adhesion molecules (CAMs), Gap junctions and interactions between glial cells and neurons.
Cell-adhesion molecules (CAMs)
located on the surfaces of neurons and other cells; can recognize molecules on other cells and adhere to them
Gap junctions
points of communication between adjacent cells; bridged by narrow tubes called connexins
Axon growth
growth of axons and dendrites after migration and aggregation
Growth cone
found at the growing tip of an axon or dendrite; extends and retracts fingerlike cytoplasmic extensions called filopodia, which are searching for a correct route
Pioneer growth cones
the first growth cones to travel along a particular route in a developing nervous system; believed to follow the correct trail by interacting with guidance molecules along the route
Fasciculation
tendency of developing axons to grow along the paths established by preceding axons.
Retinal ganglion cells
compose the optic nerve; were cut off in frogs in Sperry’s study of eye rotation and regeneration, as these cells in frogs regenerate
Chemoaffinity hypothesis
each postsynaptic surface in the nervous system releases a specific chemical label and each growing axon is attracted by the label to its postsynaptic target during both neural development and regeneration; Sperry, 1963.
Topographic gradient hypothesis
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 axons’ cell bodies are arranged on the original surface; growing axons are guided to their destination by two intersecting signal gradients.
Synapse Formation
establishment of an appropriate pattern of synapses; synapses are formed at a rate of 700,000 synapses per second.
A single neuron can grow an axon on its own but needs at least two neurons to create a synapse between them.
Synaptogenesis
formation of new synapses.
Developing neurons need high levels of cholesterol during synapse formation and the extra cholesterol is supplied by astrocytes.
Necrosis
passive cell death; cells break apart and spill their contents into the surrounding extracellular fluid, and the consequence is potentially harmful inflammation
Apoptosis
active cell death; safer than necrosis, internal structures of a cell are cleaved apart and packaged in membranes before the cell are cleaved apart and packaged in membranes before the cell breaks apart
Membrane packages contain molecules that attract microglia who engulf and consume them.
If genetic programs for apoptotic cell death are blocked, it can lead to cancer and/or neurodegenerative disease.
Triggers for Genetic Programs that Cause Apoptosis
Genetic Programming
Some developing neurons appear to be genetically programmed for an early death—once they have fulfilled their functions, groups of neurons die together in the absence of any obvious external stimulus
Limited Life-Preserving Chemicals: Some developing neurons seem to die because they fail to obtain the life-preserving chemicals that are supplied by their targets.
Neurotrophins
life-preserving chemicals supplied to developing neurons. Three lines of evidence that suggest neurons die because they fail to compete successfully for some life-preserving factor.
Implantation of an extra target site decreases neuron death.
Destroying some neurons before the period of neuron death increase the survival rate of the remainder.
Increasing the number of axons that initially synapse on a target decreases survival rate of the remainder.
Synapse Rearrangement
as cells die, the space they leave vacant on postsynaptic membranes is filled by the sprouting axon terminals of surviving neurons. Cell death results in a massive rearrangement of synaptic connections; its effect is to focus the output of each neuron on fewer postsynaptic neurons.
Neuroplasticity
ability of neural networks in the brain to change through growth and reorganization.
Neuron morphology
structural changes in the neurons, repeated or chronic stress can change the morphology of neurons in various brain areas, including the hippocampus.
Neuronal Connectivity
significant changes in neuronal connectivity; can be seen as Huntington’s Disease progresses
Neurogenesis
the generation of new neurons, there have been a number of studies showing new neurons in the olfactory bulb and gyrus dentate of the hippocampus.
Autism Spectrum Disorder (ASD)
neurodevelopmental disorder that includes impairments in language, communication skills, and social interactions combined with restricted and repetitive behaviours, interests or activities.
Genetics contribute to a child’s chances of having autism, but are not entirely responsible.
Exposure to a maternal immune response in the womb.
Gene mutations and variants in autism.
If one identical twin has autism, the other has an 80% chance of having it.
ASD as HETEROGENEOUS DISORDER
An affected individual with ASD might be severely impaired in some respects but typical, or even superior, in others. For example, individuals with ASD who have an accompanying intellectual disability often perform well on tests involving rote memory, jigsaw puz- zles, music, and art.
Second, there are substantial differ- ences in the amount of impairment amongst individuals with ASD: some have many impairments, whereas others display few.
ASD SAVANTS
are persons with general intellectual disabilities who nevertheless display amazing and specific cognitive or artistic abilities (see Treffert, 2014a). Savant abilities can take many forms: feats of memory, naming the day of the week for any future or past date, identify- ing prime numbers (any number divisible only by itself and 1), drawing, and playing musical instruments
Williams Syndrome
a neurodevelopmental disorder associated with intellectual disability and with a heterogeneous pattern of abilities and disabilities
symptoms: serious cognitive deficits, good language skills
Conversely, the thickness of the cortex in one area in people with Williams syndrome is often typical: the superior temporal gyrus, which includes primary and sec- ondary auditory cortex
