Chapter 9 - Development of the Nervous System

Question 1

The Case of Genie

Answer 1

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.

Question 2

Totipotent

Answer 2

A fertilized egg; can develop into any class of cell in the body

Question 3

Pluripotent

Answer 3

ability to develop into many, but not all, classes
of body cells

Question 4

Multipotent

Answer 4

cells are more specialized and can only develop into one class of cells (ex. different kinds of blood cells).

Question 5

Unipotent

Answer 5

can only develop into one class of cells (ex. red blood cells).

Question 6

Zygote

Answer 6

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

Question 7

Cell Differentiation

Answer 7

1. Cells must differentiate; some become muscle cells, multipolar neurons, etc…
2. Cells must migrate to their appropriate site and align with other cells around them to form particular structures.
3. Cells must establish appropriate functional relations with other cells.

Question 8

The Five Stages of Early Neurodevelopment

Answer 8

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.

Question 9

Embryonic Stem cells

Answer 9

cells that can divide and are unspecialized but have the potential to become specialized cells; totipotent, pluripotent and multipotent are all stem cells.

1. 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.
2. 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.

Question 10

Neural Plate

Answer 10

a small patch of ectodermal tissue on the dorsal surface of the developing embryo

Question 11

Three Layers of Embryonic Cells

Answer 11

Ectoderm: outermost layer.
Mesoderm: referred to as the organizer, induces the neural plate with chemical signals.
Endoderm: inner layer.

Question 12

Induction of the Neural Plate

Answer 12

The neural plate grows to form the neural groove, then forms the neural tube; and eventually becomes the cerebral ventricles and spinal cord.

Question 13

Neural Proliferation

Answer 13

the rapid increase in the number of neurons that follows the formation of the neural tube; occurs in the ventricular zone and subventricular zone.

Question 14

Two organizers areas in the neural tube

Answer 14

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).

Question 15

Radial Glial Cells

Answer 15

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

Question 16

Migration

Answer 16

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.

Question 17

Two Types of Cell Migration

Answer 17

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.

Question 18

Two Mechanisms of Cell Migration Development

Answer 18

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).

Question 19

Inside-out Pattern

Answer 19

waves of cortical cells migrating through already formed lower layers of cortex before reaching their destination

Question 20

Neural crest

Answer 20

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

Question 21

Aggregation

Answer 21

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.

Question 22

Cell-adhesion molecules (CAMs)

Answer 22

located on the surfaces of neurons and other cells; can recognize molecules on other cells and adhere to them

Question 23

Gap junctions

Answer 23

points of communication between adjacent cells; bridged by narrow tubes called connexins

Question 24

Axon growth

Answer 24

growth of axons and dendrites after migration and aggregation

Question 25

Growth cone

Answer 25

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

Question 26

Pioneer growth cones

Answer 26

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

Question 27

Fasciculation

Answer 27

tendency of developing axons to grow along the paths established by preceding axons.

Question 28

Retinal ganglion cells

Answer 28

compose the optic nerve; were cut off in frogs in Sperry’s study of eye rotation and regeneration, as these cells in frogs regenerate

Question 29

Chemoaffinity hypothesis

Answer 29

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.

Question 30

Topographic gradient hypothesis

Answer 30

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.

Question 31

Synapse Formation

Answer 31

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.

Question 32

Synaptogenesis

Answer 32

formation of new synapses. Developing neurons need high levels of cholesterol during synapse formation and the extra cholesterol is supplied by astrocytes.

Question 33

Necrosis

Answer 33

passive cell death; cells break apart and spill their contents into the surrounding extracellular fluid, and the consequence is potentially harmful inflammation

Question 34

Apoptosis

Answer 34

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.

Question 35

Triggers for Genetic Programs that Cause Apoptosis

Answer 35

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.

Question 36

Neurotrophins

Answer 36

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.

Question 37

Synapse Rearrangement

Answer 37

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.

Question 38

Neuroplasticity

Answer 38

ability of neural networks in the brain to change through growth and reorganization.

Question 39

Neuron morphology

Answer 39

structural changes in the neurons, repeated or chronic stress can change the morphology of neurons in various brain areas, including the hippocampus.

Question 40

Neuronal Connectivity

Answer 40

significant changes in neuronal connectivity; can be seen as Huntington’s Disease progresses

Question 41

Neurogenesis

Answer 41

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.

Question 42

Autism Spectrum Disorder (ASD)

Answer 42

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.

Question 43

ASD as HETEROGENEOUS DISORDER

Answer 43

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.

Question 44

ASD SAVANTS

Answer 44

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

Question 45

Williams Syndrome

Answer 45

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