106157
| Question | Answer |
| What is the process of apoptosis cell death? | DNA and other internal structures are cleaved apart and packaged into membranes, which attract scavenger microglila and other molecules which prevent inflammation. |
| How does necrosis cause inflamation? | As the cell breaks apart, the contents spill into extracellular fluid. |
| What is the dark side of apoptosis? | If genetic program is blocked it can cause cancer, if inappropriately activated it can cause a neurodegenerative disease. |
| What are the two triggers of apoptosis in neurons? | Genetically programmed for an early death after achiving function, or if don't get life-preserving chemicals which are provided by their targets |
| How has it been seen a cell will kill itself if it doesn't get the chemicals it needs? | Grafting an extra target structure to an embryo before the period of synaptogensis reduces death of neurons growing in that area, and destroying neurons will increase survival rate in area |
| What is the most prominent life preserving chemical class for axons been discovered? | Neurotophins, nerve growth factor is one. |
| What do neuron growth factor do? | Promote grow and survival of neurons, function as axon guidance molecules and stimulate synaptogensis. |
| During the period of cell death, what is likely to occur to neurons which have established incorrect connections? | They are likely to die. |
| What do dead axons create? And takes it's place? | Vacant space on postsynaptic membrane, and is filled by the sprouting axon terminals of survival neurons. |
| What does the mass neuron death lead to? | Massive rearrangement of synaptic connections. |
| What increases the selectivity of transmission in synapse rearrangement? | The focus of output of each neuron on a smaller number of postsynaptic cells. |
| What is one complication researchers face in looking at the chemical signals exchanged between two neurons? | The promiscuity which developing neurons display when it comes to synaptogenesis. |
| For a brain to function it must be wired according to a specific plan, but what has research found? | A neuron will form a synapse with any other type of neuron.But if it doesn't function properly, it tends to be eliminated |
| Why is neuron death a normal and important part of neurodevelopment? | About 50% more neurons than what are needed are produced, thus various ways of neuron death need to occur in various parts of the brain during development |
| What type of process was neuron death assumed to be, but has since been ruled out? | Passive, due to failing to get adequate nutrition. |
| What is the active process which causes neuron death in development? | A genetic program inside neurons, they are triggered and cause them to actively to commit suicide. |
| What is the names of active cell death and passive cell death? | Apoptosis (Active) and necrosis (passive) |
| Why is apoptosis safer than necrosis? | Necrosis leads to cells causing potentially harmful inflammation, but apoptosis means the cell disposes of it's remains in a safe way. |
| The patterns of proliferation and migration are different for... | Different areas of the cortex |
| Migration for what type of cell is particularly complex? | Interneurons |
| Where is the neural crest? | Dorsal to the neural tube. |
| What is the neural crest formed from? | Cells which break off the neural tube as it is being formed. |
| What does the neural crest develop into? | Neurons and glial cells of the peripheral nervous system |
| Many cells from the neural crest migrate... | Over considerable distances |
| Some of the guidance molecules are released by, what? | Glial cels |
| What is aggregation? | After migrating, developing cells align themselves with other developing neurons which have migrated to the same area to form structures of the nervous system |
| What is thought to mediate both migration and aggregation? | Cell-adhesion molecules. |
| Where are cell-adhesion molecules located? | On the surfaces of neurons and other cells. |
| What do cell-adhesion molecules have the ability to do? | Recognize molecules on other cells and adhere to them. |
| What effect has been seen of removing even one cell-adhesion molecule? What does this finding suggest? | Devastating effect on brain development. Suggesting it could be the cause of some brain disorders. |
| What has particularly been found to be prevalent during brain development? | Gap junctions between adjacent cells |
| What are gap junctions? | Points of connection between adjenct neurons. Not as wide as synapses and gaps are bridged by narrow tubes called connexins, though which cells can exchange cytoplasm. |
| Regarding gap junctions, what is there increasing evidence of? | Have a role in aggregation and migration |
| What happens once neurons have migrated and aggregated? | Axons grow, and dendrites begin to grow from them. |
| Regarding axon growth, for the nervous system to function, what must occur? | The projections must grow to appropriate targets |
| What as at each growing top of an axon/dendrite? | An amoebalike structure called a growth cone, which extends and retracts fingerlike cytoplasmic extensions called filpodia |
| How many growth cones reach their correct target? | Most |
| Who conducted a series of studies which first demonstrated axons are capable of precise growth, giving a suggestion on how it occurs? | Sperry |
| What is Sperry's chemoaffinity hypothesis of axon development? | Each postsynaptic surface in the nervous system releases a specific chemical label which each growing axon is attracted to its postsynatic target,during both neural development and regenreation |
| In the womb, what three important processes occur? | Cells differentiate, cells must find their way to the proper site, and align with cells around them forming structures, cells must establish appropriate functional relations with other cells |
| What support is there for the chemoaffinty hypothesis? | Several guidance molecules for axon growth have been identified |
| What does the chemoaffinity hypothesis fail to account for? | The discovery that some growing axons follow the same circuitous route to reach their target in every member of a species, over growing directly to it. |
| What is cells differentiation? | When they specialize into certain types of cells |
| What are the five steps of neuron development? | Induction of neural plate, neural proliferation, migration and aggregation, axon growth and synapse formation, neuron death and synapse rearrangement |
| What happens three weeks after conception? | Tissue set to become the central nervous system becomes the neural plate. |
| What is the neural plate? | Small patch of ectodermal tissue on the dorsal surface of the developing embryo. |
| What are three layers of embryobic cells? Which is the most outer one? | Ectoderm, mesoderm, and endoderm. Ectoderm is the outer one. |
| According to the revised notion, what occurs with growing axons? | Growth cones seem to be influenced by a series of chemical signals along the route. Molecules similar to ones involved in migration, in sense some attract others repel. |
| What is the first major stage of neurodevelopment in all vertebrates? | Development of neural plate |
| What seems to induce the development of the neural plate? | Chemical signals from an area of the underlying mesodem layer |
| Apart from chemicals, what else gives signals to growing axons to guide them? | Other adjacent growing axons. |
| Which layer is referred to as the organiser? | The mesoderm |
| What is found when tissue from the dorsal mesoderm from one embryo is en-planted beneath the ventral extoderm of another embryo? | Induces the development of a second neural plate in host. |
| What are pioneer growth cones? | The first growth cones to travel along a particular route in a developing system are presumed to follow the correct route via interacting with guidance molecules along route. |
| What happens when the neural plate becomes visible? | It's cells lose some of it's cotipotent (ability to become any cell in the boy) and becomes multipotent (able to develop into most nervous system cells) |
| What is the process of fasciculation? | When subsequent growth cones embark in the same journey, following the route blazed by the pioneer growth cones. |
| What are cells of neural plate often referred to as , and what are their characteristics? | Stem cells, have a seemingly unlimited capacity for self-renewal if maintained in an appropriate cell culture. Have ability to develop into different types of mature cells. |
| What happens as neural plate develops into the neural tube? | Some of it's cells become specified as future gigal cells of various types and other neurons of various types. |
| Why are the cells which become specified as future gigal cells during transition from neural plate to neural tube called gilal stem cells and neural stem cells? | The cells still have the capacity for unlimited self-renewal and are still multipotent |
| What does much of the axonal development in complex nervous systems involve? | Growth from one topographic array of neurons to another. |
| Whyt do stem cells have an almost unlimited capacity for self-renewal? | Due to when a stem cell divides, two 'daughter' cells are created, one develops into another body cell, the other a stem cell. |
| Why do stem cells cultures not last forever? | Although they could divide forever through process of mitosis, errors would occur after a while |
| Stem cells ability to become any cells is being tested for what? | As possible treatment for various illnesses and health problems |
| What was the original notion of how developing nervous system of topographical relations was maintained? But how has this changed? | By a point-to-point chemoaffinity, but seems more complex as the connections between retina and optic tectum are finished long before they reach full size, then neural connections shift as they grow |
| In around 21 days, what happens to the neural plate? Then what happens three days after that? | It folds and becomes neural grove, then lips of the neural grove fuse forming the neural tube. |
| What does the inside of the neural tube eventually become? | The cerebral ventricles, and spinal canal |
| After 40 days of conception, 3 swellings are visible at the anterior end of the human neural tube, what do they become? | The forebrain, midbrain, and hindbrain. |
| What happens when the neural tube is formed? | The cells of the tube being to proliferate, increase greatly in number |
| What does the topographic gradient hypothesis try to explain? | Accurate axonal growth involving topographic mapping in the developing brain |
| What is the characteristics of neural proliferation? | It does not occur simultaneously, or equally in all parts of the tube. |
| Where does most cell division in the neural tube occur? | In the region next to the ventricle |
| What is the topographic gradient hypothesis? | Axons growing from one topographic surface to another are guided to specific targets which are arranged on the terminal surface in the same way axon cell body are arranged on the original surface |
| What is the key part of the topographic gradient hypothesis? | Growing axons are guided to their destinations by two intersecting signal gradients. |
| What does the proliferation sequence in different parts of the neural tube reflect in most species? | Creates the pattern of swelling and folding characteristics of that species' brain |
| What evidence is there for the topographic gradient hypothesis? | Several guidance molecules have been implicated in signal gradients, but strong evidence points to strongest involvement to a group of molecules called ephrins. |
| What is the complex pattern of proliferation controlled by? | Chemical signals from two organizer areas in the neural tube, floor plate and roof plate. |
| What must axons do when they have reached their intended sites? | Must establish an appropriate pattern of synapes |
| A single neuron can grow an axon on it's own, but what does it take to form a synapse? | Co-ordinated activity from two neurons. |
| What is synaptogenesis? | Formation of new synapses. |
| What is the process of migration? | Once cells are created through cell division, they move to their appropriate location. |
| What does synaptogenesis depend on? | The presence of gligal cells, particularly astrocytes. |
| During the migration stage, what are cells like? | Cells are still immature, backing processes which characterize mature neurons. |
| What are the two major factors governing migration in the developing neural tube? | Time and location. |
| What has been found in retinal ganglion cells maintained in culture, regarding astrocytes? | When astrocyes present, formed seven times more synapses, when removed synapses were quickly lost. |
| In the early theories about the role of astrocytes in synaptogenesis, what role did they have? Why was this? | A nutritional role, as developing neurons need high levels of cholesterol during synapse formation |
| What happens in a given region of the tube? | Sub-type of neurons arise on a precise and predictable schedule and migrate together to their prescribed destinations. |
| What are the two methods which cells migrate? | Somal translocation, and glilia-mediated migration. |
| What does current evidence suggest the role of astrocyles in synaptogenesis? | A more extensive role, by processing, transferring and storing information supplied by neurons. |
| What is somal translocation? | An extension grows from the developing cell in the general direction of migration, it seems to explore the immediate environment for cues as it grows, cell body follows |
| What are the two types of cues in somal transolaction? | Attractive and replusive |
| When does glilia-mediated migration occur? | When period of neural proliferation is well underway and the walls of the neural tube are thickening. |
| What is glilia-mediated migration? | A temporary network of glial cells, called radial glial cells, appear in the developing neural tube, most cells engaging in radial migration do so by moving along the radical glial network |
| Where does most migration research focus on? | Cortex |
| What is the orderly wave of migrating cells revealed by research? | Progress from deeper to more superficial layers, as each wave of cortical cells migrate through has already formed the lower levels of cortex before reaching it's destination. |
| What is the radial pattern of cortical development been labelled? | Inside-out pattern. |
| What is the migration like for many cortical cells? | Long tangential, to reach their final destination. |
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