Chapter 9

• Totipotent - the cell has the ability to develop into any class of cell in the body.
• Pluripotent - the ability of cells to develop into many, but not all, classes of body cells.
• Multipotent - the new cells can develop into different cells of only one class.
• Unipotent - the most developing cells can develop into only one type of cell.
• Epigenetics - is the mechanism in which the cells has the ability to transcribe different sections of DNA depending on their experience.
• Neural plate is a small patch of ectodermal tissue on the dorsal surface of the developing embryo.
• Neural tube is the fuse of the neural groove.
• The growing neural plate folds to form the neural groove.
• Mesoderm Layer is the middle developmental layer between the ectoderm and endoderm, which gives rise to the skeleton, muscle, heart, and bones.
• The two regions adjacent to the ventricle are the : ventricular zone and subventricular zone.
• Neural proliferation does not occur simultaneously or equally in all parts of the tube.
• Floor plate runs along the midline of the ventral surface of the tube.
• Roof plate runs along the midline of the dorsal surface of the tube.
• Radial glial cells are evolutionary conserved embryonic NSCs that extend thin fibers toward the pia from their soma.
• Migration - once the cells have been created through cell division, in the ventricular zone of the neural tube, they migrate to the appropriate target location.
• Two major factors govern migration in the developing neural tube : time and location
• Radial migration proceeds from the ventricular zone in a straight line outward toward the outer wall of the tube.
• Tangential migration occurs at a right angle to radial migration - that is parallel to the tube's walls.
• Two mechanisms by which developing cells migrate :

  • Somal Translocation - the developing cell has a process that extends from its cell body and seems to explore the immediate environment. Allows a cell to migrate in either radial or tangential fashion.
  • Radial-Glia-Mediated Migration - the developing cell uses the long process that extends from each radial-glia cell as a sort of rope along which it pulls itself up and away from the ventricular zone. Allows a cell to migrate only a radial fashion.
• Inside-Out Pattern - the radial pattern of cortical development
• Many cortical cells engage in long tangential migrations to reach their final destinations.
• Neural crest is a structure situated just dorsal to the neural tube. Formed from cells that break off from the neural tube as it is being formed.
• Aggregation - once developing neurons have migrated, they must align themselves with other developing neurons that have migrated to the same area to form the structures of the nervous system.
• Aggregation is thought to be mediated by at least three non-exclusive mechanisms :

  • Cell-adhesion molecules (CAMs) - which are located on the surfaces of neurons and other cells. Have the ability to recognize molecules on other cells and adhere to them.
  • There is evidence that gap junctions play a role in aggregation and other aspects of neurodevelopment.
  • The process of aggregation is also achieved through interactions between glial cells and neurons.
• Axon growth - once neurons have migrated to their appropriate positions and aggregated into neural structures, axons, and dendrites begin to grow from them.
• Growth cone - extends and retracts fingerlike cytoplasmic extensions called filopodia.
• Filopodia - behave as though they are searching for the correct route. They detect chemical signals released by target cells.
• Retinal ganglion cells - compose the optic nerve, to regenerate.
• Optic tectum or the superior colliculus in mammals
• Pioneer growth cones - the first growth cones to travel along a particular route in a developing nervous system. They are believed to follow the correct trail by interacting with guidance molecules along the route.
• Fasciculation - is the tendency of developing axons to grow along the paths established by preceding axons.
• The topographic gradient hypothesis has been proposed to explain accurate axonal growth involving topographic mapping in the developing brain.
• Synapse formation - is represented as a multicomponent process whereby an initial synaptic contact nucleates organization of pre and postsynaptic specializations that are subsequently specified become endowed with specific properties.
• Synaptogenesis - the formation of new synapses.
• Neuron death during development was initially assumed to be a passive process.
• Apoptosis - safer than necrosis ; active cell death
• Nerve Growth Factor (NGF) was the first neutrotrophin to be isolated.
• The second neurotrophins to be isolated was brain-derived neurotrophic factor (BDNF).
• The most prominent class of these chemicals is the neurotrophins.
• Synapse Rearrangement - during the period of cell death, neurons that have established incorrect connections are particularly likely to die. As they die, the space thy leave vacant on postsynaptic membranes is filled by the sprouting axon terminals of surviving neurons. Thus cell death, results in a massive rearrangement of postsynaptic cells, thus increasing the selectivity of transmission.