Chapter 9 section 1 Flashcards
A fertilized egg is totipotent. What does this mean?
The cell has the ability to develop into any class of cell in the body (e.g., bone, skin, neuron, or heart cells).
After about 4 days of embryonic development, newly created cells lose their ________ and begin to specialize. At this stage, developing cells have the ability to develop into many, but not all, classes of body cells and are said to be _______.
Totipotency,
Pluripotent.
As the embryo develops, new cells are said to become more and more specialized. Eventually, new cells can develop into different cells of only one class (e.g., different kinds of bloods cells). These new cells are said to be ________.
Multipotent
Most developing cells will eventually become ______; they can develop into only one type of cell (e.g., bipolar neurons).
Unipotent
Three weeks after conception, the tissue that is destined to develop into the human nervous system becomes recognizable as the _______– a small patch of ectodermal tissue on the dorsal surface of the developing embryo.
Neural plate
The ______ is the outer most of the three layers of embryonic cells. What are the three layers of embryonic cells?
Ectoderm
1-ectoderm
2-mesoderm
3-endoderm
The development of the _______ is the first major stage of neurodevelopment in all vertebrates.
Neural plate
The development of the neural plate is induced by ________ from an area of the underlying ________- an area consequently referred to as an ________.
Chemical signals,
Mesoderm layer,
Organizer.
Tissue taken from the _______ of one embryo (i.e., the donor) and implanted beneath the ventral _______ of another embryo (i.e., the host) induces the development of an extra _______ on the ventral surface of the host.
Dorsal mesoderm,
Ectoderm,
Neural plate
The cells of the neural plate are often referred to as _________.
Embryonic stem cells.
Stem cells are cells that meet two specific criteria:
(1) they have an almost unlimited capacity for self-renewal if maintained in an appropriate cell culture.
(2) they are pluripotent.
(However, as the neural plate develops into the neural tube, the fates of many of its new cells become more specified)
The growing neural plate folds to form the ______, and then the lips of the neural fuse to form the ______.
Neural groove,
Neural tube.
The inside of the neural tube eventually becomes the _______ and _______. By 40 days after conception, three dwellings are visible at the anterior end of the human neural tube; these swellings ultimate develop into the ______, ______, and ______.
Cerebral ventricles, Spinal canal, Forebrain, Midbrain, Hindbrain.
Once the lips of the neural groove have fused to create the neural tube, the cells of the tube begin to _______. This _______ does not occur simultaneously or equally in all parts of the tube. Most cell division in the neural tube occurs in the _______– the region adjacent to the ventricle (the fluid-filled center of the tube).
Proliferate,
Neural proliferation,
Ventricular-zone.
In each species, the cells in different parts of the neural tube proliferate in a particular sequence that is responsible for the pattern of _______ and ______ that gives the brain its characteristic shape. The complex pattern of proliferation is in part controlled by chemical signals from two organizer areas in the neural tube: the _______, which runs alone the midline of the _______ surface of the tube, and the ______, which runs along the midline of the ______ surface of the tube.
Swelling, Folding, Floor plate, Ventral, Roof plate, Dorsal.
Once cells have been created through cell division in the _______ of the neural tube, they _______ to the appropriate target location. During this period of migration, the cells are still in an ______ form, lacking the processes (axons and dendrites) that characterize mature neurons.
Ventricular zone,
Migrate,
Immature.
Two major factors govern migration in the neural tube:
Time and location.
In a given region of the tube, subtypes of neurons arise on a precise and predictable schedule and then migrate together to their prescribed destinations.
Cell migration in the developing neural tube is considered to be of two kinds:
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.
Most cells engage in both ______ and _______ migration to get from their point of origin in the _______ to their target location.
Radial,
Tangential,
Ventricular zone.
There are two methods by which developing cells migrate:
Somal translocation
Glia-mediated migration
Describe somal translocation.
In somal translocation, an extension grows from the developing cell in the direction of the migration; the extension seems to explore the immediate environment for attractive and repulsive cues as it grows. Then, the cell body itself moves into and along the extending process, and trailing processes are retracted.
Describe glia-mediated migration.
Once the period of neural proliferation is underway and the walls of the neural tube are thickening, a temporary network of glial cells, called radial glial cells, appears in the developing neural tube. At this point, most cells engaging in radial migration do so by moving along the radial glial network.
Radial glial cells
Glial cells that exist in the neural tube only during the period of neural migration and that form a network along which radial migration occurs.
It is now clear that many radial glial cells eventually develop into _______.
Neurons
Inside-out pattern
The pattern of cortical development in which orderly waves of tangential migrations progress systematically from deeper to more superficial layers.
The _______ is a structure situated just dorsal to the neural tube.
Neural crest
The ______ is formed from cells that break off from the neural tube as it is being formed. _______ cells develop into the neurons and glial cells of the peripheral nervous system, and thus many must migrate over considerable distances.
Neural crest,
Neural crest
Numerous _______ guide various classes of migrating neurons by either _______ or _______ them. These guidance molecules play a critical role in neurodevelopment because the brain cannot function normally unless each class of developing neurons arrives at the correct location.
Chemicals,
Attracting,
Repelling.
Describe the process of 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.
Both migration and aggregation are thought to be mediated by ________, which are located on the surfaces of ________ and other cells.
Cell-adhesion molecules (CAMs),
Neurons.
__________ have the ability to recognize molecules on other cells and adhere to them. Elimination of just one kind of ________ in a knockout mouse has been shown to have a devastation effect on _________.
Cell adhesion molecules (CAMs),
CAM,
Brain development.
________ between adjacent cells have been found to be particularly prevalent during brain development.
Gap junctions
There is increasing evidence that ________ play a role in migration and aggregation and other aspects of neurodevelopment.
Gap junctions
Once neurons have migrated to their appropriate positions and aggregate into neural structures, ______ and ______ begin to grow from them.
Axons,
Dendrites.
At each growing tip of an axon or dendrite is an amoebalike structure called a _______, which extends and retracts fingerlike cytoplasmic extensions called _______, as if searching for the correct route.
Growth cone,
Filopodia.
What is the chemoaffinity hypothesis of axonal development?
The hypothesis that growing axons are attracted to the correct targets by different chemicals released by the target sites.
The chemoaffinity hypothesis fails to account for:
The discovery that some growing axons follow the same circuitous route to reach their target in every member of a species, rather than growing directly to it. This led to a revised theory, in where is was hypothesized that a growing axon is not attracted to its target by a single specific attractant released by the target, but influenced by a series of chemical signals along the route.
Guidance molecules are not the only signals that guide growing axons to their targets. Other signals come from ______.
Adjacent growing axons.
________- the first growth cones to travel along a particular route in a developing nervous system- are presumed to follow the correct trail by interacting with guidance molecules along the route. Then, subsequent growth cones embarking on the same journey follow the routes blazed by the _______. The tendency of developing axons to grow along the paths established by preceding axons is called ________.
Pioneer growth cones,
Pioneers,
Fasciculation.
What is fasciculation?
The tendency of developing axons to grow along the paths established by preceding axons.
In most species, the synaptic connections between the retina and optic tectum are established ______ either reaches full size. Then, as the retinas and optic tectum grow at different rates, the initial synaptic connections shift to other tectal neurons so that each retina is precisely mapped onto the ______, regardless of their _________.
Long before,
Tectum,
Relative size.
What is the topographic gradient hypothesis?
Hypothetically, axons growing from one topographic surface (the retina) to another (the optic tectum) 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 surface. The key part of this hypothesis is that the growing axons are guided to their destinations by two intersecting signal gradients (e.g., an anterior-posterior gradient and a medial-lateral gradient).
A single neuron can grow an _______ of its own, but it takes coordinated activity in at least two neurons to create a _______ between them.
Axons,
Synapse.
Perhaps the most exciting recent discovery about _______ (the formation of new synapses) is that is depends on the presence of _______, particularly ________.
Synaptogenesis,
Glial cells,
Astrocytes.
Many more neurons – about _____ more – are produced than required, and large scale ______ occurs in waves in various parts of the brain throughout development.
50%,
Neuron death.
Passive cell death is called ______; active cell death is called ______.
Necrosis,
Apoptosis.
Which is safer, apoptosis or necrosis?
Apoptosis
_______ cells break apart and spill their contents into extracellular fluid, and the consequence is potentially harmful inflammation.
Necrotic
_______ removes excess neurons in a safe, near, and orderly way.
Apoptosis.
Several life-preserving chemicals that are supplied to developing neurons by their targets have been identified. The most prominent class of these chemicals is the _______. _______ was the first ______ to be isolated.
Neurotrophins,
Nerve growth factor (NGF),
Neurotrophin.
