Last Flashcards
_________of the ovum and the
sperm – zygote
Fertilization
__________of the zygote
Multiplication
Cells________to become
muscle cells, some become
multipolar neurons, some become
glial cells, and so on.
differentiate
Cells_______themselves with the
cells around them to form particular
structures.
align
Cells______appropriate
functional relations with other cells.
establish
FIVE PHASES
OF NEURAL
DEVELOPMENT
induction of the neural plate
neural proliferation,
migration and aggregation,
axon growth and synapse formation,
neuron death and synapse rearrangement.
a small patch of
ectodermal tissue on the dorsal
surface of the developing embryo.
neural plate
The neural plate folds to form the
_______, and then the lips of
the neural groove fuse to form the
________. The inside of the neural
tube eventually becomes the
_____________.
neural groove
neural tubecerebral
ventricles and spinal canal.
Once the lips of the neural groove
have fused to create the neural
tube, the cells of the tube begin to
_______ (increase greatly in
number).
Proliferate
Most cell division in the neural tube
occurs in the __________the
region adjacent to the ventricle
(the fluid-filled center of the tube).
ventricular zone
Migration
• Two major factors govern migration in the developing neural tube:
time and location.
an extension grows from the developing
cell in the general direction of the migration;
somal translocation,
Once the period of neural
proliferation is well 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
glia-mediated migration
proceeds
from the ventricular zone in a
straight line outward toward
the outer wall of the tube;
Radial migration
occurs
at a right angle to radial
migration that is, parallel to the
tube s walls.
Tangential migration
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
Both ___________ are thought to be mediated by __________
which are located on the surfaces of neurons and
other cells_______________ have the ability
to recognize molecules on other cells and adhere to
them.
migration and aggregation
cell-adhesion molecules (CAMs),
Once neurons have migrated to their
appropriate positions and aggregated into
neural structures, axons and dendrites
begin to grow from them.
Axon Growth
For the nervous system to function, these
projections must grow to appropriate
targets. At each growing tip of an axon or
dendrite is an amoebalike structure called
a _________, which extends and
retracts fingerlike cytoplasmic extensions
called filopodia as if searching for the
correct route
growth cone
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 pioneers.
• Pioneer growth cones
The tendency of developing axons to grow along the paths
established by preceding axons is called
fasciculation
According to this hypothesis, axons growing
from one topographic surface (e.g., the
retina) to another (e.g., 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 original 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).
Topographic Gradient Hypothesis
• Once axons have reached their intended
sites, they must establish an appropriate
pattern of synapses. (synaptogenesis)
• A single neuron can grow an axon on its
own, but it takes coordinated activity in at
least two neurons to create a synapse
between them
• It depends on the presence of glial cells,
particularly astrocytes Retinal ganglion
cells maintained in culture formed seven
times more synapses when astrocytes were
present. Moreover, synapses formed in the
presence of astrocytes were quickly lost
when the astrocytes were removed.
Synapse Formation
________is a normal and important part of neurodevelopment. It was initially assumed to be a passive process wherein developing neurons died when they failed to get adequate nutrition.
• However, it is now clear that cell death during development is usually active. Genetic programs inside neurons are triggered and cause them to actively commit suicide.
• Passive cell death is called ______; active cell death is called _______
Neuron Death
necrosis and apoptosis
_________break apart and spill their
contents into extracellular fluid, and the
consequence is potentially harmful
inflammation.
Necrotic cells c cells
DNA and other internal
structures are cleaved apart and packaged in
membranes before the cell breaks apart. These
membranes contain molecules that attract
scavenger microglia and other molecules that
prevent inflammation
apoptotic cell death
________ removes excess neurons in a safe,
neat, and orderly way. But _________ has a dark
side as well. If genetic programs for ________ death are blocked, the consequence can be
cancer; if the programs are inappropriately
activated, the consequence can be
neurodegenerative disease
Apoptosis
apoptotic cell
• During the period of cell death, neurons
that have established incorrect
connections are particularly likely to die.
• As they die, the space they leave vacant
on postsynaptic membranes is filled by
the sprouting axon terminals of surviving
neurons. Thus, cell death results in a
massive rearrangement of synaptic
connections.
• This phase of synapse rearrangement
tends to focus the output of each neuron
on a smaller number of postsynaptic
cells, thus increasing the selectivity of
transmission
Synapse Rearrangement
__________ is a complex neurodevelopmental disorder. In almost
all cases, the disorder is apparent before the age of 3 and
does not increase in severity after that age. Despite
considerable between-patient variation in symptoms, three
are considered to be core symptoms because they are
displayed in some form in most cases of the disorder:
• (1) a reduced ability to interpret the emotions and intentions
of others,
• (2) a reduced capacity for social interaction and
communication, and
• (3) a preoccupation with a single subject or activity
• Although the diagnosis of autism is based on these three core
symptoms, all three are not present in every Also, there are
other characteristics that tend to occur in many cases of the
disorder
• 80% of those with autism are male, 50% suffer mental
retardation and 35% have seizures.
• Older mothers are more likely to give birth to a child with
autism, but the probability of a young mother (under 30) giving
birth to a child with autism increases if the father is over 40
AUTISM
• Aspergers syndrome, a mild _________ in which cognitive and linguistic
functions are well preserved.
• _____________ are common enough that everybody should be alert for their two main early signs:
• delayed development of language (e.g., no babbling by 12 months,
no words by 16 months, no self-initiated meaningful phrases by 24 months)
• delayed development of social interaction (e.g., no smiles or happy expressions by 9 months, no communicative gestures such as pointing or waving by 12 months).
Autism Spectrum Disorders.