Development of the Brain Flashcards
CNS development
begins at 2 weeks old
Proliferation
production of new cells
they then begin to migrate
nearly all neurons are formed within first 28 weeks of gestation
generally neurons do not form new in adults
stem cells
these remain on the ventricles of the brain and continue to divide
migration
primitive cells, not yet identifi- able as neurons or glia, begin to migrate
majority of cells migrate before birth but some continue
immunoglobulins and chemokines
guide neuron mi- gration. A deficit in these chemicals leads to impaired migration, decreased brain size, and mental retardation
differentiation
where cells start to form into what they will be;
this is when dendrites, axon, synapses form
Synaptogenesis
formation of synapses
begins long before birth and continues throughout life
mylenation
this happens later and more slowly
first in the spinal cord and then in the hindbrain, midbrain, and forebrain
Paul Weiss
discovered Chemical Pathfinding by Axons by grafting an extra leg oto salamanders
Chemical Pathfinding by Axons - Chemical Gradients
growing axon follows a path of cell surface molecules, at- tracted by certain chemicals and repelled by others, in a process that steers the axon in the correct direction
follow a gradient of chemicals
Roger Sperry
showed how sensory axons find their way to their correct targets with optic nerves of newts
Competition among Axons as a General Principle
thalamic neurons receive messages from neurons in many different places that are led towards it by checmical gradients
it rejects and accepts synapses from different locations
neural Darwinism
we start with more neurons and synapses than we can keep, and then a selection process keeps some of the synapses and rejects others. The most successful combinations survive, and the others fail
Rita Levi-Montalcini
one hypothesis was that the muscles sent chemical messages to tell the sympathetic ganglion how many neurons to form
eventually discovered that the muscles do not determine how many axons form; they determine how many survive.
nerve growth factor (NGF)
the brain is born with more neurons than is neeeded
when one of its neurons forms a synapse onto a muscle, that muscle delivers a protein called nerve growth factor (NGF) that promotes the survival and growth of the axon
it is a neurotrophin
if an axon does not receive NGF, it degenerates
apoptosis
programmed mechanism of cell death
If its axon does not make contact with an appropriate postsynaptic cell by a certain age, the neuron kills itself
neurotrophin
a chemi- cal that promotes the survival and activity of neurons
fetal alcohol syndrome
a condition marked by hyperactivity, impulsiveness, difficulty maintaining atten- tion, varying degrees of mental retardation, motor problems, heart defects, and facial abnormalities
caused by drinking during pregnancy
Alcohol inhibits receptors for glutamate, the brain’s main excitatory transmitter, and en- hances receptors for GABA, the main inhibitory transmitter. this causes neurons to stop receiving excitation
when washing away alcohol, Overstimulation at glutamate synapses can poison the mitochondria.
ferret experiments
damaged ferrets brain on one side in SC and occipital lobe; instead, optic nerves attached to the auditory area of the thalamus, developing some features of visual ability
enriched environment rat
developed a thicker cortex, more dendritic branching, and improved learning
wild-caught rats had more neurons in the visual areas of the brain and fewer in the auditory areas
often due to physical activity
far transfer
to teach something challenging and hope students get smarter in other ways
musical training
temporal cortex in the right hemisphere was about 30 percent larger in the musicians
brain changes help musicians attend to slight changes in sounds that other people might not distinguish
focal hand dystonia
Moving one finger without mov- ing another becomes more difficult
closed head injury
a sharp blow to the head that does not puncture the brain
stroke, cerebrovascular accident
temporary interruption of normal blood flow to a brain area
hemorrhage
ruptured artery
ischemia
type of stroke that is the result of a blood clot or other obstruction in an ar- tery.
edema
(the accumulation of fluid), which increases pressure on the brain and the probability of additional strokes
tissue plasminogen activator (tPA)
breaks up blood clots
Diaschisis
the decreased activity of surviv- ing neurons after damage to other neurons
denervation supersensitivity or receptor supersen- sitivity
if a certain set of synapses becomes inactive—perhaps because of damage elsewhere in the brain—the remaining synapses become more responsive, more easily stimulated
helps compensate for de- creased input
can be beneficial or harmful
collateral sprouts
After a cell loses input from an axon, it secretes neurotrophins that induce other axons to form new branches, or collateral sprouts, that take over the vacant synapses
new synapses form at a high rate, especially for the first two weeks
contributes to behav- ioral recovery in some cases
phantom limb
a continuing sensa- tion of an amputated body part
develop when the relevant portion of the somatosensory cortex reorganizes and be- comes responsive to alternative inputs
deafferented
it has lost its afferent (sensory) input
A monkey with a deafferented limb does not spontaneously use it for walking, picking up objects, or any other voluntary behaviors
but if both are deafferented then it will use them both normally
Brain-derived neurotrophic factor (BDNF)
another neurotrophin that promotes survival and activity of neurons
plays a crucial role in reinforcing plastic changes during critical periods
On performing an activity, neurons fire together, BDNF is released to consolidate the connections between the neurons, and promote growth of myelin sheaths
BDNF turns on nucleus basalis, which promote attention focusing and remembering the experiences, hence “effortless learning”
New neuronal cells
hippocampus and basal ganglia
innervate
supply (an organ or other body part) with nerves
