Chapter 5- Development and Plasticity of the Brain Flashcards
Human Central Nervous system begins to form when the embryo is how old?
2 weeks
Brain weight at Birth
350 grams
Brain weight a 1 year
1,000 grams
Brain weight as an adult
1,200- 1,400 grams
Correct pattern of development of neurons ?
Proliferation, Migration, Differentiation, Myelination, Synaptogenesis
What is Proliferation?
Production of new cells.
What are Stem cells?
Cells that remain where they are, continuing to divide
What is Migration?
movement of cells after they have differentiated as neurons of glia , some migrate much faster than others
migration is guided by immunoglobins and chemokines
What is Differentiation?
process whereby neuron forms its axons and dendrites…axons grow first
What is Myelination?
process by which glia produce insulating fatty sheaths that accelerate transmission
myelin forms first in the spinal cord and then in the hindbrain, midbrain and forebrain and continues gradually for decades
What is Synaptogenesis?
formation of synapses. Begins before birth and continues throughout life
Can the adult vertebrate brain generate new neurons?
Only olfactory receptors and stem cells,
stem cells in interior of brain sometimes divide and create “ daughter” cells that migrate to olfactory bulb and transform inso glia or neurons
According to carbon dating, the human brain forms ____ new neurons in the cerebral cortex
few or none
How do axons find their targets with such precision?
they follow path of cells-surface molecules, attracted by some chemicals, repelled by others
What is Neural Darwinism?
as nervous system develops, we start with more neurons and synapses than we keep.
Axons make trial connections with many postsynaptic cells, and then each postsynaptic cell strengthens some synapses and eliminates others
Rita Levi- Montalcini discovered…
that muscles do not determine how many axons form, they determine how many survive
A neuron’s “ suicide program” is called
Apoptosis and is a programmed mechanism of cell death. Occurs if an axon does not make contact with an appropriate postsynaptic cell by a certain age
When a neuron forms synapse onto a muscle, muscle delivers a protein called
Nerve Growth Factor ( NGF)- which promotes survival and growth of axon
How does the CNS match the number of incoming axons to the number of receiving cells?
By the brain overproducing neurons and then applying apoptosis
What is a neurotrophin?
chemical that promotes survival and activity of a neuron ( NGF)
What is the most abundant neurotrophin in adult cerebral cortex?
Brain-derived neurotropic factor ( BDNF)
True or False. Each area of the brain has a period of massive cell death?
True
True or False. Apoptosis occurs throughout a person’s lifetime?
False, after maturity apoptotic mechanisms become dormant, except under traumatic conditions
What is Fetal Alcohol Syndrome?
a condition marked by hyperactivity, impulsiveness, difficulty maintaining attention, varying degrees of mental retardation, motor problems, heart defects and facial abnormalities
most dendrites are short with few branches
True of False. Axons an
d Dendrites continue to modify their structure throughout life
True
What is an Antisaccade task?
voluntary eye movement away from a normal direction
What is a Closed Head Injury?
sharp blow to the head resulting from an accident, assault, or other sudden trauma that does not puncture the brain
What is the most common form of brain injuries?
Closed head injury
What is a stroke?
temporary loss of blood flow to a brain area . They can vary tremendously in their severity and is the most common cause of brain injury in the elderly
What is Ischemia?
result of blood clot or other obstruction in an artery. More common type of stroke
neurons are deprived of blood and lose much of their oxygen and glucose supplies
What is a hemorrhage?
less common type of stroke, caused by ruptured artery
neurons are flooded with blood and excess oxygen,calcium, and other chemicals
What is Edema?
accumulation of fluid, which increases pressure on brain and probability of additional strokes
Both hemorrhage and ischemia impair the..
sodium-potassium pump and leads to an accumulation of sodium inside neurons.
Edema and excess sodium provoke excess release of glutamate which over stimulates neurons
What is the danger of excess positive ions?
block metabolism in mitochondria and kills the neurons
What is the best attempt at treatment for strokes?
Save neurons from death by blocking glutamate synapses and blocking calcium entry.
Cooling the brain, tPA ( tissue plasminogen activator breaks up blood clots.
Cannabinoids can reduce cell loss after a stroke because of their anti-inflammatory properties. Or injection of omega-3 fatty acids
After the first days following brain damage, many of the surviving areas…
Increase or reorganize their activity
What is Diaschisis?
Decreased activity of surviving neurons after damage to other neurons
Name two ways to stimulate the brain
Electrical stimulation & Stimulant drugs ( injection of amphetamines can enhance behaviors)
Why should you never want to calm a stoke victim with tranquilizers?
It would lead to a decrease in dopamine which would impair recovery
True or False. A destroyed axon cannot be replaced
False. A destroyed axon can grow back un der certain circumstances, but can only regenerate a millimeter or two. Sometimes attaches to the wrong muscle.
If an axon in the PNS is crushed, it…
follows its myelin sheath back to the target and grows towards the periphery at the rate of 1m/ day
A possible problem that limits axon regeneration in mammals is
- a cut in the nervous system causes a scar to form which then creates a mechanical barrier
- neurons on the two sides of the cut pull apart
- when glia in the CNS react to brain damage, they release chemicals that inhibit axon growth
What is sprouting?
the brain continually adds new branches of axons and dendrites while withdrawing the old ones. Brain damage accelerates this process
What do cells that have lost their source of innervation do?
They release neurotrophins that induce axons to form collateral sprouts , attaching to the vacant synapses
What is Denervation Supersensitivity?
heightened sensitivity to a neurotransmitter after the destruction of an incoming axon
What is Disuse Supersensitivity?
Heightened sensitivity as a result of inactivity by an incoming axon
A Postsynapitc cell that is deprived of most of its synaptic inputs develops..
increased sensitivity to the neurotransmitters that it still receives
Cortex reorganization after amputation
becomes responsive to other parts of the body as the original axons degenerate leaving vacant synapses
What is Phantom Limb?
A continuing sensation of an amputated body part- can range from tingling to intense pain
What happens if an entire arm is amputated?
the stretch of the cortex that previously responded to the limb, now responds to the face.
When cells in reorganized cortex become activated, they now receive information from the face
Response not feels like stimulation on the arm, not the face
What are Deafferented limbs?
a limb that has lost its afferent ( sensory) input. Can still be used but aren’t because it’s easier to use another body part
What is the process called when a neurons develops dendrites and axon?
Differentation
What can interfere with the migration of neurons and development?
Altering chemical paths
Why does a healthy adult brain not have more connections that necessary?
Axon dies if it has not made the proper connections
What is the function of neurotrophins?
to promote survival of axons
What is the term for new branches that form in uninjured axons after damage to surrounding axons?
Collateral sprouts
Ischemia and Hemorrhage kill neurons by…
Overstimulating them
In an amputee victim that lost a finger, what does the cerebral cortex become responsive to?
Other fingers or part of the palm
What is the order of visual information process?
Receptor, Bipolar Cells, Ganglion
Animals with night vision have …
A Greater rod to cone ratio
In the trichromatic color theory what is the important factor in defining color?
Short, medium and long wavelengths
Which theory states that even if you wear yellow tinted glasses, you can still tell that a color is green?
Retinex Theory
Conscious visual perception occurs in what cortical area?
V1
What fails to develop if a kitten’s vision is restricted to one eye?
Depth Perception
The ability to recognize faces is increased by
the fusiform gyrus
What area has suffered damage if an individual has motion blindness?
MT Cortex
How do axons find their targets?
Growing axons follow paths of cells-surface molecules, attracted by some chemicals and repelled by others.
What is Neural Darwinism?
As nervous system develops, we start with more neurons and synapses than we keep
What happens when axons initially reach their target?
Each one forms synapses onto many cells in approximately the correct location, and each target cell receives synapses from many axons.
At first, axons make trial connections with many post synaptic cells, and then each post synaptic cell strengthens some synapses and eliminates others
What did Rita Levi- Montalcini discover about muscles?
That muscles do not determine how many axons form, just how many survive
What does Nerve Growth Factor ( NGF) do?
promotes survival and growth of the axon
When a neuron forms synapse onto a muscle, the muscle..
delivers a protein called NGF
What is Apoptosis?
Programmed mechanism of cell death
What is Fetal Alcohol Syndrome?
Condition marked by hyperactivity, impulsiveness, difficulty in maintaining attention, varying degrees of mental retardation, motor problems , heart defects and facial abnormalities.
Most dendrites are short with few branches
True or False? Axons and dendrites continue to modify their structure throughout life?
True.
True or False? Neurons become more responsive and finely tuned to stimuli that have been important or meaningful in the past?
True.
True or False. Practicing a skill reorganizes the brain to maximize performance of that skill?
True.
What is Focal Hand Dystonia?
stimulation of one finger excites mostly or entirely the same cortical areas of another finger
Define impulsiveness
tendency to seek immediate reward or pleasure
What is the Antisaccade task?
voluntary eye movement away from normal direction.
In old age neurons alter their synapses more…
slowly. The thickness of the temporal cortex shrinks, volume of hippocampus gradually declines
