Development And Plasticity

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Nervous system development

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Begins to take form at about an embryonic age of 2 weeks in humans

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CNS development

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Occurs around a fluid-filled cavity called a neural tube which eventually becomes the ventricles and the central canal

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Neural tube

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fluid-filled cavity which eventually becomes the ventricles and the central canal

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Cells lining the ventricles

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divide. Some of the daughter cells are primitive neurons and glia which begin to migrate toward their eventual destinations in the CNS

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Differentiation

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the process that makes one neuron different from another.

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How does differentiation begin?

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Begins as the neuron is migrating, but is also depends on the local environment of its target destination

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Proliferation

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Cells lining the ventricles divide. Some of the daughter cells are primitive neurons and glia

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Migration

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The proliferating cells begin to migrate toward their eventual destination in the CNS

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What is migration guided by?

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The migration is guided by immunoglobins and chemokines as well as radial glia

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How does differentiation begin?

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Begins as the neuron is migrating, but is also depends on the local environment of its target destination

Front 11

Proliferation

Back 11

Cells lining the ventricles divide. Some of the daughter cells are primitive neurons and glia

Front 12

Migration

Back 12

The proliferating cells begin to migrate toward their eventual destination in the CNS

Front 13

What is migration guided by?

Back 13

The migration is guided by immunoglobins and chemokines as well as radial glia

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Differentiation

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the process that makes one neuron different from another

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how does differentiation begin?

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begins an the neuron is migrating, but is also dependent on the local environment of its target destination.

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what happens fist in differntiation?

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axons develop first and the cell shape and dendrites develop once neuron reaches its target

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myelination

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production of myelin sheaths around axons

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where does myelination occur

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first occurs in the spinal cord, the hindbrain, midbrain and forebrain. it occurs gradually for decades

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synaptinogenesis

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formation of new synapses. the process of synapse formation and removal occurs throughout life

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axons grow

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before dendrites while the neuron is migrating
axons=tree stump dendrites=branches

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axons are guided

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to their targets by following gradients of guidance molecules found on the surface of cells and in the extracellular matrix

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once the neuron reaches its destination

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then dendritic growth begins and increases as incoming axons arrive

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myelination of axons begins

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during fetal development and continues many years after birth

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there are more neurons and axons

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generated during fetal development than are ultimately found in the adult brain

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what determines which neurons and connections survive

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several factors

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chemicals that promote neuron survival and growth

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nerve growth factor(NGF); brain derived neurotrophic factor(BDNF); neurotrophins 3, 4/5. and 6 (NT3, NT4/5, NT6)

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early in development neurotrophins

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promote survival and growth of selected neurons

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neurotrophins also promote

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regrowth of injured axons

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Programmed cell death

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apoptosis

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once an axon forms a synapse

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neurotrophins secreted form the target cell strengthen the connection and prevent the neuron from committing suicide

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axons that do not receive sufficient amounts of neurotrophin (NGF)

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degenerate and the cell body dies

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if the neuron does not make sufficient connections by a certain age

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then it kills itself (apoptosis)

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CNS development continues

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after birth

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generally neurons cannot

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be replaced (with some exceptions-->olfactory neurons)

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the formation of what continues to occur after birth

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dendrites, dendritic spines, axon branches, and synapses

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experience can have an impact on

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the formation of dendrites, dendritic spines, axon branches, and synapses

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behavioral compensation

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subject learns how to use remaining portions of the nervous system to compensate for the damage

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involves the development of new strategies to achieve tasks

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behavioral compensation

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if axons in the peripheral nerves are damaged

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they can regenerate

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axons in the peripheral nerves are more likely to regenerate

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if they are crushed than if they are cut

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axons in CNS cannot

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regenerate over appreciable distances

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it is thought that scar tissue and growth-inhibiting proteins

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suppress regeneration in the CNS

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axons can respond to neurotrophins released by cells in the vicinity of their terminals by

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sprouting collateral axon terminals that can fill synapses vacated by degenerating axons

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phantom limb

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refers to the continuation of sensation of an amputated body part and reflects this process

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the cortex

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reorganizes itself after the amputation of a body part by becoming responsive to other parts of the body

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original axons

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degenerate leaving vacant synapses into which other axons sprout

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denervation and disuse supersensitivity

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heightened sensitivity to a neurotransmitter after the destruction of an incoming axon or of inactivity

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potential mechanisms of denervation and disuse supersensitivity

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up-regulation of receptor proteins; up-regulation of a following cascade component (second messengers, ion channels)

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types of strokes include

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ischemia; hemorrhage

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ischemia

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the most common type of stroke, resulting from a blood clot or obstruction of an artery. neurons lose their oxygen and glucose supply

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hemorrhage

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a less frequent type of stroke resulting from a ruptured artery. neurons are flooded with excess calcium, oxygen and other products

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ischemia and hemorrhage also cause

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edema; disruption of the sodium-potassium pump leading to the accumulation of sodium ions inside neurons

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edema

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the accumulation of fluid in the brain resulting in increased pressure on the brain and increasing the probability of further strokes

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drug that helps with stroke treatment

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tissue plasminogen activator tPA

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tPA

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tissue plasminogen activator; breaks up blood clots and reduces the effects of an ischemic stroke

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research has begun to attempt to save cells in the penumbra

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by blocking glutamate synapses, but the results have not been promising

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Penumbra

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region that surrounds the immediate damage

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cannabinoids

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have also been shown to potentially minimize cell loss through anti-oxidant and anti-inflammatory actions

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what is the most effective laboratory method used to minimize damage caused by strokes

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cool the brain