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PSB2000 Study Guide Test 2 Development Primary germ layers formed and organized in their proper locations during gastrulation Endoderm internal germ layer forms the lining of the gut and other internal organs Mesoderm middle germ layer forms muscle skeletal system and circulatory system Ectoderm outer layer o A patch of tissue in ectoderm folds in to become neural plate o This fold pinches off o Chemical signals tell the cells how to develop o Eventually the tube becomes the brain The human central nervous system begins to form when the embryo is 2 years old Dorsal Surface neural tube forward end of tube becomes hindbrain midbrain and forebrain rest of neural tube becomes spinal cord Development is triggered by neural inducer cordin and noggin genes Sonic hedgehog major developmental gene called this because fruit flies with mutations to the SHH gene have extra bristles Development of neurons in the brain 1 Proliferation production of new cells neurons in the brain occurring early in life a The cells lining the ventricles divide b Some cells become stem cells that continue to divide c Some cells remain where they are or become neurons or glia that move to other locations 2 Migration movement of the new neurons and glia to their eventual locations a Some don t reach their locations until adulthood b Variety of directions through the brain c Cells follow chemical paths in the brain immunoglobins and chemokines 3 Differentiation forming of the axon and dendrite that give the neurons their distinctive shape a Axon grows first during migration then dendrites develop 4 Myelination glia produce the fatty sheath that covers the axons of some neurons a Myelin speeds the transmission of neural impulses b Occurs in spinal cord hindbrain midbrain then forebrain In that order c Occurs gradually for decades d Newborns have little myelination 5 Synaptogenesis the formation of the synapses between neurons a Occurs throughout the life as neurons are forming new connections and discarding old ones b Slows down later in life Neurogenesis formation of new nerve cells o Ex Songbirds replace neurons in singing area of brain o Stem cells differentiate into new neurons in the adult hippocampus of mammals and facilitate learning Axon Targeting axons follow a chemical trail in which they are attracted by some chemical and repelled by others to reach their appropriate target Sperry The Suicide Cell Axons form more synapses than we keep with several cells in approximate location o Some postsynaptic cells strengthen or eliminate connections with other cells o Neurotrophis chemicals that promote survival of axons NGF BDNF o Formation or elimination depends upon input form incoming axons o Apoptosis When a neuron does not get the signal to stay so it dies Developing Brain Vulnerable o Mutation Malnutrition Infection Toxins o Fetal Alcohol Syndrome Hyperactivity impulsiveness mental disability motor problems heart defects facial abnormalities Alcohol suppresses glutamate and enhances GABA Developing neurons receive less signal than normal and are pruned by apoptosis Focal hand Dystonia a result of extensive reorganization of the sensory thalamus and cortex so that touch responses to one finger overlap those of another Adolescents o Tend to be more impulsive than adults can lead to drinking risky driving sex etc and tend to discount the future o Antisaccade task looking away from an attention getter eventually improves during teens Old Age o Neurons alter synapses more slowly in old age brain structure loses volume o Intellectual decline find ways to compensate for losses from great base of knowledge and experience Plasticity ability of the brain to change Use or disuse of brain can cause it to grow or contract esp in cortex Organization and location of brain processing can change b c of learning or recovery after injury Decreases with age Greatest plasticity during infancy Allows children to learn language effectively and quickly Plasticity after damage survivors of brain damage show subtle to significant behavioral recovery o Causes of damage spinal cord damage tumors infections exposure to toxic substances degenerative diseases stroke cerebrovascular accident closed head injuries Strokes o Ischemia the most common type of stroke resulting from a blood clot or obstruction of an artery neurons lose oxygen and glucose supply o Hemorrhage less frequent type of stroke from ruptured artery neurons flooded with excess blood calcium oxygen and other chemicals o These strokes also cause edema accumulation of fluid in the brain resulting in increased pressure on the brain and increasing probability of future strokes and excess potassium They trigger the release of the excitatory neurotransmitter glutamate Overstimulation of neurons leads to sodium and other ions entering the neuron in large amounts Excess positive ions in the neuron block metabolism in the mitochondria and kill the neuron o Tissue plasminogen activator tPA breaks up blood clots reduces the effects of an ischemic stroke but can make hemorrhagic strokes worse Stroke Treatment o Cool the brain o Cannabinoids Response after damage o Surviving brain areas increase or reorganize their activity o Diaschisis decreased activity of surviving neurons after damage to other neurons o Use of drugs to stimulate activity in healthy regions of the brain after a stroke may be a mechanism of later recovery After Damage is done Lost synapses o Destroyed cell bodies cant be replaced but damaged axons can grow back o Damaged axons in the CNS don t regenerate well in mature mammals o Postsynaptic cells deprived of synaptic inputs develop increase sensitivity to the neurotransmitter to compensate for decreased input o Denervation supersensitivity heightened sensitivy to a neurotransmitter after the destruction of an incoming axon can cause chronic pain Collateral sprouts new branches formed by other non damaged axons that attach to vacant receptors Phantom Limb continuation of sensation of an amputated body part o Can lead to the feeling of sensations in the amputated part of the body when other parts of the body are stimulated Vision An ant can see 93 million miles there are no sight rays How far you see depends on how far the light traveled before it hits your eye Each sense has specialized receptors that are sensitive to a particular kind of energy Receptors for vision are sensitive to light Receptors transduce convert energy into electrochemical patterns so that the


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FSU PSB 2000 - Test 2

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