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PSB2000 EXAM 2 In Class Lecture Note Outline Summaries CHAPTER 5 Brain Development Plasticity Nervous system development begins at 2 weeks CNS development occurs at neural tube fluid filled cavity eventually becomes ventricles central canal Cells lining ventricles divide Some daughter cells are primitive neurons and glia which begin to migrate toward CNS Differentiation Process that makes neurons different Begins as neuron migrates but depends on local environment Axons develop first and the cell shape and dendrites develop once neuron reaches target site MYELINATION Production of myelin sheaths around axons Order spinal cord hindbrain midbrain forebrain SYNAPTOGENESIS Formation of new synapses Formation and removal occurs throughout life Axons grow before dendrites while the neuron is migrating Axons find way to their targets by following gradients of guidance molecules Found on surface of cells extracellular matrix Dendritic growth begins and increases Once neuron reaches destination Myelination of axons begins during fetal development and continues after birth There are more neurons and axons generated during fetal development than are ultimately found in the adult brain Several factors determine which neurons and connections survive NEUROTROPHINS Chemicals that promote neuron survival and growth Various types nerve growth factor NGF brain derived neurotrophic factor BDNF neurotrophins 3 4 5 and 6 NT3 NT 5 NT6 Early in development they promote survival and growth of selected neurons Experience leads to increases in secretion of neurotrophins which promote axonal sprouting Promote regrowth of injured axons APOPTOSIS apo tosis Programed Cell Death Once an axon forms a synapse neurotrophins secreted from the target cell strengthen the connection and prevent neuron from committing suicide Apoptosis o Axons that do not receive enough neurotrophin e g NGF degenerate and the cell body dies If the neuron does not make sufficient connections by a certain age then it kills itself apoptosis POSTNATAL DEVELOPMENT CNS development continues after birth EXCEPT SOME e g olfactory neurons BUT SOME neurons form in certain parts of the adult brain e g hippocampus and cortex Formation of dendrites dendritic spines axon branches synapses continues after birth Experience impacts these processes RECOVERY OF FUNCTION AFTER NERVOUS SYSTEM DAMAGE Behavioral Compensation learning how to use remaining parts of nervous system to compensate for damage NEURAL RESPONSE TO INJURY RECOVERY OF FUNCTION AFTER NERVOUS SYSTEM DAMAGE Axons in peripheral nerves regenerate if they are damaged More likely after nerve is crushed than cut Axons in CNS cannot regenerate over Large distances Scar tissue and growth inhibiting proteins suppress regeneration in the CNS Axons can respond to neurotrophins released by nearby cell terminals by sprouting collateral axon terminals that fill synapses vacated by degenerating axons REORGANIZATIONAL EVENTS Phantom limb continuation of sensation of an amputated body part The cortex reorganizes itself after the amputation of a body part by becoming responsive to other parts of the body Original axons degenerate leaving vacant synapses into which others axons sprout DENERVATION DISUSE SUPERSENSITIVITY More sensitivity to neurotransmitter after destruction of axon POTENTIAL MECHANISMS Up regulation of receptor proteins OR of a following cascade component e g ion channels second messengers STROKE Types of strokes include Ischemia Most common Resulting from a blood clot or obstruction of an artery Neurons lose oxygen glucose Hemorrhage Less frequent Resulting from a ruptured artery Neurons are flooded with excess calcium oxygen other Ischemia and hemorrhage also cause Edema Accumulation of fluid in brain resulting in increased pressure and increasing probability of further strokes Disruption of the sodium potassium pump leading to the accumulation of sodium ions inside neurons Excess positive ions in the neuron block metabolism in the mitochondria and kill the neuron Edema and excess sodium Triggers the release of the excitatory neurotransmitter glutamate Overstimulation of neurons leads to sodium and other ions entering the neuron in excessive amounts STROKE TREATMENT Tissue Plasminogen Activator tPA breaks up blood clots and reduces the effects of an ischemic strokes Research has begun to attempt to save cells in the penumbra or region that surrounds the immediate damage by blocking glutamate synapses BUT Results have not been promising Cannabinoids shown to potentially minimize cell loss through anti oxidant and anti inflammatory actions One of the most effective laboratory methods used to minimize damage caused by strokes is to cool the brain CHAPTER 5 Summary Nervous system development begins at 2 weeks CNS development occurs at neural tube fluid filled cavity eventually becomes ventricles central canal Differentiation refers to the process that makes neurons different Myelination is the production of myelin sheaths around axons Order spinal cord hindbrain midbrain forebrain Synaptogenesis is the formation of new synapses NEUROTROPHINS are Chemicals that promote neuron survival and growth APOPTOSIS is Programmed Cell Death Behavioral Compensation means learning how to use remaining parts of nervous system to compensate for damage Axon regeneration usually occurs if crushed NOT cut or over short distances Types of strokes include Ischemia and Hemorrhage Edema is fluid in brain that increases risk for stroke Activator tPA breaks up blood clots and reduces the effects of ischemic strokes CHAPTER 6 Vision SENSORY RECEPTORS CHEMORECEPTORS e g taste buds olfactory mucosa and liver MECHANORECEPTORS e g skin ear muscles THERMAL RECEPTORS PAIN RECEPTORS special case of mechano and thermal LIGHT RECEPTORS SENSORY RECEPTORS Adequate Stimulus Every sensory receptor is tuned to respond best to a certain type of stimulus energy Generator Potential A graded potential produced in some types of receptor cells Sensory Adaptation Receptors reduce their sensitivity if continuously stimulated Reception First physical interaction between the stimulus energy and the sensory receptor Transduction Conversion of the physical energy of the stimulus into an electrochemical response Coding Correspondence between some aspect of the physical stimulus and some aspect of neural activity NEURAL CODING Intensity Strength of the stimulus Represented by the rate of action potentials in a neuron Audition Sound pressure


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FSU PSB 2000 - CHAPTER 5: Brain Development & Plasticity

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