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7 Learning, etc

7 Learning, etc - Examples of func/on in the nervous...

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Unformatted text preview: Examples of func/on in the nervous system • Learning • Mental illness • Addic/on • Alzheimer’s disease Learning takes place in the brain when the strength of synapses changes. If a given presynap/c input produces a larger (or smaller) PSP in the postsynap/c cell, we say that the synap/c strength has changed. One process that causes synap/c connec/ons to become and to STAY stronger is called long ­term poten/a/on (LTP). ALer LTP has occurred, a given input from a presynap/c neuron causes a larger PSP in the postsynap/c neuron. When you study BILD 2 informa/on and learn it, you are producing LTP at some of your synapses! The process is complex, so we’ll go through it one step at a /me, but it depends en/rely on the mechanisms of synap/c transmission that we’ve already talked about. LTP takes place at glutamatergic synapses. A A.  Synapse prior to LTP. NMDA (glutamate) receptors are present in the membrane, but they are blocked by Mg2+, so ions can’t flow through these channels even if glutamate binds to the receptor. B.  If the postsynapJc cell is depolarized by ANOTHER synapJc input, the Mg2+ is pushed out of the ion channel in the NMDA receptors, and when glutamate binds to the receptors, Ca enters the postsynapJc neuron. This causes another type of glutamate receptor (called an AMPA receptor) to be inserted in the membrane. C.  Now when glutamate is released, both NMDA and AMPA channels allow ions to cross the membrane, producing a bigger PSP, and this change lasts for hours, days, weeks—even years. B C The brain is also the site of many problems that plague individuals and our society. We’ll briefly consider three: Mental illness (schizophrenia, major depression) Addic/on Alzheimer’s disease During a disease episode, people with schizophrenia have distorted percep/ons of reality. Several lines of evidence indicate that this is a disease of the brain: family history is a strong predisposing factor, and across all cultures that have been studied, about 1% of the total popula/on has this condi/on. Addic/ons all are based on the same parts located deep in the brain: the ventral tegmental area and the nucleus accumbens. The neurotransmiXer dopamine plays a central role, because when dopamine is released at synapses onto neurons of the reward pathway, intense feelings of pleasure are produced—in people, but also in rats and other animals. Many addic/ve drugs act on these parts of the brain. Alzheimer’s disease scrambles communica/on channels, incites massive inflamma/on, and demolishes en/re brain regions as once plump cells shrivel and die, burying memories in the wreckage. As the aXack intensifies, Alzheimer’s gradually strips away a person’s mind, and ul/mately the cogni/ve abili/es that permists a conversa/on with a loved one, a smile, or a taste of food. Laura Sanders, in Science News, March 12 issue. In Alheimer’s disease, there is massive loss of neurons in many loca/ons, and brain func/on is progressively disabled. A coronal sec/on through a brain removed from a healthy person aLer he or she died. A coronal sec/on through a brain removed from an Alzheimer’s pa/ent aLer he or she died. Both secJons were made at the same region of the brain. The demen/a of Alzheimer’s disease is (post mortem) accompanied by characteris/c pathological structures in the brain. Amyloid plaque is extracellular deposits of a par/cular protein; neurofibrillary tangles are excess deposits of an axonal protein. ...
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