synapses hhmi - Muhammad Jaffer Report#3...

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Muhammad Jaffer Report #3: Alternative-iBioSeminar IBioSeminar Lecture: Optical studies of individual synapses by Karel Svoboda In his seminar, Dr. Karel Svoboda ventures to explore the nature of synaptic activation, and the specificity of biochemical processes involved within the synapse. Before this is explored however, it is imperative to introduce the subject of neural communication. The human neural cortex is one of the most complicated structures in the world, with over 100 billion neurons. Each neuron is composed of an output system for transducing action potentials, namely the axon, and an input system for receiving neuronal signals, namely a complex network of dendrites. It is through this input-output system through which thousands of neurons communicate with each other. Action potentials originating in one neuron thus pass through a complicated network of channels in order to get to another neuron. They first move through the output system of the axon, channel into a pre-synaptic terminal, pass through a synaptic cleft in the form of neurotransmitters. Neurotransmitters are important chemicals that are transported through the synaptic cleft via vesicles from the pre-synaptic to the post-synaptic regions. Therefore, they are responsible for propagating a nerve impulse through the gap existing between adjacent neurons. In this presentation, one of the many neurotransmitters, glutamate, shall be considered, although many do in fact exist. After the nerve impulse is transferred, the neurotransmitted signals are transformed back into action potentials at the post-synaptic region of the dendritic arbor. From the dendritic arbor, the action potential is able to move through the dendrites and reach another neuron. Thus, the synapse, a collective name for the mechanism responsible for transferring an action potential from the axon of one neuron to the dendrite of another (that is, the pre-synaptic terminal, the synaptic cleft, and the post-synaptic region), is crucial for neuron-to-neuron communication. Each neuron can possess thousands of these small mechanisms branched out among its various dendrites, and collectively, the brain has over 100 trillion synapses. For the sake of this paper, however, the post- synaptic region of the dendritic arbor shall be termed as the synapse. Dr. Svoboda's major problem involves determining whether nerve impulse transmission from the axon triggers multiple synapses, or whether it triggers only one; that is, does synaptic transmission function specifically, or generally? Put in even more concrete terms, does a neurotransmitter such as glutamate activate one synapse only, or multiple when it enters the synaptic cleft? Another important question involves the local plasticity of a synapse; that is, do synapses increase in strength in groups, or individually? While these question may seem trivial, Dr. Svoboda makes it perfectly clear why it is important to clarify this issue: synapses have been found to play a major role in the process of memory
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synapses hhmi - Muhammad Jaffer Report#3...

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