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The  Synapse And The  Presynaptic And  Postsynaptic  Terminals
 

The Synapse And The Presynaptic And Postsynaptic Terminals

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    The  Synapse And The  Presynaptic And  Postsynaptic  Terminals The Synapse And The Presynaptic And Postsynaptic Terminals Presentation Transcript

    • As we learned when we talked about parts of  the neuron, neurons have specialized parts called dendrites and axons. Dendrites bring information into the neuron and axons take information away from the neuron. Neurons don’t operate in isolation. They  communicate with each other in networks. If you were to think about yourself and all your friends as connected by strings so that all of you would be part of a network of kids, then that’s a bit like neuron networks work, only the neurons are in much larger groups than a group of you and your friends. Instead of strings, the neurons are connected by the axons and dendrites.
    • However, unlike you and your friends connected by  strings, there is a gap between the place where an axon or a dendrite connects with a cell body, axon, or dendrite in the network. This gap is called the synapse. There are three major parts of the synapse:  1. a presynaptic terminal containing neurotransmitter, mitochondria (responsible for energy production in the cell) and other cell bodies, called organelles  2. a postsynaptic terminal containing receptor sites for neurotransmitter  3. a synaptic gap or space between the presynaptic terminal and the postsynaptic terminal
    • When an action potential occurs, an electrical  signal or impulse travels down the axon to the presynaptic terminal. When it reaches the presynaptic terminal, the electrical impulse causes vesicles (little packets of neurotransmitter) to move to the presynaptic membrane. There the vesicles fuse with the presynaptic membrane and release the neurotransmitters they contain into the synaptic gap
    • The neurotransmitter molecules travel across the  synaptic gap and bind on the other side with receptors on the postsynaptic terminal. This causes a change in the excitability of the postsynaptic cell. The postsynaptic cell will then be either more or less likely to fire an action potential, depending on whether the impulse is excitatory or inhibitory. If the number of excitatory postsynaptic events is large enough, the message will then be sent along to the next neuron in the network.
    • Axon and dendrites connecting at the presynaptic/postsynaptic terminals, showing the neurotransmitter being released into the synaptic gap.
    • During the process that allows synaptic transmission of  neurotransmitter to occur, a serious of things have to happen:  1. the neuron itself has to make the chemicals that will be used as neurotransmitter. These are made either in the axon’s presynaptic terminal or in the neuron’s cell body.  2. the neurotransmitter has to be transported to the presynaptic terminal if the neurotransmitter has been made in the cell body.  3. the action potential (the electrical part of the electrochemical event that causes a message to be sent) has to travel down the axon and cause calcium to enter the cell at the presynaptic terminal. Calcium causes neurotransmitter to be released from the presynaptic terminal into the synaptic gap.  4. the released neurotransmitter have to cross the synaptic gap and attach to receptor sites on the postsynaptic terminal of the neighboring neuron.  5. Left over neurotransmitter not used to send the message on through the neighboring neuron needs to either be taken back up by the presynaptic terminal, broken down and recycled so it can be used again, or disposed of.