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Chapter 48.4

Chapter 48.4. Jacob Parker, James Pittman Phillips. . Neurons communicating with other cells at synapses. Electrical synapses contain gap junctions which allow current to flow from one neuron to the other.

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Chapter 48.4

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  1. Chapter 48.4 • Jacob Parker, James Pittman Phillips 

  2. Neurons communicating with other cells at synapses • Electrical synapses contain gap junctions which allow current to flow from one neuron to the other. • Majority of synapses are chemical synapses which involve release of neurotransmitter by postsynaptic neuron. • At each terminal, presynaptic neuron synthesizes neurotransmitter and packages it with many compartments called synaptic vesicles. • Neurotransmitter diffuses across synaptic clef, narrow gap that separate presynaptic from postsynaptic cell.

  3. Chemical Synapse 3

  4. Generation of Postsynaptic Potentials • These depolarizations bring membrane potential toward threshold, called excitatory postsynaptic potentials. • Hyperpolarizations produced this way are called inhibitory postsynaptic potentials because they move membrane potential farther from threshold. • Result is generally a postsynaptic potential, a change in membrane potential of postsynaptic cell.

  5. Summation of Postsynaptic Potentials • Unlike actions potentials, post synaptic potentials are graded; magnitude varies with the amount of neurotransmitter released by presynaptic neuron. • Some occasions, two EPSPs occur at single synapse which is an effect called temporal summation. • EPSP’s produced by different synapses on same postsynaptic neuron can also create an effect called spatial summation. • Through both spatial and temporal summation, several EPSP’s depolarize the membrane to the threshold.

  6. Modulated Synaptic Transmission • There are also synapses in which receptor for the neurotransmitter is not part of an ion channel. • Variety of signal transduction pathways play role in modulating synaptic transmission.

  7. Major Neurotransmitters 7

  8. The Amazing Brain • Nerve cells use nerve impulses, also called action potential, to develop the axon at the point where it exits from the nerve cell body. • When it reaches the axon terminal, the action potential ceases. It has done the job though because when it reaches the terminal, it triggers an entirely different process.

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