Concept Practice
Structures of a Synapse

Chapter 40. Structures of a Synapse

action potential
a brief electrical charge (neural impulse) that travels down an axon
axon
part of a neuron specialized to send impulses to other neurons (or to muscles and glands)
axon terminals
branching fibers at the end of an axon that contain the neurotransmitters (also called synaptic terminals or terminal buttons)
dendrites
parts of a neuron specialized to receive messages from other neurons and conduct them toward the cell body
neural impulse
an electrical signal that carries a message along an axon
neuron
a single nerve cell, forming the basic unit of the nervous system
neurotransmitters
chemical messengers released by the axon terminal into the synaptic gap between neurons
postsynaptic membrane
membrane on the axon terminal of the sending neuron
presynaptic membrane
membrane on the dendrite of the receiving neuron
receptor
special area on a neuron's membrane that can bind with neurotransmitters
synapse
the junction of the axon terminal of the sending neuron with the dendrite or cell body of the receiving neuron
synaptic gap
the tiny space between the sending neuron and the receiving neuron; also called synaptic cleft
synaptic vesicles
sacs in the axon terminals that contain the neurotransmitters
synaptic transmission
chemical process by which the neural impulse is passed from the axon terminal of one neuron to the dendrite or cell body of another neuron
Structures of a Synapse
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The figure is a diagram of an axon, dendrite, and synapse. The axon is the part of the presynaptic cell that sends messages away from the cell body to another cell. The end of the axon resembles a bulb shape and contains vesicles. The vesicles are called synaptic vesicles and contain neurotransmitters inside them. These vesicles move to the end of the axon, which is called the axon terminal, where they release neurotransmitters into the synapse. The synapse, also called the synaptic gap, is the space between the axon of the sending neuron and dendrite of the receiving neuron. The dendrite of the postsynaptic neuron has receptors, which resemble locked gates. The neurotransmitters can fit into the lock of these receptors to keep them closed or to open them.
Learning Objectives:

Identify the major structures within a synapse.

Describe the functions of the major structures within a synapse.

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The image shows neurons connected via dendrites and axons. The image looks like a series of spider webs with large centers representing the cell bodies, with lines extending from these centers and connecting to other cell bodies.

1. Neurons interweave so intricately that even with a microscope it is hard to see where one neuron ends and another begins.

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The figure is a diagram of an axon, dendrite, and synapse. The axon is the part of the presynaptic cell that sends messages away from the cell body to another cell. The end of the axon resembles a bulb shape and contains vesicles. The vesicles are called synaptic vesicles and contain neurotransmitters inside them. These vesicles move to the end of the axon, which is called the axon terminal, where they release neurotransmitters into the synapse. The synapse, also called the synaptic gap, is the space between the axon of the sending neuron and dendrite of the receiving neuron. The dendrite of the postsynaptic neuron has receptors, which resemble locked gates. The neurotransmitters can fit into the lock of these receptors to keep them closed or to open them.

2. Each of the axon terminals of a neuron is separated from the receiving neuron by a gap less than a millionth of an inch wide. The junction of two neurons is called the synapse, and the gap between the neurons is called the synaptic gap, or synaptic cleft.

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The figure is a diagram of an axon, dendrite, and synapse. The axon is the part of the presynaptic cell that sends messages away from the cell body to another cell. The end of the axon resembles a bulb shape and contains vesicles. The vesicles are called synaptic vesicles and contain neurotransmitters inside them. These vesicles move to the end of the axon, which is called the axon terminal, where they release neurotransmitters into the synapse. The synapse, also called the synaptic gap, is the space between the axon of the sending neuron and dendrite of the receiving neuron. The dendrite of the postsynaptic neuron has receptors, which resemble locked gates. The neurotransmitters can fit into the lock of these receptors to keep them closed or to open them.

3. How do the neurons communicate? The axon terminals of the sending neuron contain synaptic vesicles filled with special chemicals known as neurotransmitters.

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The figure is a diagram of an axon, dendrite, and synapse. When an action potential travels down the axon it causes the synaptic vessicles to move to the end of the axon terminal and release neurotransmitters into the synaptic gap.

4. When the neural impulse (the action potential) from the sending neuron travels along the axon and reaches an axon terminal, the synaptic vesicles move to the presynaptic membrane, then open up and release their neurotransmitter molecules into the synaptic gap.

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The figure is a diagram of an axon, dendrite, and synapse. The synaptic vesicles have released their neurotransmitters into the synaptic gap. The neurotransmitters travel across the synaptic gap and rest on the receptors on the postsynaptic membrane of the dendrite.

5. The neurotransmitter molecules from the sending neuron diffuse across the gap and come to rest on special receptors on the postsynaptic membrane of the receiving neuron's dendrite.

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The figure is a diagram of an axon, dendrite, and synapse. The synaptic vesicles have released their neurotransmitters into the synaptic gap. The neurotransmitters travel across the synaptic gap and rest on the receptors on the postsynaptic membrane of the dendrite. When enough of the receptors have been stimulated by neurotransmitters, they pass along the message down the dendrite to the cell body of the postsynaptic cell.

6. If enough receptors are stimulated, the next neuron gets the message. This is called synaptic transmission.

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Practice 1: Functions of Synaptic Structures

Roll over each label to see a brief description.

Function of the selected synaptic structure:

carries signals from the neuron's cell body to the axon terminal

forms a junction with the dendrite of the receiving neuron

binds with the neurotransmitter and influences the new electrical signal

chemical messengers that are released into the synaptic gap

small membrane sac that contain neurotransmitters

the physical space between two neurons; also called the synaptic cleft

receives signals from other neurons

The figure is a diagram of an axon, dendrite, and synapse. Each of the following elements can be selected for a description of the function of each: axon, axon terminal, synaptic gap, receptor, dendrite of receiving neuron, neurotransmitters, and synaptic vessicle. The axon is the part of the presynaptic cell that sends messages away from the cell body to another cell. The end of the axon resembles a bulb shape and contains vesicles. The vesicles are called synaptic vesicles and contain neurotransmitters inside them. These vesicles move to the end of the axon, which is called the axon terminal, where they release neurotransmitters into the synapse. The synapse, also called the synaptic gap, is the space between the axon of the sending neuron and dendrite of the receiving neuron. The dendrite of the postsynaptic neuron has receptors, which resemble locked gates. The neurotransmitters can fit into the lock of these receptors to keep them closed or to open them.
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Practice 2: Process of Synaptic Transmission

Play the animation to view the events involved in synaptic transmission.

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    • descriptions off, selected
      dnd_test

      Quiz 1

      Drag each label to the gray area next to the appropriate structure. When all the labels have been placed, select the CHECK ANSWER button.

      The figure includes an image of two cells with a gap between them on the left side of the screen, which the various parts unlabeled. The label options include the following: synaptic gap, receptor, synaptic vessicle, neurotransmitters, axon, axon terminal, and dendrite of receiving neuron. The following descriptions are for the labels from top to bottom of the image. The first label points to the tube extending from the first cell. The second label points to the many small containers at the end of the long tube. The third label points to the base of the tube containing the small containers. The fourth label points to the items contained with the small containers at the base of the tube and those that have been released into the gap between the first and second cell. The fifth label is the gap between the base of the long tube of the first cell and the membrane of the second cell. The sixth label is for the tube of the second cell that lies at the gap. The seventh label is for the gates on the membrane of the second cell.
      Select the NEXT button and move to Quiz 2.
      Perhaps you should go back to review the structures of the synapse.
      Synaptic gap
      Receptor
      Synaptic vesicle
      Axon terminal
      Axon
      Dendrite of receiving neuron
      Neurotransmitters
      matching_test

      Quiz 2

      Match the structures of a synapse with their functions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.

      Select the NEXT button and move to the Conclusion.
      Perhaps you should go back to review the structures of the synapse.
      axon of the sending neuron
      synaptic gap
      neurotransmitters
      synaptic vesicles
      receptors
      axon terminals
      dendrite of the receiving neuron
      the physical space between the two neurons; also called the synaptic cleft
      chemical messengers that are released into the synaptic gap
      carries signals from the cell body to the axon terminal
      forms a junction with the dendrite of the receiving neuron
      receives signals from other neurons
      small membrane sacs that contain neurotransmitters
      bind with neurotransmitters; influence the new electrical signals
      end_slide
      The figure is a diagram of an axon, dendrite, and synapse. The axon is the part of the presynaptic cell that sends messages away from the cell body to another cell. The end of the axon resembles a bulb shape and contains vesicles. The vesicles are called synaptic vesicles and contain neurotransmitters inside them. These vesicles move to the end of the axon, which is called the axon terminal, where they release neurotransmitters into the synapse. The synapse, also called the synaptic gap, is the space between the axon of the sending neuron and dendrite of the receiving neuron. The dendrite of the postsynaptic neuron has receptors, which resemble locked gates. The neurotransmitters can fit into the lock of these receptors to keep them closed or to open them.
      Congratulations!
      You have completed the activity Structures of a Synapse.