Chapter 40. Structures of a Synapse

Learning Objectives

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
true
true
true
asset/activities/synapse/images/n13un01.svg
Learning Objectives:

Identify the major structures within a synapse.

Describe the functions of the major structures within a synapse.

Review

concept_review

Review

Select the NEXT button to continue with the Review.

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.

Review

concept_review

Review

Select the NEXT button to continue with the Review.

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.

Review

concept_review

Review

Select the NEXT button to continue with the Review.

asset/activities/synapse/images/n13un04.svg

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

Review

concept_review

Review

Select the NEXT button to continue with the Review.

asset/activities/synapse/images/n13un05.svg

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.

Review

concept_review

Review

Select the NEXT button to continue with the Review.

asset/activities/synapse/images/n13un06.svg

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.

Review

concept_review

Review

Select the NEXT button to continue with the Review.

asset/activities/synapse/images/n13un07.svg

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

Practice 1: Functions of Synaptic Structures

hover_review
true

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

asset/activities/synapse/images/n13un08.svg

Practice 2: Process of Synaptic Transmission

video

Practice 2: Process of Synaptic Transmission

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

Quiz 1

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.

asset/activities/synapse/images/n13un09.svg
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

Quiz 2

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

Conclusion

end_slide
asset/activities/synapse/images/n13un01b.svg
Congratulations!
You have completed the activity Title