|Making Connections - The Synapse|
Neurons have specialized
projections called dendrites and axons. Dendrites bring information to the cell body and
axons take information away from the cell body.
Information from one neuron flows to another neuron across a synapse. The synapse is a small gap separating neurons. The synapse consists of:
1. a presynaptic ending that contains neurotransmitters,
mitochondria and other cell organelles,
|See some synapses "Up Close and Personal".|
Electrical Trigger for Neurotransmission
|For communication between neurons to occur, an electrical impulse must travel down an axon to the synaptic terminal.|
Neurotransmitter Mobilization and Release
|At the synaptic terminal (the presynaptic ending), an electrical impulse will trigger the migration of vesicles (the red dots in the figure to the left) containing neurotransmitters toward the presynaptic membrane. The vesicle membrane will fuse with the presynaptic membrane releasing the neurotransmitters into the synaptic cleft. Until recently, it was thought that a neuron produced and released only one type of neurotransmitter. This was called "Dale's Law." However, there is now evidence that neurons can contain and release more than one kind of neurotransmitter.|
Diffusion of Neurotransmitters Across the Synaptic Cleft
|The neurotransmitter molecules then diffuse across the synaptic cleft
where they can bind with receptor sites on the postsynaptic ending to
influence the electrical response in the postsynaptic neuron. In
the figure on the right, the postsynaptic ending is a dendrite
(axodendritic synapse), but synapses can occur on axons (axoaxonic
synapse) and cell bodies (axosomatic synapse). |
When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential. If the number of excitatory postsynaptic events is large enough, they will add to cause an action potential in the postsynaptic cell and a continuation of the "message."
Many psychoactive drugs and neurotoxins can change the properties of neurotransmitter release, neurotransmitter reuptake and the availability of receptor binding sites.
Types of Synapses
| For another explanation
of the synapse, the Society for
Neuroscience has written a short summary called
How do nerve cells communicate?|
Play the Lost Synapse Game from the Nobel e-Museum.
|Happy 107th Birthday to the word "SYNAPSE". In 2004, the word "synapse" turned 107 years old. The word synapse was first used in a book called A Textbook of Physiology, part three: The Central Nervous System, by Michael Foster and assisted by Charles S. Sherrington, in 1897. It was probably Charles S. Sherrington who coined the term synapse. The word "synapse" comes from Greek: "syn" meaning "together" and "haptein" meaning "to clasp."|
|Try it!||Play the Interactive Word Search
Game on the neuron and neurotransmitters.|
Play an Outside Game to reinforce what you have learned about the synapse.
|BACK TO:||Exploring the Nervous System||Table of Contents|
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