http://www.ck12.org Chapter 1. Human Biology
Both types of neurons work together. Sensory neurons carry information about the environment found inside or
outside of the body to the central nervous system. The central nervous system uses the information to send messages
through motor neurons to tell the body how to respond to the information.
The Synapse
The place where the axon of one neuron meets the dendrite of another is called asynapse. Synapses are also found
between neurons and other types of cells, such as muscle cells. The axon of the sending neuron does not actually
touch the dendrite of the receiving neuron. There is a tiny gap between them, the synaptic cleft (Figure1.74).
FIGURE 1.74
This diagram shows a synapse between
neurons. When a nerve impulse arrives at
the end of the axon, neurotransmitters are
released and travel to the dendrite of an-
other neuron, carrying the nerve impulse
from one neuron to the next.The following steps describe what happens when a nerve impulse reaches the end of an axon.
- When a nerve impulse reaches the end of an axon, the axon releases chemicals calledneurotransmitters.
- Neurotransmitters travel across the synapse between the axon and the dendrite of the next neuron.
- Neurotransmitters bind to the membrane of the dendrite.
- The binding allows the nerve impulse to travel through the receiving neuron.
Did you ever watch a relay race? After the first runner races, he or she passes the baton to the next runner, who
takes over. Neurons are a little like relay runners. Instead of a baton, they pass neurotransmitters to the next neuron.
Examples of neurotransmitters are chemicals such as serotonin, dopamine, and adrenaline.
You can watch an animation of nerve impulses and neurotransmitters at http://www.mind.ilstu.edu/curriculum/neu
rons_intro/neurons_intro.php.
Some people have low levels of the neurotransmitter called serotonin in their brain. Scientists think that this is one
cause of depression. Medications called antidepressants help bring serotonin levels back to normal. For many people
with depression, antidepressants control the symptoms of their depression and help them lead happy, productive lives.
Vocabulary
- axon: Long, threadlike part of a neuron that transmits nerve impulses to other cells.
- cell body: Central part of a neuron that contains the nucleus and other cell organelles.