Neuron
Neurons (nerve cells) are cells that are specialized for communication. Each neuron communicates with many other neurons to share information.
Neurons send messages electrochemically. This means that neurons communicate using both electrical and chemical signals.
Imagine you are talking on your cell phone while walking the family dog in a park. Just as you are crossing a wooden bridge over a creek, your dog spots a squirrel and yanks hard on his leash. You are thrown off balance as your phone fumbles out of your hand and flies into the air. You reach out and catch the phone before it falls over the side of the bridge. Phew!
What happened within your nervous system to help you catch your phone? A message was sent electrochemically from neuron to neuron, from your fingertips all the way to the brain where it was processed. Since a response was needed (Grab it! Quick!), the brain then passed a message back through the neurons to cause muscle impulses and movement. At lightning speed, your brain processed an astounding amount of information and sent a message back through your neurons to your hand. Your quick-acting nervous system saved your phone from a watery end in the creek below.
Here’s how a message gets relayed from neuron to neuron (remember, this all occurs at an amazingly fast speed):
Neurons have specialized cell parts called dendrites and axons. Dendrites bring electrical signals to the cell body. Axons take information away from the cell body.
Special chemicals called neurotransmitters send information from one neuron to another. These chemicals are stored and released from the synaptic terminal of a neuron. They are released by the first neuron into a space between two neurons called a synaptic gap. The neurotransmitter is taken up by the dendrites of the second neuron. If enough neurotransmitters are taken up by the dendrites, the second neuron may fire and pass its own neurotransmitter to another neuron.
When a chemical neurotransmitter is passed from one neuron to another, it can cause an electric signal (or impulse) to be carried along the receiving neuron—and that electrical signal may cause the cell to pass its own chemical neurotransmitters to another neuron.
The electrical signals carried along neurons are called action potentials. Within each neuron, it is an "all-or-none" impulse:
Once the action potential starts, it continues without interruption down the length of the axon.
The size of the action potential stays the same as it travels down the axon.
The message of Grab it! Quick! is sent to the brain, processed, and the brain then sends a message back along the neurons causing movement among the muscles in the hand. The cell phone is saved from a plunge in the creek.
Every single one of your thoughts, behaviors, and movements result from combinations of signals passed along your neurons. The action potentials in your muscles cause contractions and movement, allowing you to hold this piece of paper, breathe, move your eyeballs to read these words, listen to music, and stay upright in your chair.