Neurons
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What are the parts of a neuron? You'll watch Neuron Garciaparra work up a sweat as he throws baseballs to demonstrate the structures and functions of the billions of neurons that reside in your body.
Neurons are nerve cells that are constantly sending signals to your brain, muscles and glands. You have over 100 billion neurons in your brain sending signals. The signals help the different parts of your body communicate with each other. Thanks to neurons, you're able to swat a mosquito if you feel it land on your arm or wave to a friend if you see her walking towards you. Neurons send chemical signals called neurotransmitters, and they work quickly to help you react to everything going on around you.
Think of these neurons as little baseball players throwing balls to each other. The baseballs are the chemical signals called neurotransmitters. So, when you see a ball flying through the air towards you, sensory neurons send signals to your brain. This sets off a chain reaction of signals, which are fired off to motor neurons that cause your muscles to react so you can catch the ball.
Now, let's take a journey inside the human body to see what happens when we see, hear or touch something. Neuron Garciaparra is warming up. He has dendrites, like catching arms, that receive signals. He also has a pitching arm that fires off signals. This pitching arm is called an axon. Like a pitcher's power sleeve, a myelin sheath covers the axon, or pitching arm, and boosts the speed at which Neuron can fire off signals. The terminal branches at the end of the axon make up the pitching hand. This is where Neuron fires off signals.
Here's how it works. When the signal (ball) comes in, it excites Neuron into action. Positively charged sodium ions begin to enter the cell membrane. There are sodium ions in sports drinks, so think of this process as Neuron drinking a sports drink to increase electrolytes like sodium ions. A neural impulse, or electric current, travels from the dendrites (catching arms) through the axon (pitching arm) to the terminal branches (pitching hand) to be fired off to another neuron. This process is called the action potential. Then he winds up his pitch and...BAM!...fires off the signal.
The all-or-none law states that, once the neuron receives the signal, it has to fire it off. Like a pitcher who winds up and starts delivering the pitch, the neuron can't balk. There's no stopping once the nerve impulse has been activated. But, if your neurons don't get the signal, they don't fire. So, you'll swat a mosquito only if you feel it land on your arm. Either you feel it and the neurons deliver the signals so you can react, or you don't.
The signal (ball) flies over the synaptic gap (field) to another neuron (player) and the process repeats itself. The dendrite receives the chemical signal or neurotransmitter > excites the neuron > sodium ions enter the neuron and charge it > an electric current travels through the axon > and the terminal branches fire off the signal over the synaptic gap to the next neuron.
The synaptic gap is less than 1 millionth of an inch! In the brain, your neurons are packed together pretty tightly. But, in the outfield, some neurons have super long axons, or pitching arms. A single axon, like the one that starts at the base of your spine and extends to your big toe, can be over three feet long!
But even with these super long neurons, the same process happens. When you run to catch a ball, the dendrites catch the neurotransmitters. The neurons get excited and sodium ions charge them. Electric currents travel through the axons all the way down your leg to the terminal branches in your toes to say pick up your feet! The terminal branches fire off neurotransmitters over the synaptic gaps to your other neurons.
And this process occurs over and over again until the signals get to where they need to be to trigger your muscles and glands into action.
After the signal is fired, the neuron goes through a refractory period. What happens during this period is the neuron pumps out the sodium ions. Neuron sweats them all out and returns to his normal state, or resting potential. He's back to being mostly negatively charged...until the next time he catches a signal, which triggers him to play ball.
So, the next time you catch a ball, think about all the sensory neurons firing signals inside to activate your motor neurons in your arms and legs. These nerve cells are responsible for your senses and reactions.