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Have you ever wondered how long a line would stretch if we lined up all the neurons in our body? Despite the fact that neurons come in different shapes and sizes, the average length of a neuron is approximately 10 microns. So if we were to line up 100 billion neurons that are of the average length, the line would stretch for a dazzling 600 miles! However, you might be wondering what a neuron is in the first place?
A neuron is a nerve cell that is the basic building block of the nervous system. Neurons are similar to other cells in the human body in a number of ways. However, the key difference between neurons and other cells are that neurons are specialized to transit information throughout the body through chemical and electrical forms.
Contents
1. Structure of the neuron
1.1 Dendrites
1.2 Soma
1.3 Axon
1.4 Terminal buttons
2. Types of neurons
2.1 Sensory neurons
2.2 Motor neurons
2.3 Interneurons
3. How a neuron communicates
3.1 Conduction
3.2 Neurotransmission
4. References
5. Test/quiz question
Structure of the neuron
There are four main parts of a neuron:
Dendrites
The dendrites are the part of the neuron that receives electrochemical information mainly from other neurons and directs that signal towards the soma.
Soma
This is where all the signals from the dendrites is collected and if the voltage of the incoming signals is higher then a specific threshold then the neuron will fire. (which means that it will send that signal to the axon)
Axon
The axon receives the signal from the soma and it carries the signal to the terminal buttons. The axon can really vary in size some are really short and some can go from your brain to your feet.
Terminal buttons
Terminal buttons are at the tips of the axon, they receive the electrochemical signal the cause the release of neurotransmitters. The neurotransmitters are received by other neurons, muscle tissue and gland cells.
Now the strange thing about neurons are that they are not actually connected to each other, there is a space between them called the synapse. In most cases the electrical signal can bridge the gap between the two neurons. But in other cases neurotransmitters are released and attach to receptor cites on the receiving neuron.
Here is a video explaining how a neuron works. It's worth watching just for the ending!
Types of neurons
Sensory neurons
There are sensory neurons in the skin, muscles, joints, and organs that indicate pressure, temperature, and pain. There are more specialized neurons in the nose and tongue that are sensitive to tastes and smells. Neurons in the inner ear are sensitive to vibration, and provide us with information about sound. And the rods and cones of the retina are sensitive to light, and allow us to see.
Motor neurons
Motor neurons are able to stimulate muscle cells throughout the body, including the muscles of the heart, diaphragm, intestines, bladder, and glands.
Interneurons Interneurons are the neurons that provide connections between sensory and motor neurons, as well as between themselves. The neurons of the central nervous system, including the brain, are all interneurons.
An interactive website which can help you understand the neuron better can be found here.
How a neuron communicates
Conduction
Neurons communicate with other cells as well as within itself. They have special abilities for sending electrical signals (action potentials) through axons, which allows them to communicate over long distances very fast; this mechanism is called conduction.
In conduction, an action potential, which is essentially an electric signal, is generated near the body of the axon. Unlike normal electric signals from electronic devices, the electric signal in a neuron occurs because ions move across the neuron’s membranes rather than electrons flowing through a wire.
The protein membrane of the neuron acts as a barrier to ions. Various gate-like passages in the membrane allows the ions to pass, although they open and close due to a neurotransmitter. The electrical property of the membrane changes when the concentration of ions inside the neuron changes. In its normal state, the potential of the membrane is -70 mv (millivolts) and it is polarized, resulting in the “doors” being closed. The increase or decrease in the concentration of the ions within the neuron will make it more positive, thus becoming depolarized. Eventually, it will reach a threshold, at which point a large electrical signal is generated.
This signal is then transmitted along the axon until it reaches a “terminal” (the point where neurotransmission begins), at which point conduction ends. From here, output to other neurons are sent. The output will be in the form of an signal itself if the neurons are physically connected to each other (electrical synapses) or a neurotransmitter if it is seperated by a fluid-filled synaptic cleft (chemical synapses).
An interactive flash media that walks through how an action potential is generated can be found here (Diagram under "Conduction"). There are also several cool media on the same page that explain neurotransmission. It is worth checking out!
Neurotransmission
Neurons communicate with each other via a process known as neurotransmission. Basically, an electrical impulse travels along the axon towards the terminal. There is a space between the two terminals which is commonly known as the synaptic space. The synaptic space is essentially brain fluid that acts as a barrier between the communications of the two neurons. The synaptic barrier is overcome by the movement of membrane sacs. When an electrical charge flows through the neuron, it pushes the membrane sacs to the terminal end of the neuron. The membrane sacs inside the membrane, which are known as vesicles, are released into the synaptic space. These vesicles then dock at the terminal end of the other neuron. This is the essence of communication between neurons.
"Lesson 2 - Neurons, Brain Chemistry, and Neurotransmissions." The Brain: Understanding Neurobiology. National Institutes of Health / National Institute of Drug Abuse, n.d. Web. 20 Apr. 2011. <science-education.nih.gov/supplements/nih2/addiction/videos/act2/transcript-activity2.htm>.
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