By Catherine A. Sanderson, Amherst College
Neurons, or the nerve cells, are the basic building block of the nervous system. They take in sensory information from the outside world and then pass it along to the entire body. This complex system of communication is responsible for all our thoughts, feelings, and actions.
The Sciatic Nerve
Neurons themselves are very small. They are smaller than the width of a strand of hair and bundle together to form nerves. The largest nerve in the entire body—the sciatic nerve—is the same width as a thumb at its widest point and stretches from the lower back to the very tip of the big toe.
Each sciatic nerve stimulates movement of the leg muscles and carries messages between the leg and spine. Pain in this nerve—often called sciatica—is very common. It can include pain, weakness, and/or decreased sensation. Although sciatica has many causes, the most common is an injury to a disc in the spinal cord.
Anatomy of a Neuron
All neurons share the same basic anatomy. The cell body, or soma, includes the nucleus containing the genetic material of the cell, that is, the chromosomes. The cell body of the neuron coordinates all of its different functions and keeps the cell alive.
The dendrites receive information from other neurons and then convey it to the cell body. The axon, on the other hand, carry information away from the cell body to the other end of the neuron, and then on to other neurons. Thus, dendrites bring messages into the cell body from other neurons, and axons send information from the cell body to other neurons.
Interestingly, there’s an easy way to distinguish between the two ends of a neuron, the dendrites and the axon—axons speak, dendrites listen.
The Axon and Myelin Sheath
The axon is covered with a layer of fatty tissue, called the myelin sheath, which helps speed up the transmission of information. Myelin is essential for normal motor function—walking; sensory function—hearing, seeing, feeling pain; and cognition—learning.
Although, at the time of birth there’s very little myelin, but during infancy, many axons develop myelin sheaths. This development corresponds with increasing cognitive and motor skills—speaking, crawling, walking.
When there’s damage to the myelin sheath, communication between neurons becomes harder. The disease multiple sclerosis, or MS, is caused by the body’s immune system attacking the myelin sheath or the cells that produce and maintain it.
In this condition, the nerves can’t easily send and receive messages. Over time, this deterioration of the myelin sheath leads to problems with coordination and balance. If this deterioration involves the neurons that control breathing or heartbeat, it can be fatal.
This article comes directly from content in the video series Introduction to Psychology. Watch it now, on Wondrium.
Sensory and Motor Neurons
Although all neurons have the same fundamental structure, they play distinctly different roles in terms of the type of information they transit. Sensory neurons transmit information from sensory cells, or receptors, to the brain. They have specialized endings that receive signals for light, sound, touch, taste, and smell.
Motor neurons transmit commands from the brain to the glands or muscles, typically through the spinal cord. They have especially long axons, allowing individual nerve cells to reach from the base of the spine to the end of long muscles at the end of your limbs.
This means that a motor neuron in the spinal cord, which reaches the toes, might be three feet long.
Interneurons connect other neurons to each other. Their functioning comes into play when we are doing everyday tasks such as reading a text message. When we read, interneurons allow the signal from the sensory neurons in our eyes to travel to the interneurons in our spinal cord and then on to our brain so that we can make sense of the words.
Other interneurons would then signal to the motor neurons controlling our finger muscles to let us type a response, thus allowing us to do the task.
Mirror Neurons and Empathy
A type of neuron specific to the brain, the mirror neuron, was discovered in 1996. A team of Italian scientists found that neurons in monkey’s brains were activated not only when the monkey grabbed an object (as one would expect) but also when the monkey simply watched another primate perform the same grabbing action.
This led to the discovery of mirror neurons, a type of brain cell that responds the same when we perform or witness someone else perform the same action.
The discovery of mirror neurons explains many previously puzzling experiences such as feeling the need to yawn when someone else yawns, or how infants mimic the facial expressions of people around them.
They might seem like simple and unconscious reactions to what we see in the world, but mirror neurons allow us to respond to what other people are thinking and feeling. They allow us to empathize with those around us.
In the words of Giacomo Rizzolatti, one of the scientists who discovered the existence of mirror neurons,
We are social beings. Our survival depends on our understanding the actions, intentions, and emotions of others. Mirror neurons allow us to understand other people’s mind, not only through conceptual reasoning but through imitation.
Mirror neurons may help explain why happiness is contagious and why it’s a good idea to watch more positive media and surround ourselves with happy people. It’s also probably why acting like we are happy—smiling, writing affirmations, laughing—can actually make us feel happier.
Common Questions about Neurons
The cell body, or soma, includes the nucleus containing the genetic material of the cell, that is, the chromosomes. The cell body of the neurons coordinates all of its different functions and keeps the cell alive.
The disease multiple sclerosis, or MS, is caused by the body’s immune system attacking the myelin sheath or the cells that produce and maintain it.
The mirror neurons were discovered in 1996. A team of Italian scientists found that neurons in monkey’s brains were activated not only when the monkey grabbed an object (as one would expect) but also when the monkey simply watched another primate perform the same grabbing action.