In last week’s post we covered some main points about the nervous system and explored an example of how your nervous system interacts with the rest of your body.
In a nutshell, the nervous system controls how you perceive and interact with the world around you.
That is, it plays a primary role in everything you do and experience throughout life.
If you missed it, you can read it here.
One point we touched but didn’t delve into in much detail was that the nervous system is a network of cells called neurons.
This week we’re going to talk about what a neuron is and how it’s structured, with a general overview of the roles three different types of neurons play.
This will help prepare us to discuss some of the higher-level functions of the different branches of the nervous system that we covered last week.
What is a neuron?
Neurons are the cells of the nervous system that communicate with muscles, glands, and other neurons.
The main parts of the neuron are the cell body, dendrites and axon (see image below).
The cell body contains the nucleus, mitochondria, and other organelles.
Dendrites are short extensions that transmit signals towards the cell body.
The axon, also called the nerve fiber, is a long extension that transmits signals from the cell body towards a receiving muscle, gland, or other neuron.
The axon is wrapped in a fatty coat called the myelin sheath, which helps speed up nerve impulses along the axon.
In the peripheral nervous system, the myelin sheath is made of what are called Schwann cells, whereas in the central nervous system the myelin sheath is made of what are called oligodendrocytes.
The little breaks between the myelin sheath cells are called “nodes of Ranvier”.
The point at which the axon of a neuron joins and communicates with another cell – neuron, muscle, glad, or otherwise – is called a synapse.
Neurons can be classified into three types – interneurons, sensory neurons, and motor neurons.
Interneurons, 90% of which of are located in the central nervous system, transmit information between one another.
Sensory neurons carry signals from the body to the central nervous system as information for interpretation.
The dendrites, cell bodies, and axons of sensory neurons are located in the peripheral nervous system, with their synapses located at the central nervous system.
Motor neurons are those that carry signals from the central nervous system to the rest of the body for action.
Motor neuron cell bodies and dendrites are located at the central nervous system, with their axons and synapses located in the peripheral nervous system.
Below is a simplified schematic diagram of how these three types of neurons interact.
Next week, we’ll talk more about the technical details of how signals are transmitted to and from neurons.
Until then, have a most excellent week!
Hoefnagels, M. (2012) Biology: Concepts and Investigations, Second Edition. New York, NY: Mcgraw-Hill.