What is a neuron?
A neuron is a specialized cell of the nervous system that transmits nerve impulses. They carry messages through an electrochemical process.
How are neurons classified?
Neurons can be classified in two ways:
- By the number of extensions that extend from the soma, or the neuron’s cell body
- By the direction that they send information
The most common classification that I’ve seen in my studies (especially for the MCAT and other standardized exams) is the direction classification.
Direction Classification of Neurons
-> Sensory (afferent) neurons: this type of neuron sends information from sensory receptors (i.e. if you smell, taste, touch, hear something) TO the Central Nervous System.
So remember, Afferent Arrives at the Central Nervous System
-> Motor (efferent) neurons: this type of neuron sends information AWAY from the Central Nervous System
So remember, Efferent Exits the Central Nervous System
-> Interneurons: this type of neuron sends information between the sensory neurons and motor neurons. These neurons need to be able to talk to one another to coordinate what to tell the body to do based off of the new information.
For example, if you touch a hot stove you pull your hand away– a movement made possible in part by the interneurons facilitating communication.
Parts of a Neuron:
Ok, so now we know what a neuron is and what types of neurons there are. But what about the parts of a neuron?
Nucleus: Contains genetic material (chromosomes) which the cell needs to survive, basically the brain of the neuron.
Dendrite: Extensions from the neuron cell body that send messages to the cell body
Cell Body (soma): The part of the neuron that contains the nucleus
Nodes of Ranvier: Gaps in the myelin sheath coating, they allow for ions to diffuse in and out of the neuron. This helps the electrical signal move down the axon.
Axon Terminals: End part of the axon that conducts electrical signals to a nerve synapse. A neurotransmitter carries this signal across a synapse to another axon.
Schwann Cells (Myelin Sheath): Schwann cells produce the myelin sheath which insulates the axon to increase the rate of electrical signals.
Axon: Long part of the neuron where impulses are conducted. It essentially takes information away from the cell body.
Here’s a cool graphic I made to help you put it all together!
Click here to learn about the most common Neurotransmitters!
Sources/Where to head to learn more: