Neuron Function
A neuron has a typical three-part structure: cell body, dendrites, and axon.
Reading a Neuron as a Route
A neuron is a cell built to process and transmit information. Its structure can be understood as an information route: signals arrive through some parts of the cell, and the neuron's output leaves through another part. The most useful way to study the structure is to follow the direction of information from input to output.
Start with direction. Dendrites receive input, the cell body is the central part named in the typical three-part structure, and the axon carries output away toward a receiving target.
Three Main Parts
A typical neuron has three main structural parts: the cell body, dendrites, and one axon. These parts are not interchangeable. Dendrites are associated with receiving input, while the axon carries the neuron's output onward. The cell body is the central cell component named alongside the dendrites and axon.
| Part | Information-flow role |
|---|---|
| Dendrites | Receive input |
| Cell body | Central part of the typical three-part structure |
| Axon | Carries output away toward a receiving target |
The parts are best distinguished by their positions in the input-to-output route.
Following the Signal
Tracing One Incoming Signal
Trace a simplified incoming signal through a neuron to a receiving target.
Arrival: The signal arrives at the dendrites, the structures associated with receiving input.
Movement toward the center: The information moves toward the cell body as part of the neuron's input-to-output route.
Output route: The neuron's output is carried away through the axon.
Electrical pulse: The output consists of action potentials, also called spikes, traveling along the axon.
Target: The axon carries the output onward toward a receiving target.
Incoming signal → dendrites → cell body → axon → action potential traveling along the axon → receiving target.
This trace does not treat the neuron as a list of unrelated labels. It uses each part in the direction of information flow. Dendrites answer the question, “Where does input arrive?” The axon answers, “Which route carries the neuron's output away?” The action potential describes the electrical pulse moving along that output route.
Action Potential Travel
An action potential, also called a spike, is an electrical pulse that travels along the axon. The axon is therefore not merely a fiber shown in a drawing; it is the route along which the neuron's output travels. To describe the event, focus on movement: the pulse travels from one section of the axon to the next and continues toward a receiving target.
What do you think happens?
If a neuron generates an electrical pulse that travels along its axon, what is that event called?
Reveal answer
Answer: An action potential, also called a spike.
The source describes the neuron's output as action potentials, or spikes, traveling along the axon. When the neuron generates a spike, it is said to fire.
Dendrites and Axons
Dendrites and axons have opposite directional roles in the simplified information route. Dendrites carry incoming information toward the cell body because they receive input. The axon carries information away from the neuron because it transports the output toward a receiving target. Remembering this contrast is more useful than memorizing the names without their functions.
When labeling a neuron diagram, add a direction arrow before trying to memorize the parts. Label the receiving structures on the input side as dendrites, the central component as the cell body, and the long output-carrying route as the axon.
Common Identification Errors
Treating dendrites and the axon as interchangeable.
Dendrites are associated with receiving input, while the axon carries output.
Fix:
Use the directional contrast: input arrives through dendrites; output travels away through the axon.Describing the axon as only a structural fiber.
The axon is the route along which action potentials, or spikes, travel.
Fix:
Mention that the axon carries the neuron's output as electrical pulses.Using the word firing without connecting it to a spike.
A neuron is said to fire when it generates a spike.
Fix:
Explain that firing means generating an action potential, also called a spike.Listing the three parts without tracing information flow.
The important distinction is how the parts participate in the input-to-output route.
Fix:
Describe dendrites as receiving input, the cell body as the central part, and the axon as carrying output toward a receiving target.
Practice the Trace
A diagram shows branching structures receiving a signal, a central cell component, and one long fiber extending away. Identify the three main parts and trace the information route from the incoming signal to the receiving target. Include the name of the electrical pulse that travels along the output route.
Hints
- The branching structures associated with receiving input are dendrites.
- The central component is the cell body.
- The long output-carrying fiber is the axon.
- The electrical pulse traveling along the axon is an action potential, also called a spike.
Checking a Complete Answer
Construct a complete one-sentence explanation of the signal route.
Name the input structure: Begin with dendrites because they receive the incoming signal.
Name the central part: Next identify the cell body as the central part in the typical three-part structure.
Name the output structure: Then identify the axon as the structure that carries output away.
Name the traveling pulse: Specify that an action potential, or spike, travels along the axon.
Input arrives through the dendrites, moves toward the cell body, and the neuron's output travels as an action potential along the axon toward a receiving target.
Key Takeaways
- A typical neuron has three main parts: the cell body, dendrites, and one axon.
- Dendrites receive input, while the axon carries output away toward a receiving target.
- An action potential, also called a spike, is an electrical pulse that travels along the axon.
- A neuron is said to fire when it generates a spike.
- A useful information trace is: incoming signal → dendrites → cell body → axon → action potential traveling along the axon → receiving target.
Key Takeaways
- The three main parts of a typical neuron are the cell body, dendrites, and axon.
- Dendrites receive incoming information, while the axon carries the neuron's output away.
- An action potential, or spike, is an electrical pulse that travels along the axon.
- To explain neuron function, trace the route from input through the dendrites and cell body, along the axon, and toward a receiving target.