My textbook doesn't do a very good job of pointing out what the differences between the two are. It basically mentions axons only in the same breath as the synapse (that synapses are the endings/tips of axons).
This reference is a bit basic, but lists the functions and differences between axons and dendrites. Specifically, dendrites receive signals from other neurons, to the cell body; whereas, axons take signals away from the cell body (essentially 'input-output'). A diagram of the parts and the processes is below:
This Youtube tutorial is a nice visual description of both, and how they function within a neuron.
- Means Trees in Greek;
- Are the input of the neuron;
- Receive information from other neurons or the external environment;
- Transfer information to the cell body and axons;
- Are numerous, relatively short, and branch extensively in a tree-like fashion
- May have numerous spines on them to provide a greater surface area for other neurons to synapse on;
- Receive information from other cells at these synapses. This makes dendrites postsynaptic.
- The connection between axons that synapse on dendrites is called axodendritic;
- The connection between dendrites that synapse on other dendrites is called dendrodendritic.
Axon - Means axis in Greek
The output of the neuron;
Transfers information to other neurons;
Begins at the axon hillock, which is a swelling at the junction of the axon and soma where there are many Na+ channels and the action potential starts;
Is relatively long (some reaching several feet);
Has terminal boutons at the end where the synapse is located. This makes axons presynaptic. These swellings at the terminal bouton is where the neuron synapses with another neuron;
Contains numerous vesicles which hold neurotransmitter;
Has many Ca2+ channels in the membrane;
The space between the terminal boutons and the next cell is known as the synaptic cleft, and is approximately 20 nm thick;
Most are myelinated, i.e., have myelin sheaths that are made by Schwann cells or oligodendrocytes. Myelin acts as insulator to help conduction of action potential. There are openings between the Schwann cells called Nodes of Ranvier. These help with the conduction of action potentials.
Synapse on other cells in various forms;
Axoaxonal: Axon is connected to another neuron’s axon;
Axodendritic: Axon is connected to another neuron’s dendrites
Axosomatic: Axon is connected directly to another neuron’s soma
In neuromuscular junctions, axons synapse directly on muscles.
Presynaptic and postsynaptic neuron. The synapse is shown enlarged in the inset. Source: Rowland Hall.