The Nervous System: Learn It 2—Neuron Structure

Neuron Structure

neuron structure

Neurons are the basic building blocks of the nervous system—about 86 billion at birth. Like all cells, they have specialized parts that allow them to process and transmit information.

  • Cell membrane: The neuron’s outer surface is semipermeable, meaning it allows small, uncharged molecules to pass through while blocking larger or charged ones.

  • Soma (cell body): Contains the nucleus, which holds the cell’s genetic material and keeps the neuron functioning.

  • Dendrites: Branching extensions that receive incoming signals from other neurons.

An illustration shows a neuron with labeled parts for the cell membrane, dendrite, cell body, axon, and terminal buttons. A myelin sheath covers part of the neuron.
Figure 1. This illustration shows a prototypical neuron, which is being myelinated by a glial cell.

Signal Transmission

  • Axon: A long fiber that carries electrical signals away from the soma. It ends in axon terminals (also called terminal buttons).

  • Synaptic vesicles: Found inside the terminals; they store and release neurotransmitters, the chemical messengers of the nervous system.

  • Myelin sheath: A fatty layer produced by glial cells that insulates the axon and speeds up signal transmission.

  • Nodes of Ranvier: Small gaps in the myelin sheath that allow the electrical signal to “jump” from node to node for faster communication.

    • Demyelination: Loss of myelin, as seen in multiple sclerosis (MS), slows neural communication and can cause fatigue, vision problems, and poor coordination.

Neural Communication

  • When an electrical impulse reaches the axon terminal, neurotransmitters are released into the synaptic cleft, or gap,—the tiny gap between neurons.

  • These molecules cross the cleft and bind to receptors on the dendrites of the next neuron.

This video shows the structure and physiology of a neuron.
You can view the transcript for “2-Minute Neuroscience: The Neuron” here (opens in new window).
How does a neurotransmitter “know” which receptor to bind to? The neurotransmitter and the receptor have what is referred to as a lock-and-key relationship—specific neurotransmitters fit specific receptors, similar to how a key fits a lock. The neurotransmitter binds to any receptor that it fits.

Image (a) shows the synaptic space between two neurons, with neurotransmitters being released into the synapse and attaching to receptors. Image (b) is a micrograph showing a spherical terminal button with part of the exterior removed, revealing a solid interior of small round parts.
Figure 2. (a) The synaptic cleft is the space between the terminal button of one neuron and the dendrite of another neuron. (b) In this pseudo-colored image from a scanning electron microscope, a terminal button (green) has been opened to reveal the synaptic vesicles (orange and blue) inside. Each vesicle contains about 10,000 neurotransmitter molecules. (credit b: modification of work by Tina Carvalho, NIH-NIGMS; scale-bar data from Matt Russell)