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Neuroscience · Structure

Neuron Diagram

The parts of a neuron and what they do: dendrites, cell body, axon hillock, axon, myelin sheath, nodes of Ranvier, axon terminals and the synapse.

A motor neuron, the nerve cell that carries commands from the spinal cord to a muscle, laid out so its signal runs from left to right, with one synapse drawn large below. Press any part to see what it does, or take the tour. Not to scale: the axon can be about a metre long.

Also called Nerve cell or Structure of a neuron.

A labelled motor neuron with the signal running left to right. Branching dendrites lead into the cell body, which holds a nucleus with a nucleolus and dark Nissl bodies. The axon leaves the cell body at the axon hillock and runs to the right, wrapped in segments of myelin sheath, each a Schwann cell with its nucleus, separated by bare nodes of Ranvier; dashed arrows below show the signal jumping from node to node. The axon ends in branching terminals with synaptic knobs. A circle below magnifies one knob: vesicles of neurotransmitter, one fusing with the membrane, the synaptic cleft, and receptors on the muscle fibre beyond. An arrow shows the direction of the signal.Saltatory conductionDirection of the signalDendritesAxon hillockSchwann cellMyelin sheathNode of RanvierAxonAxon terminalsCell body (soma)NucleusNissl bodiesSynaptic knobSynaptic vesiclesNeurotransmitterMuscle fibre (next cell)Synaptic cleftReceptors
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Press any part of the diagram, or pick one here, to see what it is and what it does.

Download the diagramChecked against its sources on 29 October 2026.

A tour

A tour of the neuron

  1. 01The neuron at a glance

    A neuron is a cell built to carry signals. This one is a motor neuron, which carries commands from the spinal cord to a muscle. Like most neurons it has three main parts: dendrites that receive signals, a cell body that keeps the cell alive, and a single long axon that sends the signal on.

  2. 02Dendrites and the cell body

    Dendrites branch out from the cell body and receive signals from other neurons at synapses on their surface. The cell body holds the nucleus and the Nissl bodies, clumps of rough endoplasmic reticulum where the neuron makes its proteins.

  3. 03The axon hillock: fire or not

    Each incoming signal nudges the membrane potential up or down a little. The changes spread to the axon hillock and the initial segment just beyond it, where they are summed. If the total reaches threshold, about −55 mV, an action potential starts, usually in the initial segment; if not, nothing is sent. The signal is all or none.

  4. 04The axon and its myelin

    The axon carries the action potential away from the cell body. Along most of its length it is wrapped in myelin: in a nerve, outside the spinal cord, each segment is a Schwann cell wound round the axon many times. The fatty layers insulate the axon, so far less charge leaks out through its membrane.

  5. 05Nodes of Ranvier: saltatory conduction

    Between the segments of myelin are short bare gaps, the nodes of Ranvier, crowded with voltage-gated sodium channels. The action potential is renewed only at the nodes, so it seems to jump from one to the next: saltatory conduction, from the Latin for leap. This makes a myelinated axon conduct far faster than a bare one of the same width.

  6. 06Axon terminals

    At its end the axon divides into fine branches, each ending in a swelling, the synaptic knob. Each knob meets the next cell at a synapse. For a motor neuron the next cells are skeletal muscle fibres, and one neuron's branches can reach many fibres at once.

  7. 07Across the synapse

    When the action potential reaches a knob, calcium flows in and vesicles fuse with the membrane, releasing neurotransmitter into the synaptic cleft. It diffuses across and binds to receptors on the next cell. At a muscle fibre the transmitter is acetylcholine, and binding starts the electrical signal that makes the fibre contract.

  8. 08One way only

    A signal passes through a neuron one way, as the arrow shows: in at the dendrites and cell body, out along the axon to the terminals. Only the knobs release neurotransmitter, and the patch of axon that has just fired is briefly refractory, so the action potential cannot turn back.

Parts

What each part of the neuron does

Dendrites
Short, branching processes that receive signals from other neurons, mostly at synapses on their surface, and carry them to the cell body. Their branches give a large surface for incoming signals.
Cell body (soma)
Holds the nucleus and most of the organelles, and makes the proteins the neuron needs. Signals from the dendrites pass through it to the axon. A motor neuron's cell body lies in the spinal cord or brainstem.
Nucleus
Holds the neuron's DNA. It is large and round, with a clear nucleolus, a sign of a cell that makes a great deal of protein. Mature neurons do not divide, so most must last a lifetime.
Nissl bodies
Clumps of rough endoplasmic reticulum and ribosomes in the cell body and the bases of the dendrites, where the neuron makes its proteins, including those it needs for its neurotransmitter. There are none in the axon hillock or the axon.
Axon hillock
The cone where the axon leaves the cell body. Here and in the stretch just beyond it, the initial segment, the incoming signals are summed; if they reach threshold, an action potential fires, usually starting in the initial segment.
Axon
The single long process that carries action potentials away from the cell body. A motor neuron's axon runs out in a nerve to a muscle and can be about a metre long.
Myelin sheath
A fatty covering made of many layers of cell membrane wrapped round the axon, in segments. It insulates the axon, so the signal travels much faster. Myelinated axons make up the white matter of the brain and spinal cord.
Schwann cells
Outside the brain and spinal cord, each segment of myelin is one Schwann cell wound round the axon many times, its nucleus pressed to the outside. Inside them, cells called oligodendrocytes make the myelin instead.
Nodes of Ranvier
Short bare gaps between the segments of myelin, where the axon's membrane is exposed and packed with voltage-gated sodium channels. The action potential is renewed at each node in turn.
Axon terminals
The axon ends in fine branches, each swelling into a synaptic knob (also called a terminal bouton). Each knob meets the next cell at a synapse, where the signal is passed on by a chemical.
Synaptic vesicles
Tiny membrane sacs in the knob, each filled with neurotransmitter. When an action potential arrives, calcium flows into the knob and vesicles fuse with its membrane, releasing their contents by exocytosis.
Neurotransmitter
The chemical messenger released into the cleft. Where a motor neuron meets a skeletal muscle fibre, it is acetylcholine.
Synaptic cleft
The narrow gap between the knob and the next cell. The neurotransmitter crosses it by diffusion in a tiny fraction of a millisecond.
Receptors
Proteins in the next cell's membrane that the neurotransmitter binds to. On a muscle fibre they are ion channels that open when acetylcholine binds, starting an electrical signal in the fibre.
Muscle fibre (next cell)
A motor neuron passes its signal to skeletal muscle fibres, at neuromuscular junctions, and the fibres contract. Other neurons pass theirs to another neuron, a gland, or smooth or heart muscle.

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Sources

Where the facts come from

Drawn and written by biofideX from these sources.

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