[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Histology](https://durgical.com/en/histology/) › [Nervous tissue](https://durgical.com/en/histology/#a-nervous) › The neuron and synapse

[Histology](https://durgical.com/en/histology/) · [Nervous tissue](https://durgical.com/en/histology/#a-nervous)

# The neuron and synapse

- Cell

Neurons are the cells that carry electrical signals; they pass the message to the next cell at a synapse.

Updated 2026-11-01

**See it in 3D:** [Spinal cord](https://durgical.com/en/anatomy/spinal-cord/) · [Grey matter of the cord](https://durgical.com/en/anatomy/grey-matter-of-spinal-cord/) · [Dorsal root ganglia](https://durgical.com/en/anatomy/spinal-ganglion/)

## Key points

- Nissl bodies = rough ER; absent in the axon hillock and axon.
- Mature neurons are permanent cells: they do not divide.
- Pseudounipolar = dorsal root ganglion sensory neurons; bipolar = retina and olfactory epithelium.
- Kinesin anterograde, dynein retrograde.
- Red neurons are the earliest marker of ischemic neuronal death.

## What it is

The neuron is the signalling cell of nervous tissue. It has a cell body (soma or perikaryon) with the nucleus, branched dendrites that receive input, and a single axon that carries the action potential away, often wrapped in myelin. At the synapse, the axon terminal releases neurotransmitter onto the next neuron, a muscle fibre or a gland. Mature neurons do not divide.

## Structure

- Cell body: large, with a round pale (euchromatic) nucleus and a prominent nucleolus, like an owl's eye.
- Nissl substance: clumps of rough endoplasmic reticulum and ribosomes that stain blue-purple in the soma and dendrites but are absent from the axon hillock and axon.
- Dendrites: tapering, branched processes with spines; the axon is a single uniform process starting at the pale axon hillock.
- Neurofilaments and microtubules run along the processes; silver stains show them.
- Lipofuscin, a brown wear-and-tear pigment, accumulates in old neurons; neuromelanin colours the neurons of the substantia nigra.

## Function

- Dendrites and soma receive and sum inputs; the action potential starts at the axon initial segment.
- Axonal transport moves cargo along microtubules: kinesin forward (anterograde), dynein back to the soma (retrograde).
- Chemical synapse: calcium entry at the terminal causes vesicles to fuse and release transmitter, which binds receptors on the postsynaptic membrane.
- Electrical synapses (gap junctions) pass current directly and are less common in humans.

## Neurons by shape

| Type | Shape | Where |
| --- | --- | --- |
| Multipolar | One axon, many dendrites | Most neurons: motor neurons of the anterior horn, cortical pyramidal cells, Purkinje cells |
| Bipolar | One axon and one dendrite | Retina, olfactory epithelium, spiral and vestibular ganglia |
| Pseudounipolar | One process that splits into a peripheral and a central branch | Sensory neurons of dorsal root and cranial ganglia |

## Clinical notes

- Parkinson disease: loss of pigmented dopaminergic neurons in the substantia nigra, with Lewy bodies (alpha-synuclein) in survivors.
- Alzheimer disease: neurofibrillary tangles (tau) inside neurons and amyloid plaques outside them.
- Red neurons: after a few hours of ischemia neurons shrink with pink cytoplasm and dark nuclei, the first sign of irreversible injury.
- Rabies and herpes viruses travel to the cell body by retrograde axonal transport; tetanus toxin uses the same route.

## Memory aid

Dendrites listen, the soma decides, the axon speaks.

## Test yourself

Think of the answer, then tap the question to see it.

## What are Nissl bodies, and where are they absent?

Clumps of rough endoplasmic reticulum and free ribosomes in the soma and dendrites; they are absent from the axon hillock and the axon.

## Which type of neuron is found in the dorsal root ganglia?

Pseudounipolar sensory neurons, whose single process splits into a peripheral and a central branch.

## Which motor protein carries cargo from the axon terminal back to the cell body?

Dynein, which drives retrograde transport along microtubules.

## What triggers vesicle release at a chemical synapse?

Depolarization of the axon terminal opens voltage-gated calcium channels; calcium entry makes vesicles fuse with the membrane and release neurotransmitter.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/histology/the-neuron-and-synapse/)

## See it in 3D

The structures of Durgical's 3D anatomy where it is found.

- [Spinal cord](https://durgical.com/en/anatomy/spinal-cord/)
- [Grey matter of the cord](https://durgical.com/en/anatomy/grey-matter-of-spinal-cord/)
- [Dorsal root ganglia](https://durgical.com/en/anatomy/spinal-ganglion/)

## Related

- [Glial cells: astrocytes, oligodendrocytes, microglia, Schwann cells](https://durgical.com/en/histology/glial-cells-astrocytes-oligodendrocytes-microglia-schwann-cells/)
- [Peripheral nerve: endoneurium, perineurium, epineurium; myelin](https://durgical.com/en/histology/peripheral-nerve-endoneurium-perineurium-epineurium-myelin/)
- [Gray and white matter, cerebellar cortex, meninges](https://durgical.com/en/histology/gray-and-white-matter-cerebellar-cortex-meninges/)
- [Nerve injury and regeneration (Wallerian degeneration)](https://durgical.com/en/histology/nerve-injury-and-regeneration/)
- [Cytoskeleton: microfilaments, intermediate filaments, microtubules](https://durgical.com/en/histology/cytoskeleton-microfilaments-intermediate-filaments-microtubules/)
- [The cell membrane and transport](https://durgical.com/en/histology/the-cell-membrane-and-transport/)

## Related conditions

- [Parkinson disease](https://durgical.com/en/conditions/parkinson-disease/)
- [Alzheimer disease](https://durgical.com/en/conditions/alzheimer-disease/)
- [Epilepsy and seizures](https://durgical.com/en/conditions/epilepsy-and-seizures/)

[← All of histology](https://durgical.com/en/histology/)

Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.

Sources: [12.2 Nervous Tissue](https://openstax.org/books/anatomy-and-physiology-2e/pages/12-2-nervous-tissue) (OpenStax, 2022); [4.5 Nervous Tissue Mediates Perception and Response](https://openstax.org/books/anatomy-and-physiology-2e/pages/4-5-nervous-tissue-mediates-perception-and-response) (OpenStax, 2022); [Nervous Tissue](https://training.seer.cancer.gov/anatomy/cells_tissues_membranes/tissues/nervous.html) (National Cancer Institute, SEER Training Modules, 2024); [12.1 Basic Structure and Function of the Nervous System](https://openstax.org/books/anatomy-and-physiology-2e/pages/12-1-basic-structure-and-function-of-the-nervous-system) (OpenStax, 2022).

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Representative model, for educational purposes only.

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