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 · Grey matter of the cord · Dorsal root ganglia

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.

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.

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See it in 3D

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

← All of 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 (OpenStax, 2022); 4.5 Nervous Tissue Mediates Perception and Response (OpenStax, 2022); Nervous Tissue (National Cancer Institute, SEER Training Modules, 2024); 12.1 Basic Structure and Function of the Nervous System (OpenStax, 2022).

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Representative model, for educational purposes only.