The human nervous system is a breathtaking network of communication, thought, and response. At the heart of this system lies a specialized, highly adaptable cell — the neuron. Also known as a nerve cell, it is responsible for transmitting information throughout the body via electrical and chemical signals. Understanding the structure of a neuron is fundamental for students preparing for exams like NEET, CBSE Class 11–12, or anyone fascinated by biology and neuroscience.
What is a Neuron?
A neuron is the basic structural and functional unit of the nervous system. These cells are responsible for receiving, processing, and transmitting information via nerve impulses — a form of electrical signaling.
The average adult human has about 86 billion neurons, most of which are found in the brain and spinal cord.
Labeled Diagram of a Neuron
The diagram above beautifully illustrates the full anatomy of a typical motor neuron, including:
- Dendrites
- Cell Body (Soma)
- Nucleus
- Nissl Bodies
- Axon
- Schwann Cell
- Node of Ranvier
- Myelin Sheath
- Axon Terminal
- Telodendria
- Synaptic End Bulb
Let’s break each part down for deeper understanding.
1. Dendrites
These are branched extensions from the cell body that receive signals from other neurons. They are the entry point of information into the neuron.
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2. Cell Body (Soma)
Contains the nucleus, cytoplasm, and organelles including Nissl bodies (granules of rough ER) that synthesize proteins. It integrates the incoming signals and decides whether to fire a signal down the axon.
3. Nucleus
Houses the genetic material of the neuron and controls all cellular activities including protein synthesis.
4. Axon
A long, thin fiber that carries nerve impulses away from the cell body toward other neurons or effectors like muscles.
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5. Myelin Sheath
A fatty insulating layer wrapped around the axon (formed by Schwann cells). It enables faster transmission of impulses by allowing the signal to jump across nodes.
6. Schwann Cells & Neurilemma
Schwann cells wrap around the axon to form the myelin sheath. The outer layer of Schwann cells is called the neurilemma, essential for axon regeneration in the PNS (Peripheral Nervous System).
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7. Node of Ranvier
These are gaps in the myelin sheath where the axonal membrane is exposed. They increase speed of nerve impulse conduction via saltatory conduction.
8. Axon Terminal, Telodendria, and Synaptic End Bulb
The axon ends in multiple branches called telodendria, each ending in a synaptic end bulb which contains neurotransmitters. These terminals connect to other neurons, muscles, or glands at a synapse.
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Table: Parts of Neuron and Their Functions
| Part | Function |
|---|---|
| Dendrites | Receive incoming signals |
| Cell Body (Soma) | Integrates signals, contains nucleus |
| Nucleus | Controls all neuron activities |
| Axon | Carries signal away from the cell body |
| Myelin Sheath | Insulates axon and speeds up impulse transmission |
| Schwann Cell | Produces myelin sheath |
| Neurilemma | Helps in axon regeneration (only in PNS) |
| Node of Ranvier | Allows rapid impulse via saltatory conduction |
| Axon Terminal | Releases neurotransmitters at the synapse |
| Telodendria | Terminal branches of the axon |
| Synaptic End Bulb | Contains neurotransmitters for signal transmission |
How a Nerve Impulse Travels Through a Neuron
- Signal Reception: Dendrites receive stimulus.
- Signal Integration: Cell body decides whether to fire.
- Action Potential Generation: If threshold is reached, impulse begins.
- Impulse Propagation: Moves down the axon, jumping between Nodes of Ranvier.
- Neurotransmitter Release: Signal arrives at synaptic bulb and releases neurotransmitters.
- Transmission to Next Cell: Neurotransmitter binds to receptors on the next neuron/muscle.
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Types of Neurons
| Type | Description | Example |
|---|---|---|
| Sensory Neuron | Carries impulse from sensory organ to CNS | Touch, heat, light detection |
| Motor Neuron | Carries impulse from CNS to muscles/glands | Causing muscles to contract |
| Interneuron | Connects neurons within CNS | Found in brain and spinal cord |
Disorders Related to Neurons
- Multiple Sclerosis: Damaged myelin sheath slows impulses.
- Guillain-Barré Syndrome: Immune system attacks Schwann cells.
- Neuropathy: Nerve damage due to diabetes or injury.
- ALS (Lou Gehrig’s Disease): Gradual degeneration of motor neurons.
Interesting Facts
- Neurons can’t regenerate in the CNS but can in the PNS if neurilemma is intact.
- The fastest nerve impulse can travel at over 100 m/s.
- Some neurons in the brain (like in the hippocampus) can form new connections lifelong — a concept known as neuroplasticity.
