Neuron: Definition, Structure, Parts, Function, Diagrams

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:47 PM IST

A neuron is a kind of cell in the nervous system that transmits signals for communication within the body. It is important to many functions, such as sensation, movement, and reflexes. This is one of the important topics in Class 11 under the chapter Neural Control and Coordination from which questions are asked in competitive exams like NEET and AIIMS BSc Nursing where biology is one of the main subjects.

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Neuron Definition
What is a Neuron?
Structure of a Neuron
Types of Neurons
Functions of Neurons
Recommended Video on Neuron

Neuron: Definition, Structure, Parts, Function, Diagrams

Neuron Definition

A neuron is a specific cell of the nervous system that carries electrical impulses along the pathway of the nerve, by which the brain, spinal cord, and other parts of the body can communicate with one another.

What is a Neuron?

The neuron is the main part of the brain and the nervous system. They participate in the reception, processing and transmission of sensory information and motor commands to the muscles, thus they control various body functions. These are the parts of nature that have specialised cells that transfer electrical and chemical signals. Hence, they are very much responsible for the nervous system's proper functioning.

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Structure of a Neuron

Knowing the general structure of a neuron will help us appreciate how it works in the nervous system.

Cell Body (Soma): The portion that includes the nucleus, regarded as the control centre of the cell.
Dendrites: These are incoming signal-receiving ends from other neurons.
Axon: Conducts electrical impulses away from the cell body
Myelin Sheath: Fatty, insulating layer of the axon, increasing the velocity of signal transmission.
Nodes of Ranvier: These are gaps in the myelin sheath that facilitate rapid transmission of signals.
Axon Terminals: These are responsible for releasing neurotransmitters to pass on the signals to the next neuron.

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Diagram: Structure Of Neuron

Types of Neurons

There can be three primary types of neurons based on their functions.

Sensory Neurons: These carry sensory information to the brain and spinal cord.
Motor Neurons: These transmit commands from the brain and spinal cord to muscles and glands.
Interneurons: These are neurons that connect other neurons, usually within the central nervous system. This means they connect sensory with motor neurons, therefore, facilitating communication between them.

Functions of Neurons

The neurons perform various crucial functions which help the nervous system function properly.

Signal Transmission: The neurons transmit electrical impulses called action potential.
Synaptic Transmission: It is the process through which neurotransmitters are released to communicate with other neurons.

Neurotransmitters

Thus, neurotransmitters are the chemical mediators of the signals transmitted from one neuron to another.

Dopamine: Participates in mechanisms related to reward and pleasure.
Serotonin: Modulates mood and social behaviour.
Acetylcholine: Involved in the action of muscles and memory.

The Synapse

The synapses are the junctions through which neurons communicate with each other.

The presynaptic terminal, synaptic cleft, postsynaptic membrane.
It allows the transmission of electrical or chemical signals from one neuron to another.

Neurogenesis and Neuron Plasticity

It is in charge of learning and recovery; it relies on the generation of new neurons and plasticity in the brain.

Neurogenesis: The process of new neuron generation in the Brain.
Neuron Plasticity: Changes a neuron undergoes as a result of new information, sensory stimulation, development, damage, or malfunction.

Neuron-related Disorders

Several neurological diseases are claimed to be connected to the failure of neurons.

Alzheimer’s Disease: A condition characterised by the death of neurons, and the consequences are memory loss and cognitive declines
Parkinson’s Disease: Involves the loss of dopamine-producing neurons, affecting movement and coordination.
Multiple Sclerosis: An autoimmune disorder that attacks the myelin sheath, disrupting neural communication.

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Autonomic Nervous System	Sympathetic Nervous System
Difference Between Brain and Spinal Cord	Reflex Action and Reflex Arc
Nerve Fibres	Cerebrospinal Fluid

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Frequently Asked Questions (FAQs)

1. What is the basic structure of a neuron?

The neuron is made up of a body, dendrites, and an axon The soma. It contains the nucleus, the dendrites are the messengers, and the axon carries the messages between neurons and muscle, skin, and glands.

2. How is the signalling done across neurons?

Messages are travelling down the axon as an Action potential, which is an electric. transpiration of axons. The axon is in motion by depolarising and relaxing. The neurotransmitters bring the signal to another neuron.

3. What are the types of neurons and what are their functions?

Sensory Neurons: They are receptors that transmit information to the central nervous system when the action of neurohormonal transmitters is stimulated by a particular signal from the brain.

Motor Neurons: These are the signals, the central nervous system sends to the muscles and glands through them.

Interneurons: They are the ones that along with the connecting of one neuron to another, within the central nervous system integrate and interpret sensory input and motor output.

4. How neurotransmitters are used in neuron communication?

Neurotransmitters are chemicals that cross the synaptic junction from one neuron to another neuron, thus the communication of the nervous system. The reason for the diversity of physiological functions and behaviours is largely related to them.

5. What are some common disorders associated with neuron function?

It is a neurodegenerative disease, a disorder of the brain in which there is degeneration of nerve cells that are supposed to synapse.

The first symptom in patients with Alzheimer’s is often seen in the short-term memory loss that they develop soon.

It can affect different parts of the brain and manifest different symptoms, which are either different or alike in patients with Alzheimer’s.

6. What is a neuron and why is it considered the basic functional unit of the nervous system?

A neuron is a specialized cell that transmits electrical and chemical signals in the nervous system. It's considered the basic functional unit because it's the primary cell type responsible for processing and transmitting information throughout the body. Neurons work together to form complex networks that enable sensation, thought, and movement.

7. How do neurons communicate with each other?

Neurons communicate through a process called synaptic transmission. When an electrical signal reaches the axon terminal, it triggers the release of chemical messengers called neurotransmitters. These neurotransmitters cross the synaptic cleft (gap between neurons) and bind to receptors on the receiving neuron, potentially triggering a new electrical signal in that neuron.

8. Why do some neurons have more dendrites than others?

The number of dendrites a neuron has is related to its function and the amount of input it receives. Neurons with more dendrites, like motor neurons in the spinal cord, can receive and integrate signals from many different sources. This allows for more complex processing and coordination of information before generating an output signal.

9. How does the structure of a neuron relate to its function?

The structure of a neuron is directly related to its function of transmitting signals. The dendrites receive signals, the cell body processes them, and the axon transmits them to other neurons or target cells. This specialized structure allows for efficient, directional signal transmission, which is crucial for the nervous system's rapid communication.

10. What is an action potential, and how does it propagate along an axon?

An action potential is a brief electrical impulse that travels along the axon of a neuron. It's triggered when the neuron's membrane potential reaches a threshold value, causing voltage-gated ion channels to open and close in sequence. This creates a wave of depolarization that propagates down the axon, maintaining its strength and shape as it travels, allowing for long-distance signal transmission.

11. What are the main parts of a typical neuron, and what does each part do?

The main parts of a typical neuron are:

12. What is the difference between myelinated and unmyelinated axons?

Myelinated axons are covered with a fatty insulating layer called myelin, which is produced by glial cells. This myelin sheath increases the speed of signal transmission through saltatory conduction. Unmyelinated axons lack this insulating layer and conduct signals more slowly. Myelination is an adaptation that allows for faster, more efficient signal transmission in certain neurons.

13. What is the significance of the myelin sheath in neural function?

The myelin sheath is crucial for rapid signal transmission in neurons. It acts as an electrical insulator, preventing the loss of electrical current from the axon. This insulation allows for saltatory conduction, where the action potential "jumps" between gaps in the myelin (nodes of Ranvier), significantly increasing the speed of signal propagation. Myelin also helps conserve energy and allows for thinner axons, which is important in the limited space of the nervous system.

14. How does the "all-or-none" principle apply to neurons?

The "all-or-none" principle states that a neuron either fires an action potential at full strength or not at all. Once the threshold potential is reached, the action potential will occur with the same magnitude regardless of the strength of the stimulus. This principle ensures reliable signal transmission and prevents signal degradation over long distances.

15. How do neurons maintain their resting membrane potential?

Neurons maintain their resting membrane potential through the action of ion pumps and channels in the cell membrane. The sodium-potassium pump actively moves sodium ions out of the cell and potassium ions in, creating concentration gradients. Additionally, the membrane is more permeable to potassium than sodium at rest. These factors combine to create a negative resting potential inside the neuron relative to the outside.

16. What is the difference between electrical and chemical synapses?

Electrical synapses allow direct ion flow between connected neurons through gap junctions, providing very fast, bidirectional signal transmission. Chemical synapses, which are more common, use neurotransmitters to convey signals across the synaptic cleft. Chemical synapses are slower but allow for more complex signaling, including amplification, inhibition, and modulation of the signal. They also provide a mechanism for signal directionality, as neurotransmitters are typically released from the presynaptic neuron to affect the postsynaptic neuron.

17. How do neurotrophic factors influence neuronal development and survival?

Neurotrophic factors are proteins that promote the growth, survival, and differentiation of neurons. They play crucial roles in:

18. How do different types of ion channels contribute to neuronal signaling?

Different types of ion channels play distinct roles in neuronal signaling:

19. How do neurotransmitter receptors influence the postsynaptic neuron's response?

Neurotransmitter receptors determine how the postsynaptic neuron responds to chemical signals:

20. What is the significance of the nodes of Ranvier in myelinated axons?

Nodes of Ranvier are gaps in the myelin sheath along a myelinated axon. They are significant because:

21. What role do neurotransmitters play in neural communication?

Neurotransmitters are chemical messengers released by neurons to communicate with other cells. They bridge the gap (synaptic cleft) between neurons, binding to specific receptors on the receiving cell. This binding can either excite or inhibit the target cell, influencing its likelihood of firing an action potential. Different neurotransmitters have various effects, allowing for complex signaling and modulation of neural activity.

22. How do neurons integrate multiple inputs to determine whether to fire an action potential?

Neurons integrate multiple inputs through spatial and temporal summation. Spatial summation occurs when multiple weak signals from different locations on the dendrites or cell body combine to reach the threshold for an action potential. Temporal summation happens when rapid, successive signals from the same source add up over time to reach the threshold. The neuron weighs all these inputs, both excitatory and inhibitory, to determine whether to fire an action potential.

23. What is the significance of the axon hillock in neuronal function?

The axon hillock is the region where the cell body transitions into the axon. It's significant because it's typically the site where action potentials are initiated. This area has a high concentration of voltage-gated sodium channels, making it particularly sensitive to changes in membrane potential. The axon hillock integrates all the signals received by the neuron and determines whether the threshold for an action potential has been reached, acting as the neuron's decision-making point.

24. How do neurons maintain their polarized structure, with distinct axonal and dendritic regions?

Neurons maintain their polarized structure through several mechanisms:

25. What is the role of the axon initial segment in neuronal function?

The axon initial segment (AIS) is a specialized region at the beginning of the axon that plays crucial roles in neuronal function:

26. How do glial cells support neuronal function?

Glial cells, though not neurons themselves, play vital supporting roles in the nervous system:

27. What is synaptic plasticity, and why is it important?

Synaptic plasticity refers to the ability of synapses to strengthen or weaken over time in response to increases or decreases in their activity. This is important because it's the basis for learning and memory. When neurons repeatedly fire together, the connections between them can be strengthened (long-term potentiation), while less active connections may weaken (long-term depression). This allows the nervous system to adapt and refine its circuitry based on experience.

28. What is the role of calcium ions in synaptic transmission?

Calcium ions play a crucial role in synaptic transmission:

29. What is the function of dendritic spines, and how do they relate to synaptic plasticity?

Dendritic spines are small protrusions on dendrites that typically receive excitatory synaptic inputs. They function to:

30. How do neurons adapt to prolonged stimulation?

Neurons adapt to prolonged stimulation through several mechanisms:

31. How do neurons regulate their internal calcium levels, and why is this important?

Neurons tightly regulate their internal calcium levels because calcium is a crucial signaling molecule. They do this through:

32. What is the difference between fast and slow synaptic transmission?

Fast and slow synaptic transmission differ in their mechanisms and timescales:

33. How do neurons maintain their energy supply to support their high metabolic demands?

Neurons have high energy demands due to constant ion pumping and neurotransmitter synthesis. They maintain their energy supply through: