5.3.1 Structure of Neuron

The neuron is the basic structural and functional unit of the nervous system. Although neurons vary considerably in size and shape, they all have three basic components: a cell body, dendrites, and an axon.

Definition

Neuron: Neurons are the basic structural and functional unit of the nervous system. Nervous coordination mainly comprises highly specialized cells called neurons.

Main Idea

• Cell body
• Dendrites
• Axon

Core Concept

• Neuron = basic structural and functional unit of nervous system
• Three basic components = cell body, dendrites, axon
• Cell body = contains nucleus and organelles
• Dendrites = receive stimuli and conduct impulses to cell body
• Axon = conducts action potentials away from cell body

Detailed Explanation

Structure of Neuron

Although neurons vary considerably in size and shape, they all have three basic components: a cell body, dendrites and an axon.

Cell Body

• The cell body is the main part of a neuron.
• It contains a mass of granular cytoplasm and cell membrane.
• The single large nucleus is centrally placed with a prominent nucleolus.
• Golgi apparatus, mitochondria and other organelles are present.
• The cytoplasm is characterised by the presence of Nissl's granules.
• These are group of ribosomes and rough ER associated with protein synthesis.

Dendrites

• Dendrites are short and thin, often highly branched cytoplasmic extensions.
• They are gradually tapered from their bases to their tips.
• Axons of other neurons form synapses with the dendrites.
• The function of the dendrite is to receive stimuli and conduct impulses to the cell body.

Axon

• An axon is comparatively a long and thick nerve fibre.
• It has a constant diameter and can vary in size from a few mm to more than a metre length.
• It may be branched or un-branched.
• Axons terminate by branching to form small extensions with enlarged ends called presynaptic terminals.
• Functionally, axons conduct action potentials from the neuron cell body to the presynaptic terminals, i.e., conduct signal (information) away from the cell body.

Summary Table of Neuron Structure

Intermediate Level

Structure of Neuron

Detailed Structure

Function of Each Part

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Neuron is the basic structural and functional unit of the nervous system.
• 2. Neurons have three basic components: cell body, dendrites, and axon.
• 3. Cell body contains nucleus and organelles.
• 4. Cell body contains Nissl's granules.
• 5. Nissl's granules are groups of ribosomes and rough ER.
• 6. Nissl's granules are associated with protein synthesis.
• 7. Dendrites receive stimuli.
• 8. Dendrites conduct impulses to cell body.
• 9. Axon conducts action potentials away from cell body.
• 10. Axon can be branched or un-branched.
• 11. Axon ends in presynaptic terminals.
• 12. Presynaptic terminals release neurotransmitters.
• 13. Axon can vary in size from a few mm to more than a metre.
• 14. Cell body has a single large nucleus.
• 15. Cell body has a prominent nucleolus.

Remember

• - Neuron = basic structural and functional unit of nervous system
• - Three basic components = cell body, dendrites, axon
• - Cell body = contains nucleus and organelles
• - Nissl's granules = ribosomes and rough ER; protein synthesis
• - Dendrites = receive stimuli; conduct impulses to cell body
• - Axon = conducts action potentials away from cell body
• - Presynaptic terminals = release neurotransmitters
• - Axon length = few mm to more than a metre
• - Nucleus = single, large, centrally placed
• - **Nucleolus** = prominent

Common Mistakes

• 1. Confusing dendrites and axons — Dendrites receive; axons transmit.
• 2. Thinking the cell body is not important — It contains the nucleus and organelles.
• 3. Forgetting the role of Nissl's granules — Protein synthesis.
• 4. Mixing up the direction of impulses — Dendrites → cell body → axon.
• 5. Thinking axons are always short — Axons can be up to a metre long.
• 6. Forgetting the presynaptic terminals — They release neurotransmitters.
• 7. Thinking neurons have multiple nuclei — Neurons have a single large nucleus.
• 8. Mixing up the structure of dendrites — Short, thin, highly branched.
• 9. Forgetting the constant diameter of axons — Axons have a constant diameter.
• 10. Believing all neurons are the same — Neurons vary in size and shape.

Quick Revision

The neuron is the basic structural and functional unit of the nervous system. Although neurons vary considerably in size and shape, they all have three basic components: a cell body, dendrites, and an axon. The cell body is the main part of a neuron. It contains a mass of granular cytoplasm and cell membrane. The single large nucleus is centrally placed with a prominent nucleolus. Golgi apparatus, mitochondria and other organelles are present. The cytoplasm is characterised by the presence of Nissl's granules. These are group of ribosomes and rough ER associated with protein synthesis. Dendrites are short and thin, often highly branched cytoplasmic extensions that are gradually tapered from their bases to their tips. Axons of other neurons form synapses with the dendrites. The function of the dendrite is to receive stimuli and conduct impulses to the cell body. An axon is comparatively a long and thick nerve fibre which has a constant diameter and can vary in size from a few mm to more than a metre length. It may be branched or un-branched. Axons terminate by branching to form small extensions with enlarged ends called presynaptic terminals. Functionally, axons conduct action potentials from the neuron cell body to the presynaptic terminals.

60-Second Revision

• Neuron = basic structural and functional unit of nervous system
• Three basic components = cell body, dendrites, axon
• Cell body = contains nucleus and organelles
• Nissl's granules = ribosomes and rough ER; protein synthesis
• Dendrites = receive stimuli; conduct impulses to cell body
• Axon = conducts action potentials away from cell body
• Presynaptic terminals = release neurotransmitters
• Warning: Dendrites receive; axons transmit

NEXT TOPIC

• Chapter:
• 5. Nervous System of Man

• Topic:
• 5.3.2 TYPES OF NEURON

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