Structure of Neuron – Easy NEET Notes
Neuron
- Neuron is the structural and functional unit of nervous system.
- It receives, processes and transmits nerve impulses.
- Neurons are also called nerve cells.
Parts of a Neuron
1. Cell Body (Cyton / Soma)
- Main part of neuron containing the cytoplasm and nucleus.
- Controls all activities of the neuron.
- Contains Nissl’s granules.
Nissl’s Granules
- Granular structures present in cytoplasm.
- Help in protein synthesis.
- Present in cell body and dendrites.
- Absent in axon.
2. Dendrites
- Short, branched fibres arising from cell body.
- Receive stimuli or nerve impulses.
- Carry impulses towards the cell body.
Important Point
- Dendrites contain Nissl’s granules.
3. Axon
- Long fibre arising from cell body.
- Conducts nerve impulses away from the cell body.
- Distal end of axon is branched.
Axon Terminal
- Terminal branches end in swollen bulb-like structures called synaptic knobs.
Synaptic Knob
- Contains synaptic vesicles.
- Vesicles contain chemicals called neurotransmitters.
Neurotransmitters
- Chemical substances that transmit impulse from one neuron to another neuron or muscle.
Synapse
- Junction between two neurons or between neuron and muscle.
- Transmission occurs through neurotransmitters.
Types of Neurons Based on Number of Axon and Dendrites
1. Multipolar Neuron
- One axon and many dendrites.
- Most common type.
- Found in cerebral cortex.
2. Bipolar Neuron
- One axon and one dendrite.
- Found in retina of eye.
3. Unipolar Neuron
- Cell body with only one process.
- Usually found in embryonic stage.
Types of Nerve Fibres
1. Myelinated Nerve Fibre
- Covered by myelin sheath.
- Myelin sheath formed by Schwann cells.
- Myelin acts as electrical insulation.
- Increases speed of impulse conduction.
- Found in spinal and cranial nerves.
Node of Ranvier
- Gaps between two myelin sheaths.
- Help in fast transmission of impulses.
2. Non-Myelinated Nerve Fibre
- No myelin sheath around axon.
- Schwann cells present but do not form myelin.
- Impulse conduction is slower.
- Found in autonomic nervous system.
Generation and Conduction of Nerve Impulse
Polarised Membrane
- Neuron membrane at rest is called polarised membrane.
- Outer surface is positively charged.
- Inner surface is negatively charged.
Why?
Because distribution of ions is unequal.
Ion Distribution During Resting State
Inside Axon (Axoplasm)
-
High concentration of:
- Potassium ions (K⁺)
- Negatively charged proteins
-
Low concentration of:
- Sodium ions (Na⁺)
Outside Axon
-
High concentration of:
- Sodium ions (Na⁺)
-
Low concentration of:
- Potassium ions (K⁺)
Sodium-Potassium Pump
- Active transport mechanism in neuron membrane.
- Pumps:
- 3 Na⁺ outside
- 2 K⁺ inside
- Maintains ionic gradient and resting potential.
Resting Membrane Potential
- Outside membrane = positive
- Inside membrane = negative
- This condition is called resting potential or polarised state.
Important NEET Points
Very Important Facts
- Dendrites carry impulse towards cell body.
- Axon carries impulse away from cell body.
- Nissl’s granules absent in axon.
- Myelin sheath formed by Schwann cells.
- Gaps in myelin sheath = Nodes of Ranvier.
- Neurotransmitters present in synaptic vesicles.
- Multipolar neurons are most common.
- Retina contains bipolar neurons.
Quick Revision Table
| Structure | Function |
|---|---|
| Dendrites | Receive impulses |
| Cell body | Controls activities |
| Axon | Conducts impulses away |
| Myelin sheath | Increases speed |
| Node of Ranvier | Fast conduction |
| Synaptic knob | Releases neurotransmitter |
| Schwann cell | Forms myelin sheath |
NCERT-Based NEET Keywords
- Neuron
- Dendrite
- Axon
- Synaptic knob
- Neurotransmitter
- Schwann cell
- Myelin sheath
- Node of Ranvier
- Polarised membrane
- Resting potential
- Sodium-potassium pump
Keywords Meaning – Neuron Chapter
Neuron
- A specialized nerve cell that transmits nerve impulses.
Nerve Impulse
- Electrical signal that travels through neuron.
Dendrite
- Short branched part of neuron that receives impulses and carries them towards cell body.
Cell Body (Cyton / Soma)
- Central part of neuron containing nucleus and cytoplasm.
Nucleus
- Control center of the cell containing genetic material.
Nissl’s Granules
- Granules in neuron cytoplasm that help in protein synthesis.
Axon
- Long fibre that carries impulses away from cell body.
Axon Terminal
- End branches of axon.
Synaptic Knob
- Bulb-like swollen end of axon terminal containing neurotransmitters.
Synaptic Vesicles
- Small sacs inside synaptic knob storing neurotransmitters.
Neurotransmitters
- Chemical messengers that transfer impulse from one neuron to another.
Synapse
- Junction between two neurons or neuron and muscle.
Types of Neurons
Multipolar Neuron
- Neuron with one axon and many dendrites.
Bipolar Neuron
- Neuron with one axon and one dendrite.
Unipolar Neuron
- Neuron having only one process from cell body.
Nerve Fibre Terms
Myelin Sheath
- Fatty insulating covering around axon that increases speed of impulse.
Schwann Cell
- Cell that forms myelin sheath around axon.
Node of Ranvier
- Gaps between two myelin sheaths.
Myelinated Nerve Fibre
- Nerve fibre covered with myelin sheath.
Non-Myelinated Nerve Fibre
- Nerve fibre without myelin sheath.
Nerve Impulse Conduction Terms
Polarised Membrane
- Resting neuron membrane with positive outside and negative inside.
Resting Potential
- Electrical charge difference across resting neuron membrane.
Axoplasm
- Cytoplasm present inside axon.
Ionic Gradient
- Difference in ion concentration across membrane.
Sodium-Potassium Pump
- Membrane pump that transports:
- 3 Na⁺ outside
- 2 K⁺ inside
Potassium Ion (K⁺)
- Positively charged ion mainly present inside axon.
Sodium Ion (Na⁺)
- Positively charged ion mainly present outside axon.
Depolarisation
- Loss of resting polarity during nerve impulse transmission.
Repolarisation
- Return of neuron membrane to resting state after impulse.
Easy Memory Tricks
Dendrite → “Door”
- Receives impulses into neuron.
Axon → “Away”
- Carries impulses away from cell body.
Myelin → “More Speed”
- Helps faster conduction.
Node of Ranvier
- “Jumping points” for impulse conduction.
Keywords Meaning – Easy Definitions
Neuron
- A nerve cell that carries messages (nerve impulses) in the body.
Dendrite
- Short branched part of neuron that receives signals and carries them towards the cell body.
Axon
- Long fibre of neuron that carries impulses away from the cell body.
Synaptic Knob
- Bulb-like end of axon that releases neurotransmitters.
Neurotransmitter
- Chemical messenger that transfers signals from one neuron to another.
Schwann Cell
- Cell that forms myelin sheath around axon.
Myelin Sheath
- Fatty insulating covering around axon that increases speed of nerve impulse.
Node of Ranvier
- Small gaps between two myelin sheaths on axon.
Polarised Membrane
- Resting neuron membrane with positive charge outside and negative charge inside.
Resting Potential
- Electrical difference between inside and outside of resting neuron membrane.
Sodium-Potassium Pump
- Membrane pump that moves:
- 3 sodium ions (Na⁺) outside
- 2 potassium ions (K⁺) inside
 |
| Structure of neuron showing dendrites, axon, myelin sheath and synaptic knob for NEET Biology preparation. |
Class 11 Biology – Neural Control and Coordination
Topic: Structure of Neuron & Nerve Impulse
Multiple Choice Questions (MCQs)
1. Structural and functional unit of nervous system is:
A. Nephron
B. Neuron
C. Osteon
D. Alveoli
Answer:
B. Neuron
2. Dendrites conduct impulses:
A. Away from cell body
B. Towards cell body
C. Outside the neuron
D. Between muscles
Answer:
B. Towards cell body
3. Which part contains neurotransmitters?
A. Node of Ranvier
B. Myelin sheath
C. Synaptic knob
D. Dendrite
Answer:
C. Synaptic knob
4. Myelin sheath is formed by:
A. Cyton
B. Schwann cell
C. Axon terminal
D. Dendrite
Answer:
B. Schwann cell
5. Gaps between myelin sheath are called:
A. Synapse
B. Axoplasm
C. Nodes of Ranvier
D. Nissl granules
Answer:
C. Nodes of Ranvier
6. Bipolar neurons are found in:
A. Cerebral cortex
B. Retina
C. Spinal cord
D. Heart
Answer:
B. Retina
7. During resting state, inside of axon contains high concentration of:
A. Na⁺
B. Ca²⁺
C. K⁺
D. Cl⁻
Answer:
C. K⁺
8. Sodium-potassium pump transports:
A. 2 Na⁺ out and 3 K⁺ in
B. 3 Na⁺ out and 2 K⁺ in
C. 2 Na⁺ in and 3 K⁺ out
D. Equal ions both ways
Answer:
B. 3 Na⁺ out and 2 K⁺ in
Very Short Answer Questions
1. What is a neuron?
Answer:
Neuron is the structural and functional unit of nervous system.
2. Define synapse.
Answer:
Synapse is the junction between two neurons.
3. Name the insulating layer around axon.
Answer:
Myelin sheath.
4. What are neurotransmitters?
Answer:
Chemical messengers that transmit impulses across synapse.
5. What is the function of dendrites?
Answer:
They receive impulses and carry them towards cell body.
Short Answer Questions
1. Differentiate between dendrites and axon.
| Dendrites | Axon |
|---|---|
| Short and branched | Long and unbranched |
| Carry impulses towards cell body | Carry impulses away from cell body |
| Usually many | Usually one |
2. Write functions of myelin sheath.
Answer:
- Protects axon
- Acts as electrical insulator
- Increases speed of impulse conduction
3. Explain resting potential.
Answer:
Resting potential is the electrical difference across neuron membrane during resting state. Outer side is positively charged while inner side is negatively charged.
4. What are Nodes of Ranvier?
Answer:
Nodes of Ranvier are gaps between two myelin sheaths that help in rapid conduction of nerve impulses.
Long Answer Questions
1. Explain the structure of neuron with labelled points.
Answer:
Neuron is the structural and functional unit of nervous system. It consists of:
(i) Cell Body
- Contains nucleus and cytoplasm.
- Contains Nissl’s granules.
(ii) Dendrites
- Short branched fibres.
- Receive impulses towards cell body.
(iii) Axon
- Long fibre carrying impulses away from cell body.
(iv) Synaptic Knob
- Terminal swollen ends of axon.
- Contain neurotransmitters.
(v) Myelin Sheath
- Fatty covering formed by Schwann cells.
- Speeds up conduction.
(vi) Nodes of Ranvier
- Gaps between myelin sheaths.
2. Explain the mechanism of resting membrane potential.
Answer:
-
Resting neuron membrane is polarised.
-
Membrane is more permeable to K⁺ than Na⁺.
-
Inside axon:
- High K⁺
- Negative proteins
-
Outside axon:
- High Na⁺
-
Sodium-potassium pump maintains ionic gradient.
- Outer membrane becomes positive and inner membrane becomes negative.
Assertion and Reason Questions
1.
Assertion (A):
Myelin sheath increases speed of nerve impulse.
Reason (R):
Myelin sheath acts as an electrical insulator.
A. Both A and R are true and R is correct explanation of A
B. Both A and R are true but R is not correct explanation
C. A is true but R is false
D. A is false but R is true
Answer:
A
2.
Assertion (A):
Dendrites carry impulses away from cell body.
Reason (R):
Axon carries impulses away from cell body.
Answer:
Dendrites statement is false but reason is true.
Fill in the Blanks
1.
The junction between two neurons is called ________.
Answer:
Synapse
2.
________ cells form myelin sheath.
Answer:
Schwann
3.
The gaps between myelin sheath are called ________.
Answer:
Nodes of Ranvier
4.
Neurotransmitters are stored in ________ vesicles.
Answer:
Synaptic
5.
Inside axon, concentration of ________ ions is high.
Answer:
Potassium (K⁺)
Case Study Questions
Case Study
A student observed a neuron under microscope and found a long fibre covered by segmented fatty layer with gaps in between. The neuron conducted impulses rapidly.
Questions
1. Name the long fibre.
Answer:
Axon
2. Name the fatty covering.
Answer:
Myelin sheath
3. What are the gaps called?
Answer:
Nodes of Ranvier
4. Which cells form the myelin sheath?
Answer:
Schwann cells
5. Why does this neuron conduct impulses rapidly?
Answer:
Due to presence of myelin sheath and saltatory conduction.
Statement-Based Questions
1. Identify true statements.
- Dendrites receive impulses.
- Axon carries impulses towards cell body.
- Schwann cells form myelin sheath.
- Synaptic knobs contain neurotransmitters.
Answer:
Statements 1, 3 and 4 are true.
2. Identify incorrect statement.
A. Multipolar neurons are common in cerebral cortex
B. Bipolar neurons occur in retina
C. Myelin sheath decreases conduction speed
D. Synapse connects neurons
Answer:
C. Myelin sheath decreases conduction speed
Match the Following
| Column I | Column II |
|---|---|
| 1. Dendrite | a. Myelin formation |
| 2. Schwann cell | b. Chemical messenger |
| 3. Neurotransmitter | c. Receives impulses |
| 4. Node of Ranvier | d. Gap in myelin sheath |
Answers:
1 → c
2 → a
3 → b
4 → d
Important NCERT-Based One-Liners
- Neuron is an excitable cell.
- Dendrites contain Nissl’s granules.
- Axon lacks Nissl’s granules.
- Myelinated fibres conduct impulses faster.
- Resting membrane is polarised.
- Sodium-potassium pump maintains resting potential.
- Internal Links
- Neural Control and Coordination Notes
- Human Nervous System Explained
- Synapse and Nerve Impulse Transmission
- Endocrine System Notes for NEET
- Animal Tissues Class 11 Notes
- Chemical Coordination and Integration
- NEET Biology MCQs with Answers
- CBSE Class 11 Biology Revision Notes
- Human Physiology Mind Maps
- Important Biology Diagrams for NEET
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