Structure of Neuron
Neuron – Structure, Discovery, and Functions
1. What is a Neuron?
- A neuron is the basic structural and functional unit of the nervous system.
- It is a specialized cell that can receive, process, and transmit information in the form of electrochemical impulses.
- Neurons make up the brain, spinal cord, and nerves, helping in activities like:
- Thinking and memory
- Sensations (touch, pain, heat, etc.)
- Reflex actions
- Movement and coordination
👉 Without neurons, the body cannot communicate internally or respond to the environment.
2. Discovery of Neurons
- Camillo Golgi (1843–1926) developed the silver staining technique in 1873, which allowed neurons to be seen under a microscope.
- Santiago Ramón y Cajal (1852–1934) improved the study, showing that the nervous system is made of individual cells (neurons) and not a continuous network.
- Together, Golgi and Cajal received the Nobel Prize in 1906 for their work on neurons.
- Cajal is known as the “Father of Modern Neuroscience.”
3. Structure of a Neuron
A typical neuron has three main parts:
- Cell Body (Cyton / Soma)
- Dendrites
- Axon
👉 Some neurons are very small, while others can be over 1 meter long (e.g., in the spinal cord to leg muscles).
4. Detailed Parts of a Neuron and Their Functions
| Part | Structure | Function |
|---|---|---|
| Cell Body (Cyton / Soma) | – Central swollen part of neuron.- Contains nucleus, cytoplasm, mitochondria, Nissl bodies (granules for protein synthesis). | – Controls all metabolic activities of neuron.- Integrates incoming signals from dendrites.- Maintains the life of the cell. |
| Dendrites | – Short, thin, branched projections from the cell body.- Numerous in number. | – Receive signals from other neurons or sensory organs.- Carry impulses towards the cell body. |
| Axon | – A single, long, cylindrical extension of the cell body.- Can be myelinated (with sheath) or non-myelinated. | – Conducts nerve impulses away from cell body to other neurons, muscles, or glands. |
| Myelin Sheath | – Fatty covering around axon.- Formed by Schwann cells (in PNS) or oligodendrocytes (in CNS). | – Acts as an insulator.- Increases speed of impulse conduction.- Prevents leakage of current. |
| Nodes of Ranvier | – Small gaps between myelin sheath segments. | – Allow impulses to “jump” from one node to another (saltatory conduction) → makes conduction much faster. |
| Axon Terminals (Synaptic Knobs) | – Branches at the end of axon.- Contain synaptic vesicles filled with neurotransmitters. | – Release neurotransmitters (like acetylcholine, dopamine).- Transfer impulse to the next neuron or effector cell across the synapse. |
| Nucleus | – Inside the cell body. | – Regulates neuron activities.- Stores genetic material (DNA). |
5. Functions of a Neuron
- Receiving signals through dendrites.
- Processing signals in the cell body.
- Transmitting signals through the axon.
- Passing information to the next neuron/muscle/gland through synapse.
Thus, neurons form the basis of communication in the nervous system.
6. Detailed information on functions of neurons :
Got it 👍 Let’s go deep into the functions of neurons in a way that is clear, systematic, and useful for exams.
Functions of Neurons (Detailed Explanation)
Neurons perform one main job: communication. They carry information throughout the body in the form of nerve impulses (electrical and chemical signals).
Their functions can be divided into several steps:
1. Receiving Information (Input Function)
- Dendrites act like tiny antennae.
- They receive signals (stimuli) from:
- The environment (heat, light, touch, pain, etc.) through sensory receptors.
- Other neurons through synapses.
- These incoming signals are then passed into the cell body.
👉 Example: When you touch a hot object, sensory neurons receive the heat stimulus.
2. Processing Information (Integrative Function)
- The cell body (cyton) integrates (collects and processes) all incoming signals from the dendrites.
- The nucleus and Nissl bodies help in metabolism and protein synthesis to keep the neuron active.
- The neuron decides whether to generate an action potential (nerve impulse) or not.
👉 Example: Your brain processes whether the sensation is dangerous (too hot) or safe (warm).
3. Transmission of Information (Conductive Function)
- If the signal is strong enough, the neuron generates an electrical impulse (action potential).
- The axon carries this impulse away from the cell body.
- In myelinated axons, the impulse jumps from one Node of Ranvier to another (saltatory conduction), which makes it very fast.
👉 Example: The impulse travels quickly from your hand to your spinal cord and brain.
4. Communication to Next Cell (Output Function)
- At the axon terminals, electrical signals are converted into chemical signals.
- Tiny sacs called synaptic vesicles release neurotransmitters (like acetylcholine, dopamine, serotonin) into the synapse (gap between two neurons).
- These neurotransmitters bind to receptors on the next neuron, muscle, or gland → passing on the signal.
👉 Example: The neuron tells your muscles to pull your hand away from the hot object.
5. Regulation of Body Functions
Through the above steps, neurons collectively help in:
- Reflex Actions – quick, automatic responses (e.g., knee-jerk reflex, pulling hand from flame).
- Voluntary Actions – controlled movements (walking, writing, speaking).
- Sensory Functions – perception of environment (vision, hearing, taste, smell, touch).
- Motor Functions – controlling muscles and glands.
- Higher Functions of Brain – learning, memory, reasoning, emotions, problem-solving.
Stimulus (light, heat, touch, sound, etc.)
↓
Receptor (sense organ detects the change)
↓
Sensory Neuron (carries impulse from receptor to CNS)
↓
CNS (Brain/Spinal Cord processes and integrates information)
↓
Motor Neuron (carries command from CNS to effector)
↓
Effector (muscle or gland produces a response)
↓
Response (action performed – e.g., move hand away, blink, speak, etc.)
6. Types of Neurons and Their Specific Functions
- Sensory Neurons (Afferent) → Carry signals from sense organs to brain/spinal cord.
- Motor Neurons (Efferent) → Carry commands from brain/spinal cord to muscles and glands.
- Interneurons (Association Neurons) → Connect sensory and motor neurons; found mostly in brain and spinal cord; help in reflexes and thinking.
Summary
- Neurons receive, process, transmit, and communicate information.
- They work in four stages: input → integration → conduction → output.
- Functions include reflexes, voluntary control, sensations, muscle movement, glandular control, learning, and memory.
- Without neurons, the nervous system cannot function.
