🧠 The Nervous System
Neuron Structure · Reflex Arc · CNS & PNS Divisions
🔬 Section 1: The Neuron — The Basic Unit of the Nervous System
What is a Neuron?
A neuron (nerve cell) is the fundamental structural and functional unit of the nervous system. Its primary role is to transmit information throughout the body using electrical and chemical signals, enabling communication between the brain, spinal cord, and the rest of the body.
Three Main Parts of a Neuron
| Part | Structure | Function |
|---|---|---|
| Dendrites | Tree-like branching extensions | Receive signals from other neurons and direct them toward the cell body |
| Cell Body (Soma) | Contains nucleus, mitochondria, ER, Golgi body | Integrates incoming signals; maintains the cell's life functions |
| Axon | Long, slender projection (can be up to 1 m long!) | Carries electrical impulses away from the cell body |
| Axon Terminals | Branched endings at the tip of the axon | Release neurotransmitters at the synapse to communicate with the next cell |
The Myelin Sheath
Many axons are insulated with a fatty substance called myelin, which helps axons conduct electrical signals much faster. In the PNS, Schwann cells produce myelin. In the CNS, cells called oligodendrocytes do this job. The gaps between myelin segments are called Nodes of Ranvier — the signal "jumps" between these gaps, speeding up transmission.
🧬 Interactive Neuron Diagram
🖱️ Drag to rotate · Scroll to zoom · Interactive 3D neuron model
Three Functional Types of Neurons
📥 Sensory Neurons
Carry impulses from receptors (e.g., skin, eyes, ears) to the CNS (brain or spinal cord).
Receptor → CNS🔄 Interneurons (Relay)
Found in the CNS. They connect sensory neurons to motor neurons and help process information.
Sensory ↔ Motor📤 Motor Neurons
Carry impulses from the CNS to effectors (muscles or glands) to produce a response.
CNS → Effector🔗 The Synapse
The synapse is the tiny gap (junction) between the axon terminal of one neuron and the dendrite of the next neuron. Signals cross this gap using chemical messengers called neurotransmitters. The electrical signal triggers the release of neurotransmitters, which diffuse across the gap and bind to receptors on the next neuron, starting a new electrical signal.