Neurones (AQA GCSE Biology Combined Science): Revision Notes
Neurones
What are neurones?
The nervous system helps humans react to their surroundings. It also helps coordinate behaviour. Neurones are the special cells that make up the nervous system.
The nervous system is essential for survival as it allows rapid responses to environmental changes and coordinates all body functions.
Neurones carry electrical impulses around your body. These impulses are like messages that travel very fast.
Types of neurones
There are three main types of neurones. Each type has a different job:
Sensory neurones
- Carry electrical impulses from receptors to the central nervous system (CNS)
- Receptors detect changes in your environment (like light, sound, or touch)
- Found in places like your eyes, ears, and skin
Relay neurones
- Found in the CNS (brain and spinal cord)
- Carry impulses from sensory neurones to motor neurones
- Act like a bridge between the other two types
Motor neurones
- Carry impulses from the CNS to effectors
- Effectors are muscles and glands that respond to the messages
- Make your muscles move or glands release substances
Remember the pathway: Receptors → Sensory neurones → Relay neurones → Motor neurones → Effectors. This sequence is crucial for understanding how your nervous system processes information and responds to stimuli.
Structure of neurones
All neurones have similar parts that work together to transmit electrical impulses:
Cell body
- Contains the nucleus
- Controls the neurone's activities
Dendrites
- Branch-like structures that collect impulses
- Receive electrical signals from other neurones or receptor cells
Axon
- Long part of the neurone
- Carries impulses over long distances
- Can be very long in some neurones
Myelin sheath
- Fatty covering around the axon
- Acts like insulation on electrical wires
- Stops electrical impulses from escaping
- Makes impulses travel much faster
Axon terminals
- Found at the end of the axon
- Pass impulses to other neurones, muscles, or glands
How neurones work
Electrical impulses travel along neurones very quickly. The myelin sheath is very important because:
- It insulates the neurone
- Electrical impulses cannot cross through the fatty myelin sheath
- The impulse jumps from gap to gap in the myelin sheath
- This speeds up transmission
Why is the myelin sheath so crucial? Without myelin, electrical impulses would leak out and travel much slower. Diseases that damage myelin (like multiple sclerosis) severely affect nerve function and can cause serious symptoms.
Worked Example: Reflex Action
When you touch something hot, here's exactly what happens:
Step 1: Sensory neurones in your skin detect heat and pain Step 2: These sensory neurones send electrical impulses to relay neurones in your spinal cord Step 3: Relay neurones process the information and send impulses to motor neurones Step 4: Motor neurones make your muscles contract to pull your hand away quickly
This whole process happens in milliseconds - faster than you can think about it!
Key Points to Remember:
- Neurones are nerve cells that carry electrical impulses
- Three types: sensory (receptors → CNS), relay (in CNS), motor (CNS → effectors)
- Key parts: dendrites collect impulses, axon carries them, myelin sheath speeds them up
- Pathway: Sensory → Relay → Motor neurones work together
- Myelin sheath acts like insulation and makes impulses travel faster