The Human Nervous System (AQA GCSE Biology): Revision Notes
Neurones and the brain
The nervous system helps us react to what's happening around us and controls our behaviour. It's made up of special cells called neurones (nerve cells). The central nervous system (CNS) includes the brain and spinal cord.
Types of neurones
There are three main types of neurones, each with a different job:
- Sensory neurones - carry electrical signals from receptors (like in your eyes or skin) to the CNS
- Relay neurones - found inside the CNS, they pass signals from sensory neurones to motor neurones
- Motor neurones - carry signals from the CNS to effectors (muscles and glands)
Think of it like a relay race: sensory neurones detect something, relay neurones pass the message, and motor neurones make you react.
Structure of neurones
Sensory neurones
Sensory neurones have several important parts:
- Dendrites - collect electrical impulses from receptor cells (like touch sensors in skin)
- Cell body - contains the nucleus and controls the neurone
- Axon - a long projection that carries impulses over long distances
- Fatty myelin sheath - wraps around the axon like insulation on a wire
The myelin sheath is crucial because it stops electrical impulses from leaking out. This means the signal travels much faster - the impulse "jumps" from gap to gap in the myelin.
Relay neurones
Relay neurones have a similar structure but are designed differently:
- Dendrites collect impulses from sensory neurones
- Cell body processes the information
- Axon terminals pass impulses to other neurones (often motor neurones)
Brain structure
The brain contains billions of connected neurones and controls complex behaviours. Different parts have specific jobs:
Cerebral cortex
This outer layer of the brain is responsible for:
- Voluntary movement - choosing to move your muscles
- Interpreting sensory information - understanding what you see, hear, feel
- Learning and memory - storing and recalling information
Medulla
This part of the brain stem controls unconscious processes like:
- Heartbeat regulation
- Breathing control
- Other automatic body functions
Cerebellum
Located at the back of the brain, the cerebellum:
- Coordinates precise and smooth movement
- Controls balance and posture
- Helps during exercise by coordinating muscle movements
The cerebellum is why you can walk smoothly or catch a ball without thinking about every tiny muscle movement.
Key Points to Remember:
- Three types of neurones: sensory (detect), relay (connect), motor (act)
- Myelin sheath speeds up nerve impulses by acting like electrical insulation
- Cerebral cortex handles conscious actions like thinking and voluntary movement
- Medulla controls automatic functions like breathing and heartbeat
- Cerebellum coordinates smooth, precise movements and balance