The nervous system and reflexes
Staying coordinated
- Your body must react to changes and coordinate its parts.
- The nervous system does this with fast electrical impulses along neurones.
- It has two parts:
- the central nervous system (CNS) — brain + spinal cord,
- the peripheral nervous system (PNS) — all the other nerves.
Practice
The central nervous system (CNS) is made of the:
The CNS is the brain and spinal cord; the PNS is all the nerves outside it.
Three kinds of neurone
- sensory neurones — carry impulses from receptors to the CNS.
- relay neurones — pass impulses on inside the CNS.
- motor neurones — carry impulses from the CNS to effectors.
Practice
Match each neurone to its job.
Sensory carries in, relay passes on inside the CNS, motor carries out to effectors.
The reflex arc
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A reflex is a fast, automatic response to a stimulus. It follows a fixed path:
receptor → sensory → relay → motor → effector (a muscle or gland)
Practice
Put the reflex arc in order.
receptor → sensory → relay → motor → effector.
You've got it
Key idea
- nervous system = CNS (brain + spinal cord) + PNS (the nerves); signals are fast electrical impulses
- three neurones: sensory (in), relay (within CNS), motor (out)
- reflex arc: receptor → sensory → relay → motor → effector