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The nervous system and reflexes
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Your nervous system carries electrical impulses around your body in fractions of a second. Reflexes use it to protect you before you even think.
Parts of the nervous system
The central nervous system (CNS) is the brain and spinal cord.
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 (muscles or glands).
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 (muscles or glands).
The reflex arc
A reflex is fast and automatic. It protects you, for example pulling your hand off a hot pan.
stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response
stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response
Synapses and neurones
A synapse is a tiny gap between neurones. A chemical called a neurotransmitter diffuses across it to start an impulse in the next neurone.
A fatty myelin sheath insulates many neurones and speeds up impulses.
A fatty myelin sheath insulates many neurones and speeds up impulses.
You touch a sharp pin and pull your hand away. Name the effector.
- The effector is the part that carries out the response.
- The response is moving the hand away.
- That is done by a muscle in the arm.
Answer: A muscle in the arm
Reflex arc: stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector, response. Synapses pass the signal chemically. Reflexes are fast and automatic.
The interactive lesson includes the diagrams for this topic.
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