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Science

Reflex actions

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Conditioned reflexes - Higher

A reflex response to a new stimulus can be learned.

A Russian scientist called Pavlov trained dogs to expect food whenever he rang a bell. The dogs eventually produced saliva when they heard the bell ring.

  1. The dog salivates naturally when given food.
  2. Pavlov rings a bell every time the dog eats.
  3. After much repetition the dog salivates when the bell rings, even when there is no food.

This is an example of a conditioned reflex. The dogs were conditioned to salivate when the bell rang.

  • The food is called a primary stimulus.
  • The ringing bell is called a secondary stimulus.

A ringing bell does not normally cause salivation in dogs. However, when the ringing bell becomes a secondary stimulus, it does cause salivation, even though the dog will not be able to eat the bell as food.

This is now called a conditioned reflex. In a conditioned reflex the final response (salivation) has no direct connection with the stimulus (ringing bell).

Why are conditioned reflexes useful?

a hoverfly with yellow and black stripes

Predators mistake the hoverfly for a wasp due to similar markings

Conditioned reflexes are useful because they increase an animal’s chances of survival.

For example, birds will not eat caterpillars with bright colouring because they are conditioned to think of bright colours as poisonous. Some caterpillars use this to their advantage. Their bright colours protect them, even though they are not poisonous.

How often have you run away from a harmless hoverfly because it has the same markings as a wasp?

Modifying a reflex response

In some circumstances the brain can modify a reflex response. It does this by sending an impulse along a motor neuron of the reflex arc. This enables us, for example, to hold onto a hot dinner plate when normally we would drop it.

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