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Unit 1 - Reflexes

The nervous system allows an organism to react to its surroundings and coordinate its behaviour, improving its chances of survival. This GCSE Biology quiz takes a closer look at reflexes - the most primitive, yet fundamental, automatic response mechanism.

Our reflexes allow us to take action without thinking, but how? Well, the mechanism works like this - in a reflex reaction, a stimulus is received by receptors and an automatic, rapid response is generated by the central nervous system without the involvement of the brain. In situations where there is a danger to the body, reflex actions can save precious fractions of a second.

This is achieved through what is termed a reflex arc. A reflex arc begins with a receptor. This passes a signal to a sensory neuron that connects to the spinal cord. In the spinal cord, a relay neuron sends the signal directly to a motor neuron. The motor neuron connects to an effector which is generally a muscle so that the body can respond. The relay neuron also sends a signal to the brain so that you are aware of what is happening.

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Two common examples of reflex actions are taking your hand away from something sharp and the iris of an eye changing the size of the pupil. In the first example, receptors detect the sharp object cutting into the skin. The signal travels rapidly through a reflex arc and the part of the body touching the sharp object (e.g. your hand if you accidentally get hold of a rose bush or bramble) rapidly releases the object or moves the body away. Fractions of a second saved here could be crucial - just imagine if the sharp object is entering the body near to one of your main arteries ...

In the second example above, too much light entering the eye could seriously damage it, so it is important for any animal to be able to limit the amount of light entering. This is done using the coloured muscle called the iris. Receptors in the eye are the starting point for a reflex arc that relaxes or contracts the iris, regulating the size of the pupil and therefore controlling the amount of light reaching the easily damaged light receptors of the retina.

Fast reflexes can make all the difference, but don't worry - you wont need them to play this quiz on our automatic response mechanism!

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  1. A reflex arc consists of a chain of which type of cells?
    Nerve cells are called neurons (sometimes spelt with an 'e' as neurones)
  2. The first cell in the reflex is which type of neuron?
    These detect stimuli
  3. If the effector is a gland, what would the response be?
    Glands are part of the endocrine system and are where hormones are produced
  4. The last cell in the reflex is which type of neuron?
    Also called an effector as it makes the body do something
  5. What is the name for the connection between two nerve cells?
    The nerve impulse is usually transmitted from neuron to neuron by a chemical
  6. Your hand touches a hot object. What is the reflex response?
    Reflexes are very fast and do not involve thinking. This protects the organism from dangers such as a hot object
  7. What is the correct order of the reflex arc?
    The brain is not involved, although the relay neuron does send a message to the brain so that the animal is aware of what is happening
  8. The synapse between the sensory and relay neurones is within which part of the body?
    The bundle of neurons in the spinal cord is referred to as the central nervous system
  9. Which of the following is an example of an effector?
    Effectors are the output organs for reflexes and they include both muscles and glands
  10. Which of the following is not true of reflexes?
    Although there is a connection to the brain, the nerve impulses that cause the reflex pass only through the central nervous system. Going through the brain would slow things down

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