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9 Science

Topic: Coordination (Biology)

REFLEXES

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INFORMATION

The diagram below shows the pathway through which messages (electrical impulses) travel in bringing about the knee jerk reflex. When the tendon is tapped, receptors in the muscle are stretched and this causes electrical impulses to be sent to the spinal cord.

QUESTIONS

1. Which structure in the diagram is the receptor? (identify it by its letter)

1. Which structure carries electrical impulses away from the spinal cord? (identify it by its letter)

1. Which structure shortens as a result of the reflex? (identify it by its letter)

1. The diagram is not drawn to scale. What would be the approximate length of the structure labelled E in the actual reflex arc? Explain your answer.

1. Assuming that impulses travel at 100 metres per second, how many seconds would it take for the impulses to travel right through this reflex arc?

Using your understanding of nerves explain what you think is happening for each of the following situations:

1. If you tickle a dog’s tummy it ‘scratches’ with its hind leg.

1. Messages travel through a reflex arc in only one direction

1. In the disease ‘Multiple Sclerosis’ the person gradually becomes extremely weak with the use of their muscles.
   

1. In the disease ‘Polio’ the person may lose the use of their legs.