I am having trouble understanding an exam question. I am given a diagram which looks like this: enter image description here

I am having a lot of trouble understanding this diagram since it looks unlike the diagrams usually depicted in biology books. There are two questions to be answered regarding this diagram:

  1. The patellar tendon is tapped just below the knee to trigger the muscle reflex. As a response, the lower leg is briefly extended. Which of the numbered neurons in the diagram in the figure above release a transmitter substance during this reflex?
  2. Stimulation of which neuron or neurons could have caused this signal in neuron 7? (There is an image of the neuron where one can see that the level of the signal goes down). Since this is a practice exam, I have the solutions, apparently for question 1 the solution is neurons 1,5,7 and 9 and for question two the solution is neurons 6 and 9.

As far as I understand, the solution for question two is due to the fact that only neurons 6 and 9 can send a negative signal, symbolised by the negative sign. For question one, I understand that there is a reflex happening in the extensor muscle, which is why the signal is transported to the spinal cord and back without going on to the brain. However, I am left with a few questions:

  1. What is the cross from neuron 5 to 8 and neuron 6 to 7 supposed to signify?
  2. Generally, why is 1,5,7 and 9 the correct solution for question 1?
  3. In question one: Why is the flexor muscle not at all involved, since as I understand the flexor and extensor muscles are antagonists, so if one contracts the other would have to expand?
  4. in question two, is it even theoretically possible to get a signal from neuron 6? In which case would that be?

Thank you in advance for your help!



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