We will use the Descartes` rule of signs and see how many times the signs change from positive to negative and from negative to positive from one term to the next ( two consecutive terms are with different signs ).
In this case it is 4 times ( +7x13 to -12x9, -12x9 to +16x5, +6x5 to -23 x and finally -23x to +42 ).
Answer: There are 4 real zeroes.
The signal will start from the eyes. The message is carried by sensory neurons to the spinal cord. There, the "impulse" will transfer to motor neurons which will carry it to the brain. So in short:
Sensory neurons --> spinal cord --> motor neurons --> brain
In external respiration carbon dioxide move from capillaries to alveoli, while oxygen move from alveoli to capillaries in internal respiration.
Trees are awesome so people suck if they cut them down
