The video says that the signal is sent from the axon terminals, but it is sent from the nucleus and then out the axon terminals.
The signal is sent from the cell and out through the axon terminals... The axon carries impulses away from the cell body of the neuron. The myelin sheath surrounds the axon in neurons. The cell body is what sends the signal and the signal goes through axon terminals. When it goes through the axon terminals it is released and tells hormones what to do.
In a fight or flight type of situation epinephrine (adrenaline) is released into the blood stream. At the surface of its target cells, it binds to the B-adrenergic receptor which spans the plasma membrane. The intracellular portion of the receptor is bound to a G protein. When epinephrine is not present the G protein is not active. The binding of the hormone (epinephrine) to its receptor causes it to be active. Since the target cels would be different in different types of situations, a different reaction would occur. Different cells can do different things and travel to different places, since this is the case when epinephrine comes into play the reaction will not always be the same. For example the calcium ions would cause the muscle cells around the sweat glands to contract which would cause sweat to come out of the gland. The sweat gland doesn't actually do anything, it's the cells around it which is given signals and being told what to do by the signal transduction pathway. In another scenario, when hair rises on the skin because the person is afraid it is caused by the muscle around the hair follicles, this would be