A neuron is a cell that is capable of sending and receiving signals throughout the nervous system. The cell membrane of a neuron contains a number of membrane proteins that facilitate communication between neurons, along with the rapid transmission of electrical impulses through the entire neuron. The dendrites of a neuron are designed to receive chemical signals, known as neurotransmitters, from other neurons. There are receptors on the dendrites that bind neurotransmitters and allow for the movement of ions according to their electrochemical gradient. If the neurotransmitter signal is strong enough, this allows for the passive diffusion of ions across the membrane of the neuronal axon, or region that is responsible for sending electrical signals. Once the electrical signal reaches the end of the axon, or axon terminal, this causes neurotransmitter-containing vesicles in this location to fuse with the membrane, releasing neurotransmitters. This process requires cellular energy in the form of ATP. Neurotransmitters travel through the aqueous (watery) fluid outside the neuron and can trigger receptors on the surface of other neurons. Neurotransmitters can then re-enter the neuron through membrane proteins in the axon terminal. If neurotransmitters were unable to re-enter the neuron that released them, too many ions could enter targeted neurons and the ability of neurons to signal each other would be reduced. Which ion movements are most likely observed along the axon?