action potentials

Action potentials are the way in which neurons send and recieve signals. Neurons can be connected directly through gap junctions, which transmit electrical impulses as a form of transmiting information. Neurons can also communicate through chemical signals over the synapse between two neurons. The chemical signals are packaged in vesicles at the axon terminal (neuroproteins are made and packaged in the ribosomes), and sent across the small gap between neurons. The chemical vessicles bind to receptors at the post-synaptic neuron's dendrite. The molecules are taken up by the post-synaptic neuron and elicite an inhibitory, or an excitatory response. The post- synaptic neuron can have an action potential if the stimulus is enough to make the post-synaptic neuron reach threshold. Once threshold is reached, an action potential must occur because action potentials are all or nothing. After the action potential occurs, there is a period of time when a second action potential cannot occur. The absolute refractory period is when the GPCRs are locked and the channels cannot open to depolerize the cell. Once the cell is hyperpolerized enough, the GPCRs will uncouple so that the cell enters the relative refractory period. A second action potential can occur during the relative refractory period if the signal is strong enough.