Thick neurons conduct action potentials faster. Impulses travel even faster if neuron has myelin insulation. Moritmer Turnipseed has the largest neuron twine-ball in the midwest. The neurons aren't physically connected to each other so the nerve impulse has to be converted to a chemical which ferries across the gap between the neurons. Chemicals as Couriers Chemicals called neurotransmitters are the signal couriers that jump across the synaptic cleft Presynaptic neuron sends the signal.
Postsynaptic neuron receives the signal.
Neurotransmitters Synaptic vesicles store the neurotransmitters. Receptor sites are tuned to respond to specific neurotransmitters. When the neurotransmitter successfully crosses the gap, it doesn't automatically trigger another action-potential. Graded in that PSP can increase or decrease the probability of an impulse in the receiving neuron. If there weren't any inhibitory PSP's, we could never stop the impulses.