Final answer:
The unidirectional flow of signals in a chemical synapse is due to specialized structures and mechanisms that allow neurotransmitters to be released from the axon terminal and bind to receptors on dendrites, initiating a new signal.
Step-by-step explanation:
The flow of signals in a synapse from the axonal end of one neuron to the dendritic end of another neuron is due to the chemical nature of synapses. In a chemical synapse, neurotransmitters are released from synaptic vesicles in the presynaptic neuron's axon terminal. These chemical signals traverse the synaptic cleft and bind to receptors on the postsynaptic neuron's dendrites, often causing ion channels to open and initiating a new electrical signal within the dendritic neuron. This process is unidirectional, meaning that it goes only from the axon of one neuron to the dendrites of another, due to the specialized structures and mechanisms involved, such as the localization of synaptic vesicles and receptors.
Electrical synapses, on the other hand, do allow for bidirectional flow of signals, but they are less common and serve different functions in the nervous system, such as synchronizing the electrical activity of a group of neurons or enabling key reflexes. They are not typically involved in the unidirectional signal transmission process seen in most neural communication.