Because of the presence of the neurotransmitter (acetylcholine) in the axonal end which converts electrical impulses to chemical impulse for its further transfer to the other dendritic end of another neurones because electric impulse cannot travel in synapse it is converted into chemical impulse so if it travel in reverse way(that is from dendritic end to axonal end of other neuron) it will not pass through synapse .. and the information will not reach at appropriate place ....

Introduction

The flow of signals in a synapse is unidirectional, meaning it goes from the axonal end of one neuron to the dendritic end of another neuron. This directional flow is essential for proper functioning of the nervous system.

Why is the Flow Unidirectional?

The unidirectional flow of signals in a synapse is primarily due to the structural and functional differences between the axonal and dendritic ends of neurons. These differences can be explained as follows:

1. Pre-synaptic and Post-synaptic Specializations
- The axonal end of a neuron, known as the pre-synaptic terminal, contains specialized structures called neurotransmitter vesicles that store and release neurotransmitters.
- The dendritic end of a neuron, known as the post-synaptic terminal, has receptor molecules that bind to the released neurotransmitters.

2. Neurotransmitter Release
- When an action potential reaches the pre-synaptic terminal, it triggers the release of neurotransmitters into the synaptic cleft.
- Neurotransmitters are released from the pre-synaptic terminal in a process called exocytosis, where they are released into the synaptic cleft and diffuse across the small gap.

3. Receptor Activation
- Once the neurotransmitters diffuse across the synaptic cleft, they bind to specific receptor molecules on the post-synaptic terminal.
- The binding of neurotransmitters to their receptors initiates a series of molecular events that generate an electrical signal in the post-synaptic neuron.

4. Molecular Machinery
- The pre-synaptic terminal is equipped with machinery for neurotransmitter release, such as voltage-gated calcium channels that allow calcium ions to enter the terminal, triggering exocytosis.
- The post-synaptic terminal is equipped with receptor molecules that are specifically designed to bind to neurotransmitters and initiate a response.

5. Absence of Neurotransmitter Reuptake Mechanisms
- In most synapses, there are no mechanisms for the reuptake of neurotransmitters from the post-synaptic terminal back into the pre-synaptic terminal.
- This absence of reuptake mechanisms prevents the reverse flow of neurotransmitters, ensuring that the signal flow remains unidirectional.

Conclusion

The flow of signals in a synapse is unidirectional from the axonal end of one neuron to the dendritic end of another neuron. This unidirectional flow is due to the presence of specialized structures and receptors, the release and binding of neurotransmitters, the molecular machinery involved, and the absence of neurotransmitter reuptake mechanisms. These factors collectively ensure the efficient transmission of signals in a one-way manner, allowing for proper functioning of the nervous system.