When an impulse reaches a synapse:

When a nerve impulse reaches a synapse, the following steps occur:

1. The electrical signal (nerve impulse) travels down the axon of the neuron until it reaches the axon terminal, which is part of the synapse.

2. The arrival of the nerve impulse at the axon terminal triggers the release of neurotransmitters. These are chemical messengers stored in small sacs called synaptic vesicles.

3. The neurotransmitters cross the synaptic cleft, which is the tiny gap between the neurons at the synapse.

4. The neurotransmitters bind to specific receptors on the dendrite of the next neuron. This binding opens ion channels, allowing charged particles to flow across the neuron's membrane.

5. This flow of ions creates a new electrical signal in the second neuron, and the process begins again.

This is a simplified explanation of a complex process, but it covers the main steps that occur when an impulse reaches a synapse.