Question

How do impulses cross the synapse?

Answer 1

By means of chemical messenger called neurotransmitters.

Explanation:

Synaptic Transmission:

• The nerve impulse arrives at presynaptic neuron and starts an action potential in it.
• This action potential can not jump from one neuron to the next neuron.
• So, there must be a mechanism for its transmission. And ofcourse there is an amazing mechanism set by Nature which is Synaptic transmission, which occurs through synapse.
• Synapse is a microscopic gap between axon-ending of presynaptic neuron and dendrite-ending of postsynaptic neuron.
• The pre-synaptic neuron has synaptic vesicles in its synaptic knob.
• These synaptic vesicles are filled with special type of chemical messenger called neurotransmitters, which offer great services in the transmission of the actin potential.
• Thus, the action potential when arrives at the axon-ending of presynaptic neuron , the synaptic vesicles fuse with synaptic membrane. As a result of this fusion, neurotransmitters are released in the synaptic cleft(gap).
• The membranes(of dendrites) of post-synaptic neuron have receptors .
• The neurotransmitters released from the presynaptic neuron binds to the receptors of the postsynaptic neuron.
• These neurotransmitter change the permeability of postsynaptic neuron for certain ions i.e `Na^+` ions.
• Thus, they start an action potential in the postsynaptic neuron.
  

This is how the two neurons work...

Hope it helps...