what isthe junction between an axon terminal and the next neuron
2) Synaptic Cleft: This is the narrow gap between the axon terminal of the presynaptic neuron, and the post-synaptic membrane of another excitable cell. It is filled with extracellular fluid. 3) Postsynaptic membrane: The membrane across the synaptic cleft is called the postsynaptic membrane.) A nerve impulse reaches the axon terminal of a presynaptic neuron; the membrane is depolarised by an action potential. 2) Depolarisation of the axon terminal during the action potential causes voltage sensitive calcium ion channels to open in the terminal knob.