Neurotransmitter

Neurotransmitters are signalling molecules released by exocytosis from vesicles in the pre-synaptic cell causing depolarisation, they diffuse across the synaptic cleft in response to an action potential. The neurotransmitter causes an electrical change in the post-synaptic cell.

The signals can be excitatory (open cation (e.g. Na⁺) channels) or inhibitory (open cl^- or K⁺ channels). Excitatory signals bring the cell closer to threshold where as inhibitory signals cause the cell to move away from threshold value. When the cell reaches threshold an action potential is fired.

References:

Alberts, B et al. (2008). Molecular Biology of the Cell. 5th ed. US: Garland Science