Synaptic transmission

Synapse.jpg

Electrical transmission occurs when an action potential reaches an axon terminal, this depolarises the presynaptic membrane. Voltage gated Ca²⁺ channels on thepresynaptic membrane open in response to this depolarisation. Ca²⁺ enters the axon terminal down aconcentration gradient through these open channels. This causes the vesicles containing the neurotransmitter acetylcholine to migrate towards the presynaptic membrane. These vesicles fuse with the presynaptic membrane, and acetylcholine molecules are released into the synaptic cleft by the process of exocytosis. Acetylcholine molecules diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane. The binding of acetylcholine causes ligand gated Na⁺ channels to open and subsequently Na⁺ rushes into thepostsynaptic membrane, depolarising it to the threshold potential, therefore setting off an action potential in the postsynaptic neurone.