synaptic transmission

• Neurotransmitters are chemicals which diffuse across the synapse to the next neuron
• Synaptic transmission involves the movement of an impulse from the presynaptic terminal, across the synaptic cleft and to the postsynaptic receptor sites
• when an impulse (action potential) reaches the presynaptic terminal located at the end of a neuron, it stimulates small sacs called vesicles, which are located on the presynaptic terminal, to release neurotransmitters
• neurotransmitters diffuse across the synaptic cleft and bind to the postsynaptic receptor sites and are converted back into an electrical impulse
• synaptic transmission causes a specific response, which will either be exciting or inhibiting
• Serotonin causes inhibition in the receiving neuron, meaning the neuron becomes more negatively charged and less likely to fire
• Adrenaline causes excitation in the receiving neuron, meaning it becomes more positively charged and so more likely to fire
• Whether the neuron does or doesn’t fire is decided by the process summation
• Action potential of the postsynaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time reaches the threshold