features of synaptic transmission

• Synapses are unidirectional, can be summated and can be inhibited. 
• Unidirectional - NT vesicles are only found in the presynaptic membrane and not in the post synaptic membrane. Ligant sodium ion gated channels (NT receptors) are only found on the postsynaptic membrane. 
• summation is when the effect of the neurotransmitters released from many neurons is added together. 
• Spatial summation - two or more presynaptic membranes release NT onto the receptors on the same postsynaptic membrane. acetylcholine only remains attached to the receptors for a moment because it breaks down rapidly. The effect of the stimulus can be magnified. 
• Temporal summation - if several impulses reach the synaptic knob in quick succession, enough acetylcholine is released for the membrane potential to reach the threshold. 
• Inhibition at synapses can occur because some neurotransmitters are inhibitory and prevent action potentials being generated in the post synaptic neurone. Inhibition enable specific pathways to be stimulated while preventing random impulses all over the body. 
• Methods of inhibition:

  • NT can cause chloride ions channels to open causing an influx of negatively charged chloride ions. 
  • NT can cause potassium ion channels to open and potassium ions diffuse out of the cell body. 
  • Both actions cause hyperpolarisation which makes it more difficult to reach the threshold value for an action potential