Synapses and neurotransmitters

• Junction between neurons or between a neuron and a receptor/effector is a synapse
• In a synapse, the end of an axon will be found very close to the membrane of a dendrite or cell body of the next neuron
• The electrical message cannot cross the synaptic cleft (gap between the two neurons) 
• Arrival of a nerve impulse causes the release of chemical transmitter substance into the the synaptic cleft called a neurotransmitter that diffuse across the space and binds to the receptors on the receiving membrane
• Activates ion channels in the membrane leading to the nervous impulse being transmitted further 
• This is why nervous messages are termed electrochemical messages because they involve electrical impulses along axons and the release of neurotransmitters across the synaptic cleft to transmit messages
• Neurotransmitters can be broken down and re activated by enzymes
• Synapses are the points between neurons where the electrical signal is converted into a chemical signal 
• Information is passed from one neuron to the next, but the neurons don't touch each other
• Neurons communicate with other neurons across the synapse via a chemical message
• These chemicals are known as neurotransmitters
• Synaptic transmission steps

  1. Neurotransmitter release

  2. Receptor binding

  3. Postsynaptic response
• Neurotransmitter release

  1. Action potential reaches axon terminal

  2. Opens calcium channels

  3. Calcium ions enter terminal

  4. Synaptic vesicles fuse with membrane

  5. Release contents into synaptic cleft
• Receptor binding

  1. Neurotransmitters diffuse across synaptic cleft

  2. Bind to specific receptors in postsynaptic neuron
• Postsynaptic response

  1. Binding can excite or inhibit postsynaptic neuron

  2. Depends on type of neurotransmitter and receptors involved