synaptic transmission

• synaptic transmission (1)

  an electrical impulse known as action potential (AP) is carried along the axon of a neuron
• synaptic transmission (2)

  when the AP reaches the end of the axon, it needs to cross a synapse to reach another neuron. the vesicles at the end of the neuron contain neurotransmitters, which are chemical messengers released when the AP reaches them.
• synaptic transmission (3)

  neurotransmitters carry signals across the synapse, bind to receptor sites on the postsynaptic neuron and produce excitatory or inhibitory effects
• synaptic transmission (4)

  neurotransmitters not bound to receptors are taken back or broken down as enzymes to the stop the impulse from repeating
• inhibitory neurotransmitter

  • calm down the brain and NS
  • inhibitory neurotransmitters that bind with postsynaptic receptors result in inhibitory synaptic potential (IPSP)
  • this means postsynaptic neurons are less likely to fire because the presence of neurotransmitters makes them negatively charged.
• excitatory neurotransmitter

  • stimulate activity in areas of the brain
  • excitatory neurotransmitters binding with postsynaptic transmitters results in excitatory synaptic potential (EPSP)
  • this means postsynaptic cells are more likely to fire because the presence of neurotransmitters makes them positively charged.
• Summation

  most/all transmitters have both excitatory/inhibitory potential but the one that dominates determines the effect it has on the postsynaptic neuron.
• the strength of EPSP can be increased in two ways

  • spatial summation
  • temporal summation
• spatial summation

  large number of ESPSs generated at many different synapses on the same postsynaptic neuron at the same time.
• temporal summation

  large number of EPSPs generated at the same synapse by a series of high frequency AP on the presynaptic neuron.
• neurotransmitters

  can only travel in one direction because there are complementary receptor sites on the postsynaptic neuron for the transmitters to bind to.