Synapse

• What is a synapse

  Gap/junction between two neurones or neurone to effector
• summarise the 3 main stages in synaptic transmission

  1. Action potential arrives at synaptic knob causing voltage gates Ca2+ channels to open
  2. Ca2+ cause vesicles containing neurotransmitters to fuse with the presynaptic membrane
  3. Neurotransmitter causes action potential to be gated in the post synaptic neurone
• Describe what occurs in the first step of a synaptic transmission

  • AP arrives at synaptic knob causing voltage gated Ca2+ chancels to open
  • Ca2+ enters synaptic knob
  • Once Ca2+ ions are not needed they are pumped back out of the synaptic knob (active transport ,needs ATP)
• Describe what occurs in the second stage of synaptic transmission

  • Ca2+ cause vesicles containing neurotransmitters to fuse with the presynaptic membrane
  • Neurotransmitters are released into the synaptic cleff by exocytosis
• Describe what occurs in the final stage of synaptic transmission

  • Neurotransmitter cause an AP to be gated in the postsynaptic neurone
  • Neurotransmitters diffuse from high to low concentration in synaptic cleff
  • voltage gated Na+ channels open due to neurotransmitters binding with specific receptors
  • sodium ions diffuse into post-synaptic neurone leading to depolarisation
  • Wave of depolarisation causes AP to be generated
  • Neurotransmitters have to be removed either by diffusing back into presynaptic neurone or enzymes destroying them
• What enters the presynaptic neurone to initiate neurotransmitter release?

  Calcium ions
• What happens to vesicles containing neurotransmitters when calcium ions enter the presynaptic neurone?

  They fuse with the presynaptic membrane
• What do neurotransmitter molecules do after being released?

  They diffuse across the synapse
• Where do neurotransmitters bind after diffusing across the synapse?

  Receptors on the postsynaptic membrane
• What is the result of sodium ions diffusing into the brain cell?

  It leads to depolarisation
• What can occur as a result of sodium ions entering the postsynaptic cell?

  An action potential can be generated
• What are the 2 ways in which an impulse can be strengthened

  1. Amplified
  2. Dispersed
• What is impulse divergence

  • Divergence
  • one neuron connects to many neurones and can be dispersed to different parts of the body
• what is impulse convergence

  • amplification
  • many neurons connect to one neuron info