L14 Synapses and chemical transmission

• Synapses:

  When an action potential reaches the end of an axon, the depolarization opens calcium gates in the presynaptic membrane which provokes a sudden release of neurotransmitters into the synpatic cleft.
• Susbstances other than neurotransmitters can diffuse into the synapse.

  • Toxines - destroy receptors
  • Drug antagonists - drugs can come in abundance and abuse the synapse causing long-term harm
• In an excitatory synapse:

  • sodium gates open
  • sodium ions enter the postsynaptic neuron
• Inhibitory synapse:

  • chloride gates open
  • chloride ions enter the postsyaptic neuron

  or

  • potassium gates open
  • potassium ions leave the postsynaptic neuron
• What is a neuromodulator?

  A neuromodulator is a messenger released from a neuron that affects the transmission of the signals between neurons.  It potentiates or inhibits the transmission of a nerve impulse but is not the actual means of transmission itself.
• The majority of neurons release two or more types of neurotransmitters.
• The strength of a synapse is defined by the size of postsynaptic potential.
• What is long-term potentiation?

  Strengthening of synaptic connections.

  Intensive use of a synapse may lead to its potentiation, and stronger effects on the postsynaptic membrane.
• What is synaptogenesis?

  Formation of synapses.
• Reuptake:

  • Reabsorption of neurotransmitters into the presynaptic neuron. This recycling process concerns serotonin and the catecholamines.
  • Other neurotransmitters are broken down
  • Big neurotransmitters diffuse
• Pharmaceutics can:

  • facilitate transmission at synapses - agonist
  • inhibit transmission at synapses - antagonist
  • impact the amount of neurotransmitter in the cleft