SYNAPTIC TRANSMISSON

• • A synapse is a junction that allows a neurone to communicate with another neurone via a chemical called a neurotransmitter.
• • There are various neurotransmitters, which all act in slightly different ways.
• A synapse that uses acetylcholine is called a cholinergic synapse.
• he synaptic cleft is very narrow (20 nm), so the diffusion distance is short.

  This speeds up synaptic transmission
• Returning a synapse to its resting state after an impulse

  • Calcium ions are actively transported out of the synaptic knob to stop neurotransmitter release into the synaptic cleft.
  • Acetylcholine is hydrolysed by an enzyme in the synaptic cleft.
  • This enzyme is called acetylcholinesterase (learn).
  • This hydrolysis produces choline and acetate.
  • Choline diffuses back into the synaptic knob by facilitated diffusion.
  • Choline is reacted with acetate (suggest where from) using an enzyme to reform acetylcholine.
  • Acetylcholine is repackaged into synaptic vesicles via active transport.
• Synaptic knobs have many mitochondria

  • This ensures much aerobic respiration so large amounts of ATP can be produced.
  • This ATP is needed to:
  • actively transport calcium ions back out of the synaptic knob after an impulse has passed through;
  • repackage acetylcholine into its synaptic vesicles via active transport.
  • This is in addition to providing ATP for the sodium ion-potassium ion pump protein for resting potential.
• The synapse is unidirectional
• Acetylcholine can only be released from the presynaptic neurone but the acetylcholine receptors are only found on the postsynaptic membrane.
• If a higher frequency of impulses travels along the presynaptic neurone, more neurotransmitter is released. The postsynaptic membrane will be more likely to reach threshold potential for an new impulse to be generated.
• If the postsynaptic membrane receives neurotransmitter from more than one presynaptic neurone, the postsynaptic membrane will be more likely to reach threshold potential for an new impulse to be generated.
• Excitatory synapses -

  • This means that the neurotransmitter will stimulate the development of new action potentials at the postsynaptic membrane.
• • Other synapses are inhibitory.
  • Inhibitory synapses can be used to inhibit the generation of new action potentials at the postsynaptic membrane.#
• • Inhibitory synapses are associated with a calming effect on the body.
• • Disruption to inhibitory synapses can increase anxiety.