Structure

  • Neurons are separated by a synaptic cleft (approx. 20-30nm wide)
  • Presynaptic neurone refers to the neuron that released the neurotransmitter
  • Postsynaptic neurone refers to the neuron that receives the neurotransmitter
  • The enlarged section of an axon is synaptic knob
    • Large amount of mitochondria
    • Large amount of smooth endoplasmic reticulum
  • Neurotransmitters Is stored in synaptic vesicles
  • Once the neurotransmitter is released from the vesicle, it diffuses across the postsynaptic cleft

Functions

  • Single impulse along one neurone to be transmitted to a number of different neurones at a synapse, therefore allowing a single stimulus to create a number of simultaneous responses
  • A number of impulses to be combined at a synapse. This allows stimuli from different receptors to interact in order to produce a single response

Transmission

  1. Action potential arrives at presynaptic neurone causing Ca2+ channels to open and therefore Ca2+ ions enter the synaptic knob
  2. Influx of Ca2+ into presynaptic neurone results in synaptic vesicles to fuse with the presynaptic membrane. This releases acetylcholine into the synaptic cleft
  3. Acetylcholine fuses with receptors on the sodium ion channel on the postsynaptic neurone resulting in sodium ion channels to open allowing Na+ to diffuse in rapidly along a concentration gradient
  4. Influx caused by the sodium ions generate a new action potential in the postsynaptic neurone
  5. Acetylcholinesterase hydrolyses acetylcholine into choline and acetyl (ethanoic acid) which diffuses back through the presynaptic neurone cleft. It also ensures that the acetylcholine does not continuously generate a new action potential in the new neurone.
  6. ATP released is used to recombine choline and acetyl to acetylcholine which is stored in the synaptic vesicles. Sodium ion channels close.