6.2.6 Structure & Function of Synpases

• Structure of a Synape

  A) Mitochondria

  B) Mylein Sheath

  C) Smooth Endoplasmic Reticulum

  D) Acetylcholine

  E) Synaptic Vesicles

  F) Synaptic Cleft

  
• Features of Synapses

  • Unidrectional = synapses act like valves only allowing impulses pass from the presynaptic to post synaptic neurone
  • Summation = rapid build up of neurotransmitters at a synapse
• Spatial summation = multiple presynaptic neurones release neurotransmitters exceeding the threshold value
• Temporal Summation = single neurone releases neurotransmitters many times over a very short period of time, exceeding the threshold value
• Inhibition

  • Presynaptic neurone releases neurotransmitter that binds to chloride ion protein channels at post synaptic neurone
  • Chloride ion enters via facilitated diffusion
  • Binding of neurotransmitter cause movement of potassium ions out of post synaptic neurone into synapse
  • Negative ion moving in and positive ions moving out causes hyperpolarisation (inside of membrane more negative)
• How might drugs decrease synaptic transmission?

  • Inhibit release of neurotransmitter
  • Decrease permeability of postsynaptic membrane to ions
  • Hyperpolarise postsynaptic membrane
• How might drugs increase synaptic transmission?

  • Inhibit acetylcholinesterase
  • Mimic shape of neurotransmitter
• Synaptic Transmission involves the presynaptic membrane depolarising, causing calcium ion channels to open, allowing calcium ions to enter the presynaptic neurone.
• Calcium ions in the neurone cause the fusion of synaptic vesicles, filled with acetylcholine, with the presynaptic membrane.
• Benefit of recycling of the neurotransmitter is that it prevents continuous generation of an action potential in the post synaptic neurone
• Neurotransmitter is then released into the synaptic cleft and diffuses towards the post synaptic neurone.
• After a new action potential is created, acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid (acetyl) which diffuses back across the synaptic cleft and back into the presynaptic neurone to be reused.