Synapses

• Action potential arrives at the synaptic knob, depolarisation leads to the opening of Ca2+ channels
• An influx of Ca2+ in the synapse triggers synaptic vesicles to fuse with the pre-synaptic membrane (exocytosis), releasing neurotransmitters into the cleft
• Neurotransmitters from the vesicles diffuse down a concentration gradient to the post synaptic neurone
• Neurotransmitters complementarily bind to receptors on the post-synaptic membrane, Na+ ion channels open, causing an influx to depolarise the neurone
• Neurotransmitters are degraded and released from the receptor, the post-synapse re-establishes resting potential, neurotransmitters return to the pre-synapse for recycling
• Synaptic transmission is uni-directional as:

  • Vesicles are only found in the pre-synapse
  • There is a neurotransmitter concentration gradient from pre- to post-
  • Receptors only found on the post-synapse membrane
• Cholinergic synapses use acetyl choline as their neurotransmitters, when released from receptors, acetylcholinases break down the neurotransmitter into acetate and choline, and reabsorb into the pre-synapse
• Summation is the process of combining the effects of multiple neurotransmitters to produce a single action potential
• Spatial summation is when multiple neurones combine neurotransmitters to trigger an action potential
• Temporal summation is when a singular neurone releases neurotransmitters repeatedly over a short period of time
• Inhibitory synapses cause chloride ions to move into the post-synapse, and K+ ions to move out, hyperpolarising the neurone to -80mv to prevent action potential