Synaptic transmission

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  • Created by: Steff06
  • Created on: 02-05-17 14:48

Structures

  • Synaptic neuron: Axon terminal with postsynaptic membrane. Vesicles filled with neurotransmitter. Ca2+ ion channels allow Ca2+ to move from extracellular fluid into neuron.
  • Synaptic cleft: In between pre and post-synaptic neuron
  • Postsynaptic neuron: Postsynaptic membrane and ion channels.
  • Inside of neuron = more negative, Outside of neuron = more positive.
  • Vesicles = Double layer of phsophate group
  • Voltage-gated ion channels: Open in response to change in membrane potential.
  • Transmitter-gated ion channels: Open in response to neurotransmitter molecule binding with channel's receptor site.

Type of neurotransmitter released determines whether synapse is excitatory or inhibitory.

  • Membrane potential at axon hillock must depolarise over -50mV for action potential to trigger
  • Depends on type of ion channel and receptor present in post-synaptic membrane
  • Integration & transformation processes are a neurons way to compute signals, what is meant by info processing (integrating charged particles in a neuron) and basis of all behaviour.
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Processes

Pre-synaptic membrane: 1. Action potential arrives, Ca2+ channels open.  2. Ca2+ ions enter axon terminal 3. Vesicles fuse with presynaptic membrane 4. Neurotransmitter released to synaptic cleft

Postsynaptic neuron: a. Neurotransmitter bind with ion channels at receptor site.  b. Ion channels open & ions enter postsynaptic neuron.  c Generates postsynaptic potential  d Neurotransmitter removed from receptor site   e Channels close

  • Post-synaptic summation: A single PSP is insufficient to trigger a new action potential, so:
  • Generator potential build up is slow + graded. GP integrates changes cause by multiple action potentials across time and space.

Neurotransmitter removal: Neurotransmitters don't change when they bind to a receptor. They have to be actively removed to stop influence on post-synaptic cell.

2 types of neurotransmitter removal = 1. Degradation - enzymes in cleft break them down. Partly recycled. 2. Reuptake - receptors at pre-synaptic axon terminal take up NT's and return into pre-synaptic cell.

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Types of channels, excitation/inhibition, summatio

Forms of transmitter-gated channels: a. Ionotropic transmitter channels which open directly.  b. Metabotropic transmitter channels which open indirectly.

  • Key into lock (neurotransmitters to receptor sites): Which type of ion enters postsynaptic neuron depends upon type of channel that opens. Which channel that opens depends on...
  • 1. Neurotransmitter that has been released and receptor sit of post-synaptic ion channel
  • 2. G-protein - respond to neurotransmitter molecule. Produces chemical as 2nd messenger
  • 1st messenger = neurotransmitter

Excitation and inhibition: Excitatory synapse = Positive ions enter (depolarisation), action potential becomes likely at axon hillock. Inhibitory synapse = Negative ions enter (hyperpolarisation) and action potential becomes less likely.

  • Temporal summation -> Combination of PSP's occuring in rapid succession together
  • Spatial summation -> Combination of PSP's occuring in close temporal proximity at different synapses of the same postsynaptic neuron
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