5 - Synaptic Transmission

• Synapse Definition


  • Each neuron is separated from the next by a tiny gap called the synapse.
• Synaptic Transmission - what is it?

  
  

  • The process by which one neuron communicates with another is synaptic transmission.
  • Signals WITHIN neurons are transmitted electrically, but signal BETWEEN neurons are transmitted chemically across the synapse.
• Synaptic Transmission Steps (1)

  • Info passed down axon of the neuron as an ELECTRICAL impulse known as action potential. Once AP (electrical impulse) reaches end of neuron/axon (presynaptic terminal) it needs to be transferred to another neuron/tissue.
  • It must cross over the SYNAPTIC CLEFT between presynaptic neuron & post synaptic neuron.
  • At end of neuron (in the axon terminal) is the synaptic vesicles, which contain CHEMICAL messengers, called NEUROTRANSMITTERS - when the electrical impulse gets to end of neuron this triggers, release of neurotransmitters from tiny sacs - synaptic vesicles.
• Synaptic Transmission Steps (2)

  • Neurotransmitters then carry the signal across the synaptic cleft. They bind to receptor sites (postsynaptic receptor) of the postsynaptic cell on the next neuron, thereby completing the process of synaptic transmission - so the impulse only ever travels in one direction.
  • The chemical message is converted back into an electrical impulse and the process of electric transmission begins again.
  • This begins again until it stops.
• Signals WITHIN neurons are transmitted ELECTRICALLY

  Signals BETWEEN neurons are transmitted CHEMICALLY across a synapse
• Label the parts needed in synaptic transmission?

  Label the parts needed in synaptic transmission?

  A) ?

  B) ?

  C) ?

  D) ?

  E) ?

  F) ?

  G) ?

  H) ?

  I) ?

  J) ?

  
• Synaptic Transmission DEFINITION 


  • The process by which one neuron communicates with another.
• Neurotransmitters definition & how relate to lock & key?

  • Neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain.
  • They all have own SPECIFIC MOLECULAR STRUCTURE (& own specific function) that fits perfectly into a post synaptic receptor site (like lock & key)
  • TWO TYPES OF NEUROTRANSMITTER:
  • Inhibitory AND Excitatory
• Neurotransmitters can be excitatory or inhibitory.
• Inhibitory Neurotransmitter example


  • GABA
• Excitatory Neurotransmitter example

  • Glutamate
• Neurotransmitters can be BOTH Inhibitory and excitatory (GABA purely inhibitory)
• Summation?

  • If the neurotransmitter is excitatory then the post synaptic neuron is more likely to fire an impulse
  • If the neurotransmitter is inhibitory then the post synaptic neuron is less likely to fire an impulse.
  • The excitatory and inhibitory influences are summed and must reach a certain threshold in order for the action potential of the postsynaptic neuron to be triggered.
  • If the NET EFFECT of the neurotransmitters is INIHIBITORY then the post synaptic neuron is LESS likely to fire (i.e. no electrical signal is transmitted) it is MORE likely to fire if the net effect is EXCITATORY.
• GABA - what, function, promoted during?

  • Purely INHIBITATORY - primary neurotransmitter in the brain
  • Effecting emotional & physical stability. Slows down your brain blocking specific signals to your CNS, calming you, subduing anxiety, pain, fear or stress. (When excitatory neurons un risk of running out of control if not checked)
  • GABA is promoted during sleep - hibernating animals experience spikes in GABA.
• Glutamate - type, what, function, negative?


  • Excitatory neurotransmitter
  • Used for every excitatory function. Involved in cognitive function like memory & learning.
  • To much Glutamate can be toxic:
  • When person experiences a head injury or stroke, glutamate floods injured area & kills the neurons by overexciting them causing brain damage.
• E.g. Neurotransmitters


  • Acetylcholine (ACh) - found where a motor neuron meets a muscle, causing muscles to contract
  • Serotonin - affects mood and social behaviour (among other things) which is why it has been implicated as a cause of depression.
• Neurotransmitters generally have either an excitatory or inhibitory effect in the neighbouring neuron

  • Adrenaline - generally excitatory, increasing the positive charge of the postsynaptic neuron neuron, making it more likely that the postsynaptic neuron will fire.
  • Serotonin - generally inhibitory, increasing the negative charge if the postsynaptic neuron, making it less likely the postsynaptic neuron will fire.
  • Dopamine - unusual neurotransmitters as it is equally likely to have excitatory or inhibitory effects on the postsynaptic neuron.
• Synaptic Transmission Steps?

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  A) ?

  
• Come hand in hand with neurone topic :)