SYNAPSE

1.      Synapse = unique junction between 2 adjacent neurones.

2.      Presynaptic neurones (bounded by a presynaptic membrane)
       =.Neurones - which carry impulses to synapse
3.      Postsynaptic neurones ( bounded by a postsynaptic membrane)

       =.Neurones - which carry impulses away from synapses,

4.      Synaptic knob (axon terminal) = swollen distal end of a motor neurons axon

5.      Within the synaptic knob are:
      -     mitochondria
      -     vesicles (packed with neurotransmitter).

6.      A neurotransmitter:
      -     chemical messenger
      -     used by neurones
      -     to communicate
      -     with each other
      -    or with effectors.

7.      On the postsynaptic membrane:
      -    there are protein receptors
      -    for the attachment of neurotransmitters.

8.      When an action potential:
      à arrives at the synaptic knob
      à causes influx of Ca²⁺ ions
      è into synaptic knob
      è stimulates the fusion of vesicles + presynaptic membrane
      è release of neurotransmitter
      è into synaptic cleft
      è by exocytosis.

9.      The neurotransmitter:
      è diffuses across the synaptic cleft
      è binds to the protein receptors
      è on the postsynaptic membrane
      è causing depolarisation.
      è  it is removed from the synaptic cleft
      è by hydrolysis
      è re-uptake into the synaptic knob
      è to prevent further unwanted effect.

10.  Cocaine:
      è preventing the reuptake of dopamine
      è into the synaptic knob,
      è resulting in generation of repeated impulses,
      è producing feeling of euphoria.

11.  Curare :
      è binding to the protein receptor for acetylcholine
      è on postsynaptic membrane
      è prevents the transmission of the impulse
      è causing paralysis.