Synapses

• Synase is junction between 2 or more neurones and enables them to communicate and signal; synaptic cleft (~20nm wide) and neurones close to it
• Action potential cannot move over it, instead neurotransmitter chemical molecules are released from one; they diffuse over cleft; causing action potentials in next neurone
• Pre-synaptic neurone: Many mitochondria (active process, needs ATP), large SER amounts, many secretory vesicles with acetylcholine and voltage-gated Ca^2+ ion channels
• Transmission across Synaptic cleft: Generator potential or post-synaptic potential is created in postsynaptic membrane, if enough potentials combine threshold potential is reached and new action potential
• Acetylcholine (cholinergic) and noradrenaline (adrenergic) are the main neurotransmitters outside the brain, more than 50 natural neurotransmitters e.g. endorphins, dopamine, serotonin
• There are many drugs which mimic natural neurotransmitters or block action (antagonistic) e.g. heroin, LSD, cocaine, nicotine, caffeine
• Many organophosphorous compounds such as malathion (insecticide) and sarin gas (nerve gas) inhibit acetylcholinesterase causing Ach to bind continuously
• Many organophosphorous compounds such as malathion (insecticide) and sarin gas (nerve gas) inhibit acetylcholinesterase causing Ach to bind continuously
• If threshold is reached, an action potential is generated in postsynaptic neurone; excitatory synapse, they can also be inhibitory; depend on neurotransmitter or synapse location
• At inhibitory synapses, neurotransmitter hyperpolarises by binding to chloride ion channels moving Cl^- and causes potassium channels to open (K^+ out); makes it more negative and prevents new impulse
• Synaptic Gap/Cleft

  A) pre-synaptic

  B) synaptic

  C) mitochondrion

  D) synaptic vesicle

  E) transmitter

  F) post-synaptic

  G) synaptic cleft

  
• Pre-synaptic Neurone

  A) SER

  B) Mitochondrion

  C) Synaptic vesicle

  D) acetylcholine

  E) Ca^2+

  F) Ca^2+

  G) Calcium ion

  H) Myelin Sheath

  I) Axon

  J) Membrane

  
• Post-synaptic neurone: Specialised Na+ ion channels with acetylcholine-specific receptor sites, when acetylcholine binds; Na+ ion channel opens

  A) 5

  B) sodium ion

  C) Acetylcholine

  D) receptor