Neurons + synaptic transmission

• Neuron's + synaptic transmission-

  Neuron's-

  • Vary from 1mm to 1m, live in the CNS
  • cell body has the nucleus
  • dendrites are alike to branches, carrying nerve impulses from other neuron's
  • Axons carry impulses away, covered by myelin sheath
  • myelin sheath- fatty layer in parts to protect (nodes of Ranvier), too large would slow the process down
  • terminal buttons on the end to communicate with other neuron’s across the synaptic gap
  • Long axons form parts of the PNS
  • called ganglia when outside the C/PNS
  • relay neurones make up 97% of all neuron's, mainly in the brain + visual system
• Neuron’s + Synaptic transmissions-

  electrical transmission-

  • rest inside the cells, and are negatively charged
  • when activated they’re positively charged, for a split second- causing action potential
  • creates electrical impulses that travel down the axons towards the neuron’s end
• Neuron‘s+ synaptic transmission-

  chemical-

  • neuron’s communicate through neural networks
  • all separated by small gaps- synapses
  • signals within the neurone travel chemically across the synapse
  • electrical impulses reach the end of the neurone (presynaptic terminal), neurotransmitters are released triggered from synaptic vesicles
• Neuron’s + synaptic transmission-

  Neurotransmitters-

  • chemicals that diffuse across the synapse to the next neurone
  • postsynaptic receptor site takes up the gap after the neurotransmitter crosses
  • chemical message is transferred back to electrical impulse - transmission repeated
  • travel direction is one way- presynaptic neurone received by the postsynaptic neurone
  • neurotransmitters have individual molecular structures perfect for the receptor sites
  • neurotransmitters have individual functions
• Neurones + synaptic transmission-

  Excitation + inhibitation-

  • serotonin inhibits the receiving neurons, making it negatively charged, and less likely to fire
  • adrenaline causes excitation of postsynaptic neurons by increasing its positive charge, making firing more likely
• Neurones + synaptic transmission-

  Summation-

  • whether a postsynaptic neurone fires
  • inhibitory influence = less likely to fire
  • excitatory influence = more likely to fire (positive charge)
  • electrical impulses travels down the postsynaptic neurone, only triggered by excitatory + inhibitory signals, once the threshold is reached