Synpatic integration

• SYNAPTIC INTEGRATION

  • exhititatory input --> mediated by calcium influx --> exhitartory postsynaptic poteintaion (epsp) --> small depolarization
  • inhibitory input --> mediated by chloride influx and potassium outflux --> inhibitory post-synaptic potentiall (ipsp) --> small hyperpolarization
  • Inhibitory input + excitatory input --> chloride and sodium influx + potassium outflux --> epsp-ipsp -->response dependent on threshold

  1. strength of synaptic input affect decision to fire action potential
  2. influence by location of synapse and firing frequency of the pre-synaptic neurons

  
• SPATIAL SUMMATION

  • psp from multiple synapses 
  • current attenudates in dendrites (current leaks out)
  • attenuation does not occur in axons (starts at hillock/ initial segment)
  • psp travel to hillock/initial segment passively and attenutate --> the more they travel, the more they attenuate 
  • synapses close to the hillock have more influence
  • closer the synapse --> the more influence (strong influence)
  • multiple inputs with synapses firing psp at the same time --> influence depdnent on their position

  1. closer they are, the more they contribute to the summative
• TEMPORAL SUMMATION

  • multiple psp from a single synapse
  • how often they are firing
  • to be effective, psp needs to be additive
  • if a new action potential arrive before the previous psp decays --> will be compounded
• SHUNTING INHIBITION

  • a single inhibitory synapse close to the cell body can shut off all excitatory inputs from the dendrites
• ENCODING

  • neurons uses an frequency modulation code 
  • both frequency and pattern of action potentional convery information
  • same action potential but different effect on postsynaptic cell --> temporal summation

  1. can be caused by pattern changes 
• HOW DOES FM ENCODING OCCUR

  • absolute refractory --> no ap can be produced
  • relative refractory --> cell is less excitable and a larger stimulus is needed

  1. influences a rate that neurons respond to

  • refractory period --> due to inactivation of sodium current and activation of potassium current
  • if a stimulus is a lot bigger than the threshold --> an increase in the firing rate during relative refractory --> larger stimulus == a quicker response from the neurons
• REWARD PATHWAY