12.6

• presynaptic neuron

  • sends message
• postsynaptic neuron

  • receives message
• electrical synapses

  • direct physical contact between cells
  • locked together at gap junctions
  • brain/eye/ciliary ganglia
• chemical synapses

  • signal transmitted across a gap by neurotransmitters
  • cells separated by synaptic cleft
  • axon terminal releases neurotrnasmitters
  • produces localized permeability and graded potential changes
• neuromuscular junction

  • chemical synapse
  • between neuron and skeletal muscle cell
• neuroglandular junction

  • chemical synapse
  • between neuron and gland cell
• cholinergic synapses

  • releases acetylcholine (ACh)
  • all neuromuscular junctions involving skeletal muscle fibers
  • neuron-to-neuron synapses in PNS
  • neuromuscular/glandular junctions in parasympathetic division of ANS
• synaptic delay

  • delay of 0.2-0.5 ms between arrival of action potential at axon terminal and effect on postsynaptic membrane
  • fewer synapses, faster repsonses
• synaptic fatigue

  • neurotransmitter cannot be recycled fast enough to meet intense stimuli demands
  • synapse reaction weakens until ACh is replenished