Synapses

• What is a synapse?


  The gap between two neurons
• What is the role of neurotransmitters at a synapse?

  To diffuse across the gap and trigger action potentials
• What happens when an action potential arrives at the synaptic knob?

  Calcium ion channels open and calcium ions enter
• Why does neurotransmitter only diffuse in one direction across the synapse?

  Vesicles are only in the pre-synaptic neuron
• What are the steps involved in neurotransmitter release at a synapse?

  1. Action potential arrives at synaptic knob
  2. Calcium ion channels open
  3. Calcium ions diffuse into synaptic knob
  4. Vesicles move to pre-synaptic membrane
  5. Neurotransmitter is released into synaptic cleft
  6. Neurotransmitter binds to post-synaptic receptors
• What is the neurotransmitter released at a cholinergic synapse?

  Acetylcholine
• What enzyme breaks down acetylcholine?

  Acetylcholine esterase
• What is the threshold potential needed to trigger an action potential?

  -55 millivolts
• What is summation in the context of synapses?

  The addition of neurotransmitters to trigger action potentials
• What are the two types of summation?

  1. Spatial summation: Multiple pre-synaptic neurons release neurotransmitters
  2. Temporal summation: One neuron releases neurotransmitter repeatedly
• How does spatial summation differ from temporal summation?

  Spatial involves multiple neurons, temporal involves one
• What occurs at inhibitory synapses?

  Chloride ions enter and potassium ions exit
• What is hyperpolarization in the context of inhibitory synapses?

  Membrane potential drops below resting potential
• Why are inhibitory synapses important?

  They prevent overwhelming responses to stimuli
• What is a neuromuscular junction?

  • A synapse between a motor neuron and muscle
  • Triggers muscle contraction instead of action potentials
  • Functions similarly to other synapses
• What are the key differences between synapses and neuromuscular junctions?

  • Synapses connect neurons; neuromuscular junctions connect neurons to muscles
  • Neuromuscular junctions are always excitatory
  • Synapses can be excitatory or inhibitory
• What binds to receptors on the muscle fiber membrane at a neuromuscular junction?

  Acetylcholine
• What is the result of acetylcholine binding at a neuromuscular junction?

  Muscle contraction is triggered
• How does the flow of information differ between synapses and neuromuscular junctions?

  Synapses can be inhibitory; neuromuscular junctions are excitatory