synapses, neuromuscular junction and summation

• What is the gap between two neurons called?

  Synapse
• What is the role of neurotransmitters at a synapse?

  To diffuse across and trigger action potentials
• What is the synaptic knob?

  The end of the neuron
• What happens when an action potential arrives at the synaptic knob?

  Calcium ion channels open
• What causes calcium ions to diffuse into the synaptic knob?

  Opening of voltage-gated calcium ion channels
• What do calcium ions trigger within the synaptic knob?

  Movement of vesicles containing neurotransmitters
• Where are neurotransmitters released from?

  Pre-synaptic neuron
• What is the synaptic cleft?

  The gap between pre and post-synaptic neurons
• Why does neurotransmitter concentration increase at the pre-synaptic end?

  Neurotransmitter is only released from that side
• What happens when neurotransmitters bind to receptors on the post-synaptic neuron?

  Sodium ion channels widen, allowing sodium ions in
• What is the significance of reaching the -55 millivolt threshold?

  It triggers an action potential in the neuron
• What happens if neurotransmitters remain attached to sodium ion channels?

  Constant triggering of action potentials occurs
• What is the final step in neurotransmitter action?

  Neurotransmitter is broken down and recycled
• What is the neurotransmitter involved in cholinergic synapses?

  Acetylcholine
• What enzyme breaks down acetylcholine?

  Acetylcholine esterase
• What is summation in the context of synapses?

  Adding up neurotransmitters to trigger action potentials
• What is spatial summation?

  Multiple pre-synaptic neurons release neurotransmitters
• What is temporal summation?

  One neuron releases neurotransmitter repeatedly
• What happens at inhibitory synapses?

  Chloride ions enter, causing hyperpolarization
• What is hyperpolarization?

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

  They prevent overwhelming sensory responses
• What is a neuromuscular junction?

  Gap between a motor neuron and muscle
• How does a neuromuscular junction differ from a synapse?

  It connects a neuron to a muscle
• What is the outcome of neurotransmitter binding at a neuromuscular junction?

  Muscle contraction occurs
• What are the similarities and differences between synapses and neuromuscular junctions?

  Similarities:

  • Both involve neurotransmitter release
  • Both result in unidirectional flow

  
  

  Differences:

  • Synapses connect neurons; neuromuscular junctions connect neurons to muscles
  • Neuromuscular junctions are always excitatory
• What are the key steps in neurotransmitter action at a synapse?

  1. Action potential arrives at synaptic knob
  2. Calcium channels open, calcium ions enter
  3. Vesicles release neurotransmitter into synaptic cleft
  4. Neurotransmitter binds to post-synaptic receptors
  5. Sodium channels open, triggering action potential
  6. Neurotransmitter is broken down and recycled
• What are the types of summation in synapses?

  • Spatial Summation: Multiple pre-synaptic neurons release neurotransmitters
  • Temporal Summation: One neuron releases neurotransmitter repeatedly