3.6.2.2 Synaptic transmission

• Describe the role of neurotransmitters at a synapse.

  • Neurotransmitters are released from the presynaptic neuron into the synaptic cleft.
  • They bind to receptors on the postsynaptic neuron, opening ion channels.
  • This triggers an action potential in the postsynaptic neuron if the threshold is reached.
  • Neurotransmitters are broken down or reabsorbed to stop the signal​
• Explain how the structure of a synapse enables one-way transmission of nerve impulses.

  • The synapse consists of a presynaptic terminal, synaptic cleft, and postsynaptic membrane.
  • Neurotransmitters are released by the presynaptic neuron and bind to receptors on the postsynaptic neuron.
  • This ensures signals only move in one direction, as receptors are only on the postsynaptic membrane​
• How do enzymes at synapses control neurotransmitters?

  • Enzymes break down neurotransmitters in the synaptic cleft
  • This prevents continuous stimulation of the postsynaptic neuron.
• Spatial summation: Multiple presynaptic neurons release neurotransmitters simultaneously.
• Temporal summation: One presynaptic neuron releases neurotransmitters repeatedly in quick succession.
• A neuromuscular junction is a synapse between a motor neuron and a muscle fibre.
• Summation is the combined effect of multiple excitatory or inhibitory signals to generate a response in the postsynaptic neuron.
• Give one similarity and one difference between a synapse and a neuromuscular junction.

  • Similarity: Both involve neurotransmitters crossing a synaptic cleft to transmit signals.
  • Difference: Synapses connect two neurons, while neuromuscular junctions connect a neuron and a muscle cell.
• Acetylcholine is released from neuromuscular junctions.
• Neurotransmitter removal:

  • To prevent continuous stimulation, neurotransmitters must be removed from the synaptic cleft.
  • Enzymatic breakdown: E.g., acetylcholinesterase breaks down acetylcholine.
  • Reuptake: Neurotransmitters are reabsorbed by the presynaptic neuron.
  • Diffusion: Some neurotransmitters diffuse away from the cleft.
• Excitatory synapses:

  • Cause depolarisation of the postsynaptic membrane.
  • Increase the likelihood of an action potential.
• Inhibitory synapses:

  • Open channels for negative ions (e.g., Cl⁻) or cause K⁺ to leave the postsynaptic neuron.
  • Hyperpolarise the membrane, making action potentials less likely.
• A synapse is the junction between two neurons or a neuron and an effector cell.
• What are the three main components of a synapse?

  1. Presynaptic neuron (with synaptic knob and vesicles).
  2. Synaptic cleft (the small gap between neurons).
  3. Postsynaptic membrane (with receptor proteins).