Neurons and Synaptic Transmission

• What are the 3 types of neurons?


  • Sensory neurons
  • Motor neurons
  • Relay neurons
• What is the function of the sensory neuron?


  Carries messages from the PNS to the CNS
• What is the structure of a sensory neuron?


  • Long dendrites
  • Short axons
• What is the function of a relay neuron?


  Connects the sensory neurons to motor or other relay neurons
• What is the structure of relay neurons?


  • Short dendrites
  • Short axons
• What is the function of the motor neuron?


  Connects the CNS to the effectors (muscles/glands)
• What is the structure of the motor neuron?


  • Short dendrites
  • Long axons
• What is the SOMA?


  The SOMA is the cell body of a neuron
• What do dendrites do?


  Dendrites carry nerve impulses to the cell body from neighbouring neurons
• What does the axon do?


  The axon carries impulses away from the cell body down the neuron
• What is the axon covered in?


  The myelin sheath (not always present on neurons)
• What is the purpose of myelin sheath on the axon?

  Protects the axon and it speeds up the transmission|
• What are the nodes of Ranvier?


  Gaps in the myelin sheath of a neuron.
• What is the purpose of the nodes of ranvier?


  Facilitates the speeding up of the transmission of impulse as they jump over the gaps
• What are terminal buttons and what do they do?


  They are at the bottom of the axon and they communicate with the next neuron in the chain across a gap (synapse)
• What is electrical transmission?


  The process of transferring electrical energy from one neuron to another.
• What is action potential?


  Change in electric potential.

  • Resting neuron has a negative inside charge
  • Activated neuron has a positive charge inside for a split-second causing ACTION POTENTIAL - creating electrical impulse
  • Impulse travels down the axon to the end of neuron
• What is synaptic transmission?


  The process by which neurons communicate with each other through the release and reception of neurotransmitters amongst neural networks
• What are the first 3 steps of synaptic transmission?

  
  

  Goes from electrical impulse to chemical and then back to electrical.

  1. Impulse (action potential) travels down the axon as an electrical impulse.
  2. The impulse reaches the presynaptic terminal where neurotransmitters are held in synaptic vesicles.
  3. The impulse triggers neurotransmitter release from the terminal button as a chemical impulse - this diffuses across the synapse.
• What are the final 3 steps of synaptic transmission?

  4. The neurotransmitter reaches the post synaptic receptor site - fits like a lock and key.

  5. The neurotransmitter is taken up by the receiving neuron.

  6. The neurotransmitter has either an excitation or inhibition effect, making the neurotransmitter more/less likely to keep firing, respectively
• What is the excitation effect?


  • More likely that the next neuron will fire - e.g. acetylcholine
  • Adrenaline (a hormone and neurotransmitter) causes excitation of post-synaptic neuron by increased positive charge, making it more likely to fire
• What is the inhibition effect?


  • Less likely that the next neuron will fire - e.g. GABA
  • The neurotransmitter serotonin causes inhibition in the receiving neuron so it will then be a higher negatively charged neuron thus the next neuron will be less likely to fire