Synapses lesson

• What is a synapse?

  The point between two connecting neurones or between a neurone and effector
• what are unable to cross a synapse?

  action potentials
• Where do neurotransmitters diffuse across?


  The SYNAPTIC CLEFT to stimulate an action potential in the post-synaptic neurone
• Neurotransmitters are what?


  Chemicals
• What do Pre-synaptic knobs contain lots of?

  Mitochondria
• Step 1 of synaptic transmission?

  As an action potential reaches the pre-synaptic knob, it raises the membrane potential and triggers voltage-gated calcium channels to OPEN
• Synaptic transmission

  
• Step 2 of synaptic transmission?

  Calcium ions diffuse into the pre-synaptic knob, causing the synaptic vesicles to move towards & fuse with the pre-synaptic membrane
• What do the synaptic vesicles contain?


  Acetylcholine
• Step 3 of synaptic transmission?

  The acetylcholine is released by EXOCYTOSIS into the synaptic cleft, where it diffuses across
• Step 4 of synaptic transmission?


  Acetylcholine binds to the receptor site on the post-synaptic membrane, triggering the sodium channels to open
• Step 5 of synaptic transmission?

  Sodium ions diffuse into the post-synaptic neurone
• Step 6 of synaptic transmission?

  This depolarises the neurone, creating an excitatory post-synaptic potential
• Step 7 of synaptic transmission?

  If enough of these generator signals combine, the threshold potential is reached and a new AP is created in the post-synaptic neurone
• what is the function of excitatory synapses?


  produce new action potentials
• give one function of synapses??

  Act as a junction within the nervous system
• Give another function of synapses?

  Inhibition of nerve impulse
• Function of synapses??

  • EXCITATORY SYNAPSES Produce new action potentials
  • act as a junction within the nervous system
  • Inhibit nerve responses
• What happens if only a WEAK SIGNAL arrives at a PRE-SYNAPTIC KNOB?


  Not enough acetylcholine will be released to sufficiently depolarise the post-synaptic neurones

  • Stopping the transmission of that AP (all or nothing principle)
• Function of synapses- acting as a junction within nervous system?

  -Multiple impulses from a receptor can stimulate a single neurone indicating the strength of stimuli

  -A single neurone can stimulate an impulse in multiple neurones- coordinating multiple responses
• Where do synapses act as a junction?

  Within the nervous system
• Signal convergence?

  By having multiple pre-synaptic neurones converging at 1 post-synaptic neurone, the Nervous system can receive stimuli from a number of different parts of the body and trigger the same response
• Signal convergence example?

  Danger warnings to the body from a number of surface receptors
• Signal divergence?

  One pre-synaptic neurone diverging to stimulate multiple post-synaptic neurones
• What does signal divergence allow?

  a single signal to stimulate multiple parts of the nervous system
• signal divergence example?

  A reflex arc