Synaptic Signalling

Question 1

What are Ionotropic receptors?

Answer 1

• Receptor operated/ ligand gated ion channels
• Excitatory or inhibitory
• E.g. glutamate AMPA, NDMA, kainate receptor subtypes
• transmitter binding
  
  • Conformational change
  • Channel opening
  • Ion movement (Na+ influx therefore membrane depolarisation or cl- to hyperpolerise)
• Fast transmission

Question 2

What are Metabotropic receptors?

Answer 2

• G-protein coupled
• G-protein can
  
  • Open or close ion channels
  • Stimulate or inhibit enzymes/secondary messenger systems
• Transmitter binding
  
  • Conformational change
  • Activates G-protein
  • Activates effector systems
  • Indirect effects on excitability
• Slower tranmission
• Longer lasting effects

Question 3

Can neurotransmitters have both metabotropic and ionotropic receptors?

Answer 3

Yes

Question 4

What is the presynaptic ‘active zone’

Answer 4

• vesicle docking

- exocytosis

Question 5

What is the postsynaptic density

Answer 5

• Receptor expression

- Machinery for intra-cellular signalling

Question 6

What are the different synaptic arrangements in the CNS?

Answer 6

• Axon-Dendrite
  
  • axodendritic
• Axon-Soma
  
  • axosomatic
• Axon-Axon
  
  • axoaxonic

Question 7

What is the influence of the point of synaptic contact?

Answer 7

• Closer to axon hillock - greater influence on action potential generation
• Inhibitory synapses often found on soma and near axon hillock
• Best positioned to control neuron excitability

Question 8

What is the Spatial summation?

Answer 8

• Summing of post synaptic potentials generated at separate synapses
• EPSPs are most effective if they coincide
• co-operation between neurons is the best way to get the postsynaptic cell excited

Question 9

What is the Temporal summation?

Answer 9

• summing of post synaptic potentials generated at same synapse if they occur in rapid succesion
• spatial more effective

Question 10

What is frequency coding?

Answer 10

• Action potentials are all or nothing
• amplitude not increased even if stimulation is above threshold
• frequency of action potential firing is directly related to the intensity of the stimulus
• signalling is frequency modulated not amplitude modulated

Question 11

What is a threshold stimulus?

Answer 11

• stimulus just strong enough to depolarise from resting to threshold potential

Question 12

What is a sustained threshold stimulus?

Answer 12

• action potentials frequency limited by the sum of absolute refractory and relative refractory

Question 13

What a supra-threshold stimulus?

Answer 13

• action potentials during the relative refractory period
• frequency of firing only limited by the absolute refractory period
• Physiologically frequencies of up to 200-300 per second