Synapses and receptors

• Stages of action potential:

  1. resting state - Na channels are closed
  2. threshold - Na voltage gated Na channels open
  3. Depolarisation - Na enter
  4. Repolarization - K+ gates open and K+ leaves
  5. Undershoot- refractory period in hyperpolarisation
• where is an action potential generated?

  At the base of the neuron called axon hillock
• where does ion exchange occur in the axon membrane?

  at the nodes of ranvier
• What is saltatory conduction?

  action potential jumping from one node to the next, allowing movement very quickly
• how do action potential fire?

  all or nothing
• when is a neuron highly active?

  when there is a high frequency of action potential
• what are the types of synapse?

  chemical, electrical
• Electrical synapse

  • gap junction
  • Directly connects the 2 cytoplasms
• chemical synapse:

  • release of neurontransmitter
  • pre-synaptic neuron that diffuses across the synaptic cleft and bind to post-synaptic neuron
• what does the arrival of action potential trigger?

  influx of ca2+ into presynaptic from synaptic cleft
• where are neurotransmitter stored?

  in synaptic vesicles
• what is a catabolism?

  degradation of neurotransmitter
• what is uptake?

  recycling of transmitter into axon terminal or glial cells
• stages of chemical synapse:

  1. depolarisation leads to opening of voltage gated ca2+ open
  2. Ca2+ increase intracellular (presynaptic)
  3. Vesicles containing neurotransmitter fuse with the plasma membrae and is released into the synaptic cleft
  4. neurotransmitter diffuses across the synapse and binds to receptor on the postsynaptic neuron, triggers Na+ channels to open and Na+ triggers action potential
  5. Synaptic communication is terminated (reuptake or degradation)
• Types of neurotransmitter:

  • excitatory - raise toward membrane threshold
  • inhibitory - lower membrane potential away from membrane threshold
• EPSP= excitatory postsynaptic potentials
• IPSP = inhibitory post synaptic potential
• what is summation?

  sums up all excitatory and inhibitory signal
• what is the criteria for a transmitter?

  synthesised in the neuron

  present at presynaptic terminal, packed in synpatic vesicle

  exogenous substance mimic the exact action of endogenously released transmitter

  Specific mechanism exist for removing transmitter from synaptic cleft
• what are the types of neurotransmitter receptors?

  Ionotropic receptor

  Metabotropic receptor
• Ionotropic receptors are also known as...

  Ligand-gated ion channels
• what is a metabotropic receptor also known as?

  A G-protein couple receptors
• which is faster an ionotropic or metabotropic?

  ionotropic (few milliseconds)
• what is the structure of ionotropic receptor like?

  4 or 5 subunits arranged aroun a central pore
• What does difference combination of subunits in ionotropic receptor lead to?

  Increase diversity between different tissues
• what is the structure of metabtropic receptors?

  composed of a sinlge protein with 7 membrane spanning regions (alpha helix)
• what is the only 5-HT receptor that is not metabotropic?

  5-HT3
• what does binding of a neurotransmitter in metabotropic receptor lead to?

  activation of a G-protein
• what does the G-protein do?

  directly on ion channel causing the ion pore to open,

  activate a second messenger
• what does the second messenger do?

  can bind and open an ion channel or initiate a signalling cascade
• what are the stages of G protein activation?

  1. transmitter binds to receptor
  2. GTP exchnage for GDP on the alpha subunit
  3. G protein dissociates from receptor
  4. subunits dissociate
  5. alpha subunit activate the ion channel
  6. alpha subunit is inactivate by hydrolysis of GTP
  7. alpha subunit recombines with other subunits and attaches to the receptors which can then bind another agonist
• what is an agonist?

  Drugs that mimic the action of neurontransmitter, leading to activation of receptor
• what is an antagonist?

  Drugs that block the action of neuron transmitter, NO activation of receptor
• What are common targets for secondary messengers?

  Adenylate cyclase -> cyclic AMP

  guanylate cyclase -> cyclic AMP

  Phospholipase C -> inositol triphosphate and diacylglycerol
• do g protein produce a fast or slow intracellular response?

  Slow
• is an ionotropic receptor open or closed at rest?


  closed, no movement of ions
• Muscarinic acetylcholine

  Metabotropic
• Alpha and Beta adrenergic receptor

  metabotropic
• nicotinic acetylcholine

  ionotropic
• 5-HT


  metabotropic