Synaptic Transmission Flashcards
What is a synapse?
The cleft between the axon terminal of one nerve and the dendrite of the next neuron
What does stimulus trigger in sensory synapses?
Activation of voltage gated Ca++ channels
WhWhat are the steps of synaptic transmission in summary?
Action potential
Voltage gated Ca++ channels open
Ca++ influx triggers exocytosis
Neurotransmitter diffuses and binds to receptor on postsynaptic neuron
Response in cell
Enzymatic degradation
Reuptake of neurotransmitter
Diffusion of neurotransmitter
What are the properties of neurotransmitters?
Be present in the pre-synaptic terminal
Be released upon depolarisation of the terminal
Specific receptors should be present for it on the post-synaptic terminal
What is the major inhibitory neurotransmitter in the brain?
Gamma-aminobutyric acid (GABA)
What is the major excitatory neurotransmitter in the brain?
Glutamate
How are neurotransmitters removed from the synapse?
Enzymatic degradation
Reuptake in the presynaptic cell
Diffusion out of the synapse
How does calciseptine work?
Blocks Ca++ channels resulting in no synaptic transmission
How does curare work?
Blocks ACh binding to receptor in NMJ
Muscle paralysis
Leads to death from respiratory failure
What do inhibitory interneurons do?
Inhibitory interneurons send APs which cancel out the effects of APs from the brain
What inhibits the inhibitory interneuron?
Descending inhibitory neuron
Where do postsynaptic potentials occur?
Dendrites and cell bodies of postsynaptic neurons
What is an excitatory postsynaptic potential?
Depolarisations that bring membrane towards threshold
What is an inhibitory postsynaptic potentials?
Hyperpolarisations that bring membrane further from threshold
Do EPSPs have a threshold?
No - graded response, no refractory period, summation
What are EPSPs likely to do?
Trigger action potentials
What are IPSPs likely to do?
Prevent action potentials
What does iberiotoxin do?
Blocks K+ channels
What is convergence?
One cell is influenced by many others
What is divergence?
One cell influences others
What is stimulus threshold?
Weakest stimulus that can be reliably detected
What is needed in spatial summation to trigger an action potential?
Two EPSPs
What does tetrodotoxin do?
Blocks voltage gated Na+ channel
When is tetrodotoxin used clinically?
Local anaesthetics
Novocaine
Lidocaine
What does saxitoxin do?
Blocks voltage gated Na+ channels
How does novocaine and lidocaine differ from tetrodotoxin?
Blocks action potentials rather the synapse - LOCAL anaesthetics
