Principles of Synaptic Transmission Flashcards
What are the two specialised junctions signals can be transferred at?
Neuron-neuron= synapse Neuron-muscle= neuromucular junction
What are the two types of synapses?
Chemical
Electrical
What is a chemical synapse?
Chemical neurotransmitters
What is electrical synapses?
Flow of current
Who first found evidence for chemical transmission?
Otto Lowei during a dream
What is Lowei’s experiment?
2 isolated frog hearts (still beating)
Reservoir of physiological solution
Perfused the first heart and went into the second heart
Stimulated a nerve on first heart connected to various pointers
When stimulated the vagus nerve, the first heart slowed down
After time the heartbeat of the second heart also slowed down
Conclusion: chemical slowed the heart beat
Who discovered acetylcholine?
Henry Dale
How is pharmacological evidence used as evidence for chemical transmission?
Drugs used to study neuromuscular junction (NMJ)
What does NMJ release?
Acetylcholine
What are agonists?
Drugs that mimic the actions of the natural transmitter
Give an example of an agonist?
Nicotine- nicotinic acetylcholine receptors
What are antagonists?
Drugs that block the actions of the neurotransmitter, bind to receptor (high affinity, low efficacy)
What is curare?
Antagonist at nicotinic receptors, paralyse at neuromuscular
What was the experiment at NMJ with curare?
Competitive antagonist
Clock with curare
Inactivate acetylcholine with serine
More acetylcholine is available- overcomes the action of curare
What can be used to show the morphological evidence of chemical transmission?
Electron microscopes
What can electron microscopes show about chemical transmission?
Presynpatic element- axon terminal
Postsynaptic element- dendrite
What are the key features of the synapse?
Synaptic cleft- space between the element (20-30nm in width) In pre-synaptic element there is the axon terminals which contain vesicles- transmitter diffuses across the synaptic cleft- synaptic delay (.5 of millisecond) Postsynaptic density (Psd)- collection of proteins- scaffold proteins etc.
What are the two actions of synapses?
Excitation
Inhibition
What is excitation?
Depolarisation of the postsynaptic membrane, i.e. less negative
Excitatory postsynaptic potentials (EPSPs)
How are action potentials generated?
Summation
What are the two types of summation?
Spatial summation
Temporal summation
What is spatial summation?
Several synapses generate EPSPs simultaneously
What is temporal summation?
Same synapse generates EPSPs rapidly
What is inhibition?
Hyperpolarisation of the postsynaptic membrane, i.e. more negative
Inhibitory postsynaptic potentials
What are the locations of inhibitory and excitatory synapses?
Inhibitory synapses on the cell body and axon hillock
Excitatory synapses on the dendritic tree
Where is presynaptic inhibition?
Spinal cord and brainstem
Where are the inhibitory synapses on the axon terminals?
Axo-axonic synapses
What effects Ca channels?
Reduce the amount of transmitter released from axon terminals
What is electrical synapses?
Direct flow of current across a low resistance junction
What is shown when you inject current into presynaptic neuron and record from target neuron?
Small voltages with same signs
Very short latencies- no synaptic delay
How is electrical transmission shown by gap junctions?
Gap junctions do not have vesicles associated with them
Membranes are closely apposed but are separated by a small gap of 2-3nm
An array of tubes or connexons are responsible for communication
What is the basis of the low resistance junction?
Connexons- responsible for communication
Large enough to allow charge power ions i.e. K+ ions
What are the functions of electrical synapses?
No synaptic delay
Escape mechanisms
Synchronising neuronal activity
