Synaptic signalling Flashcards
What is the postsynaptic density?
Where the membrane appears thicker and receptors are located
What is the presynaptic active zone?
Where vesicles fuse, can be seen down a microscope
What is a Grays type I synapse
Asymmetrical
Has thicker postsynaptic density
Usually excitatory
e.g. glutamate
What is a Grays type II synapse
Symmetrical
Thickness is equal
Usually inhibitory
e.g. glycine or GABA
What is an axodendritic synapse?
Synapse onto dendrite of neurone
What is an axosomatic synapse?
Synapse onto soma of neurone
What is an axoaxonic synapse?
Synapse onto an axon of the neurone
Why is the point of synaptic contact important?
Closer to axon hillock = greater influence on action potential generation
Inhibitory synapses are often on soma or axon hillock
This is the best position to control neuron activity
Are axodendritic synapses effective?
No
Input may not spread down dendrite to reach soma or axon hillock
Yes
Could amplify excitatory input
Increasing likelihood of action potential at axon hillock
What happens if the dendrite has no channels?
Passive spread of depolarisation
Large input required
How many synapses does a typical neuron have?
1000-10,000
What is synaptic integration of information?
The integration of multiple synaptic inputs
What does SEPSP stand for?
A small excitatory post synaptic potential
What is an SEPSP?
A small excitatory post synaptic potential is a small change in Em, smaller than threshold value
Why will multiple synaptic inputs trigger an action potential?
Combined size of SEPSP will be greater than threshold
What is spatial summation?
Summing of post synaptic potentials generated at separate synapses
What is an SIPSP?
A small inhibitory post synaptic potential
When are EPSPs most effective?
When they coincide
How can one EPSP trigger an action potential in the post synaptic neurone?
Synaptic input at a high frequency
What is temporal summation?
Summing of post synaptic potentials generated at same synapse, if they occur in rapid succession
Outline neuronal communication
Receive messages from connected neurones
Integrate all inputs
Send a frequency-encoded message
What is the purpose of frequency coding?
Action potentials are all-or-nothing
Can’t differ in amplitude
Communication therefor via frequency
Frequency of action potential firing is directly related to…
…the intensity of the stimulus
Signalling is described as being…
…frequency-modulated
What happens when a stimulus is at threshold?
Just strong enough to trigger an action potential
What happens when a stimulus is at sustained threshold level?
A 2nd action potential fires
This is delayed
Time taken = sum of absolute refractory period and relative refractory period
What happens with a supra-threshold stimulus?
Multiple action potentials fire
An action potential fires in relative refractory period
Only absolute refractory period limits action potentials firing
How frequently can action potentials fire?
200-300 times a second
