Synaptic Transmission 3 Flashcards
What are two common neuron types found in the cerebral cortex?
Pyramidal cell - larger dendritic tree, covered with spines
Stellate cell
What does the length constant determine?
The fraction of the synaptic current which reaches the axon, where the AP is generated
Short length constant = causes distant synapse to be ineffective
What are two ways to increase the length constant?
Increase cell membrane resistance
Increasing diameter of dendrite process
What is spatial summation?
The simultaneous activation of several excitatory synapses that are required to depolarize the axon to threshold
Length constant determines the degree to which the synaptic potentials sum together over distance
When will a neuron with a large dendritic tree and short length constant fire an action potential?
If many synapses are simultaneously activated
May require several dozen excitatory synapses
What is temporal summation?
The same synapse is activated more than once within a short period of time
The degree to which the individual synaptic potentials sum together is determined by the time constant
How does time constant affect temporal summation?
Short time constant - reduce probability that the neuron will fire from consecutive stimulations
Long time constant - increases the probability that the neuron will fire from consecutive stimulations
What happens if both excitatory and inhibitory synapses are simultaneously active?
The EPSPs and IPSPs will sum together to affect the membrane potential
What is the importance of synapse location on a neuron?
Synapses located on the body or axon hillock of a neuron will have a much stronger influence than those that are located on dendritic spines
E.g. glutamate on spines, GABA on body
What are presynaptic receptors?
Neurotransmitter receptors that are found on the presynaptic axon terminal membrane
What is presynaptic inhibition?
Decreases the amount of NT released by the synapse
Two most common mechanisms involve metabotropic receptors
What are the two mechanisms for presynaptic inhibition?
Opening of K channels in the presynaptic terminal
Inhibition of Ca channels from opening by the interaction of G-proteins with these channels
What is presynaptic facilitation?
Relatively uncommon in mammalian nervous system
Axo-axonic synapses activate a pathway that phosphorylates K channels and stops them from opening
What are autoreceptors?
Located on the presynaptic terminal and are activated by NT released from the same terminal
Have an inhibitory affect on NT release
What is neuromodulation?
Metabotropic receptor G-proteins can activate second messenger pathways that result in phosphorylation events that can either:
Change electrical properties of the postsynaptic cell
Alter cell function without changing membrane potential
