Low threshold spikes
Encyclopedia
Low-threshold spikes refer to action potential
s generated from a membrane potential negative to that for sodium spike threshold (firing level).
. Upon receiving excitatory stimulation (glutamate), this causes a small depolarisation, allowing the T-type Ca channel to open for a period (~100ms) and this influx of Ca depolarises the neuron.
This results in a Ca spike with a characteristic triangular shaped depolarisation which is important for the influx of Na+ ions to further depolarise the neuron resulting in a number (between 2-8) of action potentials, with interval between each AP less than 5ms.
The T-type Ca channels close after ~100ms from opening and must remain closed for at least another 100ms before another set of LTS can occur.
The functional significance of having multiple APs is so that these can 'add together' in the next neuron to allow temporal summation and a higher probability that it will activate the next neuron in the circuit
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
s generated from a membrane potential negative to that for sodium spike threshold (firing level).
Events
It occurs when the neuron is maintained (~150ms) in a hyperpolarised state (-70mV) state which deinactivates T-type calcium channelT-type calcium channel
The T-type calcium channel is a type of voltage-gated calcium channel. "T" stands for transient referring to the length of activation. As with other sub-types of voltage-gated calcium channel, the α1 subunit is the one that determines most of the channel's properties...
. Upon receiving excitatory stimulation (glutamate), this causes a small depolarisation, allowing the T-type Ca channel to open for a period (~100ms) and this influx of Ca depolarises the neuron.
This results in a Ca spike with a characteristic triangular shaped depolarisation which is important for the influx of Na+ ions to further depolarise the neuron resulting in a number (between 2-8) of action potentials, with interval between each AP less than 5ms.
The T-type Ca channels close after ~100ms from opening and must remain closed for at least another 100ms before another set of LTS can occur.
The functional significance of having multiple APs is so that these can 'add together' in the next neuron to allow temporal summation and a higher probability that it will activate the next neuron in the circuit