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Excitable Cells - Lecture 10 (01/03/2018)
Neurons communicate with eachother through Neural networks.
It takes 21 years for the nervous system to acquire its mature state.
Neuronal cells will usually either converge or diverge.
Converging cells receive inputs from numerous sources in order to become activated.
Diverging cells transmit their signal to numerous cells, activating them.
How post-synaptic cells decide when to fire Action Potentials:
A post-synaptic neuronal cell body has 1000s of inputs and some of these are excitatory and some are inhibitory.
The information the cell body receives must be first be combined before the decision to fire.
On fast synapses the neurotransmitters directly act upon the ligand gated ion channels on the post synaptic neurone (eg: Nicotinic AChR).
On slow synapses the neurotransmitters act through G proteins and 2nd messengers (eg: Muscarinic AChR).
As the neurotransmitter is released into the synaptic cleft and travels over to the post synaptic membrane, a voltmeter would display the depolarization forming across the membrane.
If the stimulus is large enough then it will generate an Excitatory Post Synaptic Potential
(ESPS) to be created in the post-synaptic membrane.
Inhibitory inputs also exist, through the influx of negatively charged Cl- ions into the post-synaptic membrane, generating an Inhibitory Post Synaptic Potential (IPSP).
The Final Input = Excitatory potential (ESPS) - Inhibitory potential (IPSP).
So if the final input is above the action potential threshold then an action potential will be generated.
An action potential is triggered by the depolarization of the plasma membrane, and when the depolarisation exceeds the threshold then an action potential is generated.
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