In the brain do signals have different strengths which result in different amounts of neurotransmitters being released into the synapse? My understanding was that there was just an activation potential but can the amount of charge vary in a neuron with strong stimuli resulting in a stronger charge which results in more neurotransmitters being released at the synapse or is the amount of neurotransmitters released and the amount of charge constant no matter what the stimuli?
I’m not an expert, but as I recall the electrical signal strength is irrelevant; it’s an on/off, binary sort of system. That’s how nerve signals can travel so far over bad conducters like nerves and still work; the on/off nature of the response eliminates the noise.
I don’t know about neurotransmitters.
Action potentials, as Der Trihs said, are binary–they happen or don’t. Stimulus strength is conveyed by how many neurons fire, which neurons fire, and the frequency with which the neuron fires.
No. As others have said action potentials are all or none, either the membrane depolarises and the neurotranmitter is released at the syanspse, or it isn’t
The amount doesn’t vary with stimulus, but it can vary with numerous other factors. The most common factor is fatigue, if a neuron is called upon to activate too often both the energy reserves and the nerurotransmitter supplies will run down. As a result at some point the neuron will depolarise, but the depolarisation wave will be weaker because the potential will be lower due to less active ion pumps. Similarly if neurotransmitter supplies haven’t had time to replenish they too will be lower. Eventually the membrane potential becomes so low or the neuron so deficient in ATP that the depolaristaion event fails to propagate at all even at supra-threshiold stimulation. If depolarisation does coocur there may be insufficient neurotransmitter released to active the next neruon.
And remember that while there’s no way to make any given activation any stronger, a neuron CAN send a stronger or weaker signal by firing more or less quickly.
The neuron is a binary transmission, but the synapse isn’t. The receiving neuron only fires when the concentration of chemical transmitters gets high enough. In some cases, the chemical transmitters in the synapse can linger long enough to build up over several activations by the transmitting neuron, leading to a stronger signal on the receiving neuron than would be sent by a single activation.