Why is it that hormonal responses are generally more longer lasting than ones from the nervous system?
Two chief factors:
(1) Hormones persist longer. Neurotransmitters don't tend to stay around very long.
(2) The kind of mechanisms that hormones use to cause change tend to be more permanent or longer lasting. Hormones are sometimes involved in changes to genetic material (switching genes off or on) and how genes are read. Neurotransmitters are a little like flicking a light off and on, its immediate but it doesn't last. Hormones are a bit closer to painting your walls pink, it takes awhile and the changes by their very nature are more permanent.
For an action potential to reach its threshold mark, roughly how much excitatory neurotransmitter is needed? Surely >50% of all received neurotransmitters? Sorry if this question is too ambiguous!
Depends on the nature of the neuron. It probably depends on stuff beyond VCE like the number of ion channels present, what kind of receptors are present, things like EPSP/IPSP and any long term changes that the neuron has. Muscle cells are generally activated at at lower thresholds of neurotransmitters for reasons beyond VCE compared to other cells for instance.
If an excitatory neuron and an inhibitory neuron meet at different dendrites of the same single post synaptic neuron:
A) the inhibitory neuron would have more of a chance of causing the action potential to occur
B) the excitatory neuron would have more of a chance of causing the action potential to occur
C) both neurons have the same chance of causing the action potential to occur
I found this question quite 'tricky' on my SAC as I thought that excitatory and inhibitory neurons cancel each other out when they meet at different dendrites of the same target nerve cell. However, since this option wasn't specified, I wasn't sure what was the correct answer.
Quite simple really. Excitatory neurons increase the probability of an action potential occurring compared to 'normal', inhibitory neurons reduce the probability of an action potential occurring compared to 'normal'.