What is generated once enough neurotransmitters attach to receptors and the firing threshold is overcome?

When enough neurotransmitters bind to receptors on the postsynaptic neuron, this leads to a significant depolarization of the neuron's membrane potential. If this depolarization is strong enough to surpass a certain threshold, it triggers the generation of an action potential. Specifically, this action potential represents a rapid and temporary change in the electrical charge across the neuron's membrane, which allows for the propagation of the electrical signal along the neuron.

In the context of the choice provided, when referring to "a compound muscle action potential," it indicates the summation of action potentials from multiple muscle fibers during muscle contraction. This occurs when motor neurons stimulate muscle fibers in response to the neurotransmitter release (typically acetylcholine) at the neuromuscular junction, and this collective electrical response in the muscle is what is detected as a compound muscle action potential.

Therefore, generating an action potential in response to sufficient neurotransmitter binding is central to how neurons communicate, leading to muscle contractions or other physiological responses.