Final answer:
Kandel and Schwartz found that c. acetylcholine (ACh) is released more when learning occurs, playing an essential role in neurotransmission and muscle contraction.
Step-by-step explanation:
Kandel and Schwartz found that acetylcholine (ACh) is the neurotransmitter that is released in greater amounts into synapses when learning occurs. During neurotransmission, ACh is released from the presynaptic neuron, diffuses across the synaptic cleft, and binds to ACh receptors on the post-synaptic membrane. This process is essential for transmitting signals in the nervous system and is especially important at the neuromuscular junction, where ACh triggers depolarization, which is critical for muscle contraction.