Katie has a rare neurological disease in which her neurons can receive new information and process it, but some of them just cannot pass the information along. this disease most likely affects the of the neuron.

Katie has a rare neurological disease in which her neurons can receive new information and process it, but some of them just cannot pass the information along. This disease most likely affects the axon of the neurons. Since axon is the signal transmitting end of the neuron, if the fusion of the vesicles containing the neurotransmitters with the cell membrane around the synaptic cleft is hampered, then the signal transmission gets disrupted.  

"d.) carbon dioxide and hydrogen sulfide"