Which of the following neurotransmitters is only excitatory?

Correct Answer: C

Rationale: Glutamate is the primary excitatory neurotransmitter in the CNS, always depolarizing postsynaptic neurons. Glycine and GABA are inhibitory, and norepinephrine has mixed effects.

Correct Answer: C

Rationale: The autonomic nervous system mediates fight-or-flight (sympathetic) and rest-and-digest (parasympathetic) responses, regulating involuntary functions like heart rate and digestion.

Correct Answer: A

Rationale: A motor neuron stimulating the hamstring is a peripheral neuron (lower motor neuron in the PNS), directly innervating muscles. Central neurons are CNS, basal nuclei are brain structures, and interneurons connect neurons.

Correct Answer: C

Rationale: The enteric nervous system (PNS) autonomously controls stomach and intestine function. CNS integrates, cranial nerves serve head, and somatic neurons control skeletal muscles.

Correct Answer: A

Rationale: Graded potentials (e.g., EPSPs) in sensory receptors or dendrites, triggered by stimuli, summate to reach the threshold for an action potential. Others are not triggers.