Neurotransmitter vs neurohormones: which statement is true?

• A. Neurotransmitters act locally at synapses; neurohormones travel through the bloodstream
• B. Neurotransmitters travel through the bloodstream; neurohormones act at synapses
• C. Neurotransmitters are produced by the liver; neurohormones are produced by the brain
• D. Neurotransmitters act globally; neurohormones act in the nervous system

Answer: (A)

Neurotransmitters and neurohormones differ mainly in where they act and how they travel. Neurotransmitters are released from a neuron into the tiny gap (synapse) between cells and bind to receptors on a neighboring neuron or a muscle cell, producing a fast, local response right where the release happened. Neurohormones are released into the bloodstream by neurosecretory neurons, then travel through the blood to distant targets, producing slower, more widespread effects.

That makes the true statement clear: neurotransmitters act locally at synapses, while neurohormones travel through the bloodstream to reach distant sites. For example, acetylcholine at a neuromuscular junction triggers a quick muscle contraction, while hormones like epinephrine circulating in the blood prepare various tissues for a body-wide response.

The other options don’t fit because they blur these distinctions: neurotransmitters do not travel in the bloodstream to act on distant targets, and neurohormones do not necessarily act only at synapses. Also, the idea that neurotransmitters are produced by the liver is inaccurate (their synthesis and storage occur in neurons), while neurohormones are typically produced by neurosecretory cells in the brain or hypothalamus, then released into blood.