efferent nerves

What Are Efferent Nerves?

Efferent nerves (also called motor nerves) carry impulses from the central nervous system outward to muscles, glands, and organs — the output pathways transmitting commands that produce physiological changes. In polygraph testing, the efferent pathways of the autonomic nervous system are the final link converting the brain's processing of a psychologically significant question into the measurable responses on the chart.

Efferent Pathways in Polygraph Physiology

When the brain processes a relevant question and activates the sympathetic response, efferent nerve fibres carry the activation signal to three primary target systems: eccrine sweat glands (producing electrodermal changes), the heart and blood vessels (producing cardiovascular changes), and respiratory muscles (producing breathing changes). Each pathway uses specific neurotransmitters: acetylcholine for eccrine glands, and noradrenaline for most cardiovascular targets.

Efferent vs. Afferent

Efferent nerves complement afferent (sensory) nerves, which carry information in the opposite direction — from receptors toward the CNS. Together they form the complete communication loop: afferent nerves bring the question stimulus to the brain, the brain processes its significance, and efferent nerves carry the resulting autonomic commands to target organs. The mnemonic "afferent arrives, efferent exits" helps distinguish the two.

Clinical Relevance

Conditions or medications affecting efferent nerve function can influence polygraph data. Autonomic neuropathy, spinal cord injuries, or medications that block efferent transmission (such as beta blockers) can attenuate physiological responses. The pre-test suitability screening addresses these factors to ensure the examinee's efferent pathways can support valid testing.