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An animal model is an animal, or an experimentally defined population of animals, used to investigate a biological process relevant to another setting, often human physiology or disease. Its usefulness depends on the specific mechanism and measured outcome. Sharing a visible phenotype does not establish that every cause or response is shared.

For example, experiments in rats tested whether a compound enhanced fear extinction by measuring fear-potentiated startle after repeated presentations of a previously threatening cue. The defined behavioural protocol made a learning mechanism experimentally accessible.^[ref] This establishes an effect on a rat learning assay; whether the same intervention improves a human clinical outcome is a further question. A good animal model makes the proposed correspondence explicit enough to test.

Ejaculation moves semen through and out of the urethra. In male reproductive physiology, emission brings sperm and glandular fluids into the urethra, while expulsion uses coordinated muscular contractions to discharge them. Contributions from the autonomic nervous system and somatic nervous system couple secretion and transport with the activity of skeletal muscles.

The coordination involves the spinal cord, rather than being an isolated contraction of one reproductive organ. A rat experiment identified a population of spinal neurons whose loss disrupted ejaculation while leaving other components of mating behavior relatively preserved.^[ref] The result supports a spinal cord coordinating mechanism in that animal model; it does not by itself establish that every aspect of human ejaculation or sexual experience has the same organization of the nervous system.