Question: where does the stimulus for muscle contraction normally originate in the body
[{'answer': 'the brain', 'provenance': [{'wikipedia_id': '1110611', 'title': 'Muscle contraction', 'start_paragraph_id': 25, 'start_character': 107, 'end_paragraph_id': 25, 'end_character': 116, 'bleu_score': 1.0, 'section': 'Section::::Vertebrates.:Skeletal muscle.\n'}]}, {'provenance': [{'wikipedia_id': '1110611', 'title': 'Muscle contraction', 'start_paragraph_id': 25, 'start_character': 0, 'end_paragraph_id': 25, 'end_character': 530, 'bleu_score': 0.9757530668325981, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14669445779131865688}, 'section': 'Section::::Vertebrates.:Skeletal muscle.\n'}]}]