Final answer:
By the ninth week of embryonic development, the brain and spinal cord have begun to control various functions, including the heart rate, due to the growth and maturation of the central nervous system.
Step-by-step explanation:
Yes, at 9 weeks, the development of the brain and the spinal cord are at a stage where they start exerting control over bodily functions, including the heart. The primitive central nervous system begins to form at around 25 days post-fertilization, with the anterior end becoming the brain and the posterior becoming the spinal cord, evolving into basic tissue arrangements that further develop into complex neural structures by the fourth week of embryonic life.
The human heart, the first functional organ to develop, begins beating by day 21 or 22 after fertilization. It underscores the essential role of the heart in distributing nutrients, and oxygen, and in waste management for the developing embryo. The brainstem and other nuclei in the brainstem, which controls involuntary muscle functions such as heart rate, will have begun to function by this stage. Therefore, by the ninth week of development, the embryonic nervous system including the brain and spinal cord indeed starts to control the heart and many vital functions related to it.