Final answer:
Motorcycle helmets might not be required for riders over 21 in some places if they meet conditions like having health insurance or taking a safety course, but wearing one is still a vital safety measure to prevent head injuries.
Step-by-step explanation:
In jurisdictions where the law allows, a motorcycle helmet is not required for riders 21 and over if they meet certain conditions, which may include possessing adequate health insurance or successfully completing a motorcycle safety course. However, wearing a helmet is a major safety precaution and protects from head injuries, which could lead to lifelong disability. Furthermore, investing in personal safety extends beyond helmets to include protecting your eyes with safety goggles or sunglasses, using ear plugs to safeguard your hearing, and adhering to safety measures in various activities to minimize risks to the nervous system.
Other safety recommendations include wearing a safety belt in motor vehicles, avoiding dangerous stunts on bikes, and ensuring water is safe for diving to prevent brain or spinal cord injuries. It's crucial to understand that although a helmet may not be legally required after a certain age, the choice to wear one can significantly reduce the risk of serious injury.