A marathon runner approaches the finish line and suddenly collapses from exhaustion and passes out just yards from victory. Although the scene may sound familiar, what we probably don’t know is thatIt is not due to wasting of the muscles but to a brain mechanism that puts a brake on excess activity when we overreach. It is what is known as“central fatigue”, a type of extreme tiredness that affects the brain and nervous system.
Scientists from the University of Copenhagen have investigated the mechanisms that lead to this process and have concluded that it has to do withserotonin. Serotonin is a neurotransmitter released when we exercise, generates well-being and helps us stay active,functioning as a “throttle” that helps the muscles work. However, from certain amounts it can also act as a brake, as explained by neuroscientist Jean-François Perrier and his colleagues in the latest issue of the journalPNAS.
The brain communicates with the muscles using a special type of neurons, themotoneuron, which cause muscle fibers to contract. To order body movements, the brain must be able tocontrol motor neuron impulses so that they fire in the correct order and with the necessary intensity. The excitability of motor neurons increases when serotonin levels rise, in such a way that when this neurotransmitter reaches such levels that it “overflows” its action is no longer local at the junctions between neurons and reaches more distant sites, such as the segment initial axon of neurons, which conducts nerve impulses, and inhibits them. The control mechanism now identifiedprevents motor neurons from becoming overactiveand reduces muscle activity that could be harmful.
The findcould help fight dopingAs to achieve this “it is crucial to identify what methods athletes can use to prevent central fatigue and continue to perform beyond what is naturally possible.” The discoveryit will also help to understand why people who take antidepressants get tired sooneras these drugs raise the level of serotonin to improve mood.
