Intermediate 8 minutes
The nervous system and diving
The organ that makes every decision underwater is also the most sensitive to pressure
Underwater, all your gear can be working perfectly and all your calculations can be correct, and the dive can still go wrong. The reason is that the instrument doing the evaluating, your own brain, is also under pressure.
In this article you'll see how the nervous system is organized, how pressurized gases affect it, what the human dive reflex is, and how stress changes decision-making underwater.
Most diving incidents don't start with an equipment failure: they start with a decision. Understanding what happens to the nervous system at depth is understanding why those decisions can deteriorate without you noticing.
How it's organized
The nervous system is divided into two parts. The central nervous system, brain and spinal cord, processes information and makes decisions. The peripheral nervous system is the network of nerves that connects that center with the rest of the body, carrying sensory signals in and motor commands out.
Within the peripheral system there's a division especially relevant to diving: the autonomic nervous system, which regulates what you don't consciously control, heart rate, blood vessel diameter, digestion. It has two complementary branches: the sympathetic, which prepares the body for action and effort, and the parasympathetic, which dominates during rest and recovery.
Nervous tissue has two characteristics that make it especially vulnerable underwater: it consumes a very high proportion of the body's oxygen relative to its weight, and it tolerates interruptions to its supply very poorly. Any change in gas delivery affects it before almost any other tissue.
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