Glossary — Page 440, Lesson 687

I want to walk you through the glossary of key terms that are essential for understanding human performance and limitations in aviation. Let's start with the Autonomic Nervous System. This is the part of your nervous system that controls many functions essential to life — things like respiration, arterial pressure, gastrointestinal motility, urinary output, sweating, and body temperature. It also controls the General Adaptation Syndrome, which you might know better as the Fight or Flight Response. The key point here is that we normally have no conscious control over this system. It runs automatically, keeping your body alive and responding to stress without you having to think about it. Next, Barotrauma. This is pain caused by the expansion and contraction of air trapped in the body's cavities due to changes in outside pressure. The most common places this happens are the intestines, the middle ear, the sinuses, and even teeth. As a pilot, barotrauma can cause anything from discomfort to extreme pain — enough to interfere with your ability to operate the aircraft. That's why we learn to equalise pressure during climbs and descents. Now, Bends. This term comes from decompression sickness. When nitrogen bubbles form in your body during rapid decompression, they can affect the joints and cause pain. That's the "bends" — joint pain from those nitrogen bubbles. Let's move to the Blind Spot. This is a specific site on the retina where the optic nerve enters the eyeball. There are no light-sensitive cells in this area, so if an image falls on that part of the retina, your eye simply won't detect it. That's why it's called a blind spot — you literally cannot see anything that lands there. Blood Pressure is measured in millimetres of mercury, or mm Hg, and is given as two figures — for example, 120 over 80. The first, higher figure is the systolic pressure. That's the pressure at systole, when the left ventricle of the heart contracts to send oxygenated blood around the body to the tissues. The lower figure is the diastolic pressure — the constant pressure in the system even when the heart is not contracting, between beats. Next, Body Mass Index, or BMI. This is a measure of any excess fatty tissue in the body. It relates your height to your weight using this formula: BMI equals weight in kilogrammes divided by height in metres squared. So if you weigh 80 kilogrammes and are 1.8 metres tall, your BMI would be 80 divided by 3.24 — about 24.7. Finally, Bronchus. This is a division in the respiratory system. Air drawn into the nose and mouth passes first through the trachea, which then divides into two large airways — the left bronchus and the right bronchus. The bronchi carry air deeper into the lungs. The excerpt cuts off there, but that's the basic structure: trachea splits into two bronchi, one for each lung. These are all foundational terms. Each one relates directly to how your body functions in the aviation environment — from pressure changes to vision to stress responses.