Glossary — Page 448, Lesson 695

I want to walk you through the glossary terms starting with Habituation. This is another word for sensory adaptation — your body getting used to a constant stimulus and no longer reacting to it. It's also sometimes used when talking about environmental capture, which is an error caused by habit, where you do something automatically without thinking because you've done it so many times before. Next, Haemoglobin. This is a molecule found inside your red blood cells. It's made of protein combined with a chemical called heme, and right in the middle of that heme molecule is an atom of iron. That iron atom is what gives haemoglobin its key property: it can unite with oxygen in a reversible way to form oxyhaemoglobin. That means it picks up oxygen in the lungs and then releases it to tissues that have little or no oxygen. But here's the critical point for you as a pilot: haemoglobin has a much greater affinity — a much stronger chemical attraction — for carbon monoxide (CO) than it does for oxygen. So if carbon monoxide is present in the air you're breathing, it will bind to haemoglobin instead of oxygen, and that reduces the amount of oxygen your blood can carry. That's why even small amounts of CO in a cockpit are dangerous. Moving to Hearing Loss. There are several causes. If there's a breakdown in the eardrum or the ossicles — those tiny bones in your middle ear — that's called Conductive Deafness. The natural hearing loss that comes with getting older is Presbycusis. And then there's Noise Induced Hearing Loss, or NIHL, which is damage to the sensitive membrane inside the cochlea caused by the intensity and duration of loud noises. That's why hearing protection matters around aircraft. Heart Attack — also called Myocardial Infarction. This happens when one of the coronary arteries — the arteries that supply blood to the heart muscle itself — gets blocked, usually by a clot. That blockage deprives part of the heart muscle of oxygen. The effects are dramatic: severe chest pain, collapse, and sometimes the heart stops completely. Homeostasis is the body's process of maintaining physiological equilibrium — a stable internal environment — through your organs and internal control mechanisms, even when external conditions are changing. Your body constantly works to keep things like temperature, pH, and fluid balance within a narrow range. Hydrostatic Variation refers to the difference in blood pressure between your legs and lower body compared to the blood pressure at your heart. This matters in aviation because of G-forces — when you pull positive Gs, blood pools in your lower body and the pressure difference becomes significant. Hypermetropia is long-sightedness. The eyeball is shorter than normal, so the image forms behind the retina. That makes close objects appear blurred. Hypertension is simply high blood pressure. Hyperventilation means overbreathing. It changes the acid/base balance of your body. It can be caused not only by hypoxia — lack of oxygen — but also by anxiety, motion sickness, vibration, heat, high G-forces, or shock. So you need to be aware that hyperventilation can mimic hypoxia symptoms. Hypoglycaemia is low blood sugar, normally caused by fasting or not eating regularly. For a pilot, that's a risk if you skip meals on duty. Hypovigilance refers to sleep patterns showing up on an EEG — an electroencephalogram that measures brain activity — during human activity. So it's when your brain shows sleep-like patterns even though you're awake and supposedly active. Hypoxia is inadequate oxygen supply to the body's tissues. In mild cases you might hardly notice the symptoms, but as hypoxia increases, symptoms become more severe, leading in some cases to unconsciousness and even death. This is one of the most critical concepts for you as a pilot. Finally, Iconic memory — this is the visual sensory store. Physical stimuli that reach your sensory receptors — like your eyes or ears — can be stored for a brief period after the input has stopped. Iconic memory specifically deals with vision, and it only lasts about 0.5 to one second. But that brief storage is important because it gives you enough time to process new information before your brain has spare capacity to deal with it. It's why you can still 'see' an image for a split second after you close your eyes.