Glossary — Page 448, Lesson 697

I want to walk you through the glossary terms that are central to understanding human performance in aviation. Let's start with Infarct, or Infarction — this is the death of a portion of a tissue or organ because the blood supply has failed. When that happens to part of the heart muscle because one of the coronary arteries has failed to deliver blood, we call it a coronary infarction. That's the medical term for a heart attack, and it's obviously a critical condition for any pilot. Next, Insomnia — this is the inability to get enough sleep. The glossary divides it into two types: Clinical Insomnia, which is a medical disorder, and Situational Insomnia, which is temporary and caused by circumstances like stress or a disrupted schedule. Both matter for aircrew because sleep is essential for performance. Inspiratory Reserve Volume is a lung capacity term. It's the extra volume of air you can inhale over and above your normal tidal volume — that's the amount you breathe in and out during quiet, resting breathing. So if you take a deep breath on top of your normal breath, that extra air is your inspiratory reserve volume. Now, The Leans — this is a very important aviation sensation. It happens when the vestibular apparatus of your ear gives you an incorrect assessment of your aircraft's attitude. Your inner ear tells your brain you're banking, for example, but your eyes — the visual picture — tell you that you're straight and level. That mismatch between what your body feels and what you see is the leans, and it can be disorienting. Long Sightedness — the glossary simply tells you to see hypermetropia, which is the proper medical term. We'll cover that when we get to the H entries. Mental Schemas are mental representations we build for categories of objects, events, and people. They're like mental templates that help us quickly understand and predict the world around us. Mesopic Vision is vision that uses both types of light-sensitive cells in your retina — the rods and the cones. Rods handle low light and peripheral vision; cones handle colour and detail in bright light. Mesopic vision is the in-between state, like at dusk. Metabolism refers to all the chemical processes in a living organism that produce energy and enable growth. It's how your body converts fuel into usable power. Metacommunications is a broad term covering communication in its complete sense. It includes everything from body language and facial expressions to simple voice communication — anything that enables a transfer of information between people. Microsleeps are very short periods of sleep, lasting from a fraction of a second up to two or three seconds. You can be in the middle of a task and your brain briefly shuts down. For a pilot, even a two-second microsleep during a critical phase of flight is extremely dangerous. Myopia is short sightedness. It happens when the eyeball is longer than normal, so the image forms in front of the retina instead of directly on it. If the eye's focusing mechanism — accommodation — cannot compensate, distant objects appear out of focus. Narcolepsy is a recognized medical disorder where an individual has a tendency to fall asleep even when they have adequate sleep credit — that means even when they're not sleep-deprived. It can happen while driving or flying, and the glossary states clearly that it is undesirable in any aircrew. Neuron is simply a nerve cell — the basic building block of the nervous system. NIHL stands for Noise-Induced Hearing Loss — the glossary directs you to that entry for the full definition. Oculogravic Illusion — this is a visual illusion. It's the apparent movement of an object that is actually fixed in position relative to you, caused by displacement of the otoliths in your inner ear. The otoliths are part of your vestibular system that sense linear acceleration and gravity. When they're displaced, your brain misinterprets the orientation, and you think a stationary object is moving. Orthodox Sleep is another term for slow wave sleep — the deep, restorative stage of sleep. Ossicles are the three small bones in the middle ear. Their job is to transmit the vibration of the eardrum to the cochlea in the inner ear, where it's converted into nerve signals. Paradoxical Sleep is another term for REM Sleep — Rapid Eye Movement sleep. It's called paradoxical because although the person is definitely asleep, the brain activity looks very similar to someone who is fully awake. Finally, Parasympathetic Nervous System — the glossary directs you to Autonomic Nervous System for the full explanation. The parasympathetic branch is the 'rest and digest' system, which calms the body down after stress. Those figures on the screen show the structure of the ear and the vestibular apparatus, which are directly relevant to the leans and the oculogravic illusion we just covered.