Glossary — Page 440, Lesson 685

I want to walk you through the glossary of terms for Human Performance and Limitations. This is intended as a quick reference for technical terms you'll encounter in the subject, so let's go through them in order. First, Accommodation — this is the changing of the shape of the lens of the eye, through the ciliary muscles, to achieve the final focusing onto the retina. So when you shift your gaze from a distant instrument to a close chart, your ciliary muscles squeeze or relax the lens to bend light exactly onto the retina. That whole process is accommodation. Next, Acuity — it is the ability to discriminate at varying distances. The glossary gives a specific example: an individual with an acuity of 20/20 vision should be able to see at 20 feet that which the so-called normal person is capable of seeing at this range. So 20/20 is the standard benchmark — if you have 20/20, you see at 20 feet what a normal person sees at 20 feet. If you had 20/40, you'd need to be at 20 feet to see what a normal person sees at 40 feet. Adrenaline — a stress hormone which causes a massive release of sugar reserves from the liver and prompts the body into certain actions aimed primarily to assist survival. So when you're under threat, adrenaline floods your system, mobilises energy from the liver, and prepares you for fight or flight. Alveoli — these are the final division in the lungs; very fine sac-like structures where blood in the alveolar capillaries is brought into very close proximity with oxygen molecules. Under the effect of a pressure gradient, oxygen diffuses across the capillary membrane from the alveolar sac into the blood. So the alveoli are the tiny air sacs deep in your lungs where the actual gas exchange happens — oxygen moves from the air you breathe into your bloodstream. Anaemia — this occurs when cells of the various tissues are deprived of oxygen through insufficient haemoglobin or red blood cells. So it's not a lack of oxygen in the air; it's that your blood can't carry enough oxygen to the tissues because you don't have enough haemoglobin or enough red blood cells to transport it. Angina — the pain developing in the chest, or sometimes the neck, shoulder or arms, which is caused by a narrowing of the coronary arteries carrying blood to the heart muscle. The narrowing or gradual blockage of the coronary arteries results in insufficient blood reaching the muscle, and the effect is to deprive part of the muscular pump of oxygen when demands are placed on it by exertion or emotion. So angina is a warning sign — the heart muscle isn't getting enough oxygen when it's working hard. Anthropometry — the study of human measurement. Simple enough — it's about measuring body dimensions, which matters for cockpit design, seat positioning, reach to controls, and so on. Anxiety — a state of apprehension, tension and worry. It can also be a vague feeling of danger and foreboding. So it's not just being nervous about a specific thing; it can be a diffuse sense that something bad is going to happen. Aorta — the main artery leaving the heart's left ventricle before dividing into smaller arteries to carry the oxygenated blood around the body. So after the left ventricle pumps oxygen-rich blood out, it goes straight into the aorta, which is the biggest artery, and from there it branches out to supply the entire body. Arousal — the measure of the human being's readiness to respond. It can be said to be the general activation of the physiological systems. So arousal is your level of alertness — from asleep to fully alert and ready to act. Too little arousal and you're sluggish; too much and you might be overstressed. Attention — attention is the deliberate devotion of the cognitive resources to a specific item. So it's not just being awake; it's actively choosing to focus your mental processing on one thing, like a particular instrument reading or a radio call. Atrium — the left and right atria (also called auricles) are the upper chambers of the heart. The right atrium collects venous blood — that's deoxygenated blood — and passes it to the right ventricle, from where it is pumped into the lungs to receive oxygen. The left atrium collects the oxygenated blood from the lungs and passes it to the left ventricle, from where it can be passed around the body to the various tissues. So the atria are the receiving chambers — they gather blood coming into the heart and pass it down to the ventricles for pumping. Audiogram — this instrument measures hearing. So if you've ever had a hearing test where they put headphones on you and play tones at different volumes and frequencies, that's an audiogram test. Autokinesis — this occurs in the dark when a static light may appear to move after being stared at for several seconds. This is a visual illusion — if you fix your gaze on a single light in an otherwise dark environment, your eye muscles fatigue and your brain interprets tiny involuntary eye movements as the light actually moving. This is particularly dangerous in aviation when you're looking at another aircraft's light at night — it can appear to drift, leading you to misjudge its position.