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• Investigating Human Reaction Times • It is possible to investigate the effects of various factors on human reaction times through a practical experiment. • Testing reaction time Investigating Human Reaction Times It is possible to investigate the effects of various factors on human reaction times through a practical experiment. Testing reaction time Factors • Caffeine and exercise are factors that could affect human reaction time • Their effect can be tested by dropping and catching a ruler. experiment. Testing reaction time Factors Procedure The steps in the practical procedure are: 1. Hold a ruler vertically from one end. The test subject should have their thumb and finger on either side of the ruler at the 50cm mark. 2. Drop the ruler. The subject should try to catch it between their thumb and forefinger as fast as possible. 3. Note down the distance from the 50cm mark that the ruler travels before the subject catches it. 4. Use a table to convert this distance into a reaction time. 5. Repeat the experiment on a subject who has just had a coffee, or who has just done exercise. 6. Compare reaction times. Variables • The independent variable is whether or not the subject has had caffeine or exercised. • The dependent variable is the subject’s reaction time. Thermoregulation (Control of Body Temperature) Our body temperature needs to be kept as close to 37°C as possible. Receptors detect temperature changes and relay the information to the central nervous system (CNS). The CNS then allows effectors (muscles or glands) to respond: Receptors on the skin • Receptors on the surface of the skin monitor the temperature at the surface of the body. Receptors in the brain • Receptors in the thermoregulatory centre of our brain monitor the internal body temperature as blood flows through the brain. Thermoregulation Our body temperature needs to be kept as close to 37°C as possible. If your body is: Thermoregulation of different processes that take place to control our body temperature when it is too cold or too hot. Too hot • Sweat is released from sweat glands under the skin. • Hairs lie flat. • Blood vessels dilate to allow more blood to enter capillaries that pass close to the skin surface (vasodilation). Too cold • Muscle contractions increase, causing shivering. • Hairs stand on end. • Blood vessels constrict to reduce blood flow in capillaries (vasoconstriction). Thermoregulation Your optimal body temperature is 37 degrees Celsius. • Sweating is a reaction to being too hot. • Shivering (muscle contractions) is a response to low body temperature. Vaso means that something is related to blood vessels: • Vasodilation - Blood vessels dilate to allow more blood to enter capillaries. • Vasoconstriction - Blood vessels constrict to reduce blood flow in capillaries Sweating and Shivering When our body temperature becomes too high, we sweat. When our body temperature becomes too low, we shiver. Here's how sweating and shivering work: Sweating • Sweat glands release water, which covers the skin. • Heat energy from the body is transferred to this water and, when it has enough energy, it evaporates. • As it evaporates, it takes the heat energy with it. This lowers the average temperature of the body. Shivering • When we are too cold, muscles start to contract automatically. This makes us shiver. • This process requires energy, which is generated through respiration. • Respiration produces heat, which warms us up. Body Hairs Each hair on the body is controlled by a hair erector muscle. Too hot • When we are too hot, the hair erector muscle relaxes, causing the hair to lie flat. Too cold • When we are too cold, the hair erector muscle contracts, causing the hair to stand on end (which pulls on the skin giving you goosebumps). • When all the hairs are standing on end, they trap an insulating layer of air around the body. It helps keep heat in. Thermoregulation - Blood Vessels Blood vessels deep in the skin have layers of smooth muscle tissue in their walls. They respond differently when we are too hot or too cold. Too cold • If we are too cold, then the muscular walls contract. • This is called vasoconstriction. • This reduces the blood flow to the skin surface and heat energy is kept inside the body. Blood Flow in Ducks If humans are too cold, the walls of our blood vessels contract, and we reduce the amount of blood near the skin. Ducks • Ducks lose heat from their feet when they are in cold water. • They have evolved to decrease the blood flow to their feet. • This blood is also cooled so that less heat is lost to (conducted away by) the cold water when it reaches the ducks' fe