I Used to Know That_ Stuff You Forgot From School - Caroline Taggart [26]
☞ THE RESPIRATORY SYSTEM
Air passes into the body through the trachea or windpipe via the mouth and nose. With the help of contractions from the diaphragm, which is a large muscle extending across the bottom of the rib cage, it is carried down into the lungs via two smaller tubes, called bronchi, which then split into even smaller bronchioles. Inside the lungs are lots of little air sacs, or alveoli. Within the alveoli oxygen is extracted from the air, absorbed into the bloodstream, and carried off to the heart via the pulmonary artery. The pulmonary vein brings “used” blood back to the alveoli, and the process is reversed as we breathe out air that now has a high carbon dioxide content.
☞ THE NERVOUS SYSTEM
The brain, spinal cord, and nerves make up perhaps the most important and intricately complex system in the human body. The nervous system essentially controls all the other systems in your body. It is what allows you to remember things, or at least remember that you used to know something. It tells your muscles and organs what to do and how to do it. The three interconnected parts of the nervous system are:
• the central nervous system, composed of the brain and spinal cord, which sends nerve impulses and analyzes information from the sense organs (eyes, ears, nose, mouth, skin, etc.). These organs enable you to see, touch, taste, hear, and feel.
• the peripheral nervous system, which includes the craniospinal nerves, a vast network of nerves that extends from your brain and spinal cord to all parts of your body and carries signals back and forth. It carries nerve impulses from the central nervous system to the muscles and glands.
• the autonomic nervous system (ANS), which regulates involuntary actions, such as pulse rate and digestion. The ANS is broken into the sympathetic nervous system (fight or flight), the parasympathetic nervous system (rest so you can digest), and the enteric nervous system (the digestive system’s personal messenger).
However, no discussion of the nervous system is complete without those trusty neurons, the nerve cells that send and carry the signals throughout your body. A neuron consists of a main cell body with a long nerve fiber, called an axon, branching from it. Electrical signals pass from axon to axon through small gaps called synapses. In order to do this, these electrical signals turn into chemical ones, called neurotransmitters. In fact, right now the neurons in the temporal lobe of your brain (which interprets language), your frontal lobe (which involves reasoning), and your occipital lobe (which controls sight) are firing away!
Chemistry
This is the study of elements and compounds and the reactions they undergo—which is a definition that surely cries out for a few more definitions.
atom: the smallest particle in an element that can take part in a chemical reaction, made up of a nucleus, which is containing positively charged protons and neutral neutrons; and a number of electrons, which are negatively charged particles that orbit the nucleus. Each atom normally has the same number of protons and electrons, leaving it with a neutral charge. The movement of electrons is responsible for most commonly observed chemical, electrical, or magnetic reactions. If an atom loses or gains an electron, it becomes either positively or negatively charged and is known as an ion.
element: a substance that cannot be decomposed into a simpler substance by a chemical process. Groups of elements come together to form a compound. So, for example, a combination of the element hydrogen (H) and the element oxygen (O) can form the compound water (H2O).
mole: also known as Avogadro’s number or Avogadro’s constant, a mole contains the same number of particles as there are in 12 g of carbon-12 atoms—that is, 6.022 x 1023 particles. Carbon has three naturally occurring isotopes (forms of the same substance with different numbers of neutrons), and one of these is carbon-12.