’s first cigarette of the day can increase his or her heart rate by 10 to 20 beats a minute. Scientists have found that a smoked substance reaches the brain more quickly than one swallowed, snorted (such as cocaine powder) or even injected. Indeed, a nicotine molecule inhaled in smoke will reach the brain within 10 seconds. The nicotine travels through blood vessels, which branch out into capillaries within the brain. Capillaries normally carry nutrients but they readily accommodate nicotine molecules as well. Once inside the brain, nicotine, like most addictive drugs, triggers the release of chemicals associated with euphoria and pleasure.

　　Just as it moves rapidly from the lungs into the bloodstream, nicotine also easily diffuses through capillary walls. It then migrates to the spaces surrounding neurones – ganglion cells that transmit nerve impulses throughout the nervous system. These impulses are the basis for our thoughts, feelings, and moods. To transmit nerve impulses to its neighbour, a neurone releases chemical messengers known as neurotransmitters. Like nicotine molecules, the neurotransmitters drift into the so-called synaptic space between neurones, ready to latch onto the receiving neurone and thus deliver a chemical “message” that triggers an electrical impulse.

　　The neurotransmitters bind onto receptors on the surface of the recipient neurone. This opens channels in the cell surface through which enter ions, or charged atoms, of sodium. This generates a current across the membrane of the receiving cell, which completes delivery of the “message”. An accomplished mimic, nicotine competes with the neurotransmitters to bind to the receptors. It wins and, like the vanquished chemical, opens ion channels that let sodium ions into the cell. But there’s a lot more nicotine around than the original transmitter, so a much larger current spreads across the membrane. This bigger current causes increased electrical impulses to travel along certain neurones. With repeated smoking, the neurones adapt to this increased electrical activity, and the smoker becomes dependent on the nicotine.

　　Questions 1 – 7

　　1. Although nicotine is probably the well-known chemical in cigarettes, it is not necessarily the one that changes the psyche of the smoker when cigarettes are smoked.

　　2. In spite of the difficulties, according to the text more than thirty-five million people a year give up smoking.

　　3. It has been shown that nicotine in cigarettes can improve people’s abilities to perform some actions more quickly.

　　4. Added ammonia in cigarettes allows smokers to inhale more nicotine.

　　5. Snorted substances reach the brain faster than injected substances.

　　6. Nicotine dilates the blood vessels that carry it around the body.

　　7. Nicotine molecules allow greater electrical charges to pass between neurones.

　　Questions 8 - 10

　　8. Cigarette companies would have to cut the nicotine content in cigarettes by _________ to prevent them from being addictive.