Most of us have heard the term "runner's high," but what exactly does this mean? Exercise creates chemical responses in the brain, which lead to both temporary and long-term mental health benefits. Here is how it works:

What happens when we are stressed?

●Cortisol（皮质醇）: This stress hormone is linked to mood, motivation and fear. It also alters immune system responses and suppresses the digestive system.

●Adrenaline（肾上腺素）: This stress hormone raises your heart rate, elevates blood pressure, and boosts energy stores.

●Hypothalamus（下丘脑）: This region of the brain is the body's natural alarm system which stimulates the production of cortisol and adrenaline.

●Hippocampus（海马体）: Too much cortisol cuts cell production in the brain's hippocampus region, damaging thought organization and memory formation.

Feeling overwhelmed? Hit the gym!

As your heart begins to pound, your brain chemistry reacts almost immediately to get you feeling better both physically and mentally.

Brain derived neurotrophic factor: BDNF protects the brain from emotional disorders and repairs damage from stress and depression.	Norepinephrine: This neurotransmitter works with dopamine（多巴胺）as a "feel good" mood-boosting chemical. It is also critical in the decision-making process.
GABA: Exercise lowers stress levels, which triggers the release of this calming neurotransmitter（神经递质）. Frequent boosts of GABA build immunity to stress, enhancing your ability to take on life's challenges.	Antibodies（抗体）: Both exercise and happiness increase antibody production. Antibodies are special proteins produced by the immune system to help fight viruses, bacteria and diseases.
Endocannabinoids: These natural chemical compounds play a role in processing appetite, pain sensation, mood and memory. They are very closely related to the active ingredients of the cannabis（大麻）plant.	Dopamine: This neurotransmitter is a "feel good" mood-boosting chemical. It also controls the brain's reward and pleasure center and is responsible for feelings of relaxation and great joy.
Endorphins: Endorphins naturally get most of the credit for feelings of extreme happiness, but they play only a small part in the exercise-induced rush. These pain fighting peptides increase with as little as 20 minutes of exercise.	Serotonin（血清素）: This neurotransmitter is responsible for feelings of calmness and hopefulness. Low levels are linked to depression. Antidepressants increase these levels, and so does exercise.

【小题1】John has been feeling anxious since he started his new job. According to the article, he would NOT likely to      if he failed to adapt himself to his new working environment.

A．frequently get sick	B．have a poor memory
C．easily lose his temper	D．lose his appetite

【小题2】Having exercised regularly for one month, John found that he felt better when it comes to making decisions. According to the article, this is largely due to the increased levels of         in his brain following workouts.

A．GABA	B．dopamine
C．endorphins	D．norepinephrine

【小题3】Where can we probably find the text?

A．In a fashion magazine.	B．In a physics textbook.
C．In a popular science book.	D．In an academic paper.