Extroverts focus on the external world and gain energy from it, introverts find the inner-world of thinking more interesting, and gain energy from spending time alone.
The main difference between the two is the way they respond to the reward-seeking neurotransmitter: dopamine. A release in this chemical motivates us to earn money, find a partner and to keep going. Both introverts and extroverts become alert to their environment and appear curious and engaged when dopamine floods the brain.
However, introverts prefer to use a different chemical called acetylcholine. Like dopamine, acetylcholine too provides pleasure, but the difference is that the pleasure is turned inwards. It helps you think deeply, to reflect and be creative. It relaxes you, makes you turn to calm environments, and pushes you towards getting lost in a movie.
Acetylcholine is also nicknamed the "rest-and-digest" system. Your muscles relax, energy is stored, your heart rate and blood pressure lowers, and your body gets ready to hibernate and think deeply.
Both types of people use both neurotransmitters, the preference is what separates them. For extroverts, that is dopamine, which belongs to the body's ‘fight, flight or freeze’ system. Here, blood sugar is elevated to provide more energy and the person becomes active, risky and alert.
Whether you are an extrovert, ambivert or introvert, know that you all have your strengths and weaknesses. No one person is better than the other, and you shouldn't reduce your identity to a single word.