How humans respirate?

Answer 1

In a part of our brain called medulla oblongata, there is a respiratory centre which consists of a inspiratory centre, expiratory centre and pneumotaxic higher controller.

The inspiratory centre generates basal ramp signal to the main respiratory muscle of our body which is our diaphragm to contract. Expiration occurs without any neuronal intervention via elastic recoil of our longs and it occurs after the Hering-Breuer Reflex(cessation of inspiratory signal upon detection by stretch receptors).

So,that's the physiology part...below is what should be covered within the domain of Biology.

INSPIRATION

Outer Intercostal Muscle contracts

Inner Intercostal Muscle relaxes

Diaphragm contracts

Thoracic Volume increases

Rib cage moves forward and upward

Intra-thoracic pressure decreases

For EXPIRATION, the opposite occurs

Note that there are other muscles involved in breathing as well and these muscles can be classified as primary, accessory and airway respiratory muscles.

Primary - Intercostal Muscles, Diaphragm

Accessory(commonly used during strenuous exercise, Asthma or other respiratory illness)- sternoceidomastoid muscle, pectoralis major, quadratus lumborum and more.

Airway(people who snores a lot have inactivity in this muscles during sleep) - Laryngeal, Pharyngeal and genioglossus.