The larynx is a vocal organ and the gateway to the respiratory tract, with important physiological functions, mainly respiration, vocalization, protection of the lower respiratory tract function and breath-holding function. 1, respiratory function The larynx is an important part of the respiratory channel, and is the necessary path for air inhalation and exhalation. The voice gate is the narrowest part of the laryngeal cavity. Under normal conditions, the central nervous system controls the movement of the vocal cords through the laryngeal nerve, and the movement of the vocal cords can change the size of the vocal fissure. When breathing calmly, the vocal folds are located in the light outer booth. The vocal folds widen slightly during inhalation and narrow slightly during exhalation. During vigorous exercise, the vocal folds are extremely abducted and the vocal folds are wide open, minimizing resistance to airflow. The larynx also has a supporting role in alveolar ventilation and maintaining the acid-base balance of body fluids. 2, vocal function The larynx is the articulatory organ, and the main part of human pronunciation is the vocal folds. The central nervous system controls the movement of vocal folds through the laryngeal nerve. When a normal person vocalizes, he or she first inhales air, then the vocal cords are inwardly closed and tightened, and the exhalation is controlled. The exhaled airflow from the lungs impels the vocal cords to vibrate and make sound. The strength of the sound is determined by the pressure under the vocal folds and the resistance of the vocal folds during exhalation. The tone of the voice is determined by the length, tension, quality and position of the vocal cords during vibration. The sound from the larynx is enhanced and modified by the resonance of the pharynx, mouth, nose, sinuses, trachea and lungs to become the sound heard daily. The tongue, lips, teeth and soft palate complete the composition of words. 3.Protect the function of lower respiratory tract When eating and swallowing, the 3 lines of defense formed by the larynx close at the same time, the upper esophagus opens and food enters the esophagus through the pear-shaped fossa. The three lines of defense of the larynx are: ① when swallowing, the larynx is lifted up, and the epiglottis goes down to cover the entrance of the larynx, forming the first line of defense to protect the lower respiratory tract; ② at the same time, the two sides of the ventricular zone close in to the midline, forming the second line of defense; ③ the vocal folds close in and the vocal cords close to form the third line of defense. 4, breath-holding function The larynx can close the vocal hatch and raise the pressure in the abdominal and thoracic cavities to complete the coughing, vomiting, defecation, childbirth and upper limb exertion. At this time, the vocal cords are inwardly closed, and the vocal chambers are tightly closed, which is called breath holding. The breath-hold is followed by inspiration, respiratory pause, fixation of the thoracic cavity, downward movement of the diaphragm, and contraction of the thoracic muscles and abdominal muscles. The vocal fold time varies according to the need, but it is short when coughing and long when defecating, giving birth and lifting heavy objects.