**2. Anatomy**

### **2.1 Laryngeal framework**

Paediatric airway differs considerably from adult airway. Location of the larynx in the neonates is high up in the neck opposite to cervical third and fourth vertebra which gradually descends down with age. Thyrohyoid membrane is short compared to the adult; thus, the thyroid notch lies either posterior or just inferior to the hyoid bone. Subglottis is the narrowest part of the larynx in neonates and the abundance of soft tissue in the subglottis and supraglottis make them vulnerable to swelling during inflammation. In the glottis, arytenoids make up the 50% of antero-posterior length and the vocal cords, next 50%.

### **2.2 Laryngeal musculature**

Larynx comprises of two groups of muscles: intrinsic and extrinsic. Intrinsic muscles are usually responsible for various movements of vocal cords. Posterior cricoarytenoid is the only muscle of the larynx that abducts the vocal cords. Lateral cricoarytenoid and interarytenoid muscles act as adductor of the vocal cord. Thyroarytenoid and cricothyroid muscles act as tensor of the vocal cords.

### **2.3 Nerve supply**

Both sensory and motor supplies to larynx come from vagus nerve via superior and recurrent laryngeal nerve. All the muscles of the larynx are supplied by recurrent laryngeal nerve except for the cricothyroid, which is supplied by the external branch of superior laryngeal nerve. Sensory supply of the supraglottis and glottis is provided by the internal branch of superior laryngeal nerve, and the subglottis is provided by recurrent laryngeal nerve.

The abductor fibers in the recurrent laryngeal nerve are phylogenetically newer compared to the adductor fibers and occupy the periphery of the nerve. This makes them more vulnerable to injury from any organic lesion (*Semon's law*).
