There are 8 intrinsic muscles of the larynx, of which only 1 is not paired (transverse arytenoid) and only 1 is not innervated by the recurrent laryngeal nerve (cricothyroid muscle).
The muscles can be split into 2's to help remember them:
2 Trans-Arytenoid Muscles
2 Crico-Arytenoid Muscles
2 Vocal Cord Pitch Changing Muscles
2 Muscles that close the laryngeal aperture.
The transverse arytenoid muscles is the only unpaired muscle. It extends from the posterior aspect of one arytenoid cartilage to the other.
The oblique arytenoid is running obliquely across it, more externally.
These two muscles bring the arytenoid cartilages closer together, and thus both adduct the vocal cords.
The posterior and lateral cricoarytenoid muscles both insert into the muscular process of the arytenoid cartilage (which is a process facing laterally, almost at 90 degrees to the vocal process which attaches the vocal cord). The posterior arises on the posterior surface of the cricoid cartilage (medial to the arytenoid) and the lateral on the lateral surface.
When the lateral pulls the muscular process towards it, the arytenoid rotates internally, the vocal cords adduction.
When the posterior pulls the muscular process towards it, the arytenoid rotates externally, the vocal cord abducts.
Posterior Cricoarytenoid (PCA): only vocal fold ABductor (RLN)**
Lateral Cricoarytenoid (LCA): vocal fold ADductor (RLN)**
Thyroarytenoid (TA): increases vocal fold tension, vocal fold**
ADductor, the medial aspect of the TA is called the vocalis (RLN)**
Cricothyroid: ADductor, increases vocal fold tension and length, - chief pitch-changing muscle (external branch of SLN)**
Interarytenoid: only unpaired muscle, ADductor (RLN)*