Muscles of the Head That Move the Eyeballs (Extrinsic Eye Muscles) and the Upper Eyelids PDF

## 11.5 Muscles of the Head That Move the Eyeballs (Extrinsic Eye Muscles) and the Upper Eyelids **Objective** * Describe the origin, insertion, action, and innervation of the muscles that move the eyeballs and the upper eyelids. The muscles that move the eyeballs are called the **extrinsic eye mu...

## 11.5 Muscles of the Head That Move the Eyeballs (Extrinsic Eye Muscles) and the Upper Eyelids **Objective** * Describe the origin, insertion, action, and innervation of the muscles that move the eyeballs and the upper eyelids. The muscles that move the eyeballs are called the **extrinsic eye muscles**. They are so named because they originate outside of the eyeballs (in the orbit) and insert on the external surface of the sclera (the “white of the eye”). The extrinsic eye muscles are among the most rapidly contracting and precisely controlled skeletal muscles. - **Three pairs of extrinsic eye muscles control the movement of the eyeballs:** 1. **Superior and inferior rectus**, 2. **lateral and medial rectus**, and 3. **superior and inferior oblique**. - The four rectus muscles originate from a tendinous ring within the orbit and insert into the sclera. - As their names suggest, the **superior** and **inferior rectus** muscles move the eyeballs **upward** and **downward**, respectively. - The **lateral** and **medial rectus** muscles move the eyeballs **laterally** and **medially**, respectively. - The actions of the oblique muscles cannot be deduced from their names. - The **superior oblique** muscle originates posteriorly near the tendinous ring, travels anteriorly over the medial rectus muscle, and ends in a tendon. The tendon passes through a pulley-like fibrocartilaginous loop called a **trochlea**, located in the anteromedial portion of the orbit's roof. Finally, the tendon reflects and inserts on the posterolateral surface of the eyeball. As a result, the superior oblique muscle moves the eyeballs **inferiorly and laterally**. - The **inferior oblique** muscle originates on the maxilla, on the anteromedial surface of the orbit’s floor. From there, it runs posterolaterally and inserts on the posterolateral surface of the eyeball. Because of this arrangement, the inferior oblique muscle moves the eyeball **superolaterally**. - Unlike the rectus and oblique muscles, the **levator palpebrae superioris** muscle does not move the eyeballs: its tendon passes over the eyeball and inserts onto the upper eyelid. Its function is to elevate the upper eyelids (i.e., open the eyes). Therefore, it is an antagonist to the orbicularis oculi, which closes the eyes.