Chapter 16 - Section 16.5 - Study Guide - Assess Your Learning Outcomes - Page 626: 2

The extrinsic eye muscles are a group of six muscles responsible for controlling the movement of the eyeballs within the eye sockets. These muscles allow for precise and coordinated eye movements, enabling us to focus on objects, track moving targets, and maintain proper alignment of both eyes. The six extrinsic eye muscles, their anatomy, the eye motions they produce, and the cranial nerves that control them are as follows: 1. **Lateral Rectus Muscle**: - **Anatomy**: The lateral rectus muscle is located on the outer side of each eye, near the temporal region. - **Eye Motion**: Contraction of the lateral rectus muscle causes the eye to move laterally, or away from the nose. This motion is known as abduction. - **Cranial Nerve Control**: The lateral rectus muscle is primarily innervated (controlled) by the Abducens nerve (CN VI). 2. **Medial Rectus Muscle**: - **Anatomy**: The medial rectus muscle is situated on the inner side of each eye, near the nasal region. - **Eye Motion**: Contraction of the medial rectus muscle causes the eye to move medially, or toward the nose. This motion is known as adduction. - **Cranial Nerve Control**: The medial rectus muscle is primarily innervated by the Oculomotor nerve (CN III). 3. **Superior Rectus Muscle**: - **Anatomy**: The superior rectus muscle is positioned above the eye, near the upper eyelid. - **Eye Motion**: Contraction of the superior rectus muscle elevates the eye, moving it upward. This motion is known as elevation or supraduction. - **Cranial Nerve Control**: The superior rectus muscle is primarily innervated by the Oculomotor nerve (CN III). 4. **Inferior Rectus Muscle**: - **Anatomy**: The inferior rectus muscle is located beneath the eye, near the lower eyelid. - **Eye Motion**: Contraction of the inferior rectus muscle depresses the eye, moving it downward. This motion is known as depression or infraduction. - **Cranial Nerve Control**: The inferior rectus muscle is primarily innervated by the Oculomotor nerve (CN III). 5. **Superior Oblique Muscle**: - **Anatomy**: The superior oblique muscle runs diagonally along the inner side of each eye. - **Eye Motion**: Contraction of the superior oblique muscle primarily causes the eye to rotate downward and outward. This motion is known as incyclotorsion, depression, and abduction. - **Cranial Nerve Control**: The superior oblique muscle is primarily innervated by the Trochlear nerve (CN IV). 6. **Inferior Oblique Muscle**: - **Anatomy**: The inferior oblique muscle runs diagonally along the outer side of each eye. - **Eye Motion**: Contraction of the inferior oblique muscle primarily causes the eye to rotate upward and outward. This motion is known as excyclotorsion, elevation, and abduction. - **Cranial Nerve Control**: The inferior oblique muscle is primarily innervated by the Oculomotor nerve (CN III). These extrinsic eye muscles work in coordination to enable various eye movements, allowing us to perceive and interact with our surroundings. Dysfunction or weakness in these muscles can result in conditions like strabismus (eye misalignment) and can affect vision and depth perception.

The extrinsic eye muscles are a group of six muscles responsible for controlling the movement of the eyeballs within the eye sockets. These muscles allow for precise and coordinated eye movements, enabling us to focus on objects, track moving targets, and maintain proper alignment of both eyes. The six extrinsic eye muscles, their anatomy, the eye motions they produce, and the cranial nerves that control them are as follows: 1. **Lateral Rectus Muscle**: - **Anatomy**: The lateral rectus muscle is located on the outer side of each eye, near the temporal region. - **Eye Motion**: Contraction of the lateral rectus muscle causes the eye to move laterally, or away from the nose. This motion is known as abduction. - **Cranial Nerve Control**: The lateral rectus muscle is primarily innervated (controlled) by the Abducens nerve (CN VI). 2. **Medial Rectus Muscle**: - **Anatomy**: The medial rectus muscle is situated on the inner side of each eye, near the nasal region. - **Eye Motion**: Contraction of the medial rectus muscle causes the eye to move medially, or toward the nose. This motion is known as adduction. - **Cranial Nerve Control**: The medial rectus muscle is primarily innervated by the Oculomotor nerve (CN III). 3. **Superior Rectus Muscle**: - **Anatomy**: The superior rectus muscle is positioned above the eye, near the upper eyelid. - **Eye Motion**: Contraction of the superior rectus muscle elevates the eye, moving it upward. This motion is known as elevation or supraduction. - **Cranial Nerve Control**: The superior rectus muscle is primarily innervated by the Oculomotor nerve (CN III). 4. **Inferior Rectus Muscle**: - **Anatomy**: The inferior rectus muscle is located beneath the eye, near the lower eyelid. - **Eye Motion**: Contraction of the inferior rectus muscle depresses the eye, moving it downward. This motion is known as depression or infraduction. - **Cranial Nerve Control**: The inferior rectus muscle is primarily innervated by the Oculomotor nerve (CN III). 5. **Superior Oblique Muscle**: - **Anatomy**: The superior oblique muscle runs diagonally along the inner side of each eye. - **Eye Motion**: Contraction of the superior oblique muscle primarily causes the eye to rotate downward and outward. This motion is known as incyclotorsion, depression, and abduction. - **Cranial Nerve Control**: The superior oblique muscle is primarily innervated by the Trochlear nerve (CN IV). 6. **Inferior Oblique Muscle**: - **Anatomy**: The inferior oblique muscle runs diagonally along the outer side of each eye. - **Eye Motion**: Contraction of the inferior oblique muscle primarily causes the eye to rotate upward and outward. This motion is known as excyclotorsion, elevation, and abduction. - **Cranial Nerve Control**: The inferior oblique muscle is primarily innervated by the Oculomotor nerve (CN III). These extrinsic eye muscles work in coordination to enable various eye movements, allowing us to perceive and interact with our surroundings. Dysfunction or weakness in these muscles can result in conditions like strabismus (eye misalignment) and can affect vision and depth perception.