Final answer:
The inferior rectus muscle's primary function is to depress the eye and help with angled movements, requiring coordination with the lateral rectus muscle. It is innervated by the oculomotor nerve and is one of six extraocular muscles facilitating eye movement, such as saccades for visually tracking objects.
Step-by-step explanation:
The function of the inferior rectus muscle is to move the eye downward, known as depression, and contribute to movements at an angle due to the eyes not being perfectly aligned on the sagittal plane. This muscle, like the superior, medial, and lateral rectus muscles, originates from the bones of the orbit and inserts into the surface of the eyeball. As the inferior rectus contracts, the eye is pulled downward. Since the inferior rectus is not perfectly aligned with the line of sight, its contraction also causes slight adduction of the eye (movement toward the nose), coordinating with the lateral rectus muscle and the activity of the medial longitudinal fasciculus (MLF) to adjust the eye's position properly for focused vision.
It is one of the six extraocular muscles innervated by cranial nerves. Specifically, the oculomotor nerve (third cranial nerve) innervates the inferior rectus along with most of the other extraocular muscles, except for the lateral rectus and superior oblique muscles, which are controlled by the abducens (sixth cranial nerve) and trochlear (fourth cranial nerve) nerves respectively. These nerves and muscles work together for the rapid and coordinated eye movement known as a saccade, which is essential for locating and focusing on visual stimuli.