There are six distinctive extrinsic ocular muscles which are responsible for the range of motion each eyeball is capable of performing. The bony orbit of the eye is the originating point for each of these muscles, which then leads into the eye via an attached tendon to the leathery outer tunic of the eyeball.
There are four distinct recti muscles, each named for the direction they can encourage the eye to move. There is the superior rectus muscle, which moves the eye superiorly, the inferior rectus, the lateral rectus, and the medial rectus, which moves the eyeball inferiorly, laterally, and medially. The superior and inferior oblique muscles are responsible for the eye’s ability to rotate on its axis. The superior oblique muscles goes through a pulley system within the structure of the ocular set up before attaching to the eyeball itself. This loop of cartilage is known as the trochlea.
Each individual muscle is capable of producing a very specific eye movement, yet most movements of the eye are actually created by the cohesive working of two or more extrinsic muscles. The motor units associated with these muscles are actually the most minute within the human body. For every motor neuron, 10 muscle fibers are affected. This allows for extremely specified and precise movements. The eyes are able to achieve synchronous movement through the contraction of synergistic muscle during the complimentary relaxation of the antagonistic muscles. Three cranial nerves serve the extrinsic ocular muscle and innervate them as necessary to perform such tasks.
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Extrinsic ocular muscles
