Definitions

Muscles_of_orbit

Muscles of orbit

There are six Orbital Muscles; Four of the muscles control the movement of the eye going up and down and side to side. Two of the muscles control the eye to move while the head moves. For instance look in the mirror sometime, you can see your eyes looking right at it. Then stare at the mirror while moving your head side to side. You can see your eyes move but you still are looking at the mirror. That is what the other two muscles do.

   
   
   
   
   
 
   
   
   
   
   
 
   
   
   
   
   
 
   
   
   
   
   
 
   
   
   
   
   
 
   
   
   
   
   
 
   
   
   
   
   
 
   
   
   
   
   
 
Muscle Innervation Primary function Secondary function Tertiary function
Levator palpebrae superioris Oculomotor nerve Elevation of the superior (upper) eyelid . .
Superior rectus Oculomotor nerve Elevation Intorsion Adduction
Inferior rectus Oculomotor nerve Depression Extorsion Adduction
Lateral rectus Abducens nerve Abduction . .
Medial rectus Oculomotor nerve Adduction . .
Superior oblique Trochlear nerve Intorsion Depression Abduction
Inferior oblique Oculomotor nerve Extorsion Elevation Abduction

A good mnemonic to remember which muscles are innervated by what nerve is to paraphrase it as a molecular equation: LR6SO4R3.
Lateral Rectus - Cranial Nerve VI,
Superior Oblique - Cranial Nerve IV,
the Rest of the muscles - Cranial Nerve III.

Another way to remember which nerves innervate which muscles is to understand the meaning behind all of the Latin words. The fourth cranial nerve, the trochlear, is so named because the muscle it innervates, the superior oblique, runs through a little fascial pulley that changes its direction of pull. This pulley exists in the superiomedial corner of each orbit, and "trochl-" is Latin for "pulley." The sixth cranial nerve, the abducens, is so named because it controls the lateral rectus, which abducts the eye (rotates it laterally) upon contraction. All of the other muscles are controlled by the third cranial nerve, the oculomotor, which is so named because it is in charge of the movement (motor) of the eye (oculo-).

Purpose

The motor apparatus, precisely and rapidly, controls eye movement for exact alignment with the fovea, since this is the area that deals with sharp vision. This swift and accurate motion is evident in reading. When keeping the gaze on a small object, like a golf ball, the eyes must compensate for the small movements of the head to keep the object on the fovea. The eyes can be controlled by voluntary means, as one can deliberately change focus. However, most eye movmeent is done without awareness. This is evident when viewing moving objects or head or body movement. Studying the movements of the eyes depend on reflexes brought on by factors in the environment or the individual, keeping in mind the voluntary control.

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