出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/10/31 01:58:25」(JST)
| Extraocular muscles | |
|---|---|
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| MRI scan showing lateral and medial rectus muscles. | |
| Latin | musculi externi bulbi oculi |
| Origin | |
| Insertion | |
| Artery | |
| Nerve | CNIII, IV, VI |
| Actions | |
The extraocular muscles are the seven muscles that control the movements of the (human) eye (there are four in bovines). The actions of the extraocular muscles depend on the position of the eye at the time of muscle contraction.
Contents
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| Muscle | Innervation | Origin | Insertion | Primary function | Secondary function | Tertiary function | Distance inserted into the sclera |
|---|---|---|---|---|---|---|---|
| Superior rectus | Superior branch of oculomotor nerve | Annulus of Zinn | eye (anterior, superior surface) | Elevation | Intorsion | Adduction[1] | 7.9mm |
| Inferior rectus | Inferior branch of oculomotor nerve | Annulus of Zinn | eye (anterior, inferior surface) | Depression | Extorsion | Adduction[1] | 6.6mm |
| Lateral rectus | Abducens nerve | Annulus of Zinn | eye (anterior, lateral surface) | Abduction | 7.0mm | ||
| Medial rectus | Inferior branch of oculomotor nerve | Annulus of Zinn | eye (anterior, medial surface) | Adduction | 5.8mm | ||
| Superior oblique | Trochlear nerve | Annulus of Zinn via the Trochlea of superior oblique | eye (posterior, superior, lateral surface) | Intorsion | Depression | Abduction[1] | |
| Inferior oblique | Inferior branch of oculomotor nerve | Maxillary bone | eye (posterior, inferior, lateral surface) | Extorsion | Elevation | Abduction[1] | |
| Levator palpebrae superioris | Oculomotor nerve | Sphenoid bone | tarsal plate of upper eyelid | Retracts & elevates eyelid |
Since only the fovea provides sharp distinct vision, the eye must move to follow a target. It must be precise and fast. This is seen in scenarios like reading, wherein the reader must shift gaze constantly, or following a small object like a golf ball, in which the extraocular muscles must lead the eye to follow the head movements. Although under voluntary control, most movement is done without thinking, such as those based on head or other body movement, or movement of objects in the area. Researchers still have some work in order to find the parallel nature of the environment-based (involuntary) and voluntary control.[2]
orbiculris oris- facial nerve
The nuclei or bodies of these nerves are found in the brain stem. The nuclei of the abducens and oculomotor nerves are connected. This is important in coordinating motion of the lateral rectus in one eye and the medial action on the other. In one eye, in two antagonistic muscles, like the lateral and medial recti, contraction of one leads to inhibition of the other. Muscles shows small degrees of activity even when resting, keeping the muscles taut. This "tonic" activity is brought on by discharges of the motor nerve to the muscle.[2]
Note that intorsion and extorsion are not included in the following table; their actions are accounted for via summation of other actions.
| Medial (towards nose) | Lateral (towards temple) |
| Elevation, adduction: Inferior oblique |
Elevation, abduction: Superior rectus |
| Adduction: Medial rectus |
Abduction: Lateral rectus |
| Depression, adduction: Superior oblique |
Depression, abduction: Inferior rectus |
In an eye examination, the inability of the patient to move the eye in the specified direction can indicate a problem with the associated muscle, and the nerve associated with that muscle.
Intermediate directions are controlled by simultaneous actions of multiple muscles. When one shifts the gaze horizontally, one eye will move laterally (toward the side) and the other will move medially (toward the midline). This may be neurally coordinated by the central nervous system, to make the eyes move together and almost involuntarily. This is a key factor in the study of squint, namely, the inability of the eyes to be directed to one point.
There are two main kinds of movement: conjugate movement (the eyes move in the same direction) and disjunctive (opposite directions). The former is typical when shifting gaze right or left, the latter is convergence of the two eyes on a near object. Disjunction can be performed voluntarily, but is usually triggered by the nearness of the target object. A "see-saw" movement, namely, one eye looking up and the other down, is possible, but not voluntarily; this effect is brought on by putting a prism in front of one eye, so the relevant image is apparently displaced. To avoid double vision from non-corresponding points, the eye with the prism must move up or down, following the image passing through the prism. Likewise conjugate torsion (rolling) on the anteroposterior axis (from the front to the back) can occur naturally, such as when one tips one's head to one shoulder; the torsion, in the opposite direction, keeps the image vertical.
The muscles show little inertia - a shutdown of one muscle is not due to checking of the antagonist, so the motion is not ballistic.[2]
View of right eye from the right:
1 = Annulus tendineus communis
2 = Superior rectus muscle
3 = Inferior rectus muscle
4 = Medial rectus muscle
5 = Lateral rectus muscle
6 = Superior oblique muscle
7 = Trochlea of superior oblique
8 = Inferior oblique muscle
9 = Levator palpebrae superioris muscle
10 = Eyelid
11 = Eyeball
Five of the extraocular muscles have their origin in the back of the orbit in a fibrous ring called the annulus of Zinn.
Four of these then course forward through the orbit and insert onto the globe on its anterior half (i.e., in front of the eye's equator). These muscles are named after their straight paths, and are called the four rectus muscles, or four recti.[2]
orbicularis oculi-facial nerve (Note that lateral and medial are relative to the subject, with lateral toward the side and medial toward the midline, thus the medial rectus is the muscle closest to the nose).
The other two extraocular muscles follow more complicated paths.
The superior and inferior recti are not strictly vertical. The oblique pull of the obliques causes a rolling opposite each other. Although bearing mutual strict antagonism, the superior and inferior rectus team up with the inferior and superior oblique to move the eye up or down, respectively. The extent of rolling in the recti is less than the oblique, and opposite from it.[2]
A good mnemonic to remember which muscles are innervated by what nerve is to paraphrase it as a molecular equation: LR6SO4R3.[7] or (LR6SO4)3 i.e. "LR 6 SO 4 Whole 3."
Another way to remember which nerves innervate which muscles is to understand the meaning behind all of the Latin words.
Nerves of the orbit. Seen from above.
Figure showing the mode of innervation of the Recti medialis and lateralis of the eye.
Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.
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| リンク元 | 「眼筋」 |
| 関連記事 | 「ocular」「muscle」 |