Medial rectus is inserted on the medial aspect of sclera at what distance from sclerocorneal junction?
Ans. A. 5.5 mmMedial Rectus:The medial rectus is the largest of the ocular muscles and stronger than the lateral.# Origin- The medial rectus muscle arises from the annulus of Zinn. It has a wide origin to the medial side of and below the optic foramen from both parts of the common tendon, and from the sheath of the optic nerve.# Insertion - The medial rectus inserts medially, in the horizontal meridian about 5.5 mm from the limbus.# Blood supply - The medial rectus is supplied by the inferior muscular branch of ophthalmic artery and 2 anterior ciliary arteries.# Size - The medial rectus muscle is 40.8 mm long; tendon is 3.7 mm long and 10.3 mm wide.# Innervation- The inferior division of the 3rd nerve innervates the medial rectus on its lateral surface at about the junction of its middle and posterior thirds.# Action. - The medial rectus is a pure adductor.Inferior Rectus:The inferior rectus is the shortest of the recti muscles.# Origin-It arises below the optic foramen, from the middle slip of the lower common tendon of the annulus of Zinn at the apex of the orbit.# Insertion- inserted inferiorly, in vertical meridian about 6.5 mm from the limbus. The inferior rectus is also attached to the lower lid by means of the fascial expansion of its sheath.# Blood supply - the inferior muscular branch of ophthalmic artery and infraorbital artery, 2 anterior ciliary vessels# Size - 40 mm long; tendon is 5.5 mm long and 9.8 mm wide# Innervation- The inferior rectus is supplied by the inferior division of the 3rd nerve, which enters it on its upper aspect at about the junction of the middle and posterior thirds.# Actions - The inferior rectus makes the eye look downwards or medially or wheel-rotates it laterally (extorsion). By means of its fascial expansion it also depresses the lower lid. The principal action is depression which increases as the eye is turned out and is nil when the eye is adducted. The inferior rectus is the only depressor in the abducted position of the eye.Lateral Rectus:# Origin - arises from the annulus of Zinn and spans the superior orbital fissure.# Insertion - inserted laterally, in horizontal meridian 6.9 mm from the limbus# Blood supply - the lacrimal artery (the only rectus muscle with a single blood supply)# Size - 40.6 mm long; tendon is 8 mm long and 9.2 mm wide# Relations- The structures which go through the two heads of the lateral rectus, within the cone of muscles or within the annulus of Zinn, have been referred to as the oculomotor foramen.# Innervation- The 6th nerve (abducens) enters it on its medial aspect, just behind its middle.# Actions- The lateral rectus is a pure abductor - that is, makes the eye look directly laterally in the horizontal plane.Superior Rectus:# Origin - The superior rectus arises from the upper part of the annulus of Zinn above and to the lateral side of the optic foramen and from the sheath of the optic nerve. This origin lies below that of the levator, and is continuous on the medial side with the medial rectus and on the lateral with the lateral rectus.# Insertion - inserted superiorly, in vertical meridian 7.7 mm from limbus# Blood supply - Superior muscular branch of ophthalmic artery and 2 anterior ciliary a.# Size - 41.8 mm long; tendon is 5.8 mm long and 10.6 mm wide# Innervation - The superior rectus is supplied by the superior division of the oculomotor (3rd cranial), which enters the under-surface of the muscle at the junction of the middle and posterior thirds.# Actions - The superior rectus makes the eye look upwards or medially or wheel-rotates it medially (intorts). It also helps the levator to lift the upper lid.Superior Oblique:The superior oblique is the longest and thinnest eye muscle.# Origin - arises above and medial to the optic foramen by a narrow tendon which partially overlaps the origin of the levator. The origin is just outside the medial rectus and blends with the periosteum of the sphenoid bone.# Insertion - inserted to trochlea at orbital rim, then inferior and under superior rectus posterior to center of rotation# Blood supply - the superior muscular branch of ophthalmic artery supply blood# Size - 40 mm long; tendon is 20 mm long and 10.8 mm wide# Actions - The superior oblique moves the eye downwards or laterally or (wheel-) rotates it inwards (i.e. makes twelve o'clock on the cornea move towards the nose).- The principal is the depression, and this increases as the eye is adducted. The superior oblique is the only muscle which can depress in the adducted position. Its action is practically nil when the eye is abducted.- The abduction and intorsion are the subsidiary actions, and increase as the eye turns out.- The superior oblique acts with the inferior rectus to make the eye look directly down. The abductor component of the action of the oblique muscles is due to their being inserted behind the equator of the globe.# Innervation - The superior oblique is supplied by the 4th or trochlear nerve which, having divided into three or four branches, enters the muscle on the upper-surface near its lateral border; the most anterior branch at the junction of the posterior and middle thirds, the most posterior about 8 mm. from its origin.# Blood-supply comes from the superior muscular branch of the ophthalmic artery.Inferior Oblique:# Origin - The inferior oblique is the only extrinsic muscle to take origin from the front of the orbit; arises from a rounded tendon in a depression on orbital floor near orbital rim (maxilla), just behind the orbital margin and lateral to orifice of the naso-lacrimal duct. Some of its fibres may, in fact, arise from the fascia covering the lacrimal sac.# Insertion - inserted posterior inferior temporal quadrant at level of macula# Blood supply - the inferior branch of ophthalmic artery and infraorbital artery# Size - 37 mm long; the shortest tendon of insertion ( essentially no tendon) and it is 9.6 mm wide at insertion.# Innervation- the inferior division of the oculomotor nerve, crosses above the posterior border to enter the muscle on its upper-surface at about the middle of the muscle.# Blood-supply comes from the infraorbital artery and the inferior muscular branch of the ophthalmic a.# Actions- The inferior oblique makes the eye look upwards or laterally or wheel-rotates it laterally (extorts). The principal action is the elevation which increases as the eye is turned in and is nil in abduction. The inferior oblique is the only elevator in the adducted position.Levator Palpebrae Superioris Muscle:# striated muscle to elevate the eyelid.# The levator palpebrae superioris arises from the under-surface of the lesser wing of the sphenoid above and in front of the optic foramen by a short tendon which is blended with the underlying origin of the superior rectus.# The flat ribbon-like muscle belly (about 40 mm in length) passes forwards below the roof of the orbit and on the superior rectus to about 1 cm. behind the orbital septum (at the upper fornix or a few millimeters in front of the equator of the eye), where it ends in a membranous expansion or aponeurosis. From the equator forward about 10-15 mm of levator tendon spreads out in a fan-shaped manner, so as to occupy the whole breadth of the orbit and thus gives the whole muscle the rough form of an isosceles triangle.# Attachments. - (a) The main insertion of the levator is to the skin of the upper lid at and below the upper palpebral sulcus. It reaches this by intercalating with the fibres of the orbicularis.# (b) To the Tarsal Plate. - Some of the fibres of the aponeurosis are attached to the front and lower part of the tarsal plate, but the main attachment of the levator here is via the smooth superior palpebral muscle of Muller. This is continuous with the fleshy part of the levator, and is attached to the upper border of the tarsus.# Innervation- The Superior Division of the 3rd, which reaches the muscle either by piercing the medial edge of the superior rectus.# Action. - The levator raises the upper eyelid, thus uncovering the cornea and a portion of the sclera, and deepens the superior palpebral fold. Its antagonist is the palpebral portion of the orbicularis.Muller's muscle-The superior palpebral muscle is a smooth muscle that acts a an eyelid elevator.# Origin- arises from the inferior or bulbar aspect of the levator palpebrae behind the fornix.# Insertion-upper edge of the tarsal plate, between the levator and conjunctiva.# Action- eyelid elevator# Size- 15-20 mm at its origin, 10 mm in vertical length, slightly sider at its insertion# Relations-lies between the tendon of the levator and the conjunctiva in the eyelid# Innervation- sympathetic fibers
5.5 mm
6 mm
6.5 mm
7mm
Anatomy