The inferior oblique (IO) muscle is the only EOM that does not arise from the orbital apex, but rather originates from the lateral border of the lacrimal fossa, which is anterior and nasal within the orbit.
What muscles originate from the annulus of Zinn?
The tendinous ring, also known as the annulus of Zinn, is the common origin of the four rectus muscles (extraocular muscles). The tendinous ring straddles the lower, medial part of the superior orbital fissure.
Which structure does not pass through the annulus of Zinn?
Correct Answer: Ophthalmic artery
The lacrimal, frontal and trochlear nerves, as well as the ophthalmic vein, pass through the superior orbital fissure outside of the annulus of Zinn.
Which extraocular muscle does not arise from the tendinous ring of the orbit?
The superior oblique is one of the two noteworthy oblique extraocular muscles. These muscles are unique in that they do not originate from the common tendinous ring, have an angular attachment to the eyeball, and they attach to the posterior aspect of the eyeball.
Which extrinsic eye muscle does not originate from the tendinous ring around the opening of the optic canal?
Unlike the other extraocular muscles (recti and superior oblique), the inferior oblique muscle does not originate from the common tendinous ring (annulus of Zinn).
What goes through the common tendinous ring?
The tendinous ring straddles the lower, medial part of the superior orbital fissure. It attaches to a tubercle on the greater wing of the sphenoid bone (at the margin of the superior orbital fissure). Through it (from superior to inferior) pass: superior division of the oculomotor nerve (CN III)
Does optic nerve go through common tendinous ring?
The annulus of Zinn, also known as the annular tendon or common tendinous ring, is a ring of fibrous tissue surrounding the optic nerve at its entrance at the apex of the orbit.
Why does superior oblique depress the eye?
The superior oblique muscle, therefore, originates functionally from the trochlea at the superior medial orbital rim and inserts on the top of the globe behind its equator. When the eye is in adduction , this muscle exerts a more or less direct downward pull and depresses the eye.
What is orbital apex syndrome?
Orbital apex syndrome is characterized by vision loss from optic neuropathy and ophthalmoplegia due to the involvement of ocular motor nerves in the anatomical region of the orbital apex.
Why is the Trochlear nerve unique?
The trochlear nerve is unique among the cranial nerves in several respects: It is the smallest nerve in terms of the number of axons it contains . It has the greatest intracranial length. It is the only cranial nerve that exits from the dorsal (rear) aspect of the brainstem.
What is eye abduction?
Inferior Oblique (IR) Rotates the top of the eye away from the nose (extorsion) Moves the eye upwards (elevation) Moves the eye outwards (abduction)
What is eye Intorsion?
Elevation and depression of the eye are termed sursumduction (supraduction) and deorsumduction (infraduction), respectively. ... Incycloduction (intorsion) is nasal rotation of the vertical meridian ; excycloduction (extorsion) is temporal rotation of the vertical meridian.
What is the function of the inferior oblique?
[2] The inferior oblique is responsible for extorsion, elevation, and abduction . Because of their course, the superior and inferior oblique muscles are the only muscles that can depress or elevate the eye, respectively when the eye moves in adduction.
Which of the following is not an eye muscle?
The inferior oblique muscle (b) is not an intrinsic eye muscle.
Are extrinsic eye muscles voluntary or involuntary?
In mammals, there are six muscles that are responsible for voluntary and reflexive eye movement (Buttner-Ennever, 1988). As a group, these muscles are called extrinsic eye muscles. The six muscles in this group are: medial rectus, lateral rectus, superior rectus, superior oblique, inferior rectus and inferior oblique.
What is the muscle that encircles the eye known as?
The orbicularis oculi muscle closes the eyelids and assists in pumping the tears from the eye into the nasolacrimal duct system. The orbital section of the orbicularis oculi is more involved in the voluntary closure of the eyelid, such as with winking and forced squeezing.
