The tendinous ring straddles the lower, medial part of the superior orbital fissure
What makes up the common tendinous ring?
Two specialized parts of this fibrous ring may be made out: a
lower, the ligament or tendon of Zinn, which gives origin to
the Rectus inferior, part of the Rectus internus, and the lower head of origin of the Rectus lateralis; and an upper, which gives origin to the Rectus superior, the rest of the Rectus medialis, and …
What structures pass through the annulus of Zinn?
The lacrimal, frontal and trochlear nerves, as well as the ophthalmic vein
, pass through the superior orbital fissure outside of the annulus of Zinn. The superior and inferior divisions of cranial nerve III, cranial nerve VI, and the nasociliary nerve pass through the fissure within the Annulus of Zinn.
Which extraocular muscle arise from the tendinous ring of the orbit?
All the extraocular muscles apart from
the inferior oblique
originate from a common tendinous ring (the annulus of Zinn). This tendinous ring surrounds the anterior end of the optic canal and the middle third of the superior orbital fissure.
What travels through superior orbital fissure?
This fissure, which separates the greater and lesser wings of the sphenoid and lies between the optic foramen and the foramen rotundum, provides passage to the three motor nerves to the extraocular muscles of the orbit:
oculomotor nerve (CN III), trochlear nerve (CN IV), and abducens nerve (CN VI)
.
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 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 the function of the inferior oblique muscle?
[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.
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 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.
Are eye muscles voluntary or involuntary?
The eyes are
under voluntary control
, and it is thought that the cortical area subserving voluntary eye movements is in the frontal cortex.
How does inferior oblique move the eye?
Function. Due to its oblique course and attachment on the posterolateral side of the eyeball, contraction of the inferior oblique muscle
pulls the eyeball in a direction posterior to its vertical axis
, and therefore rotates the eye laterally around this axis.
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.
Which foramina and fissures are associated with the orbit?
| Foramen caecum Emissary veins | Optic canal Optic nerve (CNII), ophthalmic artery, dural sheath of optic nerve | Superior orbital fissure Oculomotor nerve (CNIII), trochlear nerve (CN IV), ophthalmic division of the trigeminal nerve (CNV1), abducent nerve (CNVI), ophthalmic veins |
|---|
What are the fissures of the orbit?
The superior orbital fissure is
the communication between the cavernous sinus and the apex of the orbit
. It is straddled by the tendinous ring which is the common origin of the four rectus muscles (extraocular muscles).
What travels through the foramen ovale?
The foramen ovale is another opening located at the base of the greater wing of the sphenoid. It is positioned posterolateral to the foramen rotundum within the middle cranial fossa. It conducts
the mandibular nerve (branch of the trigeminal nerve, CN V) and the accessory meningeal artery
.
