Week 1 - Revision: Muscles part 1 and 2 Flashcards
What muscles comprise the Muscle Cone?
• Superior Rectus
• Lateral Rectus
• Medial rectus
• Inferior rectus
• Superior oblique
• Inferior oblique
Where do all the muscles originate?
• Common Tendon of Zinn
- Comes through the superior orbital fissure
What is the spiral of Tillaux?
• Rectus muscle passes throgh the tendons capsule and insert into sclera
• Muscles insert into at different distances from the cornea
• The insertion pattern is a spiral with the medial rectus closest to the cornea (5.5 mm) and the superior rectus the furthest away from the cornea (7.4 mm).
What are the distances for the spiral if Tillaux?
• Medial - 5.5mm
• Inferior - 6.7mm
• Lateral rectus - 6.9mm
• superior rectus - 7.7mm
Measured from the Limbus to insertion:
S - 8mm
L - 7mm
I - 6mm
M - 5mm
What is Tenon’s capsule?
• Is the bulk of the orbital fascial system
•Forms the envelope within which the eyeball moves
• Fuses posteriorly with optic nerve sheath, anteriorly with the intermuscular septum
• Posterior portion is thin and flexible
Posterior to the equator, it is thick and tough, suspending the globe to the periorbital tissues
ALL MUSCLES attach to Tenons capsule; with the obliques penetrating through it
Describe the medial rectus:
• Originates on both the upper and lower limb of the common tendous ring and the optic nerve sheath.
• Inserts vertically 5.5 mm from the cornea. The horizontal plane of eye bisects the insertion.
• Fascial expansion from muscle sheath forms the medial check ligament and attach to medial wall of orbit.
What nerves and innervations does the medial rectus have?
• Innervation is via cranial nerve III, the oculomotor nerve, and the specific branch runs along the inside of the muscle cone, on the lateral surface.
• The superior oblique, ophthalmic artery and nasociliary nerve all lie above the medial rectus.
What is the Origin, Insertion, direction, innervation, bloody supply and action of medial rectus?
× Origin: annulus of zinn
* Insertion: medially, in hori meri, 5.5 mm from limbus
* Direction: 90°
* Innervation: lower CN III
* Blood supply: Inf. Mus. Branch Of Oph. A.
× Action: adduction- inwards to middle
Where is the origination and insertion of the lateral rectus?
• Originates on both the upper and lower limb of the common tendous ring, AND a process of the greater wing of the sphenoid bone.
• Inserts parallel to medial rectus 6.9 mm from the cornea. (Tendon 9.2 mm wide, 8.8 long).
• Fascial expansion from muscle sheath forms the lateral check ligament and attach to lateral wall of orbit at Whitnalls tubercle.
What is the innervation, bloody supply and innervations of the lateral rectus muscle?
• Innervated by the abducens nerve, Cranial n VI which enters the muscle on the medial surface.
• The lacrimal artery and nerve run along the superior border.
• The abducens n., ophthalmic artery and ciliary ganglion lie medial to the lateral rectus and between it and the optic nerve.
What is the Origin, insertion, innervation, bloody supply and action of the lateral rectus?
- Origin: annulus of zinn
- Insertion: laterally, in horizontal meridian, 6.9mm from limbus
- Innervation: CN VI
- Blood supply: Inf. Mus. Branch Of Oph. A.
- Action: abduction or outwards
What is the origin and insertions of the superior rectus?
• Originate on superior limb of the tendonous ring, and optic nerve sheath.
• Muscle passes forward underneath the levator, but the two sheaths are connected resulting in coordinated movements.
• Insertion 7.4 mm from limbus, and obliquely.
• The angle from the origin to the insertion is 23° beyond the sagital axis.
How do the nerves and blood supply innervate the superior rectus?
• Frontal nerve runs above the s. rectus & levat.
• The nasociliary nerve and ophthalmic artery run below.
• The tendon for insertion of the superior oblique muscle runs below the anterior part of the superior rectus.
• Innervations via superior division of CN III, from the inferior surface; additional branches make their way to the levator.
What is the action of the superior rectus?
• Primary action is elevation . But since the insertion on the globe is lateral as well as superior, contraction will produce rotation about the vertical axis toward midline
• Thus secondary action is adduction
Finally, because the insertion is oblique, contraction produces torsion nasally Intorsion.
What is the Origin, insertion, direction, innervation and action of the superior rectus?
• Origin: annulus of zinn
• Insertion: superiorly, in ver. Mer. 7.7 mm from limbus
• Direction:23°
• Innervation: upper CN III
• Action: Elevation , Intorsion, Adduction
What are the insertions and origins of the inferior rectus?
• Originates on lower limb of common tendonous ring.
• Inserts 6.7 mm from limbus, insertion is an arc
• It is parallel to superior rectus, making a 23° angle beyond the sagittal axis.
• Innervated by inferior division of CN III which runs above it (within the muscle cone).
• Below is the floor of the orbit and inf. oblique
What is the Origin, Insertion, direction, innervation and action of the Inferior rectus?
• Origin: annulus of zinn
• Insertion: inferiorly, in ver. Mer. 6.5 mm from limbus
• Direction:23°
• Innervation: lower CN I
• Action: Depression. Extorsion, Adduction,
Where is the inferior rectus bound to the lower eyelid?
• The inferior rectus muscle is distinctly bound to the lower eyelid by the fascial extension from its sheath
What is the superior oblique, where is its origin and what is it innervated by?
• Anatomical origin: lesser wing of the sphenoid bone. The physiological origin is the trochlea, a cartilagenous “U” on the superior medial wall of the orbit.
• Longest thinnest EOM, the muscle ends before the trochlea, tendon is 2.5 cm, smooth movement through trochlea.
• Innervation by CN IV, the trochlear nerve posterior in the orbit.
What is the action of Sup. Oblique?
• Primary action: depression and intorsion
• Due to insertions laterally and posterior:
- ABDUCTION
- DEPRESSION
What is the origin, insertion, innervation and action of superior oblique?
• Origin: superior of annulus of zinn (func. At trochlea
• Insertion: post. to equator in suprotemp.
• Innervation: CN IV, 4 , Trochlear
• Action: Intorsion, Dep, Abd,
What is the Origination, insertion and innervation of the inferior oblique?
• Originates on the maxillary bone inferior to the nasolacrimal fossa. The ONLY EOM originating in the anterior orbit.
• Inserts on the posterior. lateral aspect of globe mostly inferior, below the ant.-post.
horizontal plane.
• Innervation from inferior division of CN III inserts on the upper surface (within muscle cone.)
What is the action of Inf. Oblique?
• Primary is extorsion
• 2° is due to posterior, lateral, inferior insertion being pulled around, underneath globe and toward the anterior inferior insertion medially.
• Rotation about the Z axis will be nasal to temporal (abduction).
• Rotation about the X axis will be elevation
What is the origin, insertion, length, direction, innervation and action of the inferior oblique?
• Origin: behind of lacrimal fossa
• Insertion: post. to equator in macular area.
• Direction:51°
• Innervation: lower CN III
• Action: Ext, Elev, Abd,
