Ocular Anatomy: Extraocular Muscles (Lecture 5; Exam 2)

Extraocular Muscles

• Voluntary, Extrinsic muscles

• Striated skeletal muscles

Where do the extraocular muscles attach?

Sclera.

What do the extraocular muscles do?

Control movement of the globe.

Anatomy of Striated Skeletal Muscle:

Connective tissue compartmentalizes and supports muscle fibers (myofibers).

What are the different layers of the striated skeletal muscle?

• Epimysium

• Perimysium

• Endomysium

What is the Epimysium layer of the striated skeletal muscle?

Connective tissue surrounding entire muscle.

What is the Perimysium layer of the striated skeletal muscle?

Connective tissue network organizing myofibers into bundles.

(also called fascicles.)

What is the Endomysium layer of the striated skeletal muscle?

Connective tissue sheath surrounding individual muscle fibers.

Anatomy of myofibers:

• Long

• Cylindrical

• Multinucleated

What are the striated skeletal muscles surrounded by?

Sarcolemma.

What are Transverse (T-) Tubules?

Extensions of sarcolemma into muscle fiber.

What do transverse tubules do?

Allow for rapid ion passage.

Each myofiber is made up of many ____.

Myofibrils.

Each myofibers is made up of many ____.

Myofilaments.

Myofilaments are what kind of proteins?

Cytoskeletal proteins.

Actin:

Thin filament.

Myosin:

Thick filament.

Sarcoplasmic Reticulum in Striated skeletal muscle:

Specialized smooth endoplasmic reticulum.

What does the sarcoplasmic reticulum do?

Stores and releases calcium ions (Ca2+).

Recap: Anatomy of striated skeletal muscle:

Muscle → Myofibers → Myofibrils → Myofilaments

How do extraocular muscles differ from skeletal muscle?

• More dense blood supply

• More delicate connective tissue sheaths

• Richer in elastic fibers

• Faster, more precise fine motor control

• More fatigue-resistant

Why do extraocular muscles have more precise fine motor control and move faster than extraocular muscles?

• Fewer muscle fibers per motor unit

• Denser innervation

Orbital Connective Tissue Structures:

• Dense connective tissue septa form network / framework in orbit

• Medial check ligament

  • Connects medial rectus to medial orbital wall.

• Lateral check ligament

  • Connects lateral rectus to lateral orbital wall.

Each extraocular muscle has a ___.

Pulley; soft tissue encircling the muscle.

What are the extraocular muscle ‘pulleys’ made of?

Collagen, elastin and smooth muscle.

What else is connected to each extraocular muscle pulleys?

Tenon’s capsule.

Where are these pulleys attached to?

The orbital wall.

What do the extraocular muscle pulleys do?

• Control positioning and movement

• Stabilize muscle path

• Determine effective direction of pull;

  • “(Functional origin” of muscles.)

• Prevent muscle displacement during globe movement.

What are all of the Extraocular Muscles?

1. Superior Rectus (SR)

2. Inferior Rectus (IR)

3. Medial Rectus (MR)

4. Lateral Rectus (LR)

5. Superior Oblique (SO)

6. Inferior Oblique (IO)

What origin do all of the Rectus Muscles share?

Common Tendinous Ring (annulus of Zinn).

What is the common tendinous ring?

Oval band of connective tissue that is continuous with the periorbita.

Where is the Common Tendinous Ring located?

Located at the apex of the orbit anterior to the optic canal.

What is the oculomotor foramen?

Area enclosed by the common tendinous ring;

(Nerves and vessels pass through this region after entering the orbit via the superior orbital fissure or optic canal.)

What nerves/vessels pass through the oculomotor foramen?

• Nasociiary nerve

• Oculomotor nerve

  • Superior and inferior divisions

• Abducens nerve

• Optic nerve

• Ophthalmic artery

What muscle sheaths also attach to the dural sheath of the optic nerve?

• Medial recti muscle sheath

• Superior recti muscle sheath

Where do ALL rectus muscles insert?

They insert into the globe anterior to equator.

(insert at different locations relative to limbus).

What is the order of insertion for rectus muscles?

Insertion in order of closest from limbus.

(Medial → Inferior → Lateral → Superior (“MILS”)

(This creates Spiral of Tillaux)

What Orbital Compartments are Intraconal?

(Within the muscle cone).

• Optic nerve (and other nerves)

• Ophthalmic artery

• Central retinal artery and vein

• Adipose tissue

Medial Rectus Origin

Common Tendinous Ring (CTR) and optic nerve sheath

Lateral Rectus Origin

Common Tendinous Ring (CTR) and greater wing of sphenoid.

Superior Rectus Origin

Common Tendinous Ring (CTR) and optic nerve sheath.

Inferior Rectus Origin

Common Tendinous Ring (CTR)

Superior Oblique Origin

Anatomic; Lesser wing of sphenoid

Physiologic; Trochlea

Inferior Oblique Origin

Medial maxillary bone

Medial Rectus Insertion

Anterior globe (sclera!)

Lateral Rectus Origin

Anterior globe (sclera!)

Superior Rectus Insertion

Superior, anterior globe (sclera!)

Inferior Rectus Insertion

Inferior, anterior globe (sclera!)

Superior Oblique Insertion

Superior, posterior, lateral globe

Inferior Oblique Insertion

Inferior, posterior, lateral globe

Medial Rectus Innervation:

Inferior division of oculomotor (CN III)

Lateral Rectus Innervation:

Abducens (CN VI)

Superior Rectus Innervation:

Superior division of oculomotor (CN III)

Inferior Rectus Innervation:

Inferior division of oculomotor (CN III)

Superior Oblique Innervation:

Trochlear (CN IV)

Inferior Oblique Innervation:

Inferior division of oculomotor (CN III)

What parts of the orbit are extraconal to the rectus muscles?:

Extraconal: Outside the muscle cone.

• Lacrimal gland

• Adipose tissue

• Nerves

What muscle is the longest rectus muscle?

Superior Rectus.

Unique characteristics of Superior Rectus:

• Longest rectus muscle

• Sheath is connected to levator muscle sheath

• Coordinates eye movement with eyelid position

What is the longest extraocular muscle?

Superior Oblique.

What is the thinnest extraocular muscle?

Superior Oblique.

Trochlea:

U-shaped piece of cartilage attached to the orbital plate of the frontal bone.

What is the only extraocular muscle that has an anterior origin?

Inferior oblique.

The insertion points of ALL oblique muscles are ____ to the equator.

Posterior.

The insertion points of ALL rectus muscles are all ____ to the equator.

Anterior.

What is the shortest rectus muscle?

Inferior rectus.

What muscle has an effective/physiologic orgin that differs from its anatomic origin?

Superior oblique.

(Anterior - where muscle anatomically originates)

(Effective / Physiologic - determines muscle action)

Lateral Rectus Unique Characteristic:

Fascia from muscle sheath connects to the orbital wall and forms lateral check ligament.

Medial Rectus Unique Characteristics:

• Largest extraocular muscle

• Fascia from muscle sheath connects to orbital wall and forms medial check ligament.

Fick’s Axes

All eye movements occur around three main axes.

1. X-axis = horizontal

2. Y-axis = sagittal

3. Z-axis = vertical

Fick’s Axes: X-axis

Horizontal.

• Runs nasal to temporal

• Eye moves up / down around this axis

Fick’s Axes: Y-axis

Sagittal.

• Runs anterior to posterior

• Eye intorts and extorts around this axis

Fick’s Axes: Z-axis

Vertical.

• Runs superior to inferior

• Eye moves left / right around this axis

What are ductions?

Movements involving just one eye. (monocular)

Ductions: Rotations around the X-axis

• Elevation: Eye moves UP

• Depression: Eye moves DOWN

Ductions: Rotations around the Y-axis

• Intorsion: Eye rotates TOWARD the nose

• Extorsion: Eye rotates AWAY from nose.

Ductions: Rotations around the Z-axis

• Adduction: Eye moves TOWARD midline

• Abduction; Eye moves AWAY from midline

What are versions?

Binocular, conjugate eye movements .

BOTH eyes move in the SAME direction!

What is dextroversion?

Right gaze.

What is levoversion?

Left gaze.

What is supraversion?

Up gaze.

What