week 18- Extraocular muscles and Eye movements

• Why is accurate eye alignment important?


  It ensures both eyes point to the object of focus, requiring precise movements in size, timing, and direction.
• How many muscles move each eye, and what are they?


  Six muscles:

  • Rectus muscles: Superior (SR), Inferior (IR), Lateral (LR), Medial (MR).
  • Oblique muscles: Superior (SO), Inferior (IO).Additionally, the levator palpebrae elevates the eyelid.
• What are the primary actions of the rectus muscles?


  • SR: Elevation.
  • IR: Depression.
  • MR: Adduction.
  • LR: Abduction.
• What are the primary actions of the oblique muscles in primary gaze?


  • SO: Depression and intorsion.

  IO: Elevation and extorsion.
• Where do rectus muscles insert, and why is this significant?


  They insert anterior to the eye's equator, affecting their power based on their distance from the limbus.
• What are the origins of the oblique muscles?


  • SO: Originates at the annulus of Zinn and passes through the trochlea.

  IO: Originates at the medial orbital wall, bypassing the annulus.
• Which cranial nerves innervate the EOMs?

  • CN III (Oculomotor): MR, SR, IR, IO.
  • CN IV (Trochlear): SO.
  • CN VI (Abducens): LR.
• What are ductions, versions, and vergences?


  • Ductions: Monocular movements (e.g., elevation, depression, intorsion, extorsion).
  • Versions: Binocular movements where eyes move in the same direction (e.g., conjugate gaze).
  • Vergences: Disconjugate movements (e.g., convergence for near focus, divergence for distance).
• How do eyes move in vertical, horizontal, and rotational versions?


  • Vertical: Both eyes move in the same direction (e.g., elevation).
  • Horizontal: Eyes move oppositely (e.g., RE abducts, LE adducts).

  Rotational: Opposite rotations (e.g., RE intorts, LE extorts).
• How do muscles work during convergence and divergence?


  • Convergence: Medial recti contract, lateral recti relax.
  • Divergence: Lateral recti contract, medial recti relax.
• What are the primary, secondary, and tertiary actions of the EOMs?


  • Rectus muscles:
  • MR: Adduction.
  • LR: Abduction.
  • SR: Elevation, adduction, intorsion.
  • IR: Depression, adduction, extorsion.
  • Oblique muscles:
  • SO: Intorsion, depression, abduction.
  • IO: Extorsion, elevation, abduction.
• When do rectus and oblique muscles function best?


  • Rectus: Best in abducted gaze (e.g., SR for elevation).
  • Oblique: Best in adducted gaze (e.g., SO for depression).
• What are contralateral synergists, and how do they work?


  Pairs of muscles, one from each eye, coordinate to move eyes in the same direction. E.g., Right SR and Left IO work together for upward gaze.
• What is the general organization of cranial nerves?


  There are 12 paired cranial nerves, each connecting to a nucleus in the brainstem or cerebrum for sensory or motor functions.
• What does CN III innervate?


  MR, SR, IR, IO, levator palpebrae superioris, pupil sphincter, and ciliary muscle.
• What is the function of CN III?


  Convergence, accommodation, and pupil constriction (near triad).
• What muscle does CN IV supply, and what is its function?


  Supplies the SO for depression and intorsion, especially during inward gaze (e.g., reading).
• What does CN VI innervate, and what is its function?


  Supplies the LR for abduction (eye moves outward).
• Why is the cavernous sinus important for eye movements?


  It encases CNs III, IV, and VI, which control EOMs, and is close to critical structures like the pituitary gland.
• How do cerebral aneurysms affect cranial nerves?


  Swellings on blood vessels may press on cranial nerves, with CN III being most vulnerable, followed by VI and IV.
• How many muscles are involved in eye movement, and what are they?

  Each eye has six extraocular muscles:

  • Four rectus muscles: Superior (SR), Inferior (IR), Lateral (LR), Medial (MR).
  • Two oblique muscles: Superior (SO), Inferior (IO).
• What additional muscle is responsible for eyelid elevation?

  The levator palpebrae superioris.
• What movements do the rectus muscles perform?

  • SR: Elevation.
  • IR: Depression.
  • MR: Adduction.
  • LR: Abduction.
• What are the primary actions of the oblique muscles?

  • SO: Depression and intorsion.
  • IO: Elevation and extorsion.
• Where do the rectus muscles insert on the eye?

  They insert anterior to the equator of the eye, with varying distances from the limbus.
• What are the origins of the oblique muscles?

  • SO: Annulus of Zinn, passing through the trochlea.
  • IO: Medial orbital wall, bypassing the annulus of Zinn.
• How do the extraocular muscles achieve coordinated movements?

  They work in pairs (synergists and antagonists) for precision.
• Which cranial nerves innervate the extraocular muscles?

  • CN III (Oculomotor): SR, IR, MR, IO, and levator palpebrae.
  • CN IV (Trochlear): SO.
  • CN VI (Abducens): LR.
• What are monocular eye movements called, and what are some examples?

  They are called ductions, including elevation, depression, abduction, adduction, intorsion, and extorsion.
• What are binocular movements, and how are they classified?

  • Versions: Conjugate movements (both eyes move in the same direction).
  • Vergences: Disconjugate movements (e.g., convergence for near focus or divergence for distance).
• What happens during horizontal version movements?

  One eye abducts while the other adducts (e.g., looking to the left or right).
• How do rotational versions work?

  One eye intorts while the other extorts, allowing coordinated torsional movement.
• What occurs during convergence?

  Both eyes move inward for near focus (medial recti contract, lateral recti relax).
• What occurs during divergence?

  Both eyes move outward for distance focus (lateral recti contract, medial recti relax).
• What are the actions of the vertical rectus muscles in primary gaze?

  • SR: Elevation, adduction, intorsion.
  • IR: Depression, adduction, extorsion.
• What are the actions of the oblique muscles in primary gaze?

  • SO: Intorsion, depression, abduction.
  • IO: Extorsion, elevation, abduction.
• When are vertical rectus muscles most effective?

  In abducted gaze (SR for elevation, IR for depression).
• When are oblique muscles most effective?

  In adducted gaze (SO for depression, IO for elevation)
• How do contralateral synergists work in version movements?

  Paired muscles coordinate (e.g., right SR and left IO for upward gaze).
• What role do antagonists play during eye movements?

  They relax as synergists contract to ensure smooth movements.