Motor Control of Eye Movements Flashcards
what are the two types of eye movements and what do they do?
conjugate - eyes move in the same direction
vergence - focus shifts between near and far objects where the eyes move in opposite directions
what are the two types of conjugate movement?
saccadic- rapid movement where vision moves from target to target (voluntary)
smooth pursuit- maintains image of moving target fixed on retina
what are the two types of vergence movements?
convergence - visual axis of eyes converge (near focus)
divergence- visual axis of eyes diverge (far focus)
what are the 6 extra-ocular muscles of the eye and the 3 cranial nerves that innervate them?
lateral rectus, medial rectus, superior rectus, inferior rectus, superior oblique and inferior oblique
CN III
CN IV
CNVI
what is strabismus and what cranial nerve and muscle may not be functioning?
strabismus also called cross eye is when the lateral rectus muscle is not functioning due to CN VI (6th nerve palsy)
what are the steps for a patient looking to the right?
left frontal eye field——> PPRF ——> right abducens nucleus ——-> deccusation ——-> right abducens nerve to lateral rectus of right eye and interneuron (LMLF) to left oculomotor nucleus/nerve to medial rectus of left eye
what is a brainstem gaze center, what are the three centers and where is each located?
collection of neurons serving extra-ocular muscles
horizontal gaze center - located in pons
vertical gaze center- located in midbrain
vergence gaze center- located in the midbrain
Telling a patient to look to the right will use what frontal eye field and what gaze center? What happens if there is a lesion?
left frontal eye field and the horizontal gaze center (PPRF)
both the patients eyes will not move to the right if lesion is to either of the two
what if there is a lesion in the left medial longitudinal fasciculus and you ask the patient to look to the right? what is this issue called?
the left eye will continue to look straight while the right eye will look to the right
left internal nuclear ophthalmoplegia
what if there is a lesion to the abducens nerve and you ask the patient to look to the right?
the right eye will stay looking straight but the left eye will look to the right
the MLF pathway (nerve) is highly myelinated, therefore what disease can cause issues in this pathway????
multiple sclerosis causing demyelination which will not allow signal to go through
Where is the vertical gaze center, where do the fibers cross and where do they project to?
located in the rostral midbrain and fibers cross at the posterior commissure where the pineal gland is in close proximity where they synapze at oculomotor subnuclei
What is the primary CN associated with the vertical gaze center and the muscles?
CN III, superior and inferior rectus
where is the vergence gaze center located and where do the neurons project?
located in the reticular formation of the rostral midbrain
neurons project to CN III for convergence and CN VI for divergence
what are the four cortical gaze centers?
frontal eye field, parietal eye field, occipital eye field and temporal eye field
the frontal eye field is involved in what types of movement and projects to what gaze centers?
voluntary saccadic movement
vertical and horizontal centers as well as superior colliculus
parietal eye field influences what type of movement?
saccadic
the temporal eye field influences what type of movement?
smooth pursuit
the occipital eye field influences what type of movement and signals to which CN’s?
influences vergence movements, focus shifts from faraway or near target
signals to oculomotor (convergence) or abducens nuclei (divergence)
what does LR6SO4AO3 stand for?
lateral rectus CN 6, superior oblique CN4, all other CN3
if a patient has an affected left eye that is elevated and adducted which CN and muscle is affected?
superior oblique and CN 4
superior oblique is referred to as the what muscle?
depression and abduction (down and out)
what is the only way to test if your CN IV is functioning properly?
ask your patient to look medially then look down (superior oblique to depress an already adducted globe)
what are the primary and secondary actions of the medial rectus muscle?
primary: adduction
secondary: none
what are the primary and secondary actions of the lateral rectus muscle?
primary: abduction
secondary: none
what are the primary and secondary actions of the superior rectus muscle?
primary: elevation
secondary: adduction, intorsion
what are the primary and secondary actions of the inferior rectus muscle?
primary: depression
secondary: adduction. extorsion
what are the primary and secondary actions of the superior oblique muscle?
primary: intorsion
secondary: depression, abduction
what are the primary and secondary actions of the inferior oblique muscle?
primary: extorsion
secondary: elevation, abduction
a patient complains of double vision and compensates for this with a slight head tilt, what is the issue?
cranial nerve IV palsy of the right eye causes the right eye to be extorted and slightly elevated which is why she tilts her head to the left
