Visual System Flashcards
What is the MLF ?
The medial Longitudinal Fascuculous- It interconnects the third, fourth, and sixth cranial nerves as well as the reticular center of the brain stem.
What does the medial longitudinal fasciculous actually do ?
Allows synergistic and coordinated movements of the two eyes and adjustments of eye position in response to movements of the head.
It maintains conjugate gaze
Where does the MLF originate ?
In the vestibular nuclei in the rostral medulla. It is divided into ascending and descending tracts
What does the descending MLF do ?
It controls the head and neck position
What does the ascending tract do ?
It coordinates the synchronization of all the major classes of eye movements.
What is gaze ?
The coordinated synergistic movements of the eyes to targets in the environment. Gaze directs the targets onto the fovea of the wye which is the section with the highest visual acuity.
Where is the horizontal gaze center ?
Paramedian Pontine reticular formation (PPRF). So a lesion in the pons will decrease the ability for horizontal gaze to be maintained.
Where is the vertical gaze center ?
Midbrain reticular formation.
What are saccades ?
Rapid eye movements that orient gaze so that the target is on the fovea of the eye which has the maximal visual acuity.
What is smooth pursuit ? And what is required to accomplish this ?
Smooth Persuit is the slow tracking of a moving object to keep the image in the retina. To accomplish this the cerebellar imput, vestibular input and cortical input must all be coordinated.
What is the difference between smooth pursuit and saccadic movements ?
Smooth pursuit just keeps the image in the retena. Saccadic movements orient the eye toward a target.
What is the vestibule ocular reflex ?
This reflex rapidly adjusts eye orientation in response to head movements to keep an image in the retena.
What are Nystagmus ?
Rapid back and fourth eye movements. They consist of a quick flick in one direction and a slow drift in the opposite direction.
What are vestibular nystagmus ?
When the head rotation exceeds what the VOR can compensate for the reticular system will initiate a nystigmas in the same direction as the rotation so the eyes can catch up.
What is an optokinetic neostygmas ?
It is a neostigmus that is initiated by something rapidly passing through the visual fields. The example given is when a telephone pole passes through your field of view.
