Extra ocular muscles and their origin
The six extraocular muscles are responsible for the position and rotation of the eye.
5 of those extraocular muscles originiate from the annulus of zinn, a tendionous ring surrounding the optic never at the oribits apex. 4 of these are the recti muscles (superior, inferior, medial, lateral) superior oblique.
The 6th extraocular muscle originates in the lower nasal quadrant of the orbit
Striated muscles
Extraocular muscles are composed of striated muscles. Two types of striated muscles cells: twitch fibres for saccadic eye movement and tonic fibres for maintaining steady position
Primary action of medial and lateral rectus
Adduction and abduction
Types of eye movement
Conjugate
Saccades
Smooth
Vergence
Conjugate
Involves the movement of both eyes in the same direction
Saccades
Saccades are rapid, voluntary action initiated to place an object on the fovea. They have a latency of 200ms and vary in duration depending on angular exteny
Smooth prusuit
Smooth pursuit movement are used for smoothly tracking an object.They typically follow the velocity of the traget and have a latency of 100ms. Effective for slow moving targets.
Vergance eye movement
Vergance eye movement involves the individual eye rotation in the opposite direction and is mediated by the vergeance system
Characteristic of vergance response
Vergance movements are relatively slower than saccades and have a latency of 150-200ms and can take 500ms to complete. The step velocity of vergence movement is proportional to the step size required
Innevation of extraocular muscles
Midbrain nucli, including the occulomotor, trocular and abduce innervate with the extraocular muscles.
Intranuclear neurons coordinated muscles innervate yolked eye movements
Sympathetic originates arrises from superior cervical ganglion
Neural control of vergence system
The occulomotor neurones and abdunce neuli play a role in both conjugate and vergance ye movement.
Specific cell group in the midbrain encode for the vergance angle and velocity
