Kinematics 2 Flashcards
Sherrington’s Law of reciprocal Innervation
When a muscle contracts, its direct antagonist relaxes an equal extent.
Neural excitation= Neural inhibition
Allows for smooth movement.
This antagonistic movement occurs on the same eye. Ex: Lateral rectus and medial rectus. Superior rectus and inferior rectus. All antagonistic pairs.
Hering’s Law of Equal Innervation
Between the TWO eyes.
Synergistic EOMs receive equal and simultaneous innervation. Contraction of one EOM occurs with equal and simultaneous contraction of the contralateral agonist.
“yoked muscles” H charts as if pt is looking at me. The H chart represents which muscle is working the hardest at any given gaze. Don’t confuse with primary, secondary and tertiary actions of a muscle.
Is it more likely for a muscle to be over acting or under acting?
Under acting, so it looks as if the antagonist muscle is overacting.
Forced duction test. what does a negative or positive result indicate?
If eye cannot move to a specific gaze, you can do a forced duction test to determine if something is in the way or if it is nerve related.
Positive: If eye RESISTS going in the direction it’s being pulled. Due to something being in the way.
Negative: Eye does move. Nerve related.
Can use cotton swab to push eye in direction it won’t go.
Words that correspond to X, Y, and Z axis
X- pitch
Y- Yaw
Z- Roll
Clinically, which axis’ are switched?
Y and Z are switched
Is 2 dimensional translation commutative? Ex: Is going to the right and up same as going up and to the right?
What about 3 dimensional movements/rotations?
2D: Does not matter which way we go first. Commutative.
3D: Not commutative. Object attains a new orientation relative to the previous one. This is because space is curved and every rotation you make is around a curved line. Think of coke can example.
Translations vs rotations
Translations: In 2D, it is combative. In 3D, the end position can be described by 3 cartesian coordinates. A single translation through space never results in returning to original position.
Rotations in 3D: End position cannot be described only using 3 coordinates. The space for all rotations is curved. If you keep rotating, you get back to the same orientation eventually. (A single rotation can result in returning to original position).
Who created the first mechanical model of the eye and its muscles?
Ruete
What were Ruete and Danders curious about when they studied the movement of their own eyes?
Looked at a red cross, obtained green afterimage. Observed on a flat screen with a grid. Tested all cardinal planes. 1840s.
Donder’s Law
The torsional position of the eye is always the same for a given gaze direction, regardless of how the eye got there. Donder’s Law does not specify what the resultant torsional angle is, just that there is only one.
For each direction of eye movement, that rotation along the line of sight is exactly the same. Imagine 12 o clock position changing each time. Would be so hard for brain to interpret image landing on diff area of the retina with each change of gaze.
How did sherington measure that neural excitation in one muscle = neural inhibition in the antagonist muscle?
Used EMG tracing from LR and MR. When eye adducts, MR increases EMG activity as the muscle contracts. EMG activity in the lateral rectus muscle is absent until the MR stops contracting.
Synergistic EOMs
Receive equal and simultaneous innervation. Basis of Hering’s law.
Which law states that contraction of one EOM occurs with equal and simultaneous contraction of the contralateral agonist?
Herings.
Translation in 3 dimensions. The end point can be described by
3 Cartesian coordinates. Center of the eye is reference. A single translation never results in returning to original position.
