4 - Physiologie motrice Flashcards

Question

Quel est l'arc de contact (en mm) de l'oblique inférieur?

Answer 1

The **point where the muscle first contacts the globe** is the effective insertion of the muscle.

Answer 2

As the muscle contracts and the eye rotates toward the muscle, the effective insertion moves forward on the globe, toward the scleral insertion point, as the arc of contact decreases.

Answer 3

An individual motor nerve fiber and its several muscle fibers constitute a motor unit. Unité motrice = 1 motoneurone + fibres musculaires

Answer 4

* Recruitment is the orderly increase in the number of activated motor units, thus increasing the strength of muscle contraction. * For example, as the eye moves farther into abduction, more and more lateral rectus motor units are activated and brought into play by the brain to help pull the eye temporally. * In addition, as the eye fixates farther into abduction, the firing frequency of each motor unit increases until it reaches a peak (several hundred per second, for some motor units).

Answer 5

Ductions are **monocular** rotations of the eye.

Answer 6

Synergist: the muscle in the same eye as the agonist that acts with the agonist to produce a given movement. Ex. the inferior oblique muscle is a synergist with the agonist superior rectus muscle for elevation of the eye

Answer 7

Sherrington’s law of **reciprocal innervation states** that **increased innervation of a given EOM is accompanied by a reciprocal decrease in innervation of its antagonist**. For example, as the right eye abducts, innervation of the right lateral rectus muscle increases and innervation of the right medial rectus muscle decreases.

Answer 8

Field of action refers to the gaze position (one of the cardinal positions) in which the effect of the EOM is most readily observed. The clinical significance of fields of action is that a deviation (strabismus) that increases with gaze in some directions may result * From weakness of the muscle normally pulling the eye in that direction * From restriction of its action by its antagonist muscle * Or from a combination of these 2 factors

Answer 9

When binocular eye movements are **conjugate** and the **eyes move in the same direction**, such movements are called versions.

Answer 10

When the eye movements are **dysconjugate** and the **eyes move in opposite directions**, such movements are known as vergences.

Answer 11

Right gaze (dextroversion) is movement of both eyes to the patient’s right.

Answer 12

Dextroversion

Answer 13

Left gaze (levoversion) is movement of both eyes to the patient’s left.

Answer 14

Levoversion

Answer 15

Elevation, or upgaze (sursumversion), is an upward rotation of both eyes.

Answer 16

Sursumversion

Answer 17

Depression, or downgaze (deorsumversion), is a downward rotation of both eyes.

Answer 18

Deorsumversion

Answer 19

Dextrocycloversion is rotation of the superior pole of the vertical meridian of both eyes to the patient’s right.

Answer 20

Dextrocycloversion

Answer 21

Levocycloversion is movement of both eyes so that the superior pole of the vertical meridian rotates to the patient’s left.

Answer 22

Levocycloversion

Answer 23

Vrai. Each EOM in one eye has a yoke muscle in the other eye.

Answer 24

* The term yoke muscles is used to describe **2 muscles (1 in each eye) that are the prime movers of their respective eyes into a given position of gaze**. For example, when the eyes move into right gaze, the right lateral rectus muscle and the left medial rectus muscle are **simultaneously innervated and contracted**. These muscles are said to be “yoked” together.

Answer 25

Hering’s law of motor correspondence states that **when the eyes move into a gaze direction**, there is a **simultaneous and equal increase in innervation to the yoke muscles** for that direction. Hering’s law has important clinical implications when the practitioner is evaluating a paralytic or restrictive strabismus.

Answer 26

Hering’s law has important clinical implications when the practitioner is evaluating a **paralytic or restrictive strabismus**.

Answer 27

Because the amount of innervation supplied to both eyes is **always determined by the fixating eye**, the angle of deviation varies according to which eye is fixating.

Answer 28

Because the **amount of innervation supplied to both eyes is always determined by the fixating eye**, the angle of deviation varies according to which eye is fixating. When the **sound eye is fixating** (**prism over the affected eye** when the prism alternate cover test is performed), the amount of misalignment is called the **primary deviation**. When the **affected eye is fixating** (**prism over the sound eye** when the prism alternate cover test is performed), the amount of misalignment is called the **secondary deviation**. The **secondary deviation is larger than the primary deviation because of the increased innervation necessary to move the affected eye to the position of fixation**. This extra innervation is shared by the yoke muscle in the sound eye, which causes **excessive action of that muscle and a larger angle of deviation**. *En pratique, Dr Anderson veut toujours opérer la déviation maximale donc il préférable de mesurer avec la déviation secondaire.*

Answer 29

Because the amount of innervation supplied to both eyes is always determined by the fixating eye, the angle of deviation varies according to which eye is fixating. When the **sound eye is fixating** (**prism over the affected eye** when the prism alternate cover test is performed), the amount of misalignment is called the **primary deviation**. When the **affected eye is fixating** (**prism over the sound eye** when the prism alternate cover test is performed), the amount of misalignment is called the **secondary deviation**.

Answer 30

Convergence is movement of both eyes nasally relative to a given starting position. Divergence is movement of both eyes temporally relative to a given starting position. The medial rectus muscles are yoke muscles for convergence, and the lateral rectus muscles are yoked for divergence.

Answer 31

With vertical vergence movements, **one eye moves upward, and the other moves downward**.

Answer 32

Incyclovergence is a rotation of both eyes such that the superior pole of the vertical meridian is rotated nasally Excyclovergence is a rotation of both eyes such that the superior pole of the vertical meridian rotates temporally.

Answer 33

Accommodation, convergence, and miosis

Answer 34

A certain amount of accommodative convergence (AC) occurs with each diopter of accommodation (A), giving the accommodative convergence/accommodation (AC/A) ratio.

Answer 35

Vrai : Abnormalities of this ratio are common and are important causes of strabismus.

Answer 36

With an abnormally high AC/A ratio, the excess convergence tends to produce **esotropia during near fixation that is greater than esotropia at distance.**

Answer 37

An abnormally low AC/A ratio tends to make the **eyes less esotropic, or even exotropic, when the patient looks at near targets**.

Answer 38

A movement to converge and **position the eyes so that similar retinal images project on corresponding retinal areas**. Fusional convergence is **activated when a target in the midline is seen with bitemporal retinal image disparity**.

Answer 39

Proximal (instrument) convergence An induced convergence movement caused by a psychological awareness that the object of fixation is near. This movement is particularly apparent when a person looks through an instrument such as a **binocular microscope**.

Answer 40

The constant innervational tone to the EOMs when a person is awake and alert. Because of the anatomical shape of the bony orbits and the position of the rectus muscle origins, the position of the eyes during complete muscle paralysis is divergent. Therefore, **convergence tone is normally necessary** in the awake state for the eyes to be aligned. For example, an esotropic patient under general anesthesia may become less esotropic or even exotropic with suspension of tonic convergence.

Answer 41

A conscious application of the near reflex.

Answer 42

A movement to diverge and position the eyes so that similar retinal images project on corresponding retinal areas. Fusional divergence is activated when a target in the midline is seen with binasal retinal image disparity.

Answer 43

**Fusional DIVERGENCE** is activated when a target in the midline is seen with **biNASAL** retinal image disparity. **Fusional CONVERGENCE** is activated when a target in the midline is seen with **biTEMPORAL** retinal image disparity.

Answer 44

A superior movement of one eye and inferior movement of the other to reduce vertical disparity so that similar retinal images project on corresponding retinal areas.

Answer 45

Intorsion of both eyes (incyclovergence) or extorsion of both eyes (excyclovergence) to reduce torsional disparity so that similar retinal images project on corresponding retinal areas. While it can be enhanced by special training, cyclovergence is normally very limited, and fusion of torsional disparity is mostly accomplished by sensory adaptation.