Week 3: Background Info Eyes

Question 1

What sort of eye movements do your eyes make?

Answer 1

• voluntary eye movements
• reflex eye movements (automatic adjustment of the eye position to stabilise an image on the eye e.g. if something jumps up then look to see in case dangerous)

Question 2

What are names of eye movements?

Answer 2

• Smooth tracking pursuit: ability to follow moving object, not voluntary, combined head and eye tracking (1 object targeted and remains clear on retina, rest of visual world in motion (standard stimulus for for optokinetic reflex)
• Saccades: quick jumps, saccadic eye movements, voluntary initiation
• Fixation (actually just mini saccades): holding steady gaze on target, do with fovea, even when sleeping, baby’s born blind will not be able to fixate (eyes roll about)

Question 3

Types of reflex eye movements (3)

Answer 3

• Vestibular Ocular Reflexes (VOR): if you move your head, eyes can maintain fixation upon target, ears tell head your moving not room= VOR reflex
• Optokinetic Reflex: Stimulus is rapid motion of world such as steam or looking out window in car, combined smooth eye movements and saccades= train eye staggering- follow something then eye flicks back
• Nystagmus: alternating slow and quick phases of movement (mini-nystagmus=tremors: high freq litter in position)

Question 4

What happens if you perfectly stabilise an image on retina?

Answer 4

• It would eventually disappear and fade.
• Some retinal motion is necessary aka some movement of the image across the retina must be present or the image fades e.g. when staring at cinema screen and edges of visual field start to fade.

Question 5

Where is the position that the eyes moves called?

Answer 5

Nodal point (hypothetical point)

Question 6

What are Fick’s Axes?

Answer 6

• X axis = nasal to temporal (or L to R ear)
• Y axis = anterior to posterior (or back of head to front of face)
• Z axis = superior to inferior (or top of head to chin)

Question 7

Where do Fick’s axis intersect at the centre of rotation?

Answer 7

A fixed point defined as 13.5mm behind the cornea (all eye movements pivot around this point)

Question 8

What are Ductions?

Answer 8

Single eye movements that occur 1 eye at a time.

• Rotation about the Z axis (vertical); Medial rotation (eyes go in) and Lateral rotation (eyes out)
• Rotation about the X axis(horizontal); Upward elevation (supraduction), Downward depression (infraduction)

Question 9

What is Torsion?

Answer 9

• Cyclorotations, rotation around the Y axis which runs horizontally from anterior (optic nerve) to posterior (lens)
• described with respect to a point at 12 o’clock on the superior limbus
• Intorsion (incyclorotaion) rotation nasally (towards nose like forward)
• Extorsion (excylorotation) rotation of the 12 o’clock position temporally (towards brain like backwards) -Counteracting head tilt (<=7.9degrees)

Question 10

What’s the difference between version and vergences?

Answer 10

• some eye movements are paired, both eyes do the same thing (both looking L or R) = VERSIONS
• sometimes eyes may move in opposite directions simultaneously (both looking in or out) = VERGENCES

Question 11

What are the types of Vergences?

Answer 11

• Disjunctive eye movements (opposite movments). Non-yolked motion (not connected movement)
• Convergence (simultaneous movement nasally) (eyes move in)
• Divergence (simultaneous temporal movement) (go outwards)
• Encyclovergence (intorsion) (rotate in opposite ways)
• Excyclovergence (extorsion) (rotate in opposite ways)

Question 12

What are types of versions?

Answer 12

-conjugate eye movements
•Dextroversion - rightward gaze (demo) (ask someone to look to R, both eyes move to R)
•Levoversion - leftward gaze (ask someone to look to L) (L and Left)
•Supraversion - elevation (look up)
•Infraversion - depression (look down)
•Also up and right, up and left
•Down and right, down and left
•ALL BEHAVIOR IS THAT OF YOLKED EYES (when eyes are moving the same way e.g. put rod around wrists so move in the same directions).

Question 13

What is the Annulus of Zinn?

Answer 13

A cone-shaped structure behind eyeball composed of five Extraocular muscles (medial rectus, lateral rectus, superior rectus, inferior rectus and superior oblique)
-within runs the optic nerve (cranial nerve 2), ophthalmic artery and ophthalmic vein.

Question 14

What is the structure of muscle cells?

Answer 14

• Skeletal muscles consist of 100,000s of muscle cells (also known as “muscle fibers”) that perform the functions of the specific muscle of which they are a part.
• Each myofibril consists of two types of protein filaments called thick filaments, and thin filaments.
• There are hundreds of myofibrils in each muscle fibre.
• Adjacent myofibrils line up with each other such that the Z-lines (formed from adjacent Z-discs) of each sarcomere in one myofibril lines up with the Z-lines of the sarcomeres in adjacent myofibrils.

Question 15

How do muscles work? (Ratchet model structure)

Answer 15

• Myosin head binds to actin filament.
• The ratchet motion moves the two filament about 12 nm with respect to each other.
• It takes only 5 ms
• Because of the large number of z-line segments or contractile units along a fiber, a fast motion is attained

Question 16

EOM thick and thin fibres?

Answer 16

• thick fibres are motor fibres and are innervated by one nerve, include fast and slow twitch fibres, all or none contractions.
• thin fibres are multiply in berated by many branches from one nerve, thought to be slow sustained, graded contractions.