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Neural Biology 1 > iris > Flashcards

iris Flashcards

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1
Q

What is the part of the iris closest to the ciliary body called?

A

ciliary zone

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2
Q

What is the part of iris nearest to the pupil known as?

A

pupillary zone

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3
Q

What is the collarette?

A

where pupillary zone and ciliary zone merge

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4
Q

What is the ora serata ?

A

where the ciliary body joins onto the retina

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5
Q

What is the limbal region?

A

sclera merges onto the cornea

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6
Q

What is involved in aqueous drainage?

A

-trabecular meshwork and canal of schlemn

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7
Q

What is the iris attached to?

A

the ciliary body

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8
Q

What is the iris root?

A

where the iris joins the ciliary body

-this is where the thinnest

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9
Q

What is the iris like in the collarette?

A

the thickest

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10
Q

What is the posterior surface of the iris covered in?

A

a double pigmented epithelium

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11
Q

What are the outer cells of the ciliary body covered in?

A

-pigmented epithelium

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12
Q

What are the inner cells of the ciliary body covered in?

A

non-pigmented

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13
Q

How is it changed on the iris root on the posterior surface of iris?

A

both layers of the epithelium are pigmented whereas with ciliary body only one layer of cells are pigmented

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14
Q

What are the 2 layers of epithelium on the posterior surface of the iris joined by?

A

a variety of junctions to ensure they don’t separate during movement of the iris/ during pupillary constriction and dialation

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15
Q

What are the 2 layers of the pigment epithelial cells of the iris joined by?

A
  • mechanical interdigitating microvilli between 2 pigment epithelial layers of iris - to make sure they don’t separate during pupillary constirciton and dialation
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16
Q

What are some other junctions which are between the 2 layers of pigment epithelial cells of the iris?

A
  • Desmosomes

- Gap junctions

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17
Q

What peeps through the pupil?

A
  • Posterior pigment iris epithelium which peeps over the pupil
  • the dark rim around pupil- from pigmented epithelium which is visible from the rear surface of the iris at the pupillary rim whereas it peeps over the front of the iris / iris margin
  • would be clear if the lighter iris
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18
Q

What is pupillary ruff?

A

when the -Posterior pigment iris epithelium which peeps over the pupil

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19
Q

Where do you see the darkly pigmented epithelium reaching the top of iris and peeping over and looking out through the pupil?

A

as you go up the iris and get to where the pupil begins / rear of pupil you can see this
-so, therefore, why you when you see iris from the front you can see a dark pigmented ring around the iris which is the pupillary ruff

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20
Q

Why do we have pigmented epithelia inside the eye?

A

because eye is optical instrument- hence dont want stray light bouncing around- so painted black on the inside
-to absorb stray light

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21
Q

Where does the eye absorb stray light?

A
  • such as in the ciliary body you have a single layer of pigmented epithelium which serves to absorb stray light
  • layer of pigmented epithelium behind retina - which also serves to absorb stray light that doesn’t get absorbed by photoreceptors
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22
Q

Why does the ciliary body have 1 pigmented epithelium but the iris has 2?

A
  • the iris needs 2 layers of pigmented epithelium - need to be heavily pigmented- as the main function of the iris is to form the pupil - so the only light that gets into the eye goes through the pupil
  • Iris acts as aperture stop-that’s why the posterior surface of the iris has a double layer of the pigmented epithelium to make sure only light that gets into the eye is through the pupil
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23
Q

Why does the iris act as an aperture stop?

A

-the light that impinges on the iris does not go through the iris and into the eye -iris acts as an aperture stop

24
Q

What is another significant thing of the iris?

A

-muscle

25
Q

What muscle is there in the iris?

A
  • Iris dilator muscle - this is the darker blue next right next to the posterior epithelium - runs from iris root to 2/3rds of the way of the iris
  • responsible for dilating the pupil
  • contained in anterior of 2 pigmented epithelium cell layers
26
Q

How does the transverse section/ microscope view of human iris appear like on the microscope?

A

as light is coming from left to right the 2 layered pigmented epithelium of the iris is on the rear right and then in the middle right is the iris dilator muscle and vice versa

27
Q

What is the difference between the most posterior and most anterior layer of the ‘POSTERIOR’ pigmented epithelial cell in iris?

A

most posterior of epithelial cell layer- regular pigmented cell - filled with melanin
-the most anterior of the pigmented epithelium-has one half-filled with melanin and other half with iris dilator muscle
-

28
Q

What is the iris dilator muscle said as?

A

a myoepithelial cell- an epithelial cell which makes up the actin and myosin which makes it a muscle

29
Q

What are the muscles of the iris?

A
  • iris dilator

- iris sphincter

30
Q

What is the dilator muscle?

A 
-The dilator muscle is
a radial muscle and
its contraction thus
results in pupil
dilation.
31
Q

What type of muscle is the dilator muscle?

A

smooth muscle- nspindle shaped muscle cells- small - one

32
Q

How is the dilator muscle innervated?

A

It is sympathetically innervated (wide-eyed with ‘fear’?)
due it being smooth muscle so innervated by ANS - by the sympathetic branch- contracts dilator muscle and so increases the size of the pupil

33
Q

How is the ciliary body muscle innervated?

A

-parasympathetically

34
Q

What is the iris dilator muscle made of?

A
  • Smooth muscle (spindle-shaped)
  • as it’s small it then has lots of spindle-shaped cells next to each other which are joined by tight and gap junctions (Acting as a unit) so when an Action potential arrives at one it rapidly spread to all the other cell- forms a syncytium -which is sympathetically innervated
35
Q

What is anterior to the iris dilator muscle?

A

the anterior iris stroma

36
Q

What does the iris stroma area consist of?

A
  • consists of loosely arranged collagen (loose aerolar)
  • pigment cells
  • fibroblasts to make collagen
  • mast cells
37
Q

Why are loose collagen fibres necessary in iris?

A

allows iris to change shape as it constricts and relaxes.

38
Q

What is the consequence of the loose collagen fibre in iris?

A

the aqueous humour will easily infiltrate in loose areolar connective tissue

39
Q

What is near the pupillary margin?

A

iris sphincter muscle

  • circular muscle that runs around the rim of the pupil
  • individual sphincter muscles go 1/4 way around pupil
40
Q

How is the dilator muscle different from the sphincter muscle of the iris?

A

there is an obvious gap between the epithelium in the iris sphincter whereas in dilator which is part of the epithelium

41
Q

How are sphincter muscles joined?

A

individual muscle cells like in the dilator are bound together by sheets of c.t so they can function as one unit

42
Q

What is the sphincter muscle?

A

Since this is a circular
muscle, when it contracts
the pupil constricts.

43
Q

how is the sphincter muscle innervated?

A

It is parasympathetically innervated

44
Q

What are the iris sphincter muscle cells joined by?

A

the individual smooth muscle cells are bound together by gap junctions so they can function as one unit

45
Q

How is the iris sphincter muscle visible?

A

clearly visible in the pale iris

-around 1/4 around the rim of the pupil

46
Q

What does the iris stroma contain?

A

blood supply to iris

47
Q

What is the major iridic circle?

A
  • the base of iris near the iris root has arterial circle running all the way around the iris root
  • get the major arterial supply along with the iris
48
Q

What happens at the level of collarette?

A
  • you get a 2nd incomplete arterial circle- minor arterial circle-
  • arteries run to the top of crisis and loop over and become veins and go straight back down the iris and the deoxygenated blood is drained in major veins of the eye
49
Q

How is this iris seen in an angiogram?

A

the vessels are seen by fluorescence injected in the body and can visualise it in iris

  • -iris muscle short straight line to the pupillary rim- as muscle is constricted
  • walls are thicker in arteries
  • the capillaries are fenestrated and are tightly joined(endothelial cells) so when inject dye into eye does not leak out - vessels of the iris is not involved with nutrient transfer with the aqueous- due to loose nature of stroma of iris- capillary endothelial cells are tight together- help withstand stress when pupil dilates and constrict
50
Q

What does the iris stroma contain?

A
  • impermeable vessels
  • melanocytes
  • fibroblast
  • loose collagen
  • clump cells
51
Q

What is the clump cells?

A

stuffed with melanin
-form of macrophage
often in vicinity of sphincter muscle

number and size increase with age

often full of melanin – more so than melanocytes

probably as a result of ingesting numerous melanocytes and other cellular debris from epithelial cell death

clean up important to keep aqueous free of debris

-

52
Q

What is the anterior border layer of iris?

A
  • first layer
  • not composed of epithelial cells
  • composed of a dense sheet of fibroblasts
  • have a layer of melanocytes beneath the fibroblasts- which determine the colour of the iris
  • accumulate locally in iris- so get the appearance of iris freckles
  • anterior surface of iris is richly textured from with no epithelial cells.
53
Q

What is the nerve supply of the muscles of the iris?

A

-Most behaviours can be explained by a ‘reflex arc’
-have receptor, sensory neurone, CNS, motor neurone, muscle, response (dilator or constrict muscle)
-

54
Q

What are the smooth muscles controlled by?

A

-As the iris muscles are smooth, they are controlled by the ANS

55
Q

What is the sympathetic innervation of the eye?

A

Postganglionic sympathetic fibres to the eye, including those going to the iris dilatator muscle, originating from the superior cervical ganglion

56
Q

What is the difference of ANS branches?

A

sympathetic ganglia close to the spinal cord

-parasympathetic ganglia close to the eye

57
Q

Neural pathway underlying pupil constriction?

A

Preganglionic parasympathetic fibres originate in the Edinger-Westphal nucleus (EWN).
-They travel to the ciliary ganglion (CG) in the IIIrd nerve and synapse with postganglionic fibres in the ciliary ganglion

Neural Biology 1 (58 decks)

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