Introduction to the Nervous System

Question 1

Why does the cornea have two basement membranes?

Answer 1

Because it has two layers of epithelium

Question 2

What are the names of the basement membranes?

Answer 2

Bowmans membrane (basement membrane of corneal epithelium) and descents layer which is the basement membrane of the endothelium.

Question 3

What type of epithelium is the outer epithelium of the cornea?

Answer 3

Stratified squamous non-keratinised

Question 4

How does the cornea receive nutrition?

Answer 4

Diffusion, no blood vessels

Question 5

Damage to which layer of the cornea will result in scar formation?

Answer 5

Bowmans membrane

Question 6

What does OD and OS mean?

Answer 6

OD means right eye and OS means left eye

Question 7

How does the cornea remain transparent?

Answer 7

1. Histologically – regular arrangement of collagen in stroma
2. No blood vessels
3. Endothelium cell layer has a pump that actively keeps the aqueous humor out.

Question 8

What is the advantage of avascularity of the cornea in terms of transplant?

Answer 8

Means there is a lesser chance of foreign antigens from a corneal graft being recognised by the recipient, so lesser chance of graft rejection.

Question 9

What is responsible for suspending the lens?

Answer 9

Suspensory ligaments

Question 10

What is the anterior/posterior segment?

Answer 10

Behind the lens is the posterior segment, in front is the anterior segment.

Question 11

What makes up the anterior segment of the eye?

Answer 11

Anterior segment contains an anterior and posterior chamber.

Question 12

Where does aqueous humour flow?

Answer 12

Flows out of the angle of the anterior chamber.

Question 13

Which layer of the retina contains the nerve fibre layer?

Answer 13

Layer 9

Question 14

Which layer of the retina contains the layer of rods and cones?

Answer 14

Layer 2

Question 15

Which level of the retina contains the pigment epithelial layer?

Answer 15

Layer 1

Question 16

What is the significance of the fovea centralis?

Answer 16

Packed with cones, area of maximum visual acuity

Question 17

What is different about the layers of the membrane over the fovea centralis?

Answer 17

All the upper layer of membrane is pushed aside so that light can directly strike rods and cones - very thin layer

Question 18

What is meant by cataract?

Answer 18

Lens opacification

Question 19

Why is the lens predisposed to becoming opaque?

Answer 19

It is avascular and has its basement membrane on the outside - therefore the lens cannot shed its old fibres

Question 20

What shapes your eyelid?

Answer 20

Tarsal plate

Question 21

What is the function of the tear film?

Answer 21

1. Keeps cornea moist , prevents drying
2. Washes away any particulate foreign bodies
3. Has antibodies and lysozymes to kill microbes
4. Smooths outer surface of cornea providing smooth surface for refraction.

Question 22

What are the three layers of the tear film?

Answer 22

• Layer 1: mucinous layer (~30%) overlying corneal epithelium
• Layer 2: aqueous layer (~69%) lies over the mucinous layer
• Layer 3: oily layer (<1%) is the most superficial

Question 23

What nerves are responsible for the secretion of tears into the conjunctival sac?

Answer 23

Parasympathetic nerves from CN2

Question 24

What happens when we blink?

Answer 24

Sharp lower border of the upper eyelid distributes the tear film evenly

Question 25

What stimulates blinking?

Answer 25

Tears evaporate and oily layer becomes close to the mucin layer, when the 2 layers touch each other this stimulates further blinking