Fitz

Question 1

Eyelid movements are mediated by what three muscles?

How are they innervated?

Answer 1

Three muscles

orbicularis oculi and levator palpebrae superioris (ACh acts on nicotinic receptros to cause contraction)

superior tarsal muscle (sympathetic innervation via a₁ receptors)

Question 2

dopaminergic

Question 3

emmetropic

Question 4

focusing power =

Answer 4

1/focal length

Question 5

accomodation

Answer 5

focusing power

fatter lens = more accomodation

Question 6

Distance vision

Answer 6

sympathetic activation!

relaxation of ciliary muscle

via activation of ß2 receptors

Question 7

Near vision

Answer 7

parasympathetic activation

contraction of ciliary muslces

muscarinic receptors

Question 8

hyperopia

Answer 8

farsightedness

Axial length < focal length

caused by lens that is too short or lens that is too weak

correct with convex lens to increase refractive power

Question 9

Myopia

Answer 9

nearsightedness

correct with concave lens

axial length > focal length

Question 10

presbyopia

Answer 10

less flexible lens

decrease in accomodation

middle age…

Question 11

astigmatism

Answer 11

uneveness in lens

part of visual field will be out of focus

Question 12

cataracts

Answer 12

opaquness in lens

physical damage, radiation, high [glucose]

remove lens, replace

Question 13

pupillary light reflex

Answer 13

causes miosis (parasympathetic stimulation of sphincter pupillae via muscarinic receptors)

and

mydriasis (sympathetic stimulation (a₁ receptors) that activates the dilator pupillae muscles)

light in one eye –> constriction in another… used to test brain injury.

Question 14

increased intraocular pressure can cause permanent vision loss

Answer 14

closed angle glaucoma (medical emergency) – caused by blockage of fluid outflow

open angle glaucoma (slowly developes) – caused by increase in aqueous humour production or a blockage of outflow

increased interocular pressure!!

1. cornea – halos, blurring; 2. photoreceptor pressure; 3. optic nerve pressure; 4. arterial supply

Question 15

aqueous humor volumn and intraocular pressure

Answer 15

inflow – sympathetics –> ß2 (increases flow) and alpha₁ (decreases flow) of H2O via carbonic anhydrase

outflow – parasympathetics –> canal of Schlemm contract sphincter pupillae

intraocular pressure = 20 mmHg (>30 glaucoma)

(Pressure = flow x resistance (V = IR))

Question 16

Cells and circritry of the retina

Answer 16

1. Generate receptor potential– transduction
2. Bipolar cells – graded potential
3. Ganglion cells – action potential generated (axons form optic nerve)

Question 17

Rods and Cones

Answer 17

Rods are responsible for scotopic vision (black and white; monochromatic vision)–high sensitivity! less precise!

Cones; 3 types– blue, green, and red; or short, medium, and long (respectively).

Cones have better spatial and temporal resolution than rods; photopic vision

Question 18

visual acuity

Answer 18

spacial acuity: where is something in space (snellen eye chart to determine). Cones: Best in fovea.

Temporal acuity: ability to distinguish 2 events as separate.

Spectral acuity: ability to distinguish differences in wavelength (color) – how well cone system is functioning

Question 19

phototransduction

Answer 19

1. activation of rhodopsin
2. rhodopsin joins with transducin
3. GTP –> GDP; activated phosphodiesterase, which breaks down cGMP
4. cGMP holds open Na+ channel, which then releases.